NO144484B - LAVPOROES AGGREGATIVE CEMENT MIXTURE. - Google Patents

Description

The present invention relates to a low-porous aggregate-containing cement mixture. More particularly, the invention relates to a low-porosity cement which is prepared from a gypsum-free hydraulic cement which includes alkali bicarbonates and lignosulfonates and which provides cement pastes with an extended setting time, reduced expansion due to alkali aggregate reactions and other advantages.

Cements are produced by calcination; of suitable raw materials, generally a mixture of calcareous and clayey substances, to produce a sintered "clinker". Portland types are by far the most important cements based on the quantity produced.

The clinker is suitably mixed with a small amount of gypsum, ie up to 9%, and ground, usually in some form of ball mill, to a finely divided state with a relatively large surface area to obtain the finished cement.

The painted clinker containing gypsum is mixed with

a suitable amount of water to form a paste. Correctly prepared cement pastes settle within a couple of hours and then harden slowly. Cement pastes are combined with aggregates, either fine aggregates or sand to produce mortar or larger aggregates such as gravel, stone and the like to produce concrete. The paste acts as cementing material and the composition has

a decisive effect on the strength and other properties of the resulting mortar or concrete.

One of the main factors that determine the properties

for hardened cement pastes and thereby also for mortar and concrete,

is the ratio between water and cement in the fresh mix. The lower the ratio of water to cement, the higher the strength,

the lower the shrinkage and the better the frost and corrosion resistance

the ability to stand. ' The desirability of having a low water-cement ratio,

in common practice this is between 0.4 and 0.6, is to obtain a concrete or a mortar with minimal shrinkage and an increased ultimate strength.■ However, a simple reduction of the water-cement ratio for ordinary Portland cements is not the answer.

Although a reduction of the water content improves the properties of the hardened cement, this can unfortunately only be used to a limited extent as a reduction of the water content simultaneously results in a poorer workability of the concrete mixture. The requirements for sufficient workability for the fresh concrete mixture are the reason for the fact that the water content of concrete mixtures that are usually used is far above the amount required for total hydration of the cement.

While the amount of water required for total hydration of the cement is determined to be around 22-23%, the minimum amount of water used in ordinary concrete is close to 40% and usually between 45 and 80%.

Even with the use of common means for reducing the water content (usually lignosulfonate from used sulphite cooking liquids) it is only possible to reduce the added water by 10%. The water that remains in the concrete mix made from ordinary cement is still far above the requirements necessary for total hydration of the cement. Thus, if the water content is to be further reduced without impairing the workability or without introducing other degrading factors, a significant gain in strength and an improvement in certain other properties of the hardened concrete could be achieved.

Attempts have long been made to produce low-porosity cements by reducing the ratio between water and cement. US patent no. 2,174,051 describes e.g. that an increase in strength is achieved with a low ratio between water and cement and that certain organic compounds such as tartaric acid, citric acid etc. can be added to reduce the setting time.

US patent no. 2,374,581 describes that a small amount of tartaric acid, tartrates and bicarbonates can be added to ordinary (gypsum-containing) Portland cement at ordinary ratios between water and cement to delay the setting rate at high temperatures when cementing oil wells.

US Patent No. 2,646,360 describes that an alkali metal or alkaline earth metal lignin sulfonate and an alkali metal salt of an inorganic acid (eg, sodium carbonate) can be added; to a gypsum-containing cement slurry to reduce water loss and thus the amount of water needed to begin with.

US Patent No. 3,118,779, on the other hand, discloses that sodium bicarbonate when added to a Portland cement type III (containing gypsum) without lignin present acts as an accelerator.

US patent no. 3,689,296 describes that formaldehyde-modified calcium lignosulfonates can be used in Portland cements to replace all or part of the gypsum that is usually added and that the amount of water required for a mixture with a given degree of fluidity is reduced.

US Patent No. 3,689,294 describes recent attempts to produce low-porosity cements by grinding Portland-type cements without gypsum to a specific surface area of between 6000 and 900-0 Blaine (cm/g) and mixing with alkali or alkaline earth lignosulfonate, alkali carbonate and water.

US Patent No. 3-782,984 discloses that the addition of 0-5%-5% acid alkali metal carbonates to Portland-type cements accelerates setting time.

The French publication "Les Adj uvants Du Ciment", by Albert Joisel (Soisy, France 1973, published by the author) describes on page 102, that sodium bicarbonate in ordinary Portland cement is a retarder and on page 132 that sodium bicarbonate can be added to Portland cement along with gypsum in a regular way.

The object of the present invention is to produce an improved low-porous free-flowing and aggregate-containing cement mixture by incorporating sodium bicarbonate as an additive.

The invention thus relates to a cement mixture which is characterized in that it comprises: (a) a Portland cement with a Blaine fineness of over 3500 which does not contain calcium sulphate, (b) alkali bicarbonate in an amount from 0.1 - 2.0%, calculated on the weight of the dry ground cement, and (c) an alkali or alkaline earth lignosulphonate or - sulphonated lignin in an amount from 0.1 - 1.0%, calculated on the weight of the dry ground cement,

which aggregate-containing cement mixture is worked up to a water-cement ratio of between 0.4 and 0.2.

The cement mixture according to the invention is produced by combining ground hydraulic cement without gypsum with from 0.1 to about 1.0% of an alkali or alkaline earth lignosulfonate or sulfonated lignin, and with 0.1-2.0% alkali bicarbonate together with 20-40% water. In an alternative embodiment, alkali bicarbonate is mixed with the cement and the lignin is added to the mixing water, after which the two mixtures are combined. In a further embodiment of the method, the lignin is mixed with cement while alkali bicarbonate is added to the water and then the two mixtures are mixed together. In a further embodiment, lignin, bicarbonate and water are mixed together before combining with ground cement. These methods demonstrate the desirability of using alkali bicarbonates in low porosity cements instead of alkali carbonates.

The present invention is applicable to cements of the "hydraulic cements" type. These include but are not limited to Portland cements, natural cements, white cements, aluminum cements, "grappies cements", hydraulic lime and pozzolanic cements including those derived from industrial slags. The most commonly used hydraulic cement is Portland cement. Clinker a<y> the type specified above is ground to 3500 cm /g (Blaine) and finer, e.g. up to 9000 cm<2>/g.

In order to support the achievement of the desired fineness, it is common practice in the cement industry to use grinding aids that increase the efficiency of the grinding. Satisfactory grinding aids include, among others, water-soluble polyols such as ethylene glycols, polyethylene glycols as well as other water-soluble diols. The grinding aids are usually added to the clinker in an amount of from 0.005$ to 130$, based on the weight of the cement, and the ground cement may include an inhibitor for clumping when packed. Additional examples of grinding aids can be found in US Patent Nos. 3,615,785 and 3,689,294. Although grinding aids are typically used in the manufacture of the cement, they form no part of the present invention.

The production of cement mixtures thus starts with a ground hydraulic cement without gasps. According to the invention, low-porosity mortars and concretes can be made from the cement paste. As used herein, the term "low-porous" cement is defined as a free-flowing and workable cement paste with a water/cement (v/s) ratio of less than 0.4 and down to 0.2, with workable mortars and concretes preferably from 0, 35 and down to 0.25.

The hydraulic cement without gypsum is combined in one embodiment of the method with 0.1$ to about 1.0$, preferably 0.3$-0.8$, calculated on the weight of the dry ground cement, of an alkali or alkaline earth lignosulfonate or earth-alkaline sulfonated equation. The lignosulphonates are obtained as by-products from sulphite cooking of wood materials. The waste liquids from such pulp cooking processes contain large amounts of lignin and lignin products in connection with other materials. The sulphonated lignins, on the other hand, are produced by reacting lignins obtained from alkaline pulp boiling, acid hydrolysis or other known recovery processes with an inorganic sulphite, e.g. sodium sulphite, whereby sulphonate groups are added to the lignin. For use according to the invention, any of the various water-soluble sulphonated lignins or lignosulphonates can be used. However, it is preferred to use sulphonated lignins which are free of carbohydrate substances. Sulphonated lignins obtained from the reaction between sulphites and alkali lignin do not contain any significant amount of these carbohydrates and can thus be used as such. is. The sulfonated lignins can be converted into water-soluble alkaline earth salts and used as such as described in US patent no. 2,141,570.

In an alternative embodiment of the process may

the sulphonated lignin is combined with the ground cement or with the mixing water or a part of the sulphonated lignin can be added to the cement and part added to the mixing water. No significant differences in results are noted when using these methods. Therefore, part of the lignin can be combined with the ground cement and the remaining part added to the mixing water.

An alkali bicarbonate in an amount of 0.3-2.0%, preferably 0.7-1.5%, calculated on a weight basis of the dry cement, is used. Sodium bicarbonate is preferred. It is unimportant how the bicarbonate is added, this can e.g. happen by regularly incorporating a bicarbonate or by adding soda and then carbonating. It has been found that when the alkali bicarbonate is used, an unexpected increase in setting time and workability is achieved compared to what is achieved when alkali carbonate is used, at water-cement ratios below 0.4. It has also been found that when alkali bicarbonate is added to the cement, an unexpected increase in setting time and workability is achieved compared to alkali carbonate. Even more surprisingly, it has been found that when the alkali bicarbonate is dissolved in mixing water, even better results are achieved with regard to regulation of the setting time and the improved fluidity than when other mixing sequences are used. The amount of water used is 20-40 wt.-$, calculated on the weight of dry cement, or a water-cement ratio of 0.4-0.2. The way in which the bicarbonate combines with water can vary. For example, bicarbonate can be added as such or you can add soda and then carbonate.

It may also in some cases be desirable to add a third component to the low-porous system in order to achieve a significant extension of the plastic period for mortars and concretes while they still have sufficient compression "strengths" after 1 day. These components are used in small quantities , e.g., 0.1-0.2$, and primarily fall into two types of materials: surfactants and conventional water reducers/debonding retarders. Anionic surfactants may include the sodium salt of sulfonated alkali diphenyl oxide, while nonionic surfactants include polyethylene glycol etc. Substances of this type include carbohydrates such as tremolasse, sucrose, dextrose and hydroxy acids such as sodium gluconate. Typical air-removal agents such as tributyl phosphate can also be used with advantage in low-porous systems.

Another important feature of the invention is that it was found that the addition of alkali bicarbonate substantially reduces the possibility of the alkali aggregate reaction that occurs when alkali (NaOH) is formed in the cement. The potential expansion that can occur when using alkali carbonate and bicarbonate in low porosity systems was measured using a highly reactive aggregate (crushed pyrex glass) according to the method specified in A.S.T.M. C-227. The results showed a reduced expansion for a low porosity mortar prepared with NaHCO 3 compared to an equivalent Na 2 CO 3 . In addition, small amounts (0.05-1.5$) of lithium salts reduce the expansion of both alkali carbonate and bicarbonate containing low porosity pyrex glass mortars.

The different combinations of additives and mixing sequences eliminate the need for the addition of gypsum and provide a free-flowing, workable and low-porous cement paste with an extended and adjustable setting time. The superior results obtained according to the present invention are completely unexpected in the production of low-porosity cement mixtures seen in the light of the state of the art. As stated above, each of the additives has previously been used in gypsum-containing cements of the Portland type, but none of the products obtained according to the state of the art reach the level of performance obtained with the low-porosity cement mixtures according to the present invention.

The invention will be explained in more detail in the following examples.

Example 1

This example shows the extended setting time of a cement mixture using alkali bicarbonate instead of alkali carbonate. A type I Portland cement clinker ground to - 5.075 cm <2> /g (A.S.T.M. C-204) with the following analysis was used in this example:

The change in physical properties (setting time being the most notable) for cement pastes using alkali carbonates and alkali bicarbonates is shown in Table 1. The amount of sulfonated compound was kept constant at 0.45% by weight calculated on the cement, and the water-cement ratio was 0.25 . The amount of alkali carbonate was adjusted to give an equivalent molar ratio of CO 2 .

The results in Table I show the increase in setting time and a superior 7-day compressive strength for bicarbonate systems compared to carbonate systems.

Example 2

This example shows the extension of the setting time for cement pastes that use alkali bicarbonate instead of alkali carbonate and shows special mixing sequences compared to other mixing schemes that use the same substances. In this example, a type I Portland cement clinker ground to 5,075 cm 2/ g CA.S..T.M. C-204).

The change in the physical properties (setting time is the most notable) for the cement pastes using alkali carbonates and alkali bicarbonates when using the two mixing forms is shown in Table II.

The mixing schemes given in Table I indicate mixing of all the components within a parenthesis and then mixing with the next component or components. Experiments 4 and 8, which show an embodiment, thus describe mixing the cement (S) with a sulphonated alkali lignin (LS)

and mixing the alkali bicarbonate. (AC) with water (V) and then mixing these together. The trials with different numbers compare the use of an alkali carbonate while the remaining trials illustrate other mixing sequences. The amount of sulfonated lignin was kept constant at 0.45% by weight based on the weight of the cement and water-cement ratios were 0.25. The amount of alkali carbonate was adjusted to give an equivalent molar amount of CO 2 in all examples.

The results in experiments 4 and 8 in Table II clearly show

the unexpected increase in the setting time for bicarbonate systems in relation to carbonate systems and significant additional benefits of dissolving the bicarbonates in water without the other properties

creates is significantly affected (flow and compression strength).

Example . 3

This example shows that the sulphonated lignin can be dry mixed or dissolved in the mixing water. In this example, a proportion of the clinker from e.g. 1 ground up to a Blaine surface area of 4.525 cm 2 /g. The mixing schemes indicated in Table III

indicates as before that all components within a parenthesis first/t

are mixed together and then the next component is mixed in.

For example, experiment no. 1 in Table III indicates the mixture of the cement (S), the sulphonated alkali lignin (LS) and alkali carbonate (AC), in this experiment the alkali carbonate was sodium bicarbonate, and then mixing in water. The amount of sulfonated lignin was kept constant at 0.35 wt-55, calculated on the cement, and the water-cement ratio was 0.25.

The data given in Table II clearly show that the sulphonated lignin can either be added to the mixing water or dry-mixed with the cement without significant changes to the paste properties.

Example 4

This example further demonstrates the superior low porosity cement pastes produced using NaHCO 3 instead of Na 2 CO 3 from ground cements of varying surface areas using Type I clinkers from different sources. Table IV shows the comparatively longer setting times and higher 7-day compressive strengths for NaHCO^ low-porosity cement systems. The water-cement ratio was 0.25 in each trial. The amount of alkali carbonate was adjusted to give approximately equivalent molar amounts of CO 2 for each clinker at each surface area.

Example 5 This example shows that ground cement with different surface areas and from different sources other ■ than ex in 1. can be used. Clinkers B and C are type I Portland cement clinker from two different sources. The water-cement ratio is 0.25 in all cases. : ' :'

Table V shows that no significant differences are noted when using clinkers from different sources or clinkers ground to different specific surface areas.

Example 6

The use of alkali bicarbonates instead of alkali carbonate also improves fluidity in cases where marginal fluidity occurs. The addition of alkali bicarbonate to the mixing water also provides improved flow.- The examples in Table VI show these points where 0.5% sulfonated alkali lignin and an equimolar amount of CO were used together with ground clinker A and 0.50% sulfonated alkali lignin and an equimolar amount CO^ was used with painted clinker B.

These results show that cement pastes produced

in the case of ground clinkers without gypsum, but using sodium bicarbonate, had superior flow properties compared to those produced using sodium carbonate.

Example 7

The extension of the binding times by use. of bicarbonates has also been observed if lignosulfonates isolated from sulphite waste liquids are used. However, the overall properties are superior if sulphonated alkali lignins are used..'.''.'■

Example 8

This example clearly shows that a low-porosity ground pyrex glass mortar made with NaHCO^ expands significantly less, compared to corresponding low-porosity mortars using Na2C0j. Samples C-1 and C-2 in Table VIII show the reduced 14th-day and 28th-day expansion observed when ¥1^ 2^^^ is replaced with NaHCO-j (with equimolar amount of C0~) in the low-porosity pyrex glass mortar by following the procedure set out in A.S.T.M.

C-227. Samples C-3 and C-4 show a significantly reduced expansion both for NaHCO^ and Na^ ®?, low-porous systems when a lithium salt (L^CQj) is incorporated into the ground pyrex mold. These results illustrate the reduced expansion for a low porosity pyrex mortar when replacing an alkali carbonate with an alkali bicarbonate and also a reduced expansion in both cases when a lithium carbonate is incorporated into the mix.

Example 9

This example serves to illustrate the strength properties of low-porosity mortars obtained using the article according to the invention at acceptable water-cement ratios. The mortar was produced by using 2.25 parts of fine sand per some cement.

The results show that the good strength properties are maintained for the low-porous aggregate-containing mixtures.

Claims (2)

1. Low-porous aggregate-containing cement mixture, characterized in that it comprises: (a) a Portland cement with a Blaine fineness of over 3500 which does not contain calcium sulfate, (b) alkali bicarbonate in an amount from 0.1 - 2.0$, calculated on the weight of the dry ground cement, and (c) an alkali or alkaline earth lignosulphonate or - sulphonated lignin in an amount of from 0.1 - 1.0%, calculated on the weight of the dry ground cement, which aggregate-containing cement mixture is worked up to a water-cement ratio of between 0.4 and 0.2. 2. Aggregate cement mixture according to claim 1, characterized in that the alkali bicarbonate is sodium bicarbonate and is present in an amount from 0.7 - 1.5%, and that the lignin is an alkali lignin and is present in an amount from 0.3 - 0.8%.