CA1195973A - Method of preparing green concrete or mortar by prewetting aggregate with additive - Google Patents
Method of preparing green concrete or mortar by prewetting aggregate with additiveInfo
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- CA1195973A CA1195973A CA000397696A CA397696A CA1195973A CA 1195973 A CA1195973 A CA 1195973A CA 000397696 A CA000397696 A CA 000397696A CA 397696 A CA397696 A CA 397696A CA 1195973 A CA1195973 A CA 1195973A
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Abstract
ABSTRACT OF THE DISCLOSURE
When manufacturing a green concrete or mortar by admixing and kneading premeasuared amounts of at least one of fine and coarse aggregates, a powder of an hydraulic substance, at least one additive, and predetermined quantity of water, an improvement is provided. The improvement comprises the steps of: 1) dividing the predetermined quantity of water into only two predetermined quantitative portions; 2) incorporating a major portion or all of the additive into a first one of the divided predetermined quantitative water portions; 3) admixing the aggregate and all the admixture of the first predetermined quantitative water portion and the additive, thereby uniformly to pre-coat the aggregate with water; 4) admixing the powder of the hydraulic substance and any remaining quantitative portion of the additive and the mix-ture resulting from step 3); 5) admixing all the other predetermined quanti-tative portion of the water to the mixture of the hydraulic substance result-from step 4); and kneading the resulting mixture, thereby to form the green concrete or mortar. In this way, it is possible to prepare a green com-position, more particularly, green mortar or green concrete having a small percentage of bleeding water. It is also possible to obtain concrete pro-ducts having high mechanical strength and in which rusting of reinforcing steel bars can be reduced.
When manufacturing a green concrete or mortar by admixing and kneading premeasuared amounts of at least one of fine and coarse aggregates, a powder of an hydraulic substance, at least one additive, and predetermined quantity of water, an improvement is provided. The improvement comprises the steps of: 1) dividing the predetermined quantity of water into only two predetermined quantitative portions; 2) incorporating a major portion or all of the additive into a first one of the divided predetermined quantitative water portions; 3) admixing the aggregate and all the admixture of the first predetermined quantitative water portion and the additive, thereby uniformly to pre-coat the aggregate with water; 4) admixing the powder of the hydraulic substance and any remaining quantitative portion of the additive and the mix-ture resulting from step 3); 5) admixing all the other predetermined quanti-tative portion of the water to the mixture of the hydraulic substance result-from step 4); and kneading the resulting mixture, thereby to form the green concrete or mortar. In this way, it is possible to prepare a green com-position, more particularly, green mortar or green concrete having a small percentage of bleeding water. It is also possible to obtain concrete pro-ducts having high mechanical strength and in which rusting of reinforcing steel bars can be reduced.
Description
This invention relates to a method of preparing a green composi-tion, e.g., green mortar or concrete, utili~ing a hydraulic substance.
Large quantities of compositions, e.g., green mortar and green concrete, utilizing a hydraulic substance, e.g., Portland cement, blast fur-nace cement, quick setting cement or plaster, are widely used in various civil works and for constructing buildings. As is well known in the art, at the time of preparing and using such green compositions, water is segre-gated from the composition, thus forming bleeding water which prolongs the processing time including surface finishing time. Further, bleeding water results in shrinkage of the resulting concrete after setting; generation of lattices; undesired variations in the strength between the upper and lower portions of a concrete structure or block made therefrom; and a decrease in the bending strength between the cement and reinforcing steel incorpora~ed therein. These factors degrading the quality and mechanical strength of the concrete structure. Although many efforts have been made to eliminate the problem of segregation and bleeding, suitable methods have not been developed. What has usually been done was to add an excess quantity of waterlwhich corresponded to an expected quantity of the bleeding water.
Applicants have oonducted exhaustive research relating to the preparation of green compoSitions and have patented a number of inventions as disclosed in United States Patent No. 4,176,965 regarding measurement of the aggregate, United States Patent No. 4,143,541 regarding a method of measuring the fluidity of a plastic fluid.
and United States Patent No. 4,299,633 regarding a method of forming concrete shells containing a predetermined quantity of water about ~ ~3 particles of an a8gregate so as to decrease blePding and to increase the mechanical str~ngth of the concrete products.
Accordingly, it is an object of one aspect of this invention to provide a novel method of preparing green compositions capable of substantially preventing bleeding of water and hence of increasing the mechanical strength of the resulting concrete structure.
It is an obiect of another aspect of this invention to provide 2 novel method of utilizing additives for preparing a green composition.
According to a broad aspect of this invention an improved method is provided for preparing a green concrete or mortar by admix-ing and kneading premeasured amounts of at least one of f ine and coarse aggregates, a powder of a~ hydraulic substance, at least one additive, and predetermined quantity of water, the improvement which comprises the steps of: 1) dividing the predetermined quantity of water into only two predetermined, quantitative portions; 2~ incorporating a major portion of all of the additive into a first one of the divided predetermined quantitative water portions; 3) admixing the aggregate and all the ad-mixture of the first predetermined quantitative water portion and the additive, thereby uniformly to pre-coat the aggregate with water;4) admixing the powder of the hydraulic substance and any remaining quantitative portion of the additive and the mixture resulting from step 3);5); admixing all the other predetermined quantitative portion of the water to the mixture of the hydraulic substance resulting from step 4); and kneading the resulting mixture, thereby to form the green concrete or mortar.
By a variant thereof, all the powder of the hydraulic substance
Large quantities of compositions, e.g., green mortar and green concrete, utilizing a hydraulic substance, e.g., Portland cement, blast fur-nace cement, quick setting cement or plaster, are widely used in various civil works and for constructing buildings. As is well known in the art, at the time of preparing and using such green compositions, water is segre-gated from the composition, thus forming bleeding water which prolongs the processing time including surface finishing time. Further, bleeding water results in shrinkage of the resulting concrete after setting; generation of lattices; undesired variations in the strength between the upper and lower portions of a concrete structure or block made therefrom; and a decrease in the bending strength between the cement and reinforcing steel incorpora~ed therein. These factors degrading the quality and mechanical strength of the concrete structure. Although many efforts have been made to eliminate the problem of segregation and bleeding, suitable methods have not been developed. What has usually been done was to add an excess quantity of waterlwhich corresponded to an expected quantity of the bleeding water.
Applicants have oonducted exhaustive research relating to the preparation of green compoSitions and have patented a number of inventions as disclosed in United States Patent No. 4,176,965 regarding measurement of the aggregate, United States Patent No. 4,143,541 regarding a method of measuring the fluidity of a plastic fluid.
and United States Patent No. 4,299,633 regarding a method of forming concrete shells containing a predetermined quantity of water about ~ ~3 particles of an a8gregate so as to decrease blePding and to increase the mechanical str~ngth of the concrete products.
Accordingly, it is an object of one aspect of this invention to provide a novel method of preparing green compositions capable of substantially preventing bleeding of water and hence of increasing the mechanical strength of the resulting concrete structure.
It is an obiect of another aspect of this invention to provide 2 novel method of utilizing additives for preparing a green composition.
According to a broad aspect of this invention an improved method is provided for preparing a green concrete or mortar by admix-ing and kneading premeasured amounts of at least one of f ine and coarse aggregates, a powder of a~ hydraulic substance, at least one additive, and predetermined quantity of water, the improvement which comprises the steps of: 1) dividing the predetermined quantity of water into only two predetermined, quantitative portions; 2~ incorporating a major portion of all of the additive into a first one of the divided predetermined quantitative water portions; 3) admixing the aggregate and all the ad-mixture of the first predetermined quantitative water portion and the additive, thereby uniformly to pre-coat the aggregate with water;4) admixing the powder of the hydraulic substance and any remaining quantitative portion of the additive and the mixture resulting from step 3);5); admixing all the other predetermined quantitative portion of the water to the mixture of the hydraulic substance resulting from step 4); and kneading the resulting mixture, thereby to form the green concrete or mortar.
By a variant thereof, all the powder of the hydraulic substance
- 2 -' ~"
;~ :
~.g~ 73 is incorporated into the mixture of aggregate and the first predetermined quantitative portion of the water, thereby to form shells of the hydraulic substance about particles of the aggregate, the shells having higher strength than a paste between the hydraulic substance and particles of the aggregate.
By another variant, the additive incorporated into the first water portion comprises an agent that substantially prevents separation of the concrete or mo]ar.
By variations thereof, that agen~: enhances surface activity of water; or is a dispersing agent that enhances the dispersion of the hydraulic substance; or accelerates setting of the hydraulic substance by hydration and aggregation; or decreases the shear strength of a slurry paste prevail-ing between particles of the aggregate.
By still other variants, the additive comprises an air-entraining agent; or comprises a rust-preventing agent.
By another variant, the fine aggregate comprises sea sand contain-ing a corrosive compound.
By yet another variant, the green concrete or mortar comprises a concrete composition utilized to form a concrete structure.
By a still further variant, the method further includes the steps of removing air film on particles of the fine aggregate; and then covering the particles with water films containing more than 1.5% by weight of the additive.
By a variation thereof, covering the particles of the additive preferentially absorbs the hydraulic substance to form shells thereof.
In the accompanying drawings:
Fig 1 is graph showing the relation between the shear strength '~-f and the increasing size of the particles, for example, (an abscissa) and air adhering to the surface of the aggregate (as ordinate) of a concrete paste prepared according to an aspect of the method
;~ :
~.g~ 73 is incorporated into the mixture of aggregate and the first predetermined quantitative portion of the water, thereby to form shells of the hydraulic substance about particles of the aggregate, the shells having higher strength than a paste between the hydraulic substance and particles of the aggregate.
By another variant, the additive incorporated into the first water portion comprises an agent that substantially prevents separation of the concrete or mo]ar.
By variations thereof, that agen~: enhances surface activity of water; or is a dispersing agent that enhances the dispersion of the hydraulic substance; or accelerates setting of the hydraulic substance by hydration and aggregation; or decreases the shear strength of a slurry paste prevail-ing between particles of the aggregate.
By still other variants, the additive comprises an air-entraining agent; or comprises a rust-preventing agent.
By another variant, the fine aggregate comprises sea sand contain-ing a corrosive compound.
By yet another variant, the green concrete or mortar comprises a concrete composition utilized to form a concrete structure.
By a still further variant, the method further includes the steps of removing air film on particles of the fine aggregate; and then covering the particles with water films containing more than 1.5% by weight of the additive.
By a variation thereof, covering the particles of the additive preferentially absorbs the hydraulic substance to form shells thereof.
In the accompanying drawings:
Fig 1 is graph showing the relation between the shear strength '~-f and the increasing size of the particles, for example, (an abscissa) and air adhering to the surface of the aggregate (as ordinate) of a concrete paste prepared according to an aspect of the method
- 3 -a7~
of this invention compared to the composition prepared according to prior art methods, shown in broken lines.
Figs. 2, 3 and 4 are graphs showing the relation between the shear strength ~f between adjacent particles of the aggregate and air adhering to the surface of the aggregate, with ~ being the ordinate and increas-ing particle size, for example, being the abscissa, of green concrete or mortar prepared by methods of aspects of this invention;
Fig. 5 is a graph showing the relation between the quantity of air necessary to make the relative dynamic elastic coefficient to be 95% and the mechanical strength of the product, percentage of bleeding and the per-centage of decrease in the weight after freeze-thaw tests, all as ordinate of a prior art composition (at the vertical point A on the abscissa) and those embodying a composition prepared by three embodiments of the mechod of aspects of this invention (at the vertical points B, C and D respectively on the abscissa);
Fig. 6 is a graph showing the relation between the compressive strength and the relative dynamic elastic coefficient, (all as ordinate) of a prior art composition (at the vertical point A on the abcissa) and those embodying compositions prepared by three ~mbodiments of the method of aspects of this invention, (at the vertical points B, C and D respectively on the abscissa), when the quantity of air is made constant (3.4 - 3.5%);
Fig. 7 is a graph showing the relation between the relative dynamic elastic coefficient, the mechanical strength and the percentage of bleeding, (all as ordinate) when an entire quantity of an air-entraining agent is incor-porated into the primary water; and Fig. 8 is a graph showing the relation between the relative dynamic elastic coefficient, the compressive strength, and the percentage of bleeding, (all as ordinate) and variations in the quantity of the primary water, (as abscissa) of a green concrete prepared according to the prior art method and one embodying a composition prepared by a method of an aspect of this in-~95~73 vention , when the air entraining agent is divided into two portions, one portion being incorporated into the primary water while the other portion is added to the secondary water.
In preparing a concrete composition, according to the conventional prior art method, water and cement are firstly mixed together and then sand or other aggregate is incorporated to the resulting mixture. According to a method of an aspect of this invention, which method is different from the above described prior art method, air adhering to the surface of the aggre-gate is substantially completely removed. The air adhering to the surface of the aggregate prevents the cement paste from completely coating the aggregate, thus resulting in an unstable coating. More particular, the ad-hering air does not diffuse into the coating of the paste but remains as "sealed off interface air" which causes the paste coating to peel off and to form a portion having the smallest shear strength between the particles of the aggregateO Accordingly, a green composition made of an assembly of such coated aggregate has a tendency to precipitate out the aggregate, which produces bleeding of water. This relation is shown in Figs. 1 - 4 which show the state of the paste between adjacent particles of the aggregate, namely that the shear strength is varied in response toldifferent positions of the paste between the sand particles. Specifically, Fig. 7 is a graph in which the ordinate represents the shear strength ~ and the abscissa represents the increasing particle size of an aggregate. As shown, the shear strength is the minimum at the interface. Such minimum shear strength causes bleeding of water. The above described prior art method, in which a cement paste is firstly prepared and then sand or gravel aggregate is incor-porated, is carried out for the purpose of obtaining an ideal flat yield strength characteristic, as shown by dotted lines in Fig. lo . . " "
5~373 The invention in its various method aspects contemplates the pro-vision of the maximum shear strength ~ at the interface of a grain of the aggregate as shown in Figs. 2, 3 and 4. Such maximum shear strength can be obtained by substantially completely removing air adhered to the surface of the aggregate particles and then covering them with water to activate them.
These water layers adhere to the surface of the aggregate due to surface tension and the adhesive force at the surface of the aggregate becomes lar-ger than the shear strength ~ of the paste between adjacent particles of the aggregate, as shown in Fig. 4. Where an additive capable of decreasing the quantity of water is used, (as shown in Fig. 3), the shear strength of the paste between the aggregate particles can be reduced. Water layers on the particles of the aggregate will preferentially absorb a powder of cement to form stable shells of cement about the particles, thus decreas-ing the cement concentration of the paste between the particles. Thus, while the green composition has the same water-to-cement ratio (W/C), the shear strength '~f can be maximized, as shown in Fig. 2~
By substantially preventing slip at the surfaces of the aggregate particles, which would cause the particles to slip in the paste therebetween, the particles precipitate in a stable manner when the green concrete com-position is app]ied or molded. In this way it is possible substantially toprevent slip or precipitation of the particles due to unstable air layers on the surface of the aggregate particles. This greatly decreases bleed-ing of water and can assure concrete products having excellent mechanical strength.
Although the air layers on the aggregate particles are removed and are then replaced by water films, if this were carried out in the atmos-phere, air films would instantly be formed again to prevent forming of water ~9~i~73 films. Thus, methods have been developed to solve such problem. Accod-to the method disclosed in the aforementioned United States Patent No.
of this invention compared to the composition prepared according to prior art methods, shown in broken lines.
Figs. 2, 3 and 4 are graphs showing the relation between the shear strength ~f between adjacent particles of the aggregate and air adhering to the surface of the aggregate, with ~ being the ordinate and increas-ing particle size, for example, being the abscissa, of green concrete or mortar prepared by methods of aspects of this invention;
Fig. 5 is a graph showing the relation between the quantity of air necessary to make the relative dynamic elastic coefficient to be 95% and the mechanical strength of the product, percentage of bleeding and the per-centage of decrease in the weight after freeze-thaw tests, all as ordinate of a prior art composition (at the vertical point A on the abscissa) and those embodying a composition prepared by three embodiments of the mechod of aspects of this invention (at the vertical points B, C and D respectively on the abscissa);
Fig. 6 is a graph showing the relation between the compressive strength and the relative dynamic elastic coefficient, (all as ordinate) of a prior art composition (at the vertical point A on the abcissa) and those embodying compositions prepared by three ~mbodiments of the method of aspects of this invention, (at the vertical points B, C and D respectively on the abscissa), when the quantity of air is made constant (3.4 - 3.5%);
Fig. 7 is a graph showing the relation between the relative dynamic elastic coefficient, the mechanical strength and the percentage of bleeding, (all as ordinate) when an entire quantity of an air-entraining agent is incor-porated into the primary water; and Fig. 8 is a graph showing the relation between the relative dynamic elastic coefficient, the compressive strength, and the percentage of bleeding, (all as ordinate) and variations in the quantity of the primary water, (as abscissa) of a green concrete prepared according to the prior art method and one embodying a composition prepared by a method of an aspect of this in-~95~73 vention , when the air entraining agent is divided into two portions, one portion being incorporated into the primary water while the other portion is added to the secondary water.
In preparing a concrete composition, according to the conventional prior art method, water and cement are firstly mixed together and then sand or other aggregate is incorporated to the resulting mixture. According to a method of an aspect of this invention, which method is different from the above described prior art method, air adhering to the surface of the aggre-gate is substantially completely removed. The air adhering to the surface of the aggregate prevents the cement paste from completely coating the aggregate, thus resulting in an unstable coating. More particular, the ad-hering air does not diffuse into the coating of the paste but remains as "sealed off interface air" which causes the paste coating to peel off and to form a portion having the smallest shear strength between the particles of the aggregateO Accordingly, a green composition made of an assembly of such coated aggregate has a tendency to precipitate out the aggregate, which produces bleeding of water. This relation is shown in Figs. 1 - 4 which show the state of the paste between adjacent particles of the aggregate, namely that the shear strength is varied in response toldifferent positions of the paste between the sand particles. Specifically, Fig. 7 is a graph in which the ordinate represents the shear strength ~ and the abscissa represents the increasing particle size of an aggregate. As shown, the shear strength is the minimum at the interface. Such minimum shear strength causes bleeding of water. The above described prior art method, in which a cement paste is firstly prepared and then sand or gravel aggregate is incor-porated, is carried out for the purpose of obtaining an ideal flat yield strength characteristic, as shown by dotted lines in Fig. lo . . " "
5~373 The invention in its various method aspects contemplates the pro-vision of the maximum shear strength ~ at the interface of a grain of the aggregate as shown in Figs. 2, 3 and 4. Such maximum shear strength can be obtained by substantially completely removing air adhered to the surface of the aggregate particles and then covering them with water to activate them.
These water layers adhere to the surface of the aggregate due to surface tension and the adhesive force at the surface of the aggregate becomes lar-ger than the shear strength ~ of the paste between adjacent particles of the aggregate, as shown in Fig. 4. Where an additive capable of decreasing the quantity of water is used, (as shown in Fig. 3), the shear strength of the paste between the aggregate particles can be reduced. Water layers on the particles of the aggregate will preferentially absorb a powder of cement to form stable shells of cement about the particles, thus decreas-ing the cement concentration of the paste between the particles. Thus, while the green composition has the same water-to-cement ratio (W/C), the shear strength '~f can be maximized, as shown in Fig. 2~
By substantially preventing slip at the surfaces of the aggregate particles, which would cause the particles to slip in the paste therebetween, the particles precipitate in a stable manner when the green concrete com-position is app]ied or molded. In this way it is possible substantially toprevent slip or precipitation of the particles due to unstable air layers on the surface of the aggregate particles. This greatly decreases bleed-ing of water and can assure concrete products having excellent mechanical strength.
Although the air layers on the aggregate particles are removed and are then replaced by water films, if this were carried out in the atmos-phere, air films would instantly be formed again to prevent forming of water ~9~i~73 films. Thus, methods have been developed to solve such problem. Accod-to the method disclosed in the aforementioned United States Patent No.
4,176,965, air is removed by evacuating the aggregate particles, then water is filled in an evacuation vessel and then excess water is removed from between the aggregate particles by using a pressure difference.
Alternatively, air films can be removed by an impact force caused by speed energy as disclosed in Japanese Patent Application NoO 12164/
1979 (Laid Open Patent Specification No. 104958/1980). According to this method, impact force with speed energy is applied to the particles of an aggregate, for example, sand particles, with a certain quantity of water adhered to the surface thereof to replace air films wi~h water layers having uniform thickness. The quantity of water necessary completely and uniformly to cover the sand particles i5 different depending upon the size of the aggregate and its surface configuratlon. In the case of a fine aggregate, that is sand, it is advantageous to make the quantity of the adhered surface water to be more ~han 3.5%
by weight, preferably more than 4% by weight. ln the foregoing the percentages are all weight percentages unless otherwise defined.
Generally9 sands are classified into coarse, medium and fine size sands and fille sand requires much more quantity of surface water.
Research has shown that the quantity of water necessary completely to cover the sand particles is principally detennined by the surface characteristics of the sand particles rather than by their size.
When a proper water coating treatment is used, sands having relatively smooth surfaces, e.g., river sand9 1 5-2% of water can form substantially completely covering water films, whereas for coarser sand prepared by `:
Alternatively, air films can be removed by an impact force caused by speed energy as disclosed in Japanese Patent Application NoO 12164/
1979 (Laid Open Patent Specification No. 104958/1980). According to this method, impact force with speed energy is applied to the particles of an aggregate, for example, sand particles, with a certain quantity of water adhered to the surface thereof to replace air films wi~h water layers having uniform thickness. The quantity of water necessary completely and uniformly to cover the sand particles i5 different depending upon the size of the aggregate and its surface configuratlon. In the case of a fine aggregate, that is sand, it is advantageous to make the quantity of the adhered surface water to be more ~han 3.5%
by weight, preferably more than 4% by weight. ln the foregoing the percentages are all weight percentages unless otherwise defined.
Generally9 sands are classified into coarse, medium and fine size sands and fille sand requires much more quantity of surface water.
Research has shown that the quantity of water necessary completely to cover the sand particles is principally detennined by the surface characteristics of the sand particles rather than by their size.
When a proper water coating treatment is used, sands having relatively smooth surfaces, e.g., river sand9 1 5-2% of water can form substantially completely covering water films, whereas for coarser sand prepared by `:
5~a~3 crushing stone, 2.0-2.5% of water is sufficient. Ilowever, since the thod of broad aspects of this invention i5 char~cterlzed by removing surface air layers and then replacing them with uniform water layers that substantially completely surround the sand particles rather than merely decreaslng the quan~ity of tbe surfAce wa~er, the advantage of aspects of the present invention can be en~oyed even when the qu~ntity of the s~r~ace water is larger than the quantity descrlbed above, so that, in practice, the quantity of water is made to be larger than 3%, i.e. preferably 4%. Although there is no specific upper limit where cement shells are to be formed about the ~ggregate (sand) particles, a quantity of water of less than 40%, particularly less than 35% is preferred for the purpose of increasing the stability of the formed shells. Where fine and coarse aggregates are used it is advantageous firstly to form cement shells about the fine aggregate and then to add the coarse aggregate.
When an additive, for e~ample, a water-reducing agent acting to reduce the surface water on the aggregate par~icles is added to the composition, the surface activity of the surace water of the aggregate particles is enhanced, whereby removal of the surface air layers and formation of uniform surface water layers can be made more completely. In this case, the quantity of the surface water can be decreased.
In the prior art green concrete compositions, such additives S~3 were added at a final stage of admixing concrete ingredients for the purpose of dispersing the cement powder. On the other hand, according to the method of aspects of this invention, the additive is preferably added before in-corporation of the cement powder for forming water layers of uniform thick-ness about the aggregate particles. This method is also effective to remove ` air layers on the surface of coarse aggregate.
The additives which may be utilized in the method of aspects of this invention include: (1) a super plasticizer also known as a fluidity promoting agent; (2) a water-reducing agent; (3) an air-entraining agent;
(4) a quick-setting agent; and (~) a rust-preventing agentO Examples Or quick-setting agents (4) include: (a) jet cement; (b) super early high strength cement; (c) early high strength cement; (d) ordinary Portland cement; (e) medium cement; and (f) low heat generation cement. Among these elements, (a) sets in one hour and exhibits sufficient rnechanical strength;
(b), (c), (d), (e) and (f) produce sufficient strength after 3, 7, 28 and 91 days, respectively. Where cement having a setting characteristic is used as an ingredient for preparing concrete, more efficient cement materials should be used as an additive.
The water-reducing agent (2) and ~he air-entraining agent (3) may be added to a slurry cement paste between the aggregate particles so as to decrease the shear strength of the paste and to increase the slip between aggregate particles formed with cement shells. Such cement shells make it easy to cast or mold the green concrete composition by increasing the resis-tance of the paste against precipitation of the aggregate particles and by decreasing the bleeding of water, thereby increasing the mechanical strength of the concrete products. These advantages become remarkable especially when the surface water preferentially absorbs cement powder to form stable cement shells. In the green concrete composi~ion prepared by tSle method of aspects of this in~ention, in which the shear strength at the interfaces _ 9 _ ~3~3 is improved, stable coatings of relatively small thickness are formed about the aggregate particles so that it is possible to increase the water-to-cement ratio, W/C (which means a larger quantity of water).
This makes it possible for a composition having a high sand-to cement ratio, S/C to have the excellent characteristics described above.
In a 8reen concrete composition prepared by the method of aspects of this invention utilizing a coarse aggregate ir is also possible to decrease bleeding of water. Even a green concrete composi-tion prepared by the method of an aspect of this invention not contain-ing a fine aggregate (the so-called no-fine-concrete) can also exhibit the advantages decribed above.
Where a green concrete composition incorporated with cement or other hydraulic substances is used in a cold region where the ambient temperatures descreses greatly, the strength of the concrete product gradually decreases, thereby becoming brittle, or fracturing. To prevent these defects, an air entraining agent is often used and in-corporated into the green concrete composition. ~owever, when such air-entraining agent is used, in order to increase the resistance against freezing, it is necessary to increase the quantity of the air-entrain-ing agent incorporated therein. However, use of such a large quantity of the air-entraining agent decreases the mechanical strength of the resulting concrete product. According to aspects of this invention, the water to be added to the composition is divided into two portions.
One portion is admi~ed with the major or the entire quantity of the air-entraining agent to form cement shells about the aggregate par-ticles. Then the other portion is added and kneaded with the con-stituents to obtain the desired green concrete composition. Then, ~he water, which is added firstly in a quantity smaller than the entire predetermined quantity of the water, forms cement shells about the aggregate particles, the cement shells containing air formed by the chemical reaction of the air-entraining agent, thus providing resistance against freezing.
This also increases the resistance against freezing of the resulting con-crete products. Moreover, as substantially all quantities of the air-entrain-ing agent are incorporated into the first portion of the water, the quantity of the air-entraining agent and the quantity of air bubbles in the green composition are relatively small, thereby imparting desirable mechanical strength to the concrete products.
Although the mechanism of increasing the mechanical strength of the concrete products caused by the air-entraining agent is not yet clearly understood, it is believed that the air-entraining agent generally has a lipophilic group and a hydrophilic group at both ends, the air bubbles are believed to be entrained in the green composition by the lipophilic group so that the other hydrophilic end of the air-entraining agent comes to contact with the surface of the aggregate. This is identical to a case where a water reducing agent is used to wet the surface of the aggregate particles.
As a consequence, cement shells having a relatively small thickness are formed to surround the aggregate particles, similar to a case of utilizing a water reducing agent. Moreover, air bubbles are formed on the hydrophilic side of the air-entraining agent at portions adjacent the cement shells.
These functions are believed to increase the mechanical strength and the resistance against freezing of the concrete products.
The addition of a rust-preventing agent is also desirable to the green concrete composition prepared by the method of aspects of this in-vention. More particularly, in recent years sources of river or mountain sand are decreasing owing to the use of e~tremely large quantity of con-crete, so that sea sand is now more frequently used. However, salt or other chemical commpounds contained in the sea sand corrodes reinforcing steel bars used in almost all of the concrete structures. Such corrosion or rust results in the peeling off of the concrete layer or in the formation of cracks therein which enhances peeling off and cracks. For this reason, it is therefore necessary to prevent corrosion and cracking. Although salt and other chemical compounds can be removed by washing sea sand with water or neutralization, as the quantity of concrete composition is large such treatment is troublesome. Washing of the sea sand with water requires large quantity of water, thus causing pollution of the environment. Such washing not only increases the processing steps at the field of construction but it is also virtually impossible completely to remove salt and other chemical compounds. Although various experiments have been made with regard to the use of a rust-preventing agent, unless the concentration of the rust-pre-venting agent is increased, an effective rust proofing property can not be assured, thus increasing the cost of manuEacturing.
According to various aspects of the method of this invention, however, it is possible effectively to prevent rusting with a relatively small quantity of a rust-preventing agent. More particularly, the water necessary to prepare a green concrete composition is divided into two por-tions, substantially the entire quantity of the rust-preventing agent is 2() incorporated into one predetermined quantitative portion of the water, and the resulting mixture and the other predetermined quantitative portion of the water, sea sand, a coarse aggregate and a powder of hydraulic sub-stance are admixed and kneaded at different steps to prepare a green concrete composition.
Alternatively, the green concrete composition may be prepared by adding water to cement in a quantity larger ~han that which is necessary to cover all the particles of the fine aggregate with water layers and to maintclin air voids between particles of the fine aggregate and in a quantiLy - ]2 -5~3 which is sufficient to form cement shells having a lower water-to-cement ratio, ~/C of the final composition. Then the other portion of the water is added, followed by kneading. As above described, since the ratio, W/C of the cement shells is lower than that of the final composition, the cement shells are stable and would not peel off during the succeeding addition of water and the kneading operation. To the fine ag8regate formed with cement rich (that is a small W/C ratio) shells, the other predetermined quantitative portion of the water not heretofore incorporated is added along with the rust-preventing agent. Thereafter the resulting mixture is Icneaded to pre-pare a green concrete composition. Although it is advantageous to form shells of cement paste about the coarse aggregate, the fine and coarse aggregates may be simultaneously, or alternatively separately, subjected to the shell forming treatment.
The sea sand may be of any type from any source. In one embodiment an impulsive force and a speed energy or any other method may be used to remove water adhered to the surface of the sand particles. The quantity of water firstly added to the fine aggregate together with a rust-preventing agent differs substantially in accordance with the particle size and the surface characteristics of the fine aggregate. In general terms, the quantity of the water should be higher than 3% of the weight of the fine aggregate having a particle size of less than 5 mm. In any case, it is necessary to use the primary water in a quantity which is sufficient to cover all the particles of the fine aggregate. Moreover, the quantity of the primary water should be limited within a range necessary to retain a suf-ficient number of air voids between the particles of the fine aggregate. The quantity of the primary water should be less than 20% of the weight of the fine aggregate, especially less than 15%. When the quantity of the primary water exceeds these limits, the advantageous objects of various aspects of 5~73 this invention may not be obtained. After for~ing the cement shells with the primary ~ater, a rust-preventing agent is also added to the secondary water. Any rust-preventing agent may be ~sed. Suitable rust-preventing agents includ~ nitrites of calcium or sodium. The quantity of the rust-preventing agent is determined by considering the quantity of salt contained in the sea sand.
After adding the primary water containing a rust-preventing agent the mixture is agitated to make the su~face water uniform, and then a powder of cement is added, followed by kneading. The quantity of the ce~ent added corresponds to that of the cement of the green composition obtained by adding the secondary water followed by kneading~ or to that which is neces-sary to provide a desired ratio, C/S of the finally prepared co~position.
If desired, a quantity of cement may be added at the time of adding the secondary water. In any event, it is desirable to add cement in a quantity such that the cement shells formed about the particles of the fine aggre-gate would have a W/C ratio of larger than 10%, preferably 28%.
A~ above described, where a major portion o~ the ruæ~--preventing agent i~ added to th~ primar~r water" the co~ce~
tratio~ of the rust~prevenki~g agent become~ hi,æhu In thi~
ca~e, ~ the rus~preventing agent i8 incor~orated i~to the primary water, corrosive compounds adhering to the ~urfaee of ~he ~an~ ,~>article~ are sealed in the cement shell~. More p~rticularly~ wher~ a ru~t~pr~v~nting agent ~ca7 2 is added to the primary water the cement shells formed on the surface of the sand part~cles become rich in the rust-preventing agent, thereby efficiently preveneing oozing of the corrosive compounds out of the shells. Where the cement shells are formed by means of any one of the above mentioned methods, bleeding of water can be made substantially zero or reduced greatly. In contrast, according to the prlor art method, a rust -preventing agent was added to the entire quantity of the water of the composition so that large quantities of bleeding water were formed, thus losing the rust-preventing agent. In addition, corrosive compounds oozed out of the cement shells. The method of aspects of this invention can prevent or substantially obviate these disadvantages. In other words, according to aspects of the method of this invention the advantage of the rust-preventing agent can be fully used.
To have better underst:andin& of various aspects of this invention, the following examples are given, in which al] percentages are weight percentages.
Example 1 River sand having a dry specific gravity of 2.6Z, a fineness modu-lus (F.M.) of 2.9 and a percentage of water absorption of 1.65%, and crushed stone having a dry specific gravity of 2.67, a F.M. of 7.11 and a percentage of water absorption of 0.65% were used as the aggregates.
The river sand was blasted against an impact plate with centrifugal force to adjust its surface water content to 4.17% and then was admixed with the crushed stone. Then, primary water, Wl was added in an amount-to satisfy the Wl/C ratio of 15-62% as shown in the following Table I
and to form a homogeneous mixture. Thereafter, the entire quantity of an ordinary Portland cement was incorporat-ed, fol]owed by kneading for 60 seconds to form cement she]]s about all particles of the aggregdte.
_ ~5 -~S~3 Thent secondary water, W2 was added in an amount to make the totalratio W/C of the resulting mixture (green concrete) to be equal to 63%. At the same time, 0.04% of an air--entraining a~ent, based on the weight of cement, was added and the resulting mixture was kneaded for 60 seconds to obtain a desired green concrete composition.
As a control, the same river sand, crushed stone, water, cement and air-entraining agent were simultaneously loaded into a concrete mixer and Icneaded for two hours according to the prior art method to obtain a green concrete composition.
_ 16 -I ~ ~
`1 ~
~S~73 The green concrete compositions prepared by the method of this aspect of this invention and by the prior art method as described above con-tained 271 kg/m3 of cement, 171 kg/m of water, 780 kg/m of sand, 1071 kg/m of crushed stone and 108 cc of the air-entraining agent. The air-entraining agent was incorporated at different steps and the results are also shown in the following Table I. Sample No. 1 was prepared according to the prior j art method, whereas sample No. 2 was prepared by adding surface water and a powder of cement followed by a primary kneading, then adding an air-entraining agent and then subjecting it to a secondary kneading. Sample No. 3 was lo prepared by adding the same air-entraining agent of the resin acid salt type before the primary kneading. In other words, cement shells having a - 17 _ : j ~
5~73 Wl/C ratio of 35% were formed. Although the same quantities of the additive and air, and substantially the same temperature of cement and the same specific weight were used, it is seen that the percentage of bleed-ing of sample No. 3 was onlv 0.~5%, whereas that of sample No. 1 prepared by the prior art method was 2.15%. Even when the secGndary kneading was per-formed after forming cement shells during the primary kneading, the bleeding of sample No. 3 is less than one half of that of sample NoO 2, in which the air-entraining agent was added to the secondary water. Moreover, the mechani-cal strength of samp]e No. 3 was considerably increased.
- ]8 -~able I
type and /0 mean compre~sio~
~oO W1/C of addition quantit~ slump a~ r teperature p bleeding stren~t~ ~k~/~m~l of additive of additi~re value o~ cgncrete after after ~0) ~cc3 (cm) (~) ( C~ (Xg/Q) ~ 7 day~ 28 da;srs sur- resin acid face salt water Q 0.04 108 1~c7 ~.9 26.0 2.312 2.'1517Z 2~7 re~in acid ,_ salt added to secon-2 dar~ water 4.28 0.04 108 9~4 ~8 26.0 2.312 1.10 192 282 resin acid salt added to primary 3 water ~ .,28 0~,04 108 504 3c8 26.0 2.314 0~45 219 321 ~S~3 Example 2 Medium size river sand having a F.M. of 2.54, a specific gravity of 2059 and a percentage of water absorption of 2~73%7 and crushed stone having a si~e between 20 mm and 5 mm, a F.M. of 6~47~ a specific grav.ty of 2~64 and a percentage of water absorption of 0~53% were used as the aggre-gates. Ordinary Portland cement, a resin acid type air-entraining agent, and a water-reducing agent consis~ing of naphthalene sulphona~e were pre-pared. Ater forming the cement shells, the air-entraining agent and the water-reducing agent just mentioned were incorporated into the secondary water.
More particularly, 320 kg/m of cement, 176 kg/m of water, 95S
kg/m of sand and 833 kg/m of crushed stone were mixed together. The water was divided into primary water, Wl and secondary water, W2 and the primary water was added to sand and crushed stone whose surface water has been ad-justed to 4~5% in an amount sufficient to ensure ratios, Wl/C shown in the following Table Il. The resulting mixture was then kneaded for 30 seconds to form uniform surface water layers. Then the entire quantity of cement was added followed by secondary kneading for two minutes. Cement shells were then formed about the aggregate particles. Thereafter, secondary water, W2 was added in a quantity sufficient to make the total W/C ratio of the resulting mixture to be 55% and then the mixture was kneaded for 90 seconds to obtain a green composition. At this time, a dispensing agent, SP
~5~'73 and a water-reducing agent, WR in an amount corresponding to that of cement, an air entraining agent, AE corresponding to 4% of cement, and a jet cement 9 JC (manufactured by Onoda Cement Co.) corresponding to 5% of cement were added at different steps of manufacturing the green cement or mortar com-positions. The time of incorporating the additives, their physical properties and the mechanical strength of the concrete products are shown in the following Table II.
. Table II
W1/C water and additive slump air temperature bl~eding mean compression No~ ~alue of concrete strengt~ (k~/cm~
( W1W2 ~cm) ~Yo) ~C) (0 after after 7 da~ 28 da~
1 ~5 ~ 4.6 1.3 29.0 0.65 268 384 ,2 art 902 Q.6 29~0 4.33 211 307 ~ 16 AE 10.0 4~1 29.0 0~29 24~ 358 4 20 AEWR 15~0 4.4 29~0 1~18 249 366 - AE 16.5 4.3 29.3 0.93 231 342
When an additive, for e~ample, a water-reducing agent acting to reduce the surface water on the aggregate par~icles is added to the composition, the surface activity of the surace water of the aggregate particles is enhanced, whereby removal of the surface air layers and formation of uniform surface water layers can be made more completely. In this case, the quantity of the surface water can be decreased.
In the prior art green concrete compositions, such additives S~3 were added at a final stage of admixing concrete ingredients for the purpose of dispersing the cement powder. On the other hand, according to the method of aspects of this invention, the additive is preferably added before in-corporation of the cement powder for forming water layers of uniform thick-ness about the aggregate particles. This method is also effective to remove ` air layers on the surface of coarse aggregate.
The additives which may be utilized in the method of aspects of this invention include: (1) a super plasticizer also known as a fluidity promoting agent; (2) a water-reducing agent; (3) an air-entraining agent;
(4) a quick-setting agent; and (~) a rust-preventing agentO Examples Or quick-setting agents (4) include: (a) jet cement; (b) super early high strength cement; (c) early high strength cement; (d) ordinary Portland cement; (e) medium cement; and (f) low heat generation cement. Among these elements, (a) sets in one hour and exhibits sufficient rnechanical strength;
(b), (c), (d), (e) and (f) produce sufficient strength after 3, 7, 28 and 91 days, respectively. Where cement having a setting characteristic is used as an ingredient for preparing concrete, more efficient cement materials should be used as an additive.
The water-reducing agent (2) and ~he air-entraining agent (3) may be added to a slurry cement paste between the aggregate particles so as to decrease the shear strength of the paste and to increase the slip between aggregate particles formed with cement shells. Such cement shells make it easy to cast or mold the green concrete composition by increasing the resis-tance of the paste against precipitation of the aggregate particles and by decreasing the bleeding of water, thereby increasing the mechanical strength of the concrete products. These advantages become remarkable especially when the surface water preferentially absorbs cement powder to form stable cement shells. In the green concrete composi~ion prepared by tSle method of aspects of this in~ention, in which the shear strength at the interfaces _ 9 _ ~3~3 is improved, stable coatings of relatively small thickness are formed about the aggregate particles so that it is possible to increase the water-to-cement ratio, W/C (which means a larger quantity of water).
This makes it possible for a composition having a high sand-to cement ratio, S/C to have the excellent characteristics described above.
In a 8reen concrete composition prepared by the method of aspects of this invention utilizing a coarse aggregate ir is also possible to decrease bleeding of water. Even a green concrete composi-tion prepared by the method of an aspect of this invention not contain-ing a fine aggregate (the so-called no-fine-concrete) can also exhibit the advantages decribed above.
Where a green concrete composition incorporated with cement or other hydraulic substances is used in a cold region where the ambient temperatures descreses greatly, the strength of the concrete product gradually decreases, thereby becoming brittle, or fracturing. To prevent these defects, an air entraining agent is often used and in-corporated into the green concrete composition. ~owever, when such air-entraining agent is used, in order to increase the resistance against freezing, it is necessary to increase the quantity of the air-entrain-ing agent incorporated therein. However, use of such a large quantity of the air-entraining agent decreases the mechanical strength of the resulting concrete product. According to aspects of this invention, the water to be added to the composition is divided into two portions.
One portion is admi~ed with the major or the entire quantity of the air-entraining agent to form cement shells about the aggregate par-ticles. Then the other portion is added and kneaded with the con-stituents to obtain the desired green concrete composition. Then, ~he water, which is added firstly in a quantity smaller than the entire predetermined quantity of the water, forms cement shells about the aggregate particles, the cement shells containing air formed by the chemical reaction of the air-entraining agent, thus providing resistance against freezing.
This also increases the resistance against freezing of the resulting con-crete products. Moreover, as substantially all quantities of the air-entrain-ing agent are incorporated into the first portion of the water, the quantity of the air-entraining agent and the quantity of air bubbles in the green composition are relatively small, thereby imparting desirable mechanical strength to the concrete products.
Although the mechanism of increasing the mechanical strength of the concrete products caused by the air-entraining agent is not yet clearly understood, it is believed that the air-entraining agent generally has a lipophilic group and a hydrophilic group at both ends, the air bubbles are believed to be entrained in the green composition by the lipophilic group so that the other hydrophilic end of the air-entraining agent comes to contact with the surface of the aggregate. This is identical to a case where a water reducing agent is used to wet the surface of the aggregate particles.
As a consequence, cement shells having a relatively small thickness are formed to surround the aggregate particles, similar to a case of utilizing a water reducing agent. Moreover, air bubbles are formed on the hydrophilic side of the air-entraining agent at portions adjacent the cement shells.
These functions are believed to increase the mechanical strength and the resistance against freezing of the concrete products.
The addition of a rust-preventing agent is also desirable to the green concrete composition prepared by the method of aspects of this in-vention. More particularly, in recent years sources of river or mountain sand are decreasing owing to the use of e~tremely large quantity of con-crete, so that sea sand is now more frequently used. However, salt or other chemical commpounds contained in the sea sand corrodes reinforcing steel bars used in almost all of the concrete structures. Such corrosion or rust results in the peeling off of the concrete layer or in the formation of cracks therein which enhances peeling off and cracks. For this reason, it is therefore necessary to prevent corrosion and cracking. Although salt and other chemical compounds can be removed by washing sea sand with water or neutralization, as the quantity of concrete composition is large such treatment is troublesome. Washing of the sea sand with water requires large quantity of water, thus causing pollution of the environment. Such washing not only increases the processing steps at the field of construction but it is also virtually impossible completely to remove salt and other chemical compounds. Although various experiments have been made with regard to the use of a rust-preventing agent, unless the concentration of the rust-pre-venting agent is increased, an effective rust proofing property can not be assured, thus increasing the cost of manuEacturing.
According to various aspects of the method of this invention, however, it is possible effectively to prevent rusting with a relatively small quantity of a rust-preventing agent. More particularly, the water necessary to prepare a green concrete composition is divided into two por-tions, substantially the entire quantity of the rust-preventing agent is 2() incorporated into one predetermined quantitative portion of the water, and the resulting mixture and the other predetermined quantitative portion of the water, sea sand, a coarse aggregate and a powder of hydraulic sub-stance are admixed and kneaded at different steps to prepare a green concrete composition.
Alternatively, the green concrete composition may be prepared by adding water to cement in a quantity larger ~han that which is necessary to cover all the particles of the fine aggregate with water layers and to maintclin air voids between particles of the fine aggregate and in a quantiLy - ]2 -5~3 which is sufficient to form cement shells having a lower water-to-cement ratio, ~/C of the final composition. Then the other portion of the water is added, followed by kneading. As above described, since the ratio, W/C of the cement shells is lower than that of the final composition, the cement shells are stable and would not peel off during the succeeding addition of water and the kneading operation. To the fine ag8regate formed with cement rich (that is a small W/C ratio) shells, the other predetermined quantitative portion of the water not heretofore incorporated is added along with the rust-preventing agent. Thereafter the resulting mixture is Icneaded to pre-pare a green concrete composition. Although it is advantageous to form shells of cement paste about the coarse aggregate, the fine and coarse aggregates may be simultaneously, or alternatively separately, subjected to the shell forming treatment.
The sea sand may be of any type from any source. In one embodiment an impulsive force and a speed energy or any other method may be used to remove water adhered to the surface of the sand particles. The quantity of water firstly added to the fine aggregate together with a rust-preventing agent differs substantially in accordance with the particle size and the surface characteristics of the fine aggregate. In general terms, the quantity of the water should be higher than 3% of the weight of the fine aggregate having a particle size of less than 5 mm. In any case, it is necessary to use the primary water in a quantity which is sufficient to cover all the particles of the fine aggregate. Moreover, the quantity of the primary water should be limited within a range necessary to retain a suf-ficient number of air voids between the particles of the fine aggregate. The quantity of the primary water should be less than 20% of the weight of the fine aggregate, especially less than 15%. When the quantity of the primary water exceeds these limits, the advantageous objects of various aspects of 5~73 this invention may not be obtained. After for~ing the cement shells with the primary ~ater, a rust-preventing agent is also added to the secondary water. Any rust-preventing agent may be ~sed. Suitable rust-preventing agents includ~ nitrites of calcium or sodium. The quantity of the rust-preventing agent is determined by considering the quantity of salt contained in the sea sand.
After adding the primary water containing a rust-preventing agent the mixture is agitated to make the su~face water uniform, and then a powder of cement is added, followed by kneading. The quantity of the ce~ent added corresponds to that of the cement of the green composition obtained by adding the secondary water followed by kneading~ or to that which is neces-sary to provide a desired ratio, C/S of the finally prepared co~position.
If desired, a quantity of cement may be added at the time of adding the secondary water. In any event, it is desirable to add cement in a quantity such that the cement shells formed about the particles of the fine aggre-gate would have a W/C ratio of larger than 10%, preferably 28%.
A~ above described, where a major portion o~ the ruæ~--preventing agent i~ added to th~ primar~r water" the co~ce~
tratio~ of the rust~prevenki~g agent become~ hi,æhu In thi~
ca~e, ~ the rus~preventing agent i8 incor~orated i~to the primary water, corrosive compounds adhering to the ~urfaee of ~he ~an~ ,~>article~ are sealed in the cement shell~. More p~rticularly~ wher~ a ru~t~pr~v~nting agent ~ca7 2 is added to the primary water the cement shells formed on the surface of the sand part~cles become rich in the rust-preventing agent, thereby efficiently preveneing oozing of the corrosive compounds out of the shells. Where the cement shells are formed by means of any one of the above mentioned methods, bleeding of water can be made substantially zero or reduced greatly. In contrast, according to the prlor art method, a rust -preventing agent was added to the entire quantity of the water of the composition so that large quantities of bleeding water were formed, thus losing the rust-preventing agent. In addition, corrosive compounds oozed out of the cement shells. The method of aspects of this invention can prevent or substantially obviate these disadvantages. In other words, according to aspects of the method of this invention the advantage of the rust-preventing agent can be fully used.
To have better underst:andin& of various aspects of this invention, the following examples are given, in which al] percentages are weight percentages.
Example 1 River sand having a dry specific gravity of 2.6Z, a fineness modu-lus (F.M.) of 2.9 and a percentage of water absorption of 1.65%, and crushed stone having a dry specific gravity of 2.67, a F.M. of 7.11 and a percentage of water absorption of 0.65% were used as the aggregates.
The river sand was blasted against an impact plate with centrifugal force to adjust its surface water content to 4.17% and then was admixed with the crushed stone. Then, primary water, Wl was added in an amount-to satisfy the Wl/C ratio of 15-62% as shown in the following Table I
and to form a homogeneous mixture. Thereafter, the entire quantity of an ordinary Portland cement was incorporat-ed, fol]owed by kneading for 60 seconds to form cement she]]s about all particles of the aggregdte.
_ ~5 -~S~3 Thent secondary water, W2 was added in an amount to make the totalratio W/C of the resulting mixture (green concrete) to be equal to 63%. At the same time, 0.04% of an air--entraining a~ent, based on the weight of cement, was added and the resulting mixture was kneaded for 60 seconds to obtain a desired green concrete composition.
As a control, the same river sand, crushed stone, water, cement and air-entraining agent were simultaneously loaded into a concrete mixer and Icneaded for two hours according to the prior art method to obtain a green concrete composition.
_ 16 -I ~ ~
`1 ~
~S~73 The green concrete compositions prepared by the method of this aspect of this invention and by the prior art method as described above con-tained 271 kg/m3 of cement, 171 kg/m of water, 780 kg/m of sand, 1071 kg/m of crushed stone and 108 cc of the air-entraining agent. The air-entraining agent was incorporated at different steps and the results are also shown in the following Table I. Sample No. 1 was prepared according to the prior j art method, whereas sample No. 2 was prepared by adding surface water and a powder of cement followed by a primary kneading, then adding an air-entraining agent and then subjecting it to a secondary kneading. Sample No. 3 was lo prepared by adding the same air-entraining agent of the resin acid salt type before the primary kneading. In other words, cement shells having a - 17 _ : j ~
5~73 Wl/C ratio of 35% were formed. Although the same quantities of the additive and air, and substantially the same temperature of cement and the same specific weight were used, it is seen that the percentage of bleed-ing of sample No. 3 was onlv 0.~5%, whereas that of sample No. 1 prepared by the prior art method was 2.15%. Even when the secGndary kneading was per-formed after forming cement shells during the primary kneading, the bleeding of sample No. 3 is less than one half of that of sample NoO 2, in which the air-entraining agent was added to the secondary water. Moreover, the mechani-cal strength of samp]e No. 3 was considerably increased.
- ]8 -~able I
type and /0 mean compre~sio~
~oO W1/C of addition quantit~ slump a~ r teperature p bleeding stren~t~ ~k~/~m~l of additive of additi~re value o~ cgncrete after after ~0) ~cc3 (cm) (~) ( C~ (Xg/Q) ~ 7 day~ 28 da;srs sur- resin acid face salt water Q 0.04 108 1~c7 ~.9 26.0 2.312 2.'1517Z 2~7 re~in acid ,_ salt added to secon-2 dar~ water 4.28 0.04 108 9~4 ~8 26.0 2.312 1.10 192 282 resin acid salt added to primary 3 water ~ .,28 0~,04 108 504 3c8 26.0 2.314 0~45 219 321 ~S~3 Example 2 Medium size river sand having a F.M. of 2.54, a specific gravity of 2059 and a percentage of water absorption of 2~73%7 and crushed stone having a si~e between 20 mm and 5 mm, a F.M. of 6~47~ a specific grav.ty of 2~64 and a percentage of water absorption of 0~53% were used as the aggre-gates. Ordinary Portland cement, a resin acid type air-entraining agent, and a water-reducing agent consis~ing of naphthalene sulphona~e were pre-pared. Ater forming the cement shells, the air-entraining agent and the water-reducing agent just mentioned were incorporated into the secondary water.
More particularly, 320 kg/m of cement, 176 kg/m of water, 95S
kg/m of sand and 833 kg/m of crushed stone were mixed together. The water was divided into primary water, Wl and secondary water, W2 and the primary water was added to sand and crushed stone whose surface water has been ad-justed to 4~5% in an amount sufficient to ensure ratios, Wl/C shown in the following Table Il. The resulting mixture was then kneaded for 30 seconds to form uniform surface water layers. Then the entire quantity of cement was added followed by secondary kneading for two minutes. Cement shells were then formed about the aggregate particles. Thereafter, secondary water, W2 was added in a quantity sufficient to make the total W/C ratio of the resulting mixture to be 55% and then the mixture was kneaded for 90 seconds to obtain a green composition. At this time, a dispensing agent, SP
~5~'73 and a water-reducing agent, WR in an amount corresponding to that of cement, an air entraining agent, AE corresponding to 4% of cement, and a jet cement 9 JC (manufactured by Onoda Cement Co.) corresponding to 5% of cement were added at different steps of manufacturing the green cement or mortar com-positions. The time of incorporating the additives, their physical properties and the mechanical strength of the concrete products are shown in the following Table II.
. Table II
W1/C water and additive slump air temperature bl~eding mean compression No~ ~alue of concrete strengt~ (k~/cm~
( W1W2 ~cm) ~Yo) ~C) (0 after after 7 da~ 28 da~
1 ~5 ~ 4.6 1.3 29.0 0.65 268 384 ,2 art 902 Q.6 29~0 4.33 211 307 ~ 16 AE 10.0 4~1 29.0 0~29 24~ 358 4 20 AEWR 15~0 4.4 29~0 1~18 249 366 - AE 16.5 4.3 29.3 0.93 231 342
6 16 WRWR 3~ 3 29.8 0 277 404 C~
7 26 WRWR 3~ 3~5 29.2 0 279 407
8 20 SPAE 17.0 3O8 29~5 0 283 422
9 20 _SP AE WR 27.0 3.7 29.5 8O8Z - 201 311 1o P~ or AESP WR 16 G Q 8.0 28.0 4.50 . 200 300 11 16 JG - 8.5 0.8 29.0 0 275 383 12 16 _ JC 7v5 0~9 29.0 0.95 255 3~1 In sample No. l, no additive was added to either of the primary and secondary water, but the ratio, Wl /C at the time of forming the cement shells was selected to be 35%. ~ith this method, the strength of the product waS increased by at least 20% over that of sample No. 2 prepared by the prior art method, and the percentage of bleeding was decreased to be less than 1%.
Sample Nos. 3 through 7 were obtained by adding, to sample No. l, an air-entraining agent, and a water-reducing agent. Those samples could produce concrete products containing 40% of air. Although the mechanical strength has decreased proportionally, sample Nos. 3,4,6 and 7, in which additives were added to the primary water, showed considerably higher strength than sample NoO 5, in which the additives were added at the time of the secondary kneading. More practically, samples Nos. 6 and 7, in which the water-decreasing agent was incorporated into the primary water, showed higher com-pression strength than that of the prior art concrete by more than 20% and showed no bleeding. In samples Nos. 8 through lO, a dispersing agent, SP, an air-entraining agent and a wa~er-decreasing agent were also incorporated.
In these cases, bV adding only the dispersing agent, SP to the primary water ~he mechanical strength was improved more than 30% and the bleeding was reduced greatly. Samples Nos. 11 and 12 were prepared by incorporating the jet cement, JC. When the jet cement was added to the primary water, the mechanical strength was increased by 15% and the bleeding was reduced further.
E~ample 3 This example was made for the purpose of preparing concrete pro-ducts having improved resistance to freezing. Resistance to freezing can be enhanced by comparing the relative dynamic resistance coefficient ater 300 cycles of freeæing and thawing with that before freezing and thawing tests, these being termed "freeze/thaw cycles". For the purpose of obtain-ing a relative dynamic elastic coefficient, i.e. larger than 95% after 300 cycles of the freezing and thawing, 309 kg/m3 of cement and 170 ~/m of water were added to obtain a sand-to-gravel ratio, S/A of 50%~ and a water-to-cement ratio, W/C of 55%, and an air-entraining agent was incorporated into the mixture such that 4.9% of air would be included. These ingredients were incorporated and kneaded at the same time according to the prior art method.
On the other hand9 according to the method of an aspect of this invention, water was divided into primary and secondary water. To 100 ~/m3 of the primary water was added the entire quantity of the air-entraining agent such that the quantity of air becomes 2.9%. Then an aggregate and cement were added and the resulting mixture was admixed for 30 seconds. The ~/m of the secondary water was added and the mixture was kneaded for two minutes.
Another sample was prepared by adding one half quantity of the air-entraining agent which ensures 3.1% of the entrained air to 70 ~/m of the primary water, and then adding an aggregate and cement followed by kneading for 30 seconds.
Thereafter 100 Rlm3 of the secondary water containing the other half of the air-entraining agent was added to the mixture and kneaded for two minutes.
Still another sample was prepared by adding, to the primary water, 0.3% of a dispersing agent based on the quantity of cement. Then 0.9% of the dis-persing agent based on the quantity of cement9 and the 0.0017% of an air-entraining agent based on the quantity of cement were incorporated into the secondary water, and the resulting mixture was kneaded for two minutes. The quantity of air, the compression strength after 2~ days, the percentage of bleeding, and the percentage of the decrease in the weight after 300 cycles of the freezing test are shown in Fig. 5.
S~3 The four units existing on the horizontal axis (abscissa) of Fig. 5 show (A) the prior art method wherein the air-entraining agent is added together with all ingredients necessary to prepare a concrete mixture; (B) a first embodiment of the method of this invention wherein the air-entrain-ing agent is incorporated with the primary water which is a part of the necessary water; (C) a second embodiment wherein a portion of the air-en-training agent is added first to the primary water and then the remainder of the air-entraining agent is added to the secondary water respectively and (D) a third embodiment wherein the air-entraining agent is added to the secondary water and another additive, that is, a dispersing agent is added both to the primary water to secondary water. The values are shown in the vertical axes above these four points.
As shown, the green concrete composition prepared by the prior art method contained 5% of air, showed percentage of bleeding higher than 6%, 304 kg/cm of strength after 28 days, and a percentage of weight decrease of 1.5%. In contrast, the samples prepared by the methods of aspects of this invention contained less than 3% of air and had a percentage of bleed-ing only 1.7%, a strength of 400 kg/cm after 28 days and a small percentage of weight decrease of 1%. This shows that the concrete products formed by using compositions prepared by the method of aspects of this invention have excellent characteristics.
As also shown in Figure 5~ in another sample in which respective one halves of the air-entraining agents were added to 70 ~/m of the primary water and to the secondary water respectively, the quantity of air slightly exceeded 3%, its percentage of bleeding was 2.70% but its strength after 28 days showed a high value of 362 kg/cm2 , and its weight decrease was only 1.1%, these characteristics being excellent when compared with the concrete products formed by the prior art method.
Another sample, also shown in Fig. S, in which a portion of the dispersing agent was added to the primary water, had an air quantity slightly higher than 3%, a lowest percentage of bleeding of 2.5%9 and a percentage of weight decrease of 2.75%. The strength after 28 days was 415 kg/cm , the highest value.
Concrete was formed by using the same composition as above described and containing 3.4 - 3.5% of air according to the prior art method. Another sample was formed by adding the entire quantity of the air-entraining agent to the primary water and in still another sample, equal portions of the air-entraining agent were added to the primary and secondary waters respectively according to the method of an aspect according to the method of an aspect of this inven~ion. After 300 cycles and 600 cycles, the relative elastic coefficient and the compression strength after 28 days were measured and shown in Yig. 6.
The hori~ontal axes of Fig. 6 have four units which are the same as those in Fig. 5, and lefthand unit of the vertical a~is (ordinate) of Fig. 6 represents the compression strength of the resulting concrete mix-tures prepared by respective methods.
As shown, the concrete product formed according to the prior art method fractured at a relative elastic coefficient of 4i after 200 cycles of the free~ing test, and had a relative elastic coefficient of 48 at the end of 180 cycles. This concrete product had a compression strength of 331 kg/cm after 28 days. In contrast, the concrete product produced by the method of an aspect of this invention in which the entire quantity of the air-entraining agent was added to the primary water had a relative elastic ~ , ~
5~3 coefficient of 90 after 300 cycles of the freezing test and 82 even after 600 cycles. The compression strength after 28 days was 425 kg/cm . In another product in which the air entraining agent was incorporated into the primary water and the secondary water respectively had a relative elastic coefficient of 95 after 300 cycles and of 80 after 600 cycles, and a com-pression strength of 401 kg/cm after 28 days. As shown in Fig. 6, the con-; crete product in which a portion of the dispersing agent was added to the primary water had a compression strength of 435 kg/cm after 28 days, and relative elastic coefficients of 96 and 74 respectively after 300 and 600 cycles of the freezing tests. This shows that with the same composition,greatly different relative elastic coefficients and commpression strengths can be obtained.
When adding an air-entraining agent to the primary water in an amount necessary to ensure an air quantity of 3.2-5% in accordance with the method of an aspect of this invention9 the quantity of water previously applied onto the surface of the aggregate as varied. The results were shown in Fig. 7~ Figure 7 shows the percentage of bleeding, the compres-sive strength after 28 days and the relative dynamic elastic coefficient after 300 freezetthaw cycles as respective ordinates, and the /O surface water or sand, the amount of air entraining agent and the percentage Wl/C
as respective abscissae. In this case when the quantity of the primary water Wl amounts to 15-20%~ more particularly 20-35% based on the weight of cement, best result was obtained. In the latter range of 20-35%, the relative elastic coefficient after 300 freeze/thaw cycles was always larger than 95 and the mechanical strength of the product was also high. It was possible , 9'73 to limit the percentage of bleeding to be less than 2% when the ratio Wl/C
lies in a range of 15-45%.
Similar tests were made except that the air-entraining agent was divided and incorporated into the primary and secondary water and the results are shown in Fig. 8, in which the ordinates and abscissae are the same as Fig. 7. In this case tooJ since half of the air-entraining agent was incor-porated into the primary water, satisfactory results were obtained when the ratio Wl/C was in a range of 15-35%. Even when ratio, Wl/C was in a range of 40-50%, better results than the prior art were obtained.
Example 4 Sea sand containing 0.3% of salt was used as a fine aggregate.
842 kg/m of this sea sand, 979 kg/m of a coarse aggregate having a particle size of less than 15 mm, 75 kg/m3 of a steel fibre, 325 kg/m of cement9 195 kg/m of water and 3 ~/m3 of a rust-preventing agent of the nitrite type were admixed to obtain a green concrete composition. When all ingredients were simultaneously incorporated according to the prior art method and slump value was 10.0 cm. This is termed a control sample.
~ ``
On the other hand, a green concret~ A prep~r~d by the method of an aspect of this invention WaS prepared by adml~ing one half of the water and the entire quantlty of the rust-preventing agent to prepare the primary water, which was sprinkled on~o the sea sand mentioned above and kneaded to cause the water uniformly to adhere to the surface of the sea sand. Then, cement was added to ~orm 8h~ h~Vi ~ a r~tio, W1/C of 25/On ~he~ th~ r~
i~g w~ter w~ added afi the second~r~r water, and th~ re~ult-i~g mixture wa~ eaded to obtai:~ the gree~ concre~e A
o h~ving ~ ~lump ~ralue o~ 6 cm.
Impul~i~re ïorc~ ~d ~p~d e~ergy were ~pplied to the sea sand to adjust the percentage of the surface wa~er to 5%.
At first the entire quantity of the rust-preventing agent was sprinkled upon the sea sand thus treated while stirring the mixture and then primary water, not containing any rust-preventing agent, was added to prepare green concrete B according to the method of another aspect of this invention.
Further, 3 ~Im3 of the rust-preventing agent was divided into two portions having a ratio of 4 : 1. 24 ~/m of the high concentration rust-preventing agent was added to the primary water. o.6 ~/m3 of low concentration rust-preventing agent was added to the secondary water and the thus prepared primary water and secondary water were used in the same manner as above described to prepare a green concrete C accord-ing to the method of yet another aspect of this invention.
9~3 Each of the green concretes (control example and the green con-cretes A, B and C) was used to prepare a sample having a diameter of 100 mm and a length of 200 mm. Each sample was molded horizontally and vertically.
The concrete sample prepared according to the prior art method had a percentage of bleeding of 1.64%, whereas samples A, B and C, which were formed with cement shells after incorporation of the primary water, had a percentage of bleeding of 0.5%, which is negligibly small.
Following a curing for 14 days, aqueduct water at 50C was sprinkled over respective samples for 12 hours. Samples were subjected to two cycles of an accelerated corrosion test of the reinforcing steel bars which was carried out at 60 C for 12 hours at a relative humidity (RH) of 95% and then at 60 C for 12 hours at a RH of 25%. The percentages of the rusted areas are shown in ~he following Table III.
- 30 _ q'able III
condition of ~ of rusted area each total /0 of rusted sam~le prepari~g green of steel bar~ a~erage average area of concrete upper lower ~t~el fibres portion portio~ b) t9/
horizo~tally ca~ted 106 1~,8 1.7 R. 1.2 1.5 verticall~ casted 0.3 0~,7 O~r7 horizontally Gasted 306 203 3-2 i. 1 ~ . 6 ~erticall~ casted 1.,2 1.2 1.2 w horizontall~ casted 3~7 4.Q ~09 C 2.,2 2c8 verticall;~ castea Q.,4 0~4 0~4 horizorltally ca~ted 9. 5 7 .4 8.4 C~ r~l 6.4 8~ 5 ~rertically cas~ed 506 3~1 4~
. . .
Even when the same quantity of the rust-preventing agent is used for the sea sand containing the same quantity of salt, the rusting of the green concrete prepared using the method of an aspect of this invention is less than 1/3 of that of the prior art. Especially, in sample A the rusting area was reduced to 1/5 and in the vertically molded sample A, the rusting was reduced to less than 1/10. Various characteristics of samples B and C
are better than those of the control sample.
Example 5 A control sample was prepared in the same manner as in Example 1 except that 895 kg/m 30f sea sand containing 0.2% of salt, 988 kg/rn of a coarse aggregate, 300 kg/m of cement, 165 kg/m of water and 2 ~/m of a rust-preventing agent of the nitrite type was used. The slump values of this control sample and of the aforementioned samples A and ~ prepared by the method of aspects of this invention, the percentage of bleeding of this control sample, and the results of accelerated corrosion tests of reinforcing steel bars are shown in the following table IV.
Table I~
~lump ~lalue bleediIlg perce~t~ge o~ rus~d Rrea sample (cm) (9~) upper por~io~ lower-por~io~
A 8.,5 0~78 0048 0~31 B ~.5 0.71 0.39 057 control B.5 1.90 2.75 . 0.~3 As can be noted from this Table IV, ascording to aspects of this invention, it is possible greatly to reduce the percentage of bleeding of water as well as to reduce the rusted area of rein-forcing steel bars.
Yet another con~rol sample was prepared and tested lnwhlch no rust-preventing agent was added. In such control sample the percentage of the rusted area of the reinforcing steel bars was 15~65% at the upper portion and llo 15% ~t the lower portion. This result shows that use of the rust-preventing agent is effective even in concrete prepared by conventional methods and the data shown in Table IV shows that this effect is much more rsmarkable in concrete prepared according to the method of aspects of this invention.
As above described according to the method of aspects of this invention, it is possible to prepare a green composition, more particularly green mortar or green concrete, having a small percen-tage of bleeding water. It is thus possible to obtain concrete pro-ducts having high mechanical strength, in which rusting of reinforcing steel bars can be reduced.
Sample Nos. 3 through 7 were obtained by adding, to sample No. l, an air-entraining agent, and a water-reducing agent. Those samples could produce concrete products containing 40% of air. Although the mechanical strength has decreased proportionally, sample Nos. 3,4,6 and 7, in which additives were added to the primary water, showed considerably higher strength than sample NoO 5, in which the additives were added at the time of the secondary kneading. More practically, samples Nos. 6 and 7, in which the water-decreasing agent was incorporated into the primary water, showed higher com-pression strength than that of the prior art concrete by more than 20% and showed no bleeding. In samples Nos. 8 through lO, a dispersing agent, SP, an air-entraining agent and a wa~er-decreasing agent were also incorporated.
In these cases, bV adding only the dispersing agent, SP to the primary water ~he mechanical strength was improved more than 30% and the bleeding was reduced greatly. Samples Nos. 11 and 12 were prepared by incorporating the jet cement, JC. When the jet cement was added to the primary water, the mechanical strength was increased by 15% and the bleeding was reduced further.
E~ample 3 This example was made for the purpose of preparing concrete pro-ducts having improved resistance to freezing. Resistance to freezing can be enhanced by comparing the relative dynamic resistance coefficient ater 300 cycles of freeæing and thawing with that before freezing and thawing tests, these being termed "freeze/thaw cycles". For the purpose of obtain-ing a relative dynamic elastic coefficient, i.e. larger than 95% after 300 cycles of the freezing and thawing, 309 kg/m3 of cement and 170 ~/m of water were added to obtain a sand-to-gravel ratio, S/A of 50%~ and a water-to-cement ratio, W/C of 55%, and an air-entraining agent was incorporated into the mixture such that 4.9% of air would be included. These ingredients were incorporated and kneaded at the same time according to the prior art method.
On the other hand9 according to the method of an aspect of this invention, water was divided into primary and secondary water. To 100 ~/m3 of the primary water was added the entire quantity of the air-entraining agent such that the quantity of air becomes 2.9%. Then an aggregate and cement were added and the resulting mixture was admixed for 30 seconds. The ~/m of the secondary water was added and the mixture was kneaded for two minutes.
Another sample was prepared by adding one half quantity of the air-entraining agent which ensures 3.1% of the entrained air to 70 ~/m of the primary water, and then adding an aggregate and cement followed by kneading for 30 seconds.
Thereafter 100 Rlm3 of the secondary water containing the other half of the air-entraining agent was added to the mixture and kneaded for two minutes.
Still another sample was prepared by adding, to the primary water, 0.3% of a dispersing agent based on the quantity of cement. Then 0.9% of the dis-persing agent based on the quantity of cement9 and the 0.0017% of an air-entraining agent based on the quantity of cement were incorporated into the secondary water, and the resulting mixture was kneaded for two minutes. The quantity of air, the compression strength after 2~ days, the percentage of bleeding, and the percentage of the decrease in the weight after 300 cycles of the freezing test are shown in Fig. 5.
S~3 The four units existing on the horizontal axis (abscissa) of Fig. 5 show (A) the prior art method wherein the air-entraining agent is added together with all ingredients necessary to prepare a concrete mixture; (B) a first embodiment of the method of this invention wherein the air-entrain-ing agent is incorporated with the primary water which is a part of the necessary water; (C) a second embodiment wherein a portion of the air-en-training agent is added first to the primary water and then the remainder of the air-entraining agent is added to the secondary water respectively and (D) a third embodiment wherein the air-entraining agent is added to the secondary water and another additive, that is, a dispersing agent is added both to the primary water to secondary water. The values are shown in the vertical axes above these four points.
As shown, the green concrete composition prepared by the prior art method contained 5% of air, showed percentage of bleeding higher than 6%, 304 kg/cm of strength after 28 days, and a percentage of weight decrease of 1.5%. In contrast, the samples prepared by the methods of aspects of this invention contained less than 3% of air and had a percentage of bleed-ing only 1.7%, a strength of 400 kg/cm after 28 days and a small percentage of weight decrease of 1%. This shows that the concrete products formed by using compositions prepared by the method of aspects of this invention have excellent characteristics.
As also shown in Figure 5~ in another sample in which respective one halves of the air-entraining agents were added to 70 ~/m of the primary water and to the secondary water respectively, the quantity of air slightly exceeded 3%, its percentage of bleeding was 2.70% but its strength after 28 days showed a high value of 362 kg/cm2 , and its weight decrease was only 1.1%, these characteristics being excellent when compared with the concrete products formed by the prior art method.
Another sample, also shown in Fig. S, in which a portion of the dispersing agent was added to the primary water, had an air quantity slightly higher than 3%, a lowest percentage of bleeding of 2.5%9 and a percentage of weight decrease of 2.75%. The strength after 28 days was 415 kg/cm , the highest value.
Concrete was formed by using the same composition as above described and containing 3.4 - 3.5% of air according to the prior art method. Another sample was formed by adding the entire quantity of the air-entraining agent to the primary water and in still another sample, equal portions of the air-entraining agent were added to the primary and secondary waters respectively according to the method of an aspect according to the method of an aspect of this inven~ion. After 300 cycles and 600 cycles, the relative elastic coefficient and the compression strength after 28 days were measured and shown in Yig. 6.
The hori~ontal axes of Fig. 6 have four units which are the same as those in Fig. 5, and lefthand unit of the vertical a~is (ordinate) of Fig. 6 represents the compression strength of the resulting concrete mix-tures prepared by respective methods.
As shown, the concrete product formed according to the prior art method fractured at a relative elastic coefficient of 4i after 200 cycles of the free~ing test, and had a relative elastic coefficient of 48 at the end of 180 cycles. This concrete product had a compression strength of 331 kg/cm after 28 days. In contrast, the concrete product produced by the method of an aspect of this invention in which the entire quantity of the air-entraining agent was added to the primary water had a relative elastic ~ , ~
5~3 coefficient of 90 after 300 cycles of the freezing test and 82 even after 600 cycles. The compression strength after 28 days was 425 kg/cm . In another product in which the air entraining agent was incorporated into the primary water and the secondary water respectively had a relative elastic coefficient of 95 after 300 cycles and of 80 after 600 cycles, and a com-pression strength of 401 kg/cm after 28 days. As shown in Fig. 6, the con-; crete product in which a portion of the dispersing agent was added to the primary water had a compression strength of 435 kg/cm after 28 days, and relative elastic coefficients of 96 and 74 respectively after 300 and 600 cycles of the freezing tests. This shows that with the same composition,greatly different relative elastic coefficients and commpression strengths can be obtained.
When adding an air-entraining agent to the primary water in an amount necessary to ensure an air quantity of 3.2-5% in accordance with the method of an aspect of this invention9 the quantity of water previously applied onto the surface of the aggregate as varied. The results were shown in Fig. 7~ Figure 7 shows the percentage of bleeding, the compres-sive strength after 28 days and the relative dynamic elastic coefficient after 300 freezetthaw cycles as respective ordinates, and the /O surface water or sand, the amount of air entraining agent and the percentage Wl/C
as respective abscissae. In this case when the quantity of the primary water Wl amounts to 15-20%~ more particularly 20-35% based on the weight of cement, best result was obtained. In the latter range of 20-35%, the relative elastic coefficient after 300 freeze/thaw cycles was always larger than 95 and the mechanical strength of the product was also high. It was possible , 9'73 to limit the percentage of bleeding to be less than 2% when the ratio Wl/C
lies in a range of 15-45%.
Similar tests were made except that the air-entraining agent was divided and incorporated into the primary and secondary water and the results are shown in Fig. 8, in which the ordinates and abscissae are the same as Fig. 7. In this case tooJ since half of the air-entraining agent was incor-porated into the primary water, satisfactory results were obtained when the ratio Wl/C was in a range of 15-35%. Even when ratio, Wl/C was in a range of 40-50%, better results than the prior art were obtained.
Example 4 Sea sand containing 0.3% of salt was used as a fine aggregate.
842 kg/m of this sea sand, 979 kg/m of a coarse aggregate having a particle size of less than 15 mm, 75 kg/m3 of a steel fibre, 325 kg/m of cement9 195 kg/m of water and 3 ~/m3 of a rust-preventing agent of the nitrite type were admixed to obtain a green concrete composition. When all ingredients were simultaneously incorporated according to the prior art method and slump value was 10.0 cm. This is termed a control sample.
~ ``
On the other hand, a green concret~ A prep~r~d by the method of an aspect of this invention WaS prepared by adml~ing one half of the water and the entire quantlty of the rust-preventing agent to prepare the primary water, which was sprinkled on~o the sea sand mentioned above and kneaded to cause the water uniformly to adhere to the surface of the sea sand. Then, cement was added to ~orm 8h~ h~Vi ~ a r~tio, W1/C of 25/On ~he~ th~ r~
i~g w~ter w~ added afi the second~r~r water, and th~ re~ult-i~g mixture wa~ eaded to obtai:~ the gree~ concre~e A
o h~ving ~ ~lump ~ralue o~ 6 cm.
Impul~i~re ïorc~ ~d ~p~d e~ergy were ~pplied to the sea sand to adjust the percentage of the surface wa~er to 5%.
At first the entire quantity of the rust-preventing agent was sprinkled upon the sea sand thus treated while stirring the mixture and then primary water, not containing any rust-preventing agent, was added to prepare green concrete B according to the method of another aspect of this invention.
Further, 3 ~Im3 of the rust-preventing agent was divided into two portions having a ratio of 4 : 1. 24 ~/m of the high concentration rust-preventing agent was added to the primary water. o.6 ~/m3 of low concentration rust-preventing agent was added to the secondary water and the thus prepared primary water and secondary water were used in the same manner as above described to prepare a green concrete C accord-ing to the method of yet another aspect of this invention.
9~3 Each of the green concretes (control example and the green con-cretes A, B and C) was used to prepare a sample having a diameter of 100 mm and a length of 200 mm. Each sample was molded horizontally and vertically.
The concrete sample prepared according to the prior art method had a percentage of bleeding of 1.64%, whereas samples A, B and C, which were formed with cement shells after incorporation of the primary water, had a percentage of bleeding of 0.5%, which is negligibly small.
Following a curing for 14 days, aqueduct water at 50C was sprinkled over respective samples for 12 hours. Samples were subjected to two cycles of an accelerated corrosion test of the reinforcing steel bars which was carried out at 60 C for 12 hours at a relative humidity (RH) of 95% and then at 60 C for 12 hours at a RH of 25%. The percentages of the rusted areas are shown in ~he following Table III.
- 30 _ q'able III
condition of ~ of rusted area each total /0 of rusted sam~le prepari~g green of steel bar~ a~erage average area of concrete upper lower ~t~el fibres portion portio~ b) t9/
horizo~tally ca~ted 106 1~,8 1.7 R. 1.2 1.5 verticall~ casted 0.3 0~,7 O~r7 horizontally Gasted 306 203 3-2 i. 1 ~ . 6 ~erticall~ casted 1.,2 1.2 1.2 w horizontall~ casted 3~7 4.Q ~09 C 2.,2 2c8 verticall;~ castea Q.,4 0~4 0~4 horizorltally ca~ted 9. 5 7 .4 8.4 C~ r~l 6.4 8~ 5 ~rertically cas~ed 506 3~1 4~
. . .
Even when the same quantity of the rust-preventing agent is used for the sea sand containing the same quantity of salt, the rusting of the green concrete prepared using the method of an aspect of this invention is less than 1/3 of that of the prior art. Especially, in sample A the rusting area was reduced to 1/5 and in the vertically molded sample A, the rusting was reduced to less than 1/10. Various characteristics of samples B and C
are better than those of the control sample.
Example 5 A control sample was prepared in the same manner as in Example 1 except that 895 kg/m 30f sea sand containing 0.2% of salt, 988 kg/rn of a coarse aggregate, 300 kg/m of cement, 165 kg/m of water and 2 ~/m of a rust-preventing agent of the nitrite type was used. The slump values of this control sample and of the aforementioned samples A and ~ prepared by the method of aspects of this invention, the percentage of bleeding of this control sample, and the results of accelerated corrosion tests of reinforcing steel bars are shown in the following table IV.
Table I~
~lump ~lalue bleediIlg perce~t~ge o~ rus~d Rrea sample (cm) (9~) upper por~io~ lower-por~io~
A 8.,5 0~78 0048 0~31 B ~.5 0.71 0.39 057 control B.5 1.90 2.75 . 0.~3 As can be noted from this Table IV, ascording to aspects of this invention, it is possible greatly to reduce the percentage of bleeding of water as well as to reduce the rusted area of rein-forcing steel bars.
Yet another con~rol sample was prepared and tested lnwhlch no rust-preventing agent was added. In such control sample the percentage of the rusted area of the reinforcing steel bars was 15~65% at the upper portion and llo 15% ~t the lower portion. This result shows that use of the rust-preventing agent is effective even in concrete prepared by conventional methods and the data shown in Table IV shows that this effect is much more rsmarkable in concrete prepared according to the method of aspects of this invention.
As above described according to the method of aspects of this invention, it is possible to prepare a green composition, more particularly green mortar or green concrete, having a small percen-tage of bleeding water. It is thus possible to obtain concrete pro-ducts having high mechanical strength, in which rusting of reinforcing steel bars can be reduced.
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of preparing a green concrete or mortar by admix-ing and kneading premeasured amounts of at least one of fine and coarse aggregates, a powder of an hydraulic substance, at least one additive, and predetermined quantity of water, the improvement which comprises the steps of:
1) dividing said predetermined quantity of water into only two predetermined quantitative portions;
2) incorporating a major portion of all of said additive into a first one of said divided predetermined quantitative water portions;
3) admixing said aggregate and all said admixture of said first predetermined quantitative water portion and said additive, thereby uni--formly to pre-coat said aggregate with water;
4) admixing said powder of said hydraulic substance and any remain-ing quantitative portion of said additive and the mixture resulting from step 3);
5) admixing all said other predetermined quantitative portion of said water to said mixture of said hydraulic substance resulting from step 4);
and 6) kneading the resulting mixture, thereby to form said green concrete or mortar.
1) dividing said predetermined quantity of water into only two predetermined quantitative portions;
2) incorporating a major portion of all of said additive into a first one of said divided predetermined quantitative water portions;
3) admixing said aggregate and all said admixture of said first predetermined quantitative water portion and said additive, thereby uni--formly to pre-coat said aggregate with water;
4) admixing said powder of said hydraulic substance and any remain-ing quantitative portion of said additive and the mixture resulting from step 3);
5) admixing all said other predetermined quantitative portion of said water to said mixture of said hydraulic substance resulting from step 4);
and 6) kneading the resulting mixture, thereby to form said green concrete or mortar.
2. The method according to claim 1 wherein all said powder of said hydraulic substance is incorporated into said mixture of aggregate and said first predetermined quantitative portion of said water, thereby to form shells of said hydraulic substance around particles of said aggretate, said shells having higher strength than a paste between said hydraulic substance and particles of said aggregate.
3. The method according to claim 1 wherein said additive incor-porated into said first water portion comprises an agent that substantially prevents separation of said concrete of mortar.
4. The method according to claim 3 wherein said agent that sub-stantially prevents separation of said concrete of mortar enhances surface activity of water.
5. The method according to claim 3 wherein said agent that sub-stantially prevents separation of said concrete of mortar is a dispersing agent that enhances the dispersion of said hydraulic substance.
6. The method according to claim 3 wherein said agent that sub-stantially prevents separation of said concrete of mortar accelerates set-ting of said hydraulic substance by hydration and aggregation.
7. The method according to claim 3 wherein said agent that sub-stantially prevents separation of said concrete of mortar decreases the shear strength of a slurry paste prevailing between particles of said aggregate.
8. The method according to claims 1, 2 or 3 wherein said additive comprises an air-entraining agent.
9. The method according to claims 1, 2 or 3 wherein said fine aggregate comprises sea sand containing a corrosive compound.
10. The method according to claims 1, 2 or 3 wherein said additive comprises a rust-preventing agent.
11. The method according to claims 1, 2 or 3 wherein said green concrete or mortar comprises a concrete composition utilized to form a con-crete structure.
12. The method according to claims 1, 2 or 3 which further com-prises the steps of: removing air film from said particles of said fine aggregate; and then covering said particles with water film containing more than 1.5% by weight of said additive.
13. The method according to claims 1, 2 or 3 wherein said green concrete or mortar comprises a concrete composition utilized to form a con-crete structure and wherein covering particles of said additive preferenti-ally absorbs said hydraulic substance to form shells thereof.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP20770/1982 | 1982-02-12 | ||
| JP2077082A JPS58138606A (en) | 1982-02-12 | 1982-02-12 | Method of preparing compound not hardened by hydraulic substance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195973A true CA1195973A (en) | 1985-10-29 |
Family
ID=12036398
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000397696A Expired CA1195973A (en) | 1982-02-12 | 1982-03-05 | Method of preparing green concrete or mortar by prewetting aggregate with additive |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS58138606A (en) |
| CA (1) | CA1195973A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113624582A (en) * | 2021-08-20 | 2021-11-09 | 浙大宁波理工学院 | Preparation method of surface sample of cement concrete interface transition zone |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61192522A (en) * | 1985-02-20 | 1986-08-27 | 相武生コン株式会社 | Manufacture of concrete |
| JPS62234904A (en) * | 1986-04-07 | 1987-10-15 | 山陽国策パルプ株式会社 | Manufacture of concrete |
| JP4827793B2 (en) * | 2007-05-08 | 2011-11-30 | 立兆股▲分▼有限公司 | Date code stamping system |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56126109A (en) * | 1980-03-11 | 1981-10-02 | Ito Yasuro | Method of adjusting antirust concrete |
| JPS57138906A (en) * | 1981-02-23 | 1982-08-27 | Japan National Railway | Manufacture of quick-setting cement mortar |
| JPH0796219B2 (en) * | 1981-04-03 | 1995-10-18 | 株式会社北川鉄工所 | Equipment for manufacturing raw concrete |
-
1982
- 1982-02-12 JP JP2077082A patent/JPS58138606A/en active Pending
- 1982-03-05 CA CA000397696A patent/CA1195973A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113624582A (en) * | 2021-08-20 | 2021-11-09 | 浙大宁波理工学院 | Preparation method of surface sample of cement concrete interface transition zone |
| CN113624582B (en) * | 2021-08-20 | 2024-01-19 | 浙大宁波理工学院 | Preparation method of cement concrete interface transition zone surface sample |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS58138606A (en) | 1983-08-17 |
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