A composite admixture for inhibiting alkali-aggregate reaction and a method for preparing the same

Abstract

The application discloses a composite admixture for inhibiting alkali-aggregate reaction, and each component and weight percentage thereof are as follows: 10-20 parts of nano-cobalt ferrite, 20-30 parts of silica fume, 45-55 parts of modified tuff powder, 2-4 parts of sodium fatty alcohol polyoxyethylene ether sulfate, 2-4 parts of long-chain alkyl dimethyl amine, and 4-6 parts of modified nylon fiber. + , K + , and Na + , K + contact with active SiO2 during the reaction process, and the volume deformation is controlled by using the modified fiber uniformly dispersed in multiple angles and multiple levels, so that the alkali-aggregate reaction can be effectively inhibited; the composite admixture can replace traditional cementitious materials such as cement in a large amount, and can effectively consider the good use performance of the obtained concrete, and has significant economic and environmental benefits; and the preparation method is relatively simple, the cost is relatively low, and is suitable for popularization and application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a composite admixture for inhibiting alkali-aggregate reaction and a preparation method thereof. BACKGROUND

[0002] The alkali-aggregate reaction of concrete refers to the further chemical reaction of specific internal components (such as amorphous silicon or silicon with poor crystallinity) in the aggregate with alkali substances (Na + , K + , etc.) in the cement, additive, admixture, etc. of the concrete under certain conditions, which leads to the expansion, cracking and even destruction of the concrete structure, and even collapse of the concrete structure in severe cases, and is one of the important factors affecting the durability of concrete. The alkali-aggregate reaction can be divided into two types according to the reaction mechanism: alkali-silica reaction and alkali-carbonate reaction, and the reaction mechanisms are as follows:

[0003] SiO2+Na + +(K + )+OH - →Na(K)-Si-H(gel)(alkali-silica reaction)

[0004] 2NaOH+CaMg(CO3)2=CaCO3+Mg(OH)2+Na2CO3(alkali-carbonate reaction)

[0005] Na2CO3+Ca(OH)2=2NaOH+CaCO3.

[0006] and mainly includes the following steps: (1) dissolution of alkali in concrete; (2) reaction of alkali with active SiO2 mineral to form alkali-silica solution or sol; (3) condensation of sol particles to form gels of various structures under the action of various cations such as calcium; and (4) swelling of gels by absorbing water. In the traditional Portland cement system, the alkali-silica reaction is dominant.

[0007] The current measures to prevent alkali-silica reaction mainly include: using low-alkali cement and strictly controlling the alkali content of each component in the concrete, using high-activity admixtures such as fly ash, silica fume, metakaolin, etc. auxiliary gel materials, but the required addition amount is too high, which will seriously affect the quality of concrete products; secondly, using some chemical additives such as lithium nitrate, lithium carbonate, lithium hydroxide, lithium aluminum silicate, barium carbonate, barium sulfate and barium chloride, etc. to adsorb Na + , K + , which can reduce the risk of alkali-silica reaction from the source, but the addition of these chemical additives will introduce new harmful ions (Cl - , SO4 2- , etc.), and the cost is high. SUMMARY

[0008] The main purpose of the present application is to provide a kind of composite admixture for effectively inhibiting alkali aggregate reaction, which effectively inhibits alkali aggregate reaction from multiple angles, has obvious alkali aggregate reaction inhibition effect, and the preparation method is simple, convenient to operate, green and environmentally friendly.

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0010] A kind of composite admixture for inhibiting alkali aggregate reaction, each component and its weight percentage include: 10-20 parts of nano-cobalt ferrite, 20-30 parts of silica fume, 45-55 parts of modified tuff powder, 2-4 parts of sodium fatty alcohol polyoxyethylene ether sulfate, 2-4 parts of long-chain alkyl dimethyl amine, 4-6 parts of modified nylon fiber.

[0011] In the above scheme, the average particle size of the nano-cobalt ferrite is 30-50 nm.

[0012] In the above scheme, the silica fume has 3d activity > 90%, 28d activity > 110%, and specific surface area > 15000 m 2 / kg.

[0013] In the above scheme, the modified tuff powder is modified tuff powder modified by isobutyl triethoxysilane or octyl triethoxysilane, wherein the specific surface area of the tuff powder is 400-450 m 2 / kg; the specific preparation steps of the modified tuff powder include: grinding the tuff powder to a specific surface area of 400-450 m 2 / kg, drying the tuff powder at 60-80℃ for 10-12h and naturally cooling; mixing the tuff powder with anhydrous ethanol at a mass ratio of 1:2-2.5, stirring at a speed of 400-600 rpm for 40-60 min to ensure uniform dispersion; taking 1-3% of the mass of the tuff powder of isobutyl triethoxysilane (IBTS) or octyl triethoxysilane (OTTS) aqueous solution mixture (IBTS or OTTS and deionized water at a mass ratio of 1:3-5), stirring at a speed of 400-600 rpm for 40-70 min to ensure complete hydrolysis of IBTS; then, mixing all materials and stirring at a speed of 400-600 rpm for 4-6h; finally, drying the mixed material at 100-105℃ for 22-26h.

[0014] In the above scheme, the tuff powder is high-calcium tuff, and the content of CaO in the chemical composition is ≥10%.

[0015] In the above scheme, the sodium fatty alcohol polyoxyethylene ether sulfate is an anionic surfactant, and the molecular weight is 300-350.

[0016] In the above solution, the long-chain alkyl dimethyl amine is a cationic surfactant, and the alkyl carbon number is 10-15.

[0017] In the above solution, the modified nylon fiber has a diameter of 1.0-1.5 mm and a length of 3-5 mm; the nylon fiber is soaked in a triethanolamine solution with a concentration of 4-6 wt% for 30-60 min, ultrasonically dispersed for 10-15 min to be uniform, so that the fiber is fully dispersed in the solution, the fiber is filtered out, and drying is performed at 50-80 DEG C for 1-2 h to obtain.

[0018] In the above solution, the volume ratio of the nylon fiber to the triethanolamine solution is 1:3-5.

[0019] The preparation method of the composite admixture for inhibiting alkali aggregate reaction comprises the following steps:

[0020] 1) The weighed nano-cobalt ferrite and silica ash are subjected to homogenization treatment using a mixer, and then the modified tuff powder is added and uniformly mixed to obtain a mixture;

[0021] 2) The fatty alcohol polyoxyethylene ether sodium sulfate, long-chain alkyl dimethyl amine, and modified nylon fiber are subjected to homogenization treatment using a mixer, and then the mixture is added and uniformly mixed to obtain the composite admixture.

[0022] In the above solution, the mixer used in the homogenization treatment step in step 1) has a rotation speed of 40-60 r / min, and the homogenization time is 20-30 min; the mixer used in the homogenization treatment step in step 2) has a rotation speed of 10-30 r / min, and the homogenization time is 10-15 min.

[0023] The above composite admixture for inhibiting alkali aggregate reaction is applied to concrete using alkali active aggregate, and the content is 50-60% of the mass of cementitious materials.

[0024] The principle of the present application is:

[0025] 1) The nano-cobalt ferrite introduced in the present application can effectively adsorb metal cations (Na + , K + ) in a humid environment, thereby effectively reducing Na + , K +The total amount inhibits the occurrence of alkali aggregate reaction from the source; at the same time, in the preparation process, first, the nano cobalt ferrite and silica ash are homogenized, the nano cobalt ferrite is adsorbed on the silica ash particle by electrostatic adsorption, the dispersion effect of the nano cobalt ferrite in the concrete system is effectively improved, and the inhibition of alkali aggregate is ensured; in addition, after the nano cobalt ferrite is added into the silicate cementitious system, the iron phase material can continue to participate in the development of the later strength of the silicate cement (especially the flexural strength, that is, the toughness is increased), which has a positive effect on inhibiting the volume expansion of the substrate caused by the alkali aggregate reaction.

[0026] 2) The invention uses isobutyl triethoxysilane or octyl triethoxysilane to modify tuff, and the modified tuff powder is introduced into a concrete material, due to the existence of a silicon-oxygen bond, it is easier to wrap on the surface of aggregate, and a certain amount of hydrophobic alkyl is provided on the surface of aggregate, which can effectively reduce the contact opportunity between active SiO2 in aggregate and sodium and potassium alkaline solution, thereby inhibiting the occurrence of alkali aggregate reaction;

[0027] 3) The sodium fatty alcohol polyoxyethylene ether sulfate and long-chain alkyl dimethyl amine are respectively anionic and cationic organic surfactants, and the two are used in combination to play the characteristics of organic groups and produce synergistic electrostatic effects and hydrophobic effects of the tail, thereby promoting the stability of the slurry and homogenizing the dispersion of the fiber in the slurry; in addition, the introduced long-chain alkyl dimethyl amine can also absorb water-absorbing and swelling substances (such as clay) with negative electricity, prevent the internal expansion of concrete, and eliminate the influence of alkali aggregate reaction to a certain extent;

[0028] Compared with the prior art, the invention has the following beneficial effects:

[0029] 1) The invention uses Na + , K + from the source to capture + , K + , prevents Na + , K + from contacting with active SiO2, uses uniformly dispersed modified fibers to control volume deformation, and uses multiple angles and multiple levels of improvement methods, which can effectively inhibit the occurrence of alkali aggregate reaction;

[0030] 2) The composite admixture can replace cement and other traditional cementitious materials in a large amount, and can effectively take into account the good use performance of the obtained concrete, and has significant economic and environmental benefits;

[0031] 3) The preparation method is relatively simple and low in cost, and is suitable for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The expansion rate test results of the mortar obtained by using the composite admixture obtained from the examples and comparative examples. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] In the following examples, the tuff used was provided by China Construction Western Construction Xinjiang Co., Ltd., and its main chemical composition and its mass percentage are shown in Table 1 below; the nano-cobalt ferrite has an average particle size of 30-50 nm.

[0035] Table 1 Main chemical composition of tuff (%)

[0036] SiO2 CaO Al2O3 MgO Na2O [K2O] Fe2O3 Other 42.1 13.8 10.1 10.6 1.8 1.5 15.7 4.4

[0037] The nylon fibers used have a diameter of 1.0–1.5 mm and a length of 3–5 mm.

[0038] The silica fume used was provided by Gansu Sanyuan Silicon Materials Co., Ltd., with a 3-day activity of 93%, a 28-day activity of 112%, and a specific surface area of ​​16,500 m². 2 / kg.

[0039] The sodium fatty alcohol polyoxyethylene ether sulfate used was provided by Nantong Qianhe Chemical Co., Ltd., with a molecular weight of 332.

[0040] The long-chain alkyl dimethylamine used was provided by Wuhan Xinyuhang Chemical Co., Ltd., and the alkyl carbon number is 12.

[0041] Example 1

[0042] A composite admixture for inhibiting alkali-aggregate reaction, the preparation method of which includes the following steps:

[0043] 1) Grind the tuff to a specific surface area of ​​400 m². 2 / kg, tuff powder was dried at 60℃ for 12h and then naturally cooled; tuff powder and anhydrous ethanol were mixed at a mass ratio of 1:2 and added to a beaker, and stirred at 400rpm for 60min on a magnetic stirrer to ensure uniform dispersion; 1% of the tuff powder mass of octyltriethoxysilane (OTTS) aqueous solution (OTTS to deionized water mass ratio of 1:3) was taken, and the two were mixed and stirred at 400rpm for 70min to ensure complete hydrolysis of IBTS; then, all materials were mixed and stirred at 400rpm for 6h; finally, the resulting mixture was dried at 100℃ for 26h to obtain modified tuff powder;

[0044] 2) Soak nylon fibers in a triethanolamine solution (concentration of 4wt%) for 60 min, wherein the volume ratio of nylon fibers to triethanolamine solution is 1:3. Disperse the fibers ultrasonically and stir to ensure that the fibers are fully dispersed in the solution. Filter out the fibers and dry them at 50℃ for 2 h to obtain modified nylon fibers.

[0045] 3) Select nano-cobalt ferrite with an average particle size of 50nm, weigh 10 parts of nano-cobalt ferrite and 25 parts of silica fume and put them into a mixer for homogenization treatment for 30min at a speed of 40r / min; then mix with 55 parts of modified tuff powder until uniform to obtain a mixture.

[0046] 4) Place 3 parts of fatty alcohol polyoxyethylene ether sodium sulfate, 3 parts of long-chain alkyl dimethylamine, and 4 parts of modified nylon fiber into a mixer for homogenization for 15 minutes at a speed of 10 r / min. Then add the mixture and mix evenly to obtain the composite admixture that inhibits alkali-aggregate reaction.

[0047] The composite admixture for inhibiting alkali-aggregate reaction obtained in this embodiment is applied to concrete using alkali-reactive aggregates, and its dosage accounts for 50% of the mass of cementitious materials.

[0048] Example 2

[0049] A composite admixture for inhibiting alkali-aggregate reaction, the preparation method of which includes the following steps:

[0050] 1) Grind the tuff to a specific surface area of ​​425 m². 2 / kg, tuff powder was dried at 70℃ for 11h and then naturally cooled; tuff powder and anhydrous ethanol were mixed at a mass ratio of 1:2.5 and added to a beaker, and stirred at 500rpm for 50min on a magnetic stirrer to ensure uniform dispersion; 2% of the mass of tuff powder was taken as an aqueous solution of isobutyltriethoxysilane (IBTS) (the mass ratio of IBT to deionized water was 1:4), and the two were mixed and stirred at 500rpm for 60min to ensure complete hydrolysis of IBT; then, all materials were mixed and stirred at 550rpm for 5h; finally, the resulting mixture was dried at 105℃ for 24h to obtain modified tuff powder;

[0051] 2) Soak nylon fibers in a triethanolamine solution (concentration of 5% by mass) for 45 min, wherein the volume ratio of nylon fibers to triethanolamine solution is 1:4. Disperse the fibers by ultrasonication and stirring to ensure that the fibers are fully dispersed in the solution. Filter out the fibers and dry them at 65°C for 1.5 h to obtain modified nylon fibers.

[0052] 3) Select nano-cobalt ferrite with an average particle size of 40nm, weigh 15 parts of nano-cobalt ferrite and 25 parts of silica fume and put them into a mixer for homogenization treatment for 25min at a speed of 50r / min; then mix with 50 parts of modified tuff powder until uniform to obtain a mixture.

[0053] 4) Place 3 parts of fatty alcohol polyoxyethylene ether sodium sulfate, 3 parts of long-chain alkyl dimethylamine, and 4 parts of modified nylon fiber into a mixer for homogenization for 10 minutes at a speed of 20 r / min. Then add the mixture and mix evenly to obtain the composite admixture that inhibits alkali-aggregate reaction.

[0054] The composite admixture that inhibits alkali-aggregate reaction obtained in this embodiment is applied to concrete using alkali-reactive aggregates, and its dosage accounts for 55% of the mass of cementitious materials.

[0055] Example 3

[0056] A composite admixture for inhibiting alkali-aggregate reaction, the preparation method of which includes the following steps:

[0057] 1) Grind the tuff to a specific surface area of ​​450 m². 2 / kg, tuff powder was dried at 80℃ for 10h and then naturally cooled. Tuff powder and anhydrous ethanol were mixed at a mass ratio of 1:2.5 and added to a beaker. The mixture was stirred at 600rpm for 40min on a magnetic stirrer to ensure uniform dispersion. An isobutyltriethoxysilane (IBTS) aqueous solution (IBTS to deionized water mass ratio of 1:5) was taken at 3% of the tuff powder mass and mixed with the ethanol. The mixture was stirred at 600rpm for 40min to ensure complete hydrolysis of IBTS. All materials were then mixed and stirred at 600rpm for 4h. Finally, the resulting mixture was dried at 105℃ for 24h to obtain modified tuff powder.

[0058] 2) Soak nylon fibers in a triethanolamine solution (6 wt%) for 30 min, wherein the volume ratio of nylon fibers to triethanolamine solution is 1:5. Disperse the fibers ultrasonically and stir to ensure that the fibers are fully dispersed in the solution. Filter out the fibers and dry them at 80°C for 1 h to obtain modified nylon fibers.

[0059] 3) Select nano-cobalt ferrite with an average particle size of 30nm, weigh 20 parts of nano-cobalt ferrite and 25 parts of silica fume and put them into a mixer for homogenization treatment for 20min at a speed of 60r / min; then mix with 45 parts of modified tuff powder until uniform to obtain a mixture.

[0060] 4) Place 3 parts of fatty alcohol polyoxyethylene ether sodium sulfate, 3 parts of long-chain alkyl dimethylamine, and 5 parts of modified nylon fiber into a mixer for homogenization for 10 minutes at a speed of 30 r / min. Then add the mixture and mix evenly to obtain the composite admixture that inhibits alkali-aggregate reaction.

[0061] The composite admixture that inhibits alkali-aggregate reaction obtained in this embodiment is applied to concrete using alkali-reactive aggregates, and its dosage accounts for 60% of the mass of cementitious materials.

[0062] Comparative Example 1

[0063] A composite admixture for inhibiting alkali-aggregate reaction, the preparation method of which includes the following steps:

[0064] Tuff was ground to a specific surface area of ​​425 m². 2 / kg, tuff powder was dried at 70℃ for 11h and then naturally cooled. Tuff powder and anhydrous ethanol were mixed at a mass ratio of 1:2.5 and added to a beaker. The mixture was stirred at 500rpm for 50min on a magnetic stirrer to ensure uniform dispersion. A 2% (by mass) isobutyltriethoxysilane (IBTS) solution (IBTS to deionized water mass ratio of 1:4) of the tuff powder was added and mixed. The mixture was stirred at 500rpm for 60min to ensure complete hydrolysis of IBTS. All materials were then mixed and stirred at 550rpm for 5h. Finally, the resulting mixture was dried at 105℃ for 24h to obtain modified tuff powder.

[0065] 2) Soak nylon fibers in a triethanolamine solution (concentration of 5% by mass) for 45 min, wherein the volume ratio of nylon fibers to triethanolamine solution is 1:4. Disperse the fibers by ultrasonication and stirring to ensure that the fibers are fully dispersed in the solution. Filter out the fibers and dry them at 65°C for 1.5 h to obtain modified nylon fibers.

[0066] 3) Mix 40 parts silica fume with 50 parts modified tuff powder until homogeneous to obtain a mixture;

[0067] 4) Place 3 parts of fatty alcohol polyoxyethylene ether sodium sulfate, 3 parts of long-chain alkyl dimethylamine, and 4 parts of modified nylon fiber into a mixer for homogenization for 10 minutes at a speed of 20 r / min. Then add the mixture and mix evenly to obtain the composite admixture that inhibits alkali-aggregate reaction.

[0068] The resulting composite admixture that inhibits alkali-aggregate reaction was applied to concrete using alkali-reactive aggregates, with the admixture accounting for 55% of the mass of the cementitious materials.

[0069] Comparative Example 2

[0070] A composite admixture for inhibiting alkali-aggregate reaction, the preparation method of which includes the following steps:

[0071] Tuff was ground to a specific surface area of ​​425 m². 2 / kg, tuff powder was dried at 70℃ for 11h and naturally cooled. The tuff powder and anhydrous ethanol were mixed at a mass ratio of 1:2.5 and added to a beaker. The mixture was stirred at 500rpm for 50min on a magnetic stirrer to ensure uniform dispersion. 2% of the tuff powder mass was taken as an aqueous solution of isobutyltriethoxysilane (IBTS) (the mass ratio of IBTS to deionized water was 1:4). The two were mixed and stirred at 500rpm for 60min to ensure complete hydrolysis of IBTS. Then, all materials were mixed and stirred at 550rpm for 5h. Finally, the resulting mixture was dried at 105℃ for 24h to obtain modified tuff powder.

[0072] 2) Soak nylon fibers in a triethanolamine solution (concentration of 5% by mass) for 45 min, wherein the volume ratio of nylon fibers to triethanolamine solution is 1:4. Disperse the fibers by ultrasonication and stirring to ensure that the fibers are fully dispersed in the solution. Filter out the fibers and dry them at 65°C for 1.5 h to obtain modified nylon fibers.

[0073] 3) Select nano-cobalt ferrite with an average particle size of 40nm, weigh 15 parts of nano-cobalt ferrite and 25 parts of silica fume and put them into a mixer for homogenization treatment for 25min at a speed of 50r / min; then mix with 50 parts of modified tuff powder until uniform to obtain a mixture.

[0074] 4) Put 6 parts of fatty alcohol polyoxyethylene ether sodium sulfate and 4 parts of modified nylon fiber into a mixer for homogenization for 10 minutes at a speed of 20 r / min; then add the mixture and mix evenly to obtain the composite admixture that inhibits alkali-aggregate reaction.

[0075] The resulting composite admixture that inhibits alkali-aggregate reaction was applied to concrete using alkali-reactive aggregates, with the admixture accounting for 55% of the mass of the cementitious materials.

[0076] Comparative Example 3

[0077] A composite admixture for inhibiting alkali-aggregate reaction, the preparation method of which includes the following steps:

[0078] 1) Grind the tuff to a specific surface area of ​​425 m². 2 / kg, tuff powder was dried at 70℃ for 11h and then naturally cooled; tuff powder and anhydrous ethanol were mixed at a mass ratio of 1:2.5 and added to a beaker, and stirred at 500rpm for 50min on a magnetic stirrer to ensure uniform dispersion; 2% of the mass of tuff powder was taken as an aqueous solution of isobutyltriethoxysilane (IBTS) (the mass ratio of IBT to deionized water was 1:4), and the two were mixed and stirred at 500rpm for 60min to ensure complete hydrolysis of IBT; then, all materials were mixed and stirred at 550rpm for 5h; finally, the resulting mixture was dried at 105℃ for 24h to obtain modified tuff powder;

[0079] 2) Soak nylon fibers in a triethanolamine solution (concentration of 5% by mass) for 45 min, wherein the volume ratio of nylon fibers to triethanolamine solution is 1:4. Disperse the fibers by ultrasonication and stirring to ensure that the fibers are fully dispersed in the solution. Filter out the fibers and dry them at 65°C for 1.5 h to obtain modified nylon fibers.

[0080] 3) Select nano-cobalt ferrite with an average particle size of 40nm, weigh 15 parts of nano-cobalt ferrite and 25 parts of silica fume, and mix them with 50 parts of modified tuff powder until uniform to obtain a mixture.

[0081] 4) Place 3 parts of fatty alcohol polyoxyethylene ether sodium sulfate, 3 parts of long-chain alkyl dimethylamine, and 4 parts of modified nylon fiber into a mixer for homogenization for 10 minutes at a speed of 20 r / min. Then add the mixture and mix evenly to obtain the composite admixture that inhibits alkali-aggregate reaction.

[0082] The composite admixture that inhibits alkali-aggregate reaction obtained in this embodiment is applied to concrete using alkali-reactive aggregates, and its dosage accounts for 55% of the mass of cementitious materials.

[0083] The flexural strength test method for the substrate is based on GB / T 17671 "Test Method for Strength of Cement Mortar (ISO Method)". The test mix is ​​shown in Table 2. The molded specimen size is 40mm × 40mm × 160mm, and the test time is 28 days of curing for flexural strength.

[0084] Table 2. Mix proportions for substrate toughness testing

[0085]

[0086] The results showed that, in the absence of nano-cobalt ferrite, the flexural strength of Comparative Example 1 was significantly lower than that of Examples 1-3; in the absence of cationic surfactant, the dispersibility of modified nylon fiber in mortar of Comparative Example 2 was poor, and its toughening effect was significantly weakened, with the most significant decrease in flexural strength; in Comparative Example 3, the flexural strength was also reduced when nano-cobalt ferrite was directly mixed with powders such as silica fume.

[0087] The alkali-aggregate reaction test method refers to section 5.4, "Test Method for Alkali Reactivity of Aggregates in Hydraulic Concrete" (mortar rod rapid method), of DL / T 5151 "Test Procedure for Sand and Gravel Aggregates in Hydraulic Concrete". The mix proportions used in the test are shown in Table 3. The molded specimen size is 25.4mm × 25.4mm × 285mm, the curing temperature is 80℃, and the alkali supply method is immersion curing in 1mol / L NaOH solution. (If the 14-day expansion rate is less than 0.10%, it is an inactive aggregate; if the 14-day expansion rate is greater than 0.20%, it is an active aggregate with potentially hazardous reactions; if the 14-day expansion rate is between 0.10% and 0.20%, the test observation time is extended to 28 days.) The specific test steps are as follows:

[0088] Table 3. Mix proportions for alkali-aggregate test

[0089]

[0090] (1) Experimental procedure:

[0091] ① Specimen preparation: 24 hours before molding, place the raw materials used in the test in a constant temperature room with a temperature of 20℃±2℃ and a relative humidity of greater than 50%.

[0092] ② Curing of specimens: The curing temperature is 20±2℃ and the relative humidity is 95%. After curing for 24 hours, the specimens are demolded and the initial length of the specimens is immediately tested in the standard curing room as a reference value for the baseline length.

[0093] ③ After determining the initial length of the specimen, place the specimen in a constant temperature water bath at 80℃ for 24 hours, and then test the specimen length as the reference length. The test should be completed within 15±5 seconds.

[0094] ④ Place the specimen in a curing container filled with 1 mol / L NaOH solution, and the specimen should be completely immersed in the solution.

[0095] ⑤ The test ages of the specimens were 3d, 7d and 14d, 28d, 45d and 60d respectively.

[0096] (2) Experimental Results and Analysis

[0097] from Figure 1 As can be seen, the mortar expansion rate of reactive aggregate without inhibitors after 14 days was 0.42%, which significantly exceeded the standard requirements, indicating that it is reactive aggregate with potential hazardous reactions.

[0098] When the composite admixtures of Examples 1 to 3 are incorporated, the mortar expansion rate after 14 days is only 0.04 to 0.06%, and the mortar expansion rate after 60 days is still <0.1%, with no risk of alkali-aggregate reaction, and the alkali-aggregate reaction can be effectively suppressed.

[0099] When the composite admixtures of Comparative Examples 1, 2, and 3 were added, the mortar expansion rate at 14 days was between 0.1% and 0.2%. Among them, the mortar containing the composite admixtures of Comparative Examples 1 and 2 had an expansion rate of >0.2% at 28 days, and the mortar containing the composite admixture of Comparative Example 3 had an expansion rate of >0.15% at 28 days, which posed a certain risk of alkali-aggregate reaction.

[0100] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A composite admixture for inhibiting alkali-aggregate reaction, characterized in that, The components and their weight percentages include: 10-20 parts of nano cobalt ferrite, 20-30 parts of silica fume, 45-55 parts of modified tuff powder, 2-4 parts of sodium fatty alcohol polyoxyethylene ether sulfate, 2-4 parts of long-chain alkyl dimethylamine, and 4-6 parts of modified nylon fiber. The modified tuff powder is obtained by modifying tuff powder with isobutyltriethoxysilane or octyltriethoxysilane; The modified nylon fiber is obtained by soaking nylon fiber in a triethanolamine solution for modification.

2. The composite admixture according to claim 1, characterized in that, The average particle size of the nano-cobalt ferrite is 30~50nm.

3. The composite admixture according to claim 1, characterized in that, The silica fume has a 3-day activity >90%, a 28-day activity >110%, and a specific surface area >15000 m². 2 / kg.

4. The composite admixture according to claim 1, characterized in that, The specific surface area of ​​the tuff powder is 400~450m². 2 / kg.

5. The composite admixture according to claim 1, characterized in that, The tuff powder is high-calcium tuff, with a CaO content ≥10% in its chemical composition.

6. The composite admixture according to claim 1, characterized in that, The molecular weight of the fatty alcohol polyoxyethylene ether sulfate sodium is 300-350.

7. The composite admixture according to claim 1, characterized in that, The long-chain alkyl dimethylamine has 10 to 15 alkyl carbons.

8. The composite admixture according to claim 1, characterized in that, The modified nylon fiber has a diameter of 1.0~1.5mm and a length of 3~5mm.

9. The composite admixture according to claim 1, characterized in that, Its dosage in concrete is 50-60% of the mass of cementitious materials.

10. A method for preparing the composite admixture for inhibiting alkali-aggregate reaction according to any one of claims 1 to 9, characterized in that, Includes the following steps: 1) The weighed nano cobalt ferrite and silica fume are homogenized using a mixer, and then modified tuff powder is added and mixed evenly to obtain a mixture; 2) Sodium fatty alcohol polyoxyethylene ether sulfate, long-chain alkyl dimethylamine, and modified nylon fiber are homogenized using a mixer, and then added to the mixture and mixed evenly to obtain the composite blend.

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