Additive for improving drying shrinkage of alkali slag cement mortar as well as preparation method and use method of additive

Abstract

The invention relates to an additive for improving drying shrinkage of alkali slag cement mortar as well as a preparation method and a use method of the additive, and belongs to the technical field of building materials. The admixture comprises the following components in parts by mass: 40-60 parts of lauryl sodium sulfate, 10-20 parts of modified magnesium oxide, 30-50 parts of slag, 2-6 parts of stearic acid and 0.1-0.5 part of a polyether modified organic silicon defoaming agent. Through the synergistic effect of all the components, the internal pore structure of the alkali slag cement mortar can be remarkably improved, and the surface tension of a pore solution can be reduced, so that the dry shrinkage performance of the alkali slag cement mortar is improved, meanwhile, the negative influence on the mechanical property of the alkali slag cement mortar is avoided, and excellent volume stability and durability are provided for the alkali slag cement mortar. The synthesis method is simple, raw materials are easily available, and the method is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials and relates to an admixture for improving drying shrinkage of alkali slag cement mortar and a preparation method and a use method thereof. Background Art

[0002] In recent years, alkali-activated slag (AAS), as a green, environmentally friendly, and high-performance alkali-activated material, has extremely broad development space and application prospects. Different from the "two grindings and one burning" process required for traditional cement production, AAS, as a clinker-free cement, does not require high-temperature calcination in its production process, only requires one grinding, and greenhouse gas emissions are only 15% to 40% of silicate cement. In addition, AAS cement mortar has high early strength, strong corrosion resistance, impermeability and chemical erosion resistance, and good freeze-thaw resistance, but it also has problems such as short setting time, high shrinkage and cracking. Among them, excessive drying shrinkage will accelerate CO 2 The erosion of harmful media such as acid and alkali ions poses a serious threat to the performance and durability of AAS cement mortar, which in turn limits its further promotion and application.

[0003] At present, the methods to solve the excessive drying shrinkage of AAS cement mortar are as follows:

[0004] (1) Adjust the type and amount of activator. For example, when using 4wt% sodium carbonate to activate AAS cement mortar, the shrinkage of 60d cement mortar is much lower than that of ordinary Portland cement mortar. The mechanism is that the addition of sodium carbonate can generate hydration products such as calcium carbonate, which can fill the pores and microcracks inside the cement mortar, improve the density and strength of the cement mortar, and thus enhance the anti-shrinkage ability of the cement mortar. However, excessive addition will lead to a decrease in the performance of the cement mortar.

[0005] (2) Adding fiber to toughen the mortar reduces the shrinkage of AAS cement mortar mainly through physical effects (such as moisture adsorption and regulation, fiber bridging and reinforcement), chemical and physical bonding (such as fiber-matrix bonding, and the effect on matrix hardening). However, when the fiber content exceeds a specific optimal value, it may have an adverse effect on the strength and shrinkage of the alkali-slag composite material.

[0006] (3) Adding mineral admixtures, which partially replace slag, can reduce the shrinkage rate of the alkali-slag system due to the dilution effect of mineral admixtures on the slag content and the reduction of the hydration reaction rate, but it will also weaken its compressive strength.

[0007] (4) Adding chemical additives, such as shrinkage reducers, this shrinkage reduction behavior is related to the reduction of the surface tension of the pore solution and the change of the pore structure, but the shrinkage reducers used for general-purpose silicate cement have low adaptability and stability in the high-alkali environment of alkaline slag.

[0008] (5) Changing the curing conditions, such as thermal curing, can effectively reduce the shrinkage rate of the alkali-slag system. Under high-temperature curing conditions, the hydration reaction rate is faster than the product diffusion rate. A large amount of hydration products are distributed around the unreacted particles, making the pore structure of the alkali-slag coarser and the capillary pressure reduced, thereby reducing the shrinkage of the sample. However, in large-scale applications, energy consumption and cost issues become more prominent.

[0009] Alkali slag cement mortar has received extensive attention in engineering applications due to its excellent mechanical properties, chemical corrosion resistance and environmental protection characteristics. However, due to the distribution of hydration products and capillary pore characteristics in the alkali slag system, its shrinkage performance is more significant than that of the ordinary Portland cement system, which often leads to problems such as cracking and leakage, seriously affecting the service life of the structure. In the prior art, the effect of reducing shrinkage by adding expansion agents, water reducers and other measures is limited, and may lead to strength loss. For this reason, it is of great significance to develop a composite admixture that reduces the shrinkage of alkali slag cement mortar. Summary of the invention

[0010] In view of this, one of the objects of the present invention is to provide an application of sodium dodecyl sulfate in the preparation of an admixture for improving the drying shrinkage of alkali slag cement mortar; a second object is to provide an admixture for improving the drying shrinkage of alkali slag cement mortar; a third object is to provide a preparation method of the admixture for improving the drying shrinkage of alkali slag cement mortar; and a fourth object is to provide a method for using the admixture for improving the drying shrinkage of alkali slag cement mortar.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] 1. Application of sodium dodecyl sulfate in the preparation of admixtures to improve drying shrinkage of alkali slag cement mortar.

[0013] 2. An admixture for improving drying shrinkage of alkali slag cement mortar, which comprises the following components in parts by mass: 40-60 parts of sodium lauryl sulfate, 10-20 parts of modified magnesium oxide, 30-50 parts of slag, 2-6 parts of stearic acid, and 0.1-0.5 parts of polyether modified silicone defoamer.

[0014] Preferably, the admixture comprises the following components in parts by mass: 40 parts of sodium lauryl sulfate, 10 parts of modified magnesium oxide, 30 parts of slag, 2 parts of stearic acid, and 0.1 parts of polyether-modified silicone defoamer.

[0015] Preferably, the admixture comprises the following components in parts by mass: 50 parts of sodium lauryl sulfate, 15 parts of modified magnesium oxide, 40 parts of slag, 4 parts of stearic acid, and 0.3 parts of polyether-modified silicone defoamer.

[0016] Preferably, the admixture comprises the following components in parts by mass: 60 parts of sodium lauryl sulfate, 20 parts of modified magnesium oxide, 50 parts of slag, 6 parts of stearic acid, and 0.5 parts of polyether-modified silicone defoamer.

[0017] Preferably, the modified magnesium oxide is prepared as follows:

[0018] Disperse magnesium oxide powder in water, add sodium citrate solution with a mass fraction of 1%, stir evenly, stand at 60-80°C for 30-60 minutes and then spray dry, then add melted stearic acid, stir and mix evenly; the mass volume ratio of the magnesium oxide powder, water, sodium citrate solution with a mass fraction of 1% and stearic acid is 1:4-6:4-6:0.1-0.2, g:mL:mL:g.

[0019] Preferably, the particle size of the magnesium oxide powder is 10-20 μm.

[0020] Preferably, the inlet air temperature of the spray drying is 150-200°C, and the outlet air temperature is 70-90°C.

[0021] Preferably, the slag is treated as follows: the slag is dried at 100-130° C. to constant weight, ball-milled, passed through a 16-mesh sieve, and the sieve residue is taken.

[0022] 3. A method for preparing the admixture for improving drying shrinkage of alkali slag cement mortar, the method being as follows:

[0023] After uniformly mixing the modified magnesium oxide, slag and stearic acid, sodium dodecyl sulfate is added, and shear mixing is performed at a rotation speed of 400-600 rpm for 15-25 minutes, and then a polyether modified silicone defoamer is added, and shear mixing is performed at a rotation speed of 50-150 rpm for 3-7 minutes to obtain a mixture; the mixture is dried at 55-65° C. to constant weight, and after crushing, it is passed through a 200-mesh sieve, and the sieve is taken.

[0024] 4. A method for using the admixture for improving drying shrinkage of alkali slag cement mortar, the method is as follows: the admixture is added in an amount of 3-5wt% in the alkali slag cement mortar, and the admixture is added externally.

[0025] The beneficial effects of the present invention are as follows: the present invention provides an admixture for improving the drying shrinkage of alkali slag cement mortar, and a preparation method and a use method thereof, which can significantly improve the internal pore structure of the alkali slag cement mortar and reduce the surface tension of the pore solution through the synergistic effect of various components, thereby improving the drying shrinkage performance of the alkali slag cement mortar, while avoiding the negative impact on the mechanical properties of the alkali slag cement mortar, and providing the alkali slag cement mortar with excellent volume stability and durability. The synthesis method is simple, the raw materials are easily available, and it is suitable for industrial production.

[0026] Among them, sodium dodecyl sulfate (SDS) is the core component, and its main function is to improve particle dispersibility and optimize pore structure. Specifically, SDS can reduce the surface tension between solid particles in the slurry, thereby reducing the agglomeration of particles and making the slurry more uniform. In addition, SDS makes the hydration products evenly distributed in the cement mortar, fills the pores, reduces the proportion of large pores and connected pores, and thus improves the pore structure inside the cement mortar. Furthermore, SDS can form a thin film on the pore surface, which can inhibit water evaporation, thereby effectively reducing the shrinkage of cement mortar.

[0027] Modified magnesium oxide (MgO) uses stearic acid to initially form a coating on the surface of magnesium oxide, so that the stability, fluidity and dispersibility of magnesium oxide are optimized to ensure that it can play a better role. Magnesium oxide generates magnesium hydroxide through hygroscopic reaction, and a slight expansion effect occurs, which can effectively compensate for the volume change during the shrinkage process of alkali slag cement mortar. In addition, the generated magnesium hydroxide provides an alkaline environment for slag, which can accelerate the reaction of silicates and aluminates in the slag with water, produce CSH gel and other hydration products, and improve the structural strength of cement mortar. Furthermore, magnesium oxide forms a magnesium hydroxide film on the surface of slag particles, which increases the negative charge on the surface of slag particles, enhances the electrostatic repulsion between particles, enables alkali slag to be more evenly dispersed, reduces the agglomeration of particles, thereby avoiding the internal stress caused by uneven particles during the hardening process of cement mortar, and helps to reduce shrinkage. And after the alkali slag is evenly dispersed, its reaction efficiency is improved, and the generation of hydration products is increased, thereby improving the structural strength and durability of cement mortar.

[0028] As a functional carrier material in admixtures, slag has enhanced surface activity after being refined, and can provide an auxiliary and dispersing platform for other components, ensuring that the functions of other components are fully exerted.

[0029] Stearic acid has lubricating properties and can form a hydrophobic lubricating film on the surface of solid particles, which can significantly reduce the friction between particles, improve the fluidity and dispersibility of the particles, and effectively inhibit the agglomeration of solid particles, thereby avoiding the internal stress caused by uneven particles during the hardening process of cement mortar and helping to reduce shrinkage.

[0030] Polyether modified silicone defoamer can quickly break bubbles during the preparation of cement mortar, significantly reduce the porosity in the system, and improve the density of cement mortar. At the same time, it can reduce the stress concentration caused by bubbles and ensure the structural strength and durability of cement mortar.

[0031] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0033] Figure 1 It is a graph showing the fluidity test results of the alkali-slag mortar of the comparative specimen 1, the specimens 1-1, 1-2 and 1-3 in Example 1;

[0034] Figure 2 The MIP test results of the comparative specimen 1, the specimens 1-1, 1-2 and 1-3 in Example 1 are shown in FIG. Figure 2 Figure a is the cumulative pore volume test graph. Figure 2 (b) is the incremental intrusion test diagram);

[0035] Figure 3 The drying shrinkage test results of the comparative specimen 1, the specimen 1-1, the specimen 1-2, and the specimen 1-3 in Example 1 are shown;

[0036] Figure 4 It is a graph showing the fluidity test results of the alkali-slag mortar of the comparative specimen 2 and the specimens 2-1, 2-2 and 2-3 in Example 2;

[0037] Figure 5 The MIP test results of the comparative specimen 2, the specimens 2-1, 2-2 and 2-3 in Example 2 are shown in FIG. Figure 5 Figure a is the cumulative pore volume test graph. Figure 5 (b) is the incremental intrusion test diagram);

[0038] Figure 6 The drying shrinkage test results of the comparative specimen 2, the specimen 2-1, the specimen 2-2, and the specimen 2-3 in Example 2 are shown;

[0039] Figure 7 The SEM images of the comparative specimen 3 and the specimen 3-2 in Example 3 are shown in FIG. Figure 7 A in the figure is the SEM image of the comparative specimen 3. Figure 7 (B) is the SEM image of specimen 3-2;

[0040] Figure 8 The drying shrinkage test results of the comparative specimen 3, the specimen 3-1 and the specimen 3-2 in Example 3 are shown;

[0041] Fig. 9 The mechanical properties test results of the comparative specimen 3, the specimen 3-1 and the specimen 3-2 in Example 3 are shown in FIG.

[0042] Fig.10 The drying shrinkage test results of the comparative specimen 3, the specimen 4-1 and the specimen 4-2 in Example 4 are shown in FIG.

[0043] Fig.11 The mechanical properties test results of the comparative specimen 3, the specimen 4-1 and the specimen 4-2 in Example 4 are shown in FIG.

[0044] Fig.12 The drying shrinkage test results of the comparative specimen 3, the specimen 5-1 and the specimen 5-2 in Example 5 are shown;

[0045] Fig.13 This is a graph showing the mechanical properties test results of Comparative Specimen 3, Specimen 5-1, and Specimen 5-2 in Example 5. DETAILED DESCRIPTION

[0046] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0047] The modified magnesium oxide used in each embodiment of the present invention is prepared as follows:

[0048] Magnesium oxide powder with a particle size of 10-20 μm is dispersed in deionized water, and a sodium citrate solution with a mass fraction of 1% is added and stirred evenly. After standing at 70° C. for 30 minutes, the mixture is spray-dried under the conditions of an inlet air temperature of 180° C. and an outlet air temperature of 80° C., and then melted stearic acid is added and stirred and mixed evenly. The mass volume ratio of the magnesium oxide powder, deionized water, the sodium citrate solution with a mass fraction of 1% and the stearic acid is 1:5:5:0.1, g:mL:mL:g.

[0049] The slag used in each embodiment of the present invention is prepared as follows:

[0050] Dry the slag at 120°C to constant weight, place it in a ball mill and mill it for 90 minutes, then pass it through a 16-mesh sieve and take the material under the sieve.

[0051] Comparative Example 1

[0052] Preparation of alkali-slag cement mortar specimens

[0053] Place slag and standard sand in a mortar mixing pot, stir and mix at a speed of 160rpm, stop for 10s and scrape the powder on the pot wall into the pot. Subsequently, pour water and a water glass solution with a modulus of 1.5 into the pot quickly, continue to stir at a speed of 160rpm for 20s, and then stir at a speed of 350rpm for 40s to obtain a uniformly mixed mortar. Pour the mortar into the mold at one time and place it on a vibration table for 60s to expel bubbles and make the mortar more compact. After the compaction is completed, the film is cured for 24h before demolding. The demolded test block continues to be placed under standard curing conditions (20±2℃, humidity>95%) for 28d. The test piece used to measure the shrinkage performance is placed under dry conditions (20±2℃, humidity 35±3%) after standard curing for 3d and continues to be cured to the specified age. Obtain alkali slag cement mortar comparison specimen 1, the alkali equivalent of comparison specimen 1 is 5%, and the water-cement ratio is 0.35.

[0054] Example 1

[0055] Preparation of alkali slag cement mortar specimens (with sodium lauryl sulfate as admixture only)

[0056] Place slag, sodium dodecyl sulfate and standard sand in a mortar mixing pot, stir and mix at a speed of 160rpm, stop for 10s and scrape the powder on the pot wall into the pot. Subsequently, pour water and water glass solution with a modulus of 1.5 quickly, continue to stir at a speed of 160rpm for 20s and then stir at a speed of 350rpm for 40s to obtain a uniformly mixed mortar, pour the mortar into the mold at one time, place it on a vibration table and vibrate for 60s to expel bubbles and make the mortar more compact. After completion of vibration, cover and cure for 24h before demolding. After demolding, the test block is continued to be placed under standard curing conditions (20±2℃, humidity>95%) for 28d. Among them, the test piece used to measure the shrinkage performance is placed under dry conditions (20±2℃, humidity 35±3%) after standard curing for 3d and continues to be cured to the specified age. The dosage of admixtures, alkali equivalent and water-cement ratio in the prepared alkali slag cement mortar specimens are shown in Table 1.

[0057] Table 1

[0058]

[0059] Referring to GB / T 2419-2005 "Method for Determination of Fluidity of Cement Mortar", the fluidity of the alkali-slag mortar used to prepare the comparative specimen 1, the specimens 1-1, 1-2 and 1-3 in Example 1 was tested respectively. The test results are as follows: Figure 1 As shown by Figure 1It can be seen that under the condition of W / B=0.35, with the gradual increase of SDS dosage, the fluidity of AAS mortar first showed an upward trend, and then gradually decreased. The fluidity of alkali-slag cement mortar with 0.5%, 1.0%, and 1.5% SDS increased by 0.8%, 6.1%, and 3.4% respectively compared with the alkali-slag cement mortar without SDS, indicating that the appropriate addition of SDS can effectively improve the fluidity of alkali-slag cement mortar. Among them, when the SDS dosage is 1.0%, the fluidity of AAS mortar reaches the maximum value.

[0060] 3-5 mm block samples were taken from the comparative specimen 1, specimens 1-1, 1-2, and 1-3 in Example 1 after standard curing for 28 days, respectively, and placed in anhydrous ethanol for at least 24 hours to terminate hydration, and then dried at 40°C to constant weight. The pore structure of the block samples was analyzed using an AutoPorelv9510 mercury intrusion instrument. The test conditions were a maximum mercury injection pressure of 414 MPa, an average time of 10 seconds, and an effective test pore size range of 5 nm-350 μm. The results are as follows: Figure 2 As shown, Figure 2 Figure a is the cumulative pore volume test graph. Figure 2 b is the incremental intrusion test diagram, Figure 2 As shown in Figure a, when 0.5% SDS was added, the cumulative mercury volume of the AAS mortar specimen increased significantly. As the SDS content was further increased to 1.5%, the cumulative mercury volume increased further, indicating that the addition of SDS would increase the porosity of AAS and make its pore structure coarser. Figure 2 As shown in Figure b, the peak value of the AAS mortar specimen with SDS added in the mesopore area is significantly increased and shifted to the right, indicating that SDS has a significant effect of coarsening the mesopores of the AAS mortar specimen. The pore size distribution of each block sample is shown in Table 2. It can be seen from Table 2 that the addition of SDS will increase the porosity of the AAS mortar specimen, and this increase trend becomes more obvious with the increase of SDS dosage. In addition, the average pore size of the AAS mortar specimen after adding SDS has increased, the proportion of pores <10nm has decreased accordingly, and the proportion of pores 10-20nm has increased. Therefore, it can be considered that the pore size of the AAS mortar specimen after adding SDS can be optimized within the harmless pore range. The coarsening of the capillary pores helps to reduce the capillary pressure in the AAS mortar specimen system, thereby reducing the drying shrinkage caused by it.

[0061] Table 2

[0062]

[0063] Referring to the standard JC / T 603-2004 "Test Method for Drying Shrinkage of Cement Mortar", the drying shrinkage rates of the comparative specimen 1, the specimens 1-1, 1-2 and 1-3 in Example 1 were tested respectively. The test results are as follows: Figure 3 As shown by Figure 3 It can be seen that under the condition of W / B=0.35, with the addition of SDS, the drying shrinkage of AAS mortar specimens was significantly reduced, and with the gradual increase of SDS dosage, this improvement effect became more and more obvious. When the SDS dosage reached 1.5%, the shrinkage reduction effect was most prominent. The drying shrinkage of AAS mortar specimens with 1.0% and 1.5% SDS was reduced by 17.2% and 53.2% respectively, indicating that SDS has a positive effect on the shrinkage reduction of AAS mortar.

[0064] Comparative Example 2

[0065] Preparation of alkali-slag cement mortar specimens

[0066] The preparation method refers to Comparative Example 1, and the alkali equivalent of the prepared comparative specimen 2 is 5% and the water-binder ratio is 0.45.

[0067] Example 2

[0068] Preparation of alkali slag cement mortar specimens (with sodium lauryl sulfate as admixture only)

[0069] The preparation method is as in Example 1. The dosage of admixture, alkali equivalent and water-binder ratio of each prepared alkali slag cement mortar specimen are shown in Table 3.

[0070] Table 3

[0071]

[0072] Referring to GB / T 2419-2005 "Method for Determination of Fluidity of Cement Mortar", the fluidity of the alkali-slag mortar used to prepare the comparative specimen 2, the specimens 2-1, 2-2 and 2-3 in Example 2 was tested respectively. The test results are as follows: Figure 4 As shown by Figure 4 It can be seen that under the condition of W / B=0.45, with the gradual increase of SDS dosage, the fluidity of AAS mortar first showed an upward trend, and then gradually decreased. The fluidity of alkali-slag cement mortar with 0.5%, 1.0%, and 1.5% SDS increased by 1.2%, 4.9%, and 2.5% respectively compared with the alkali-slag cement mortar without SDS, indicating that the appropriate addition of SDS can effectively improve the fluidity of alkali-slag cement mortar. Among them, when the SDS dosage is 1.0%, the fluidity of AAS mortar reaches the maximum value.

[0073] 3-5 mm block samples were taken from the comparative specimen 2, specimens 2-1, 2-2, and 2-3 in Example 2 after standard curing for 28 days, respectively, and placed in anhydrous ethanol for at least 24 hours to terminate hydration, and then dried at 40°C to constant weight. The pore structure of the block samples was analyzed using an AutoPorelv9510 mercury intrusion instrument. The test conditions were a maximum mercury injection pressure of 414 MPa, an average time of 10 seconds, and an effective test pore size range of 5 nm-350 μm. The results are as follows: Figure 5 As shown, Figure 5 Figure a is the cumulative pore volume test graph. Figure 5 b is the incremental intrusion test diagram, Figure 5 As shown in Figure a, the cumulative mercury volume gradually increases with the increase of SDS dosage, which shows that the addition of SDS increases the porosity of AAS. Figure 5 As shown in Figure b, the peak area of ​​the mesoporous range of AAS modified by SDS becomes wider, which shows that SDS can coarsen the pore size of AAS mortar specimens within the harmless pore size range. The pore size distribution of each block sample is shown in Table 4. It can be seen from Table 4 that the addition of SDS will increase the porosity of AAS mortar specimens, and this increasing trend becomes more obvious with the increase of SDS dosage. In addition, the average pore size of AAS mortar specimens after adding SDS has increased, the proportion of pore sizes <10nm has decreased accordingly, and the proportion of pore sizes of 10-20nm has increased. Therefore, it can be considered that the pore size of AAS mortar specimens after adding SDS can be optimized within the harmless pore range.

[0074] Table 4

[0075]

[0076] Referring to the standard JC / T 603-2004 "Test Method for Drying Shrinkage of Cement Mortar", the drying shrinkage rates of the comparative specimen 2, the specimens 2-1, 2-2 and 2-3 in Example 2 were tested respectively. The test results are as follows: Figure 6 As shown by Figure 6 It can be seen that under the condition of W / B=0.45, with the addition of SDS, the drying shrinkage of AAS mortar specimens was significantly reduced, and with the gradual increase of SDS dosage, this improvement effect became more and more obvious. When the SDS dosage reached 1.5%, its shrinkage reduction effect was most prominent. After adding 0.5%, 1.0%, and 1.5% SDS, the drying shrinkage was reduced by 21.4%, 30.9%, and 33.4%, respectively. This shows that SDS has a positive effect on the shrinkage reduction of AAS mortar.

[0077] Comparative Example 3

[0078] Preparation of alkali-slag cement mortar specimens

[0079] The preparation method refers to Comparative Example 1, and the alkali equivalent of the prepared comparative specimen 3 is 5% and the water-binder ratio is 0.4.

[0080] Example 3

[0081] Preparation of alkali-slag cement mortar specimens

[0082] (1) Preparation of admixtures

[0083] 10 parts of modified magnesium oxide, 30 parts of slag and 2 parts of stearic acid are added to a planetary mixer and dry-mixed until uniformly mixed. Then, 40 parts of sodium dodecyl sulfate are added and shear-mixed at a speed of 500 rpm for 20 minutes using a high-speed shear mixing device. Then, 0.1 parts of a polyether-modified silicone defoamer is added and shear-mixed at a speed of 100 rpm for 5 minutes to obtain a mixture. The mixture is dried at 60°C to constant weight, crushed, and sieved through a 200-mesh sieve to obtain the sieve.

[0084] (2) Preparation of mortar specimens

[0085] Place slag, the admixture prepared in step (1), and standard sand in a mortar stirring pot, stir and mix at a speed of 160 rpm, stop for 10 seconds and scrape the powder on the pot wall into the pot. Subsequently, water and a water glass solution with a modulus of 1.5 are quickly poured in, and stirring is continued at a speed of 160 rpm for 20 seconds and then at a speed of 350 rpm for 40 seconds to obtain a uniformly mixed mortar. The mortar is poured into the mold at one time and placed on a vibration table for 60 seconds to expel bubbles and make the mortar more compact. After completion of the vibration, the film is cured for 24 hours before demolding. The demolded test block continues to be placed under standard curing conditions (20±2°C, humidity>95%) for 28 days, among which the test piece used to measure the shrinkage performance is placed under dry conditions (20±2°C, humidity 35±3%) after standard curing for 3 days and continues to be cured to the specified age. The dosage of admixtures, alkali equivalent and water-binder ratio in the prepared alkali slag cement mortar specimens are shown in Table 5.

[0086] Table 5

[0087]

[0088] 3-5 mm block samples were taken from the comparative specimen 3, specimen 3-1 and specimen 3-2 in Example 3 after 28 days of standard curing. The pore size distribution of each block sample is shown in Table 6. It can be seen from Table 6 that the addition of admixtures will increase the porosity and average pore size of the AAS mortar specimens, and the proportion of pore sizes <10 nm will decrease accordingly, while the proportion of pore sizes of 10-20 nm will increase. Therefore, it can be considered that the pore size of the AAS mortar specimen after the addition of admixtures can be optimized within the harmless pore range. The coarsening of the capillary pores helps to reduce the capillary pressure in the AAS system, thereby reducing the drying shrinkage caused by it.

[0089] Table 6

[0090]

[0091] 3-5 mm block samples were taken from the comparative specimen 3 and the specimen 3-2 in Example 3 after standard curing for 28 days, and tested using a scanning electron microscope. The results are as follows: Figure 7 As shown, Figure 7 A in the middle is the SEM image of the comparative specimen 3. Figure 7 B is the SEM image of specimen 3-2. Figure 7 It can be seen that specimen 3-2 (i.e., the alkali-slag mortar specimen with an admixture dosage of 5%) is denser and covered with a hydrophobic film on the surface, thereby increasing the contact angle of the capillary pore wall and further reducing the capillary pressure, thereby greatly reducing the drying shrinkage.

[0092] Referring to the standard JC / T 603-2004 "Test Method for Drying Shrinkage of Cement Mortar", the drying shrinkage rates of the comparative specimen 3, the specimen 3-1 in Example 3, and the specimen 3-2 were tested respectively. The test results are as follows: Figure 8 As shown by Figure 8 It can be seen that under the condition of W / B=0.40, with the addition of admixtures, the drying shrinkage of AAS mortar specimens was significantly reduced, and with the gradual increase of admixture dosage, this improvement effect became more and more obvious. When the admixture dosage reached 5%, the shrinkage reduction effect was most prominent. The 28d drying shrinkage of the specimens with 3% and 5% admixtures was reduced by 11.13% and 53.2%, respectively, indicating that admixtures have a positive effect on the shrinkage reduction of AAS mortar.

[0093] Referring to GB / T 19671-1999 "Test Method for Strength of Cement Mortar (ISO Method)", mechanical properties tests were conducted on Comparative Specimen 3 and Specimens 3-1 and 3-2 in Example 3. The test results are as follows: Fig. 9 As shown by Fig. 9 It can be seen that compared with the alkali-slag mortar specimens without admixtures, the compressive strength of the alkali-slag mortar specimens with admixtures increases with the increase of admixture dosage, and is higher than the strength of comparison specimen 3, which indicates that the admixture has an enhancing effect on the mechanical properties of the alkali-slag mortar specimens.

[0094] Example 4

[0095] Preparation of alkali-slag cement mortar specimens

[0096] (1) Preparation of admixtures

[0097] 15 parts of modified magnesium oxide, 40 parts of slag and 4 parts of stearic acid are added to a planetary mixer and dry-mixed until uniformly mixed. Then, 50 parts of sodium dodecyl sulfate are added and shear-mixed at a speed of 400 rpm for 25 minutes using a high-speed shear mixing device. Then, 0.3 parts of a polyether-modified silicone defoamer is added and shear-mixed at a speed of 50 rpm for 7 minutes to obtain a mixture. The mixture is dried at 65°C to constant weight, crushed, and sieved through a 200-mesh sieve to obtain the sieve.

[0098] (2) Preparation of mortar specimens

[0099] The preparation method is referred to Example 3. The dosage of admixture, alkali equivalent and water-binder ratio of each prepared alkali slag cement mortar specimen are shown in Table 7.

[0100] Table 7

[0101]

[0102] Referring to the standard JC / T 603-2004 "Test Method for Drying Shrinkage of Cement Mortar", the drying shrinkage rates of the comparative specimen 3, the specimens 4-1 and 4-2 in Example 4 were tested respectively. The test results are as follows: Fig.10 As shown by Fig.10 It can be seen that under the condition of W / B=0.40, with the addition of admixtures, the drying shrinkage of AAS mortar specimens was significantly reduced, and with the gradual increase of admixture dosage, this improvement effect became more and more obvious. When the admixture dosage reached 5%, the shrinkage reduction effect was most prominent. The 28d drying shrinkage of the specimens with 3% and 5% admixtures was reduced by 12.1% and 31.2%, respectively, indicating that admixtures have a positive effect on the shrinkage reduction of AAS mortar.

[0103] According to GB / T 19671-1999 "Test Method for Strength of Cement Mortar (ISO Method)", mechanical properties of comparison specimen 3, specimens 4-1 and 4-2 were tested. The test results are as follows: Fig.11 As shown by Fig.11 It can be seen that compared with the alkali-slag mortar specimens without admixtures, the compressive strength of the alkali-slag mortar specimens with admixtures increases with the increase of admixture dosage, and is higher than the strength of comparison specimen 3, which indicates that the admixture has an enhancing effect on the mechanical properties of the alkali-slag mortar specimens.

[0104] Example 5

[0105] Preparation of alkali-slag cement mortar specimens

[0106] (1) Preparation of admixtures

[0107] Add 20 parts of modified magnesium oxide, 50 parts of slag and 6 parts of stearic acid into a planetary mixer and dry-mix until uniformly mixed, then add 60 parts of sodium dodecyl sulfate, use a high-speed shear mixing device to shear mix at a speed of 600 rpm for 15 minutes, then add 0.5 parts of polyether modified silicone defoamer, shear mix at a speed of 150 rpm for 3 minutes to obtain a mixture, dry the mixture at 55°C to constant weight, pulverize it, pass it through a 200-mesh sieve, and take the sieve.

[0108] (2) Preparation of mortar specimens

[0109] The preparation method is as shown in Example 3. The dosage of admixture, alkali equivalent and water-binder ratio of each prepared alkali slag cement mortar specimen are shown in Table 8.

[0110] Table 8

[0111]

[0112] Referring to the standard JC / T 603-2004 "Test Method for Drying Shrinkage of Cement Mortar", the drying shrinkage rates of the comparative specimen 3, the specimens 5-1 and 5-2 in Example 5 were tested respectively. The test results are as follows: Fig.12 As shown by Fig.12 It can be seen that under the condition of W / B=0.40, with the addition of admixtures, the drying shrinkage of AAS mortar specimens was significantly reduced, and with the gradual increase of admixture dosage, this improvement effect became more and more obvious. When the admixture dosage reached 5%, the shrinkage reduction effect was most prominent. The 28d drying shrinkage of the specimens with 3% and 5% admixtures was reduced by 16.6% and 41.0%, respectively, indicating that admixtures have a positive effect on the shrinkage reduction of AAS mortar.

[0113] According to GB / T 19671-1999 "Test Method for Cement Mortar Strength (ISO Method)", mechanical properties tests were conducted on the comparison specimen 3, specimens 5-1 and 5-2. The test results are as follows: Fig.13 As shown by Fig.13 It can be seen that compared with the alkali-slag mortar specimens without admixtures, the compressive strength of the alkali-slag mortar specimens with admixtures increases with the increase of admixture dosage, and is higher than the strength of comparison specimen 3, which indicates that the admixture has an enhancing effect on the mechanical properties of the alkali-slag mortar specimens.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. Application of sodium dodecyl sulfate in the preparation of admixtures to improve drying shrinkage of alkali slag cement mortar.

2. An admixture for improving drying shrinkage of alkali slag cement mortar, characterized in that: The admixture comprises the following components by weight: 40-60 parts of sodium lauryl sulfate, 10-20 parts of modified magnesium oxide, 30-50 parts of slag, 2-6 parts of stearic acid, and 0.1-0.5 parts of polyether modified silicone defoamer.

3. An admixture for improving drying shrinkage of alkali slag cement mortar according to claim 2, characterized in that: The admixture includes the following components by mass: 40 parts of sodium lauryl sulfate, 10 parts of modified magnesium oxide, 30 parts of slag, 2 parts of stearic acid, and 0.1 parts of polyether modified silicone defoamer.

4. An admixture for improving drying shrinkage of alkali slag cement mortar according to claim 2, characterized in that: The admixture includes the following components by mass: 50 parts of sodium lauryl sulfate, 15 parts of modified magnesium oxide, 40 parts of slag, 4 parts of stearic acid, and 0.3 parts of polyether modified silicone defoamer.

5. An admixture for improving drying shrinkage of alkali slag cement mortar according to claim 2, characterized in that: The admixture includes the following components by mass: 60 parts of sodium lauryl sulfate, 20 parts of modified magnesium oxide, 50 parts of slag, 6 parts of stearic acid, and 0.5 parts of polyether modified silicone defoamer.

6. An admixture for improving drying shrinkage of alkali slag cement mortar according to any one of claims 2 to 5, characterized in that: The modified magnesium oxide is prepared as follows: Disperse magnesium oxide powder in water, add sodium citrate solution with a mass fraction of 1%, stir evenly, stand at 60-80°C for 30-60 minutes and then spray dry, then add melted stearic acid, stir and mix evenly; the mass volume ratio of the magnesium oxide powder, water, sodium citrate solution with a mass fraction of 1% and stearic acid is 1:4-6:4-6:0.1-0.2, g:mL:mL:g.

7. An admixture for improving drying shrinkage of alkali slag cement mortar according to claim 6, characterized in that: The inlet air temperature of the spray drying is 150-200°C, and the outlet air temperature is 70-90°C.

8. An admixture for improving drying shrinkage of alkali slag cement mortar according to any one of claims 2 to 5, characterized in that: The slag is treated as follows: the slag is dried at 100-130° C. to constant weight, ball-milled, passed through a 16-mesh sieve, and the sieve residue is taken.

9. The method for preparing the admixture for improving drying shrinkage of alkali slag cement mortar according to any one of claims 2 to 8, characterized in that: The method is as follows: After uniformly mixing the modified magnesium oxide, slag and stearic acid, sodium dodecyl sulfate is added, and shear mixing is performed at a rotation speed of 400-600 rpm for 15-25 minutes, and then a polyether modified silicone defoamer is added, and shear mixing is performed at a rotation speed of 50-150 rpm for 3-7 minutes to obtain a mixture; the mixture is dried at 55-65° C. to constant weight, and after crushing, it is passed through a 200-mesh sieve, and the sieve is taken.

10. The method for using the admixture for improving drying shrinkage of alkali slag cement mortar according to any one of claims 2 to 8, characterized in that: The method is as follows: the admixture amount in the alkali slag cement mortar is 3-5wt%, and the admixture method is external admixture.

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