DD252369A5 - Hydraulic binder for cement mixtures and process for their preparation - Google Patents

Abstract

The invention relates to a hydraulic binder for cement mixtures containing flow agents, or "plasticizing" or "superplasticizing" agents, and a method for producing a cement mixture by mixing together a hydraulic binder, aggregate (aggregate material) and water in the presence of at least one additive the series of "plasticizers" and "superplasticizers". The flowability or water reduction effect of "plasticizers" and "superplasticizers" in cement is increased when the cement is treated with water prior to the mixing step so that 0.1 to 10 weight percent water is absorbed. Fig. 2

Description

Field of application of the invention

The invention relates to a hydraulic binder for cement mixtures containing flow agents, or "plasticizing" or "superplasticizing" agents and a method for producing a cement mixture by mixing together a hydraulic binder, aggregate (aggregate material) and water in the presence of at least one additive the series of "plasticizers" or "soperplasticizers".

Characteristic of the known technical solutions

It is known that "plasticizing" or "superplasticizing" agents are chemical additives which are advantageously used in mortars or in concrete to increase the flowability of fresh cement mixes at equal water to cement mixing ratios and to the workability and durability of the mix to improve.

Alternatively, the same additives can be used as a water reducing agent to maintain the same state of working while reducing the mixing ratio of water to cement, thereby improving all properties of the mortar or cured concrete.

According to standard methods, "superplasticizers" must be able to reduce the blended water to at least 12% while maintaining flowability, while "plasticizers" are capable of reducing the blended water by at least 5%. These additives can either be added to the water to be mixed at the moment when the fresh mortar or concrete is produced or during the manufacture of the cement so that they are present in dried form in the dry cement.

It has surprisingly been found that the liquefying or water-reducing effect of the "plasticizers" or "superplasticizers" is increased when the cement is subjected to moistening prior to mixing.

It is further known that dry cement containing flux can be obtained by spraying the cement during the milling process with an aqueous solution of the auxiliary, as described e.g. As described in U.S. Patents 2Ί41'571 and 3'856'542. However, these patents describe that the cement is treated at a temperature at which the water evaporates very rapidly and the dried flow agent is left on cement particles but the water content of the final product is not increased.

In general, the water is in the form of the hydrated minerals "Ettringite" (3CaO, AI2O33CaSO ₄ 3IH ₂ O) and / or cement absorbed in selchen amounts that it by means of the differential "scan" - (height) calorimetry (DSC) or with Help of differential thermogravimetry (DTG) or differential heat analysis (DTA) can be demonstrated.

See, for example, B. Jump "Influence of mill atmosphere on the solidification and strength of cement" in cement-lime gypsum 5, 259-267 (1974) and W.H. Duda "Cement data-Book" Bauverlag GmbH, Wiesbaden and Berlin, pages 155 and so on.

Object of the invention

It is the object of the invention to provide a hydraulic binder for cement mixes and methods for their production as well as to increase the utility of the cement mixes.

Explanation of the essence of the invention

The invention is based on the object, a hydraulic binder for cement mixtures containing superplasticizers, or "plasticizing" or "superplasticizing" agents and a method for producing a cement mixture by mixing together a hydraulic binder, an aggregate (aggregate material) and water in the presence of at least one additive from the series of "plasticizers" and "superplasticizers" which provide improved properties of the cement mixtures by influencing the machinability and durability of the workable mixture as a mortar or hardened concrete.

According to the invention the object is achieved in that the hydraulic binder is treated prior to mixing with water, so that it contains 0.1 to 10 wt .-% water.

Preferred cement mixtures are mortar and concrete. The hydraulic binder may be Portland cement, e.g. Portland cement, however, is preferred, be it "alumina" or "blended" cement, pozzolanic cement, schock cement or other types of cement.

Another preferred binder is a Portland cement formed by milling "clinker" and calcium sulfate together with "bottom-ash" obtained from a coal firing power plant. In particular, such "bottom ash", which has been cooled in water and normally has a water content of about 20-30% by weight before grinding, is dried to a water content of less than 12%, in particular less than 4-7% by weight .-%.

Advantageously, the bottom-ash contains more than 1% by weight of unburned coal and less than 1% by weight of sulphates.

Suitable "plasticizers" are products based on gluconates, ligninsulfonates and hydroxylated polymers, and suitable "superplasticizers" are condensation products based on nephtaline sulfonates or melamine sulfonates and formaldehyde, polystyrene sulfonates and hydroxyacrylates. The mixture contains mainly at least one "superplasticizer", in particular a condensation product based on a beta-Nephtalinsulfonates, especially in calcium salt form.

Further adjuvants can be present in the cement mixture according to the invention, as are customary in cement technology, for. Hardening accelerators or retarders, air entraining agents, pigments, antifreeze, etc.

The flow agent (a "plasticizer" or a "superplasticizer") may be added to the mixture with the water to be mixed or may be in the moistened cement before it is mixed.

Another form of the invention includes a hydraulic binder containing at least one additive from the series of "plasticizers" and "superplasticizers" and 0.1 to 10% by weight of absorbed water.

Advantageously, the amount of the flow agent in the cement 0.1 to 1%, in particular 0.2 to 0.5% dry weight based on the weight of the cement.

The binder may be moistened prior to the addition of the flow agent, or alternatively, a binder which already contains a flow agent is moistened.

On the other hand, as a detail of the invention, a binder can be moistened with an aqueous solution of a flow agent, so that the moistening and the addition of the flow agent take place simultaneously.

The moistening of the hydraulic binder or of the cement can be carried out in the industrial production of the cement, in particular after the grinding process, with water in liquid. Aerosol or gaseous form, so that the water is uniformly and homogeneously absorbed in an amount of 0.1 to 10% by weight of cement, in particular 0.5 to 5% by weight and very particularly 0.5 to 2% by weight. ,

These weight percent represent the weight of the absorbed absorbed water, not the weight of the water supplied.

Advantageously, water in the form of a thin liquid jet, for. As a spray added to the cement, either immediately after the grinding process or after a certain time.

It is possible according to the method of the invention. Adding water during the grinding process in an amount or at a temperature such that some water remains in the final product; but because it is difficult to control the absorbed amount of water, it is advantageous to wet the cement after the milling process.

The optimum amount of water present varies with the chemical composition and fineness of the cement, finely ground cement generally requires slightly more water than coarsely ground cement.

embodiment

The invention will be explained in more detail with reference to an embodiment. In the accompanying drawing show

Fig. 1: the apparatus for producing the cement mixtures;

Figure 2: the DSC analysis curve of cement, untreated or treated.

A suitable device for carrying out the water treatment is shown in FIG. Cement is supplied to the boiler 1 through a tube 2, which opens into a conical opening 3. A feed tube 4 with a diameter smaller than 2 leads to a spray nozzle 5 through which water or an aqueous solution of a plasticizer is pumped.

An air stream is blown through a perforated base 6 at the base of the boiler; this mixes the moistened cement; this is unloaded through the outlet pipe 7.

Figure 2 shows that the DSC "scan" curves are obtained from two examples of cements, both containing 0.4% by dry weight of a "superplasticizer", but a cement example did not receive water treatment (denoted by the dashed curve) and the other treated with 1% by weight of water (indicated by the solid curve).

The peaks in the curve which correspond to the loss of water, namely the peak a) of "ettringite" and b) of monosulphate, are clearly visible from the curve of the example treated with water.The peak c) indicates the loss of water from gypsum ,

A cement mixture produced according to the invention has an excellent combination of machinability of the mixture and load-bearing properties of the resulting hardened mortar or concrete, e.g. B. of manufactured articles made of concrete. This result is surprising in that the water absorption of cement is generally undesirable and has a negative impact on the strength of concrete.

In the following examples, in which all parts, ratios and percentages are by weight, it is intended to illustrate the invention.

example 1

Six mortar mixes are produced, each containing one part by weight of Portland cement with a high degree of strength and three parts by weight of sand using a water / cement mixing ratio of 0.45. Each contains 0.4 dry weight percent (1% based on a 40% aqueous solution) based on wt% of cement, an additive "superplasticizer", namely the calcium salt of a condensation product of betanaphthalene-sulfonic acid with formaldehyde.

From two different commercial Portland cements with a high degree of strength two mortar mixtures are produced; one made of cement, as is customary, and one made of cement treated with 1% water.

From each mortar, the flowability of the freshly prepared mixture is measured and with the aid of the flow test according to UNI 7044, the load capacity is measured after one day, after 7 and 28 days.

Table 1 shows the mean values of the three different cements.

Table 1 flow properties load-bearing capacity 7 days 28 days cement (UNI 7044). (MPa) 51.5 63.2 1 day 53.6 64.3 120 30.3 untreated 160 30.1 + 1% water

From the list in Table 1 it can be seen that cement treated according to the present invention together with a "superplasticizer" gives a mortar with significantly improved flowability and with a slightly improved load capacity compared to untreated cement.

Example 2

Two mortars having the same proportions and the same ingredients as in Example 1 are prepared; but instead of adding the "superplasticizer" separately, a cement was used in which 0.4 wt% of the same "superplasticizer" was added during the manufacturing process.

For a mortar, cement was used as it is usually obtained, for the other mortar cement was treated with 1% water.

The results of the flow test and the strength of the two mortars are recorded in Table 2.

Table 2 with water flow test load-bearing capacity 7 days 28 days cement treated flow properties MPa 60.8 73.1 1 % % • 67.8 77.5 (UNI 7044) ITAG untreated 120 38.9 1 treated 155 40.6 2

As in Example 1, the values show a remarkable improvement in flowability along with a slightly improved load capacity.

Example 3

Four mortars, each composed of one part by weight Portland Cement with high resilience and three parts sand and characterized by a water / cement ratio of 0.50, are produced. Two Portland cements are treated with 0.5% water before mixing.

Each of the mortars contains 0.1% by dry weight (0.2% of a 50% aqueous solution), based on cement weight, of a plasticizer adjuvant which is either calcium lignosulfonate or sodium gluconate.

The measured flow properties of the mixtures are listed in Table 3.

Table 3

Cement treatment Aids

(50% solution shake

based on the (%) (UNI 7044)

Dry weight)

untreated calcium lignosulfonate

0.5% water do.

untreated. sodium gluconate

0.5% water do. 95

Example 4

Eight mortars, each composed of 1 part by weight Portland Cement with high resilience and 3 parts sand and a dry weight of 0.48% (1.2% of a 40% aqueous solution) based on the weight of the cement, the "superplasticizer" aid Example For seven of the mortars, the cement used is wetted with 0.05 to 10% of water when it is prepared, and when the mortar is mixed, the amount of water used is adjusted to take into account the water contained in the cement so that the total mixing ratio of water to cement in each case is 0.45.

The flow properties of the resulting mortars are shown in Table 4.

Table 4 cement mix flow properties Mortar no. humidity relationship companies (% Water) Water / cement (%) (UNI 7044) 0 0.4500 95 1 0.05 .4495 105 2 0.10 .4490 110 3 0.50 .4450 125 4 1.00 .4400 132 5 3.00 .4200 132 6 5.00 .4000 125 7 10.00 .3500 100 8th

From the above values, it is apparent that even considering the cement moistening as the water content of the water mixture, the mortars 2-8 produced according to the present invention have a significantly improved flowability as compared with the control mortar. Humidification (irrigation) with 0.5-5% water gives especially good results.

Example 5

Eight mortars, each composed of 1 part by weight cement, 3 parts sand and 1 dry weight of 0.48% (1.2% of a 40% aqueous solution), based on the cement weight, of the superplasticizer of Example 1 and a mixing ratio of Total amount of water to cement of 0.45 Four different types of cement are used.

a) "Pozzolan" cement (with natural "Pozzolan")

b) slag cement

c) "Pozzolan" cement (with fly ash)

d) "Pozzolan" cement (with "bottom ash".) The original "bottom ash" contained 25% water and was dried to 5% water content).

Each of these cements is used directly as such or after watering with 1% water. The results of the obtained flow properties (tests) are summarized in Table 5.

Table 5 Cement type Cement treatment flow properties Mortar no. %, (UNI 7044) Natural "Pozzolan" untreated 90 1 do. 1% water 110 2 slag untreated 107 3 do. 1% water 125 4 pozzolan untreated 65 5 cement fly ash do. 1% water 85 6 "Bottom-ash". untreated 120 7 "Pozzolan" do. 1% water 170 8th

From the results, it can be seen that in cements other than Portland cement, a marked improvement in flow properties is obtained.

Example 6

Four mortars are made, each of the mortars composed of 1 part by weight Portland cement with high strength, 3 parts sand and a total mixing ratio of water to cement of 0.45. Each of the mortars contains 0.4% (1% of a 40% aqueous solution) of the "superplasticizer" of Example 1, but this was added at different states:

1) "Superplasticizer" added to the mixing water, the cement is not moistened.

2) "Superplasticizer" added during the manufacturing process.A dry cement plus "superplasticizer" not moistened.

3) Milled cement is moistened with 1% of a 40% "superplasticizer" solution.

4) Milled cement is wetted with 2% of a solution obtained by mixing the 40% superplasticizer solution with an equivalent volume of water.

Mortar 3) and 4) are therefore treated according to the invention, mortar 1) and 2) are comparative materials. Table 6 shows the flow characteristics of the mortars obtained. ·

Table 6

Mortar no.

Addition of the "superplasticizer"

Water treatment%

Flow properties% (UNI 7044)

to mixing water while -

Milling process after milling process 0.6 do. 1.6

110 105

120 125

Example 7

Two concretes are made using Portland cement which was treated with 0.4% dry weight (1% of a 40% aqueous solution) of the "superplasticizer" of Example 1 during the cementitious milling process.

In one case, the cement, as it is usually obtained, is used, in the other case it is moistened with 1% water.

Both concrete mixes containing 400 kg / m ³ of cement, the same amount of the same aggregate (with a maximum diameter of 20 mm) are mixed with water up to the same density (220 mm ± 10 mm "slump").

Table 7 gives the water content necessary to obtain the desired "slump" and the load capacity of the resulting concrete.

Table 7 inventively Water / cement "Slump" mm Load capacity (m Pa) 7 days 28 days Test no. treated Relationship ' 62.5 72.5 1 day 74.0 82.0 untreated 0.45 220 37.0 1 treated 0.41 225 46.5 2

From the table it can be seen that the water-reducing effect of the superplasticizer is increased in the treatment of the cement according to the invention.

Claims (14)

A process for producing a cement mixture by mixing together a hydraulic binder, a aggregate material and water in the presence of at least one additive from the series of "plasticizers" and "superplasticizers", characterized in that the hydraulic binder is treated with water before the mixing process, so that it contains 0.1 to 10 wt .-% water. 2. The method according to claim 1, characterized in that the additives are added to the mixed water. 3. The method according to claim 1, characterized in that the additives are present in the dry hydraulic binder before mixing. 4. The method according to claim 1, characterized in that the water treatment step is carried out after grinding the hydraulic binder. 5. The method according to claim 1, characterized in that the hydraulic binder is treated prior to the mixing step with an aqueous solution of the additive. 6. Process according to claims 1 to 5, characterized in that the additive is a condensation product of formaldehyde and a sulfonated aromatic compound. 7. The method according to claim 6, characterized in that the additive is a calcium salt of a condensation product of formaldehyde with betanaphthalenesulfonic acid. 8. Hydraulic binder, characterized in that at least one additive from the series of "plasticizers" and "superplasticizers" and 0.1 ± 10 wt .-% water are given. 9. Hydraulic binder according to claim 8, characterized in that the binder has 0.5 to 5 wt .-% water. 10. A hydraulic binder according to claim 9, characterized in that it contains 0.5 to 2Gew .-% water. 11. Hydraulic binder according to claim 8 with at least one additive from the series of "plasticizers" or "superplasticizers", characterized in that it has in the differential "scan" (raster) calorimetry "peaks" corresponding to "ettringite" and calcium monosulfate , 12. Hydraulic binder according to claims 8 to 11, characterized in that it comprises 0.2 to 0.5 wt .-% "superplasticizer", which is a condensation product of formaldehyde and a sulfonated aromatic compound. 13. Hydraulic binder according to claims 8 to 12, characterized in that the binder is made on the basis of Portland cement. 14. Hydraulic binder according to claims 8 to 12, characterized in that Pozzolanic cement obtained by grinding a "clinker" and calcium sulfate together with "bottom ash", which has been dried to a water content of less than 12% is added. For this 2 pages drawings