CN109133712B

CN109133712B - Additive for improving cracking and water absorption of alkali slag cement stone and application method thereof

Info

Publication number: CN109133712B
Application number: CN201811168515.7A
Authority: CN
Inventors: 杨长辉; 李青; 杨凯
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2018-10-08
Filing date: 2018-10-08
Publication date: 2021-08-31
Anticipated expiration: 2038-10-08
Also published as: CN109133712A

Abstract

The invention relates to an additive for improving cracking and water absorption of alkali slag cement stones and a using method thereof, belonging to the technical field of building materials, wherein the additive comprises the following components in parts by mass: 40-70 parts of stearate, 10-20 parts of alkali slag retarder, 5-10 parts of organic silicon and 45-60 parts of calcium hydroxide. By reasonably matching each component in the admixture and limiting the use amount of each component, the admixture can obviously improve the cracking problem of alkali slag set cement, further reduce the water absorption of the alkali slag set cement, does not cause too much negative influence on the mechanical property of the alkali slag set cement, has simple synthesis method and easily obtained raw materials, and is suitable for industrial production.

Description

Additive for improving cracking and water absorption of alkali slag cement stone and application method thereof

Technical Field

The invention belongs to the technical field of building materials, and particularly relates to an additive for improving cracking and water absorption of alkali slag set cement and a using method thereof.

Background

Alkali slag cement (AAS) is a novel hydraulic cementitious material obtained by exciting finely ground granulated blast furnace slag with an alkali metal compound. The alkali slag cement stone has high strength, corrosion resistance, fire resistance, chlorine salt corrosion resistance and the like which are superior to those of the common portland cement, but has larger drying shrinkage, is easier to crack slurry, mortar or concrete than the common portland cement, leads to the increase of water absorption of the common portland cement, and finally induces various durability problems, which becomes a technical bottleneck restricting the wide application of the alkali slag cement. The hydration process of alkali slag cement is complex, and a hydration product with poor orderliness has a large amount of microscopic defects in the aspects of shape and structure, which is a source of problems that alkali slag cement stones are easy to deform and crack and is one of the root causes of large water absorption.

At present, the method for solving the cracking and water absorption of alkali slag set cement is as follows:

(1) the metal ion expanding agent, such as general silicate cement expanding agent, is mixed, the mechanism is to form ettringite with strong expansion effect, in the alkali slag cement high alkali environment, ettringite is difficult to form, the expected expansion effect can not be achieved, and Ca (OH) is added at the same time₂The setting of the alkali slag cement is too fast.

(2) The shrinkage reducing agent is incorporated to reduce the surface tension of the pore solution, but the shrinkage reducing agent for general portland cement is not highly adaptable and stable in an alkali-slag high alkali environment.

(3) The aim of toughening is achieved by the 'pinning effect' of the micro-aggregate by doping the mineral particles, but the gelation property of the alkali slag cement is reduced by the doped non-gelation mineral particles, so that the mechanical property of the alkali slag cement is reduced.

However, the method of adding the swelling agent, the shrinkage reducing agent and the mineral admixture to the alkali-slag cement does not change the microscopic defects inside the cementitious material, and it is difficult to fundamentally improve the crack resistance and reduce the water absorption of the alkali-slag set cement. Therefore, an admixture capable of improving cracking and water absorption of alkali slag set cement is urgently needed on the premise of ensuring the mechanical property of the alkali slag set cement.

Disclosure of Invention

In view of the above, it is an object of the present invention to provide an admixture for improving cracking and water absorption of alkali slag set cement, and to provide a method for using the admixture for improving cracking and water absorption of alkali slag set cement.

In order to achieve the purpose, the invention provides the following technical scheme:

1. the additive for improving cracking and water absorption of alkali slag cement stones comprises the following components in parts by mass: 40-70 parts of stearate, 10-20 parts of alkali slag retarder, 5-10 parts of organic silicon and 45-60 parts of calcium hydroxide.

Preferably, the admixture consists of the following components in parts by mass: 40 parts of stearate, 10 parts of alkali slag retarder, 5 parts of organic silicon and 45 parts of calcium hydroxide.

Preferably, the admixture consists of the following components in parts by mass: 50 parts of stearate, 12 parts of alkali slag retarder, 6 parts of organic silicon and 50 parts of calcium hydroxide.

Preferably, the admixture consists of the following components in parts by mass: 60 parts of stearate, 15 parts of alkali slag retarder, 8 parts of organic silicon and 55 parts of calcium hydroxide.

Preferably, the admixture consists of the following components in parts by mass: 70 parts of stearate, 20 parts of alkali slag retarder, 10 parts of organic silicon and 60 parts of calcium hydroxide.

Preferably, the stearate is one of calcium stearate, sodium stearate, magnesium stearate or zinc stearate.

2. The use method of the additive specifically comprises the following steps: the admixture is blended in an amount of 4 to 8 wt% in the alkali slag cement.

Preferably, the admixture amount of the admixture in the alkali slag cement is 4 wt%.

The invention has the beneficial effects that: the invention provides an additive for improving cracking and water absorption of alkali slag cement stones and a use method thereof, and the additive can obviously improve the cracking problem of the alkali slag cement stones by reasonably matching various components in the additive and limiting the use amount of the various components, so as to reduce the water absorption of the alkali slag cement stones, and the additive has no negative influence on the mechanical properties of the alkali slag cement, and the additive has the advantages of simple synthesis method, easily obtained raw materials and suitability for industrial production.

The functions of the components in the admixture are as follows:

stearate salt: as the main component of the admixture, the admixture has the functions of improving the microscopic defects of the alkali slag set cement and reducing water absorption. The action mechanism is that the stearate has a surface activity effect, when slag is hydrated, the stearate is adsorbed on the surfaces of gel particles of hydration products, so that the interaction and the cohesion among the gel particles are reduced, the dispersion of the hydration products (gel particles) is facilitated, the ordering of a space network of the gel particles is further enhanced, the micro defects of a solid phase microstructure of alkali slag cement stone are reduced, and the crack resistance of the alkali slag cement stone is improved. In addition, the stearate adsorbed to the alkali-slag cement has a film-forming property, and the film layer is composed of a large number of alkyl functional groups and has strong hydrophobicity, thereby reducing the water absorption of the alkali-slag cement.

Alkali slag retarder: as a coagulation regulating component of the admixture. Independently developed by Chongqing university and granted by national invention patent. The stearate has the promotion effect on the early hydration of the alkali slag cement, so that the initial setting of the alkali slag cement paste is advanced, and the operable time is reduced. The method is one of the defects of singly modifying the alkali slag cement paste by the stearate, and therefore, the alkali slag retarder is introduced into the additive to ensure the operability of the alkali slag cement paste. Meanwhile, the alkali slag retarder can ensure that the alkali slag cement has sufficient setting and hardening time when being hydrated, is beneficial to the ordered arrangement of the microstructure of the set cement, and the coordination of the set cement and stearate further reduces the microscopic defects.

Organosilicon: as an antifoaming component of the admixture. The foam stabilizing property of the stearate ensures that bubbles introduced when the alkali slag cement is stirred and formed are difficult to eliminate, and the mechanical property of the alkali slag cement stone is reduced. The method is another disadvantage of modifying alkali slag cement stones by stearate, so that organic silicon is introduced into the additive to reduce bubbles in the alkali slag cement stones and improve the mechanical properties of the cement stones. In addition, the silicone also has hydrophobicity, and is adsorbed on the surface of the alkali slag set cement, further reducing the water absorption of the alkali slag set cement.

Calcium hydroxide: as a dispersing component of the admixture. The stearate is light and insoluble in water, can be agglomerated when stirred in alkali slag cement slurry, and has poor dispersibility and low action efficiency. The method is another disadvantage when the stearate is used for modifying the alkali slag cement, and therefore, the components above the stearate are mixed and ground with calcium hydroxide to improve the dispersibility and the action efficiency of the stearate in the alkali slag cement. In addition, the calcium hydroxide can optimize the pore size distribution of the alkali slag cement stone, reduce the capillary pressure and further improve the crack resistance of the alkali slag cement.

Through the synergistic effect of the components, the internal microscopic defects of the alkali slag set cement are reduced, and the hydrophobic film layer is introduced on the pore wall of the alkali slag set cement, so that the crack resistance of the alkali slag set cement is improved radically, and the water absorption is reduced.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

FIG. 1 is a test chart of the compressive strength of an alkali slag cement test piece 1, an alkali slag cement test piece 1-1 and an alkali slag cement test piece 1-2;

FIG. 2 is a comparative diagram showing the drying shrinkage cracking condition before and after the drying of an alkali slag cement test piece 1; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 3 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 1-1; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 4 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 1-2; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 5 is a scanning electron microscope image at 500 times after drying of an alkali slag cement test piece 1, an alkali slag cement test piece 1-1, and an alkali slag cement test piece 1-2; (A is a scanning electron microscope picture of the alkali slag cement test piece 1, B is a scanning electron microscope picture of the alkali slag cement test piece 1-1, and C is a scanning electron microscope picture of the alkali slag cement test piece 1-2)

FIG. 6 is a diagram showing a distribution of the aperture after drying of an alkali slag cement test piece 1, an alkali slag cement test piece 1-1, and an alkali slag cement test piece 1-2;

FIG. 7 is water absorption test charts of an alkali slag cement test piece 1, an alkali slag cement test piece 1-1, and an alkali slag cement test piece 1-2;

FIG. 8 is a scanning electron microscope image at 5000 times after drying of an alkali slag cement test piece 1, an alkali slag cement test piece 1-1, and an alkali slag cement test piece 1-2; (A is a scanning electron microscope picture of the alkali slag cement test piece 1, B is a scanning electron microscope picture of the alkali slag cement test piece 1-1, and C is a scanning electron microscope picture of the alkali slag cement test piece 1-2)

FIG. 9 is a test chart of the porosity of an alkali slag cement test piece 1, an alkali slag cement test piece 1-1, and an alkali slag cement test piece 1-2;

FIG. 10 is a test chart of the compressive strength of an alkali slag cement test piece 1, an alkali slag cement test piece 2-1, and an alkali slag cement test piece 2-2;

FIG. 11 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 2-1; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 12 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 2-2; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 13 is water absorption test charts of an alkali slag cement test piece 1, an alkali slag cement test piece 2-1, and an alkali slag cement test piece 2-2;

FIG. 14 is a test chart of the compressive strength of an alkali slag cement test piece 1, an alkali slag cement test piece 3-1, and an alkali slag cement test piece 3-2;

FIG. 15 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 3-1; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 16 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 3-2; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 17 is a water absorption test chart of an alkali slag cement test piece 1, an alkali slag cement test piece 3-1, and an alkali slag cement test piece 3-2;

FIG. 18 is a test chart of the compressive strength of an alkali slag cement test piece 1, an alkali slag cement test piece 4-1 and an alkali slag cement test piece 4-2;

FIG. 19 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 4-1; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 20 is a comparative diagram showing the drying shrinkage cracking condition before and after drying of an alkali slag cement test piece 4-2; (in the figure, A is a photograph before drying, and B is a photograph after drying)

FIG. 21 is a water absorption test chart of an alkali slag cement test piece 1, an alkali slag cement test piece 4-1, and an alkali slag cement test piece 4-2.

Detailed Description

The preferred embodiments of the present invention will be described in detail below.

Comparative examples

Preparation of alkali slag cement test piece

Adding water and water glass with the modulus of 1.5 into the slag by using a paste mixer, slowly stirring for 30s, stopping stirring for 10s, scraping powder on the wall of a pot into the pot, quickly stirring for 60s, then forming the uniformly stirred paste, curing for 24h in a curing box with the relative humidity of 95% and the temperature of 20 ℃, demoulding, and continuously curing for 28 days in the curing box to obtain an alkali slag cement test piece 1, wherein the alkali equivalent of the alkali slag cement test piece 1 is 5%, and the water-to-gel ratio is 0.45.

Example 1

1. Additive for improving cracking and water absorption of alkali slag cement

40 parts of calcium stearate, 10 parts of alkali slag retarder, 5 parts of organic silicon and 45 parts of calcium hydroxide are mixed and ground for 30min by a ball mill, and then ground for 30min by a vibration mill, so as to prepare the additive for improving cracking and water absorption of alkali-activated slag cement.

2. Preparation of alkali slag cement test piece

And (3) using a paste mixer, firstly, dry-mixing the additive and the slag prepared in the step (1) for 30s, then adding water and water glass with the modulus of 1.5, slowly stirring for 30s, stopping stirring for 10s, scraping powder on the wall of the pot into the pot, quickly stirring for 60s, then forming the uniformly-stirred paste, curing for 24h in a curing box with the relative humidity of 95% and the temperature of 20 ℃, demoulding, and continuously curing for 28 days in the curing box. The blending amount, alkali equivalent and water-to-cement ratio of the additives in each prepared alkali slag cement test piece are shown in table 1.

TABLE 1

The mechanical property test is carried out on the test piece 1, the test pieces 1-1 and the test pieces 1-2, the test results are shown in figure 1, and as can be seen from figure 1, compared with the alkali slag cement test piece without the additive, the compression strength of the alkali slag cement test piece with the additive is slightly increased, and the strength reduction degree is increased along with the increase of the mixing amount of the additive, which indicates that the additive has the effect of enhancing the mechanical property of the alkali slag cement stone.

Firstly, the surface laitance of the test pieces 1, 1-1 and 1-2 is cut off to leak out the inner layer slurry and photographed, then the test pieces 1, 1-1 and 1-2 are put into a drying oven with 40 ℃ and 25% of relative humidity for drying for 48 hours, and photographed again, the development conditions of cracks of the test pieces before and after drying are compared, and the results are shown in fig. 2, 3 and 4, wherein A in the three pictures is a picture before drying, B is a picture after drying, and the comparison of the pictures in fig. 2, 3 and 4 shows that the drying shrinkage cracking of the alkali slag cement test pieces is obviously improved after the admixture is doped.

In order to further observe the improvement effect of the admixture on the drying shrinkage cracking of the alkali slag cement test pieces after drying, small pieces with a length, a width and a height of about 4-7mm were gripped from each test piece by a nipper and dried in a vacuum drying oven at 40 ℃ for 48 hours. The improvement effect of the admixture on the shrinkage cracking of the alkali slag cement test piece is observed by a scanning electron microscope under 500 times, and the result is shown in fig. 5, wherein A in fig. 5 is a scanning electron microscope image of the alkali slag cement test piece with 0% admixture, B is a scanning electron microscope image of the alkali slag cement test piece with 4% admixture, and C is a scanning electron microscope image of the alkali slag cement test piece with 8% admixture, and the cracking degree of the alkali slag cement test piece in B and C in fig. 5 is obviously smaller than that of the alkali slag cement test piece in A, so that the shrinkage cracking of the alkali slag cement test piece is obviously improved after the admixture is added.

The capillary tension is the root cause of the generation and increase of the drying shrinkage cracking of alkali slag cement, and the capillary tension theory holds that the capillary tension can be expressed as (laplace equation):

in the formula

-capillary tension;

σ — liquid surface tension;

r₁，r₂radius of curvature of capillary water. As can be seen from the formula, the influence

The important parameters of are σ and r. Therefore, small pieces with the length, width and height of about 4-7mm are clamped from each test piece by using pliers, the small pieces are dried for 48 hours at 40 ℃ in a vacuum drying oven, the pore size distribution change of the alkali slag cement test piece after the admixture is mixed is tested by using MIP, and the result is shown in figure 6, and as shown in figure 6, the pore size distribution of the alkali slag cement test piece in the range of 9.1-21.1nm is gradually increased along with the increase of the admixture mixing amount, namely r is increased, so that the capillary tension is reduced, which shows that the shrinkage deformation of the alkali slag cement test piece is reduced during drying, and the cracking is improved.

The test pieces 1, 1-1 and 1-2 were tested for water absorption according to ASTM C1585, and the test results are shown in FIG. 7. from FIG. 7, it can be seen that the water absorption of the alkali slag cement test piece to which the admixture was added is 1/5 which is the water absorption of the alkali slag cement test piece to which the admixture was not added, compared with the alkali slag cement test piece to which the admixture was not added, indicating that the admixture is effective in improving the water absorption of the alkali slag cement.

In order to further investigate the effect of the admixture on improving the water absorption of the alkali slag cement test piece, the appearance of the interior of the alkali slag cement test piece was observed under a scanning electron microscope at 5000 times, and the result is shown in fig. 8. In FIG. 8, A is a scanning electron microscope image of an alkali slag cement test piece with an admixture of 0%, B is a scanning electron microscope image of an alkali slag cement test piece with an admixture of 4%, and C is a scanning electron microscope image of an alkali slag cement test piece with an admixture of 8%, and B and C can be seen from FIG. 8, wherein a hydrophobic film layer is arranged on the pore wall of the alkali slag cement test piece, and the film layer enables the water absorption of alkali slag cement stone to be greatly reduced.

The tortuosity τ of the pore structure of the test pieces 1, 1-1, and 1-2 is calculated by the following formula:

in the formula: alpha is alpha_enThe calculation results are shown in fig. 9 by reading the MIP data for the percentage of the retained mercury volume to the maximum mercury volume, and it can be seen from fig. 9 that the porosity tortuosity of the alkali slag cement test piece becomes larger with the increase of the doping amount of the additive, that is, the transmission distance of the water in the pores of the alkali slag cement test piece becomes larger, which further shows that the additive can obviously improve the water absorption of the alkali slag cement test piece.

Example 2

1. Additive for improving cracking and water absorption of alkali slag cement

50 parts of calcium stearate, 12 parts of alkali slag retarder, 6 parts of organic silicon and 50 parts of calcium hydroxide are mixed and ground for 30min by a ball mill, and then ground for 30min by a vibration mill, so as to prepare the additive for improving cracking and water absorption of alkali-activated slag cement.

Referring to the method for preparing alkali slag cement test pieces in example 1, alkali slag cement test pieces were prepared with the above-mentioned admixtures, and the test pieces were prepared as 2-1 and 2-2, respectively.

The mechanical properties of the test pieces 1, 2-1 and 2-2 were tested, and the test results are shown in fig. 10. as can be seen from fig. 10, in the first 14 days, the compressive strength of the alkali slag cement test pieces with the additives was slightly increased compared to the alkali slag cement test pieces without the additives, and the strength change degree was small with the increase of the additive amount, which indicates that the additives have an effect of enhancing the mechanical properties of the alkali slag cement.

Firstly, the surface laitance of the test pieces 2-1 and 2-2 is cut off to leak out the inner layer slurry and photographed, then the test pieces 2-1 and 2-2 are put into an oven with 40 ℃ and 25% of relative humidity for drying for 48 hours, and photographed again, the development condition of the crack of each test piece before and after drying is compared, and the result is shown in figures 11 and 12, wherein A in the two figures is a photo before drying, B is a photo after drying, and the comparison of figures 2, 11 and 12 shows that the drying shrinkage cracking of the alkali slag cement test piece is obviously improved after the admixture is doped.

The water absorption of test pieces 1, 2-1 and 2-2 was tested according to ASTM C1585, and the test results are shown in FIG. 13, and it can be seen from FIG. 13 that the water absorption of the test pieces of alkali slag cement decreased as the amount of the admixture incorporated was increased, indicating that the admixture was effective in improving the water absorption of alkali slag cement, wherein the water absorption of the test pieces of alkali slag cement having an admixture incorporated amount of 8% was 1/5 of the water absorption of the test pieces of alkali slag cement having no admixture incorporated, as compared with the test pieces of alkali slag cement having no admixture incorporated.

Example 3

1. Additive for improving cracking and water absorption of alkali slag cement

60 parts of calcium stearate, 15 parts of alkali slag retarder, 8 parts of organic silicon and 55 parts of calcium hydroxide are mixed and ground for 30min by a ball mill, and then ground for 30min by a vibration mill, so as to prepare the additive for improving cracking and water absorption of alkali-activated slag cement.

Referring to the method for preparing alkali slag cement test pieces in example 1, alkali slag cement test pieces were prepared with the above-mentioned admixtures, and the test pieces were 3-1 and 3-2, respectively.

The mechanical properties of the test pieces 1, 3-1 and 3-2 were tested, and the test results are shown in fig. 14, and it can be seen from fig. 14 that the compressive strength of the alkali slag cement test pieces with the additives added thereto was slightly increased, and the strength change degree was small with the increase in the amount of the additives added, indicating that the additives had an effect of enhancing the mechanical properties of the alkali slag cement.

Firstly, the surface laitance of the test pieces 3-1 and 3-2 is cut off to leak out the inner layer slurry and photographed, then the test pieces 3-1 and 3-2 are put into an oven with 40 ℃ and 25% of relative humidity for drying for 48 hours, and photographed again, the development condition of the crack of each test piece before and after drying is compared, and the result is shown in the pictures 15 and 16, wherein A in the two pictures is the picture before drying, B is the picture after drying, and the comparison of the pictures 2, 15 and 16 shows that the drying shrinkage cracking of the alkali slag cement test piece is obviously improved after the admixture is doped.

The test pieces 1, 3-1 and 3-2 were tested for water absorption according to ASTM C1585, and the test results are shown in FIG. 17, and from FIG. 17, it can be seen that the water absorption of the alkali slag cement test piece to which the admixture was added is 1/5 which is the water absorption of the alkali slag cement test piece to which the admixture was not added, compared with the alkali slag cement test piece to which the admixture was not added, indicating that the admixture is effective in improving the water absorption of the alkali slag cement.

Example 4

1. Additive for improving cracking and water absorption of alkali slag cement

70 parts of calcium stearate, 20 parts of alkali slag retarder, 10 parts of organic silicon and 60 parts of calcium hydroxide are mixed and ground for 30min by a ball mill, and then ground for 30min by a vibration mill, so as to prepare the additive for improving cracking and water absorption of alkali-activated slag cement.

Referring to the method for preparing alkali slag cement test pieces in example 1, alkali slag cement test pieces were prepared with the above-mentioned admixtures, and the test pieces were 4-1 and 4-2, respectively.

The mechanical property test was performed on test pieces 1, 4-1 and 4-2, and the test results are shown in fig. 18, and it can be seen from fig. 18 that, when the age was 28 days, the compressive strength of the alkali slag cement test piece with the admixture addition amount of 8% was substantially equal to that of the alkali slag cement test piece without the admixture, and the compressive strength of the alkali slag cement test piece with the admixture addition amount of 4% was higher than that of the alkali slag cement test piece without the admixture, indicating that the admixture is advantageous for the increase of the later strength of the alkali slag cement.

Firstly, the surface laitance of the test pieces 4-1 and 4-2 is cut off to leak out the inner layer slurry and photographed, then the test pieces 4-1 and 4-2 are put into an oven with 40 ℃ and 25% of relative humidity for drying for 48 hours, and photographed again, the development condition of the crack of each test piece before and after drying is compared, and the result is shown in figures 19 and 20, wherein A in the two figures is a photo before drying, B is a photo after drying, and the comparison of figures 2, 19 and 20 shows that the drying shrinkage cracking of the alkali slag cement test piece is obviously improved after the admixture is doped.

The water absorption of test pieces 1, 4-1 and 4-2 was tested according to ASTM C1585, and the test results are shown in FIG. 21, from which it can be seen that the water absorption of the test pieces of alkali slag cement decreased with the increase of the amount of admixture incorporated, indicating that the admixture is effective in improving the water absorption of alkali slag cement, wherein the water absorption of the test pieces of alkali slag cement having an admixture incorporated amount of 8% as compared with the test pieces of alkali slag cement having no admixture incorporated was 1/5 of the water absorption of the test pieces of alkali slag cement having no admixture incorporated.

Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. The additive for improving cracking and water absorption of alkali slag cement stones is characterized by comprising the following components in parts by mass: 40-70 parts of stearate, 10-20 parts of alkali slag retarder, 5-10 parts of organic silicon and 45-60 parts of calcium hydroxide.

2. The admixture for improving the cracking and water absorption of alkali slag set cement as claimed in claim 1, wherein the admixture is composed of the following components in parts by mass: 40 parts of stearate, 10 parts of alkali slag retarder, 5 parts of organic silicon and 45 parts of calcium hydroxide.

3. The admixture for improving the cracking and water absorption of alkali slag set cement as claimed in claim 1, wherein the admixture is composed of the following components in parts by mass: 50 parts of stearate, 12 parts of alkali slag retarder, 6 parts of organic silicon and 50 parts of calcium hydroxide.

4. The admixture for improving the cracking and water absorption of alkali slag set cement as claimed in claim 1, wherein the admixture is composed of the following components in parts by mass: 60 parts of stearate, 15 parts of alkali slag retarder, 8 parts of organic silicon and 55 parts of calcium hydroxide.

5. The admixture for improving the cracking and water absorption of alkali slag set cement as claimed in claim 1, wherein the admixture is composed of the following components in parts by mass: 70 parts of stearate, 20 parts of alkali slag retarder, 10 parts of organic silicon and 60 parts of calcium hydroxide.

6. An admixture for improving the cracking and water absorption of alkali slag cement as claimed in any one of claims 1 to 4, wherein said salt of stearic acid is one of calcium stearate, sodium stearate, magnesium stearate or zinc stearate.

7. The method for using the admixture according to any one of claims 1 to 4, wherein the method specifically comprises the following steps: the admixture is blended in an amount of 4 to 8 wt% in the alkali slag cement.

8. The use method according to claim 7, wherein the admixture is blended in an amount of 4 wt% in the alkali slag cement.