Waterproof chlorine salt erosion resistant recycled fine aggregate concrete and preparation method thereof

Abstract

The invention discloses waterproof chlorine salt erosion resistant recycled fine aggregate concrete and a preparation method thereof, and belongs to the technical field of building materials. The concrete is prepared from the following raw materials: 1110 to 1130 parts of natural coarse aggregate, 520 to 552 parts of recycled fine aggregate, 338 to 364 parts of cement, 72 to 80 parts of fly ash, 21 to 32 parts of silica fume, 48 to 56 parts of slag powder, 168 parts of water, 3 parts of a water reducing agent and 4.8 to 8.0 parts of methyl sodium silicate powder. According to the invention, the sodium methyl silicate is doped in a ball-milling coating manner, the impermeability and chlorine salt erosion resistance of the concrete are improved through the sodium methyl silicate, and the negative effects on the strength, compactness and the like of the concrete due to the fact that the sodium methyl silicate is doped to increase the hydrophobicity are reduced by adding the composite mineral admixture; the concrete has certain impermeability and chlorine resistance, and the strength can reach C50, so that the concrete can be used for maritime work structures.

Description

Technical Field

[0001] The invention belongs to the field of building materials, and in particular relates to a waterproof and chloride-salt-corrosion-resistant recycled fine aggregate concrete and a preparation method thereof. Background Art

[0002] my country's construction industry is developing rapidly. Today, a large number of concrete building structures are facing the dilemma of retirement. How to properly deal with these construction wastes has become a thorny issue. Recycling construction waste and preparing it into recycled fine aggregate is an effective way to alleviate the environmental problems of construction waste, and it can also alleviate the problem of shortage of natural sand.

[0003] The harsh high-chloride salt service environment such as the ocean, groundwater, salt lakes, and saline-alkali land has greatly reduced the service life of concrete. Chloride ions enter the interior of concrete through liquid penetration, matrix diffusion, capillary absorption, etc., causing steel corrosion and a series of structural safety problems. Generally, adding mineral admixtures to increase the density of concrete can reduce chloride ion erosion, but it will cause the chloride ion concentration gradient inside the concrete to be too high, which is not conducive to the long-term service of concrete. Therefore, enhancing the chloride ion resistance of concrete through waterproofing is a new idea.

[0004] Sodium methyl silicate is a new rigid building waterproof material that can form a hydrophobic layer with water and carbon dioxide, but when added internally, it will affect the hydration degree of cementitious materials and thus reduce the strength of concrete. Therefore, if the negative impact of the strength reduction caused by the addition of sodium methyl silicate to concrete can be solved, it will not only greatly enhance the hydrophobicity of concrete, which will help to increase the service life of marine structures, but also its mechanical properties can meet the needs of marine structures, which is of great significance for its application and promotion in chloride salt environments. Summary of the invention

[0005] The purpose of the present invention is to overcome the existing technical difficulties and propose a waterproof and chloride-resistant recycled fine aggregate concrete and a preparation method thereof. The compressive strength of the concrete can not only reach 50MPa, but also has good waterproof and chlorine-resistant properties. It can be used as structural concrete in a high-chloride service environment, while saving the resource consumption of natural sand.

[0006] The technical solution provided by the present invention is: a waterproof and chloride-resistant recycled fine aggregate concrete, comprising the following components in parts by weight: 1110-1130 parts of natural coarse aggregate, 520-552 parts of recycled fine aggregate, 338-364 parts of cement, 72-80 parts of fly ash, 21-32 parts of silica fume, 48-56 parts of slag powder, 168 parts of water, 3 parts of water reducer, and 4.8-8.0 parts of sodium methyl silicate powder.

[0007] Furthermore, the cementitious material includes cement, fly ash, slag powder and silica fume in a mass ratio of 13:3:2:1.

[0008] Preferably, the mass ratio of water to cementitious material is 0.33; the mass ratio of the total mass of natural coarse aggregate and recycled fine aggregate to cementitious material is 3.3.

[0009] Preferably, the physical properties of the natural coarse aggregate conform to Class II crushed stone and above in GB / T14685-2022, and the particle size is 4.75-31.5 mm.

[0010] Preferably, the recycled fine aggregate is obtained by crushing waste concrete, and its physical properties meet the requirements of Class III and above as specified in GB / T25176-2010, with a particle size of 0.15-4.75 mm.

[0011] Preferably, the cement is P.O52.5 ordinary Portland cement.

[0012] Preferably, the fly ash is Class I fly ash.

[0013] Preferably, the slag powder is S105 granulated blast furnace slag powder.

[0014] Preferably, the silica fume is grade I silica fume with an average particle size of 2.43 μm.

[0015] Preferably, the sodium methyl silicate is a white powdery solid with a purity of 98%, a pH of 13±1, and an alkali content of 29%.

[0016] Preferably, the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent with a water reducing efficiency of 40%.

[0017] The method for preparing the waterproof and chloride-resistant recycled fine aggregate concrete comprises the following steps:

[0018] S1: Weigh each component according to mass fraction;

[0019] S2: putting fly ash, silica ash, slag powder and sodium methyl silicate powder into a planetary ball mill;

[0020] S3: Add 30% of the total mass of recycled fine aggregate, coarse aggregate and water into a mixer and mix;

[0021] S4: adding cement and ball-milled composite powder into a mixer and mixing;

[0022] S5: Continue stirring, and slowly add 70% of the total mass of water and water reducing agent during the stirring process;

[0023] S6: After the mixing is completed, the concrete is molded, demolded and cured to obtain a waterproof and chlorine-resistant recycled fine aggregate concrete.

[0024] Furthermore, in step S2, the rotation speed of the ball mill is 200 rpm, the time is 1.5 to 2.0 h, and grinding balls are used.

[0025] Furthermore, in step S3, the stirring speed is 90 rpm and the time is 60 to 75 s.

[0026] Furthermore, in steps S4 and S5, the stirring speed is 90 rpm and the time is 30 to 45 s.

[0027] The methyl silicate ions in sodium methyl silicate can react with water and carbon dioxide to form methyl silicate alcohol, which then dehydrates and condenses between the methyl silicate alcohols and between the methyl silicate alcohols and the mortar matrix to form a methyl hydrophobic layer on the surface of the mortar. The hydrophobic layer can further reduce the intrusion of chloride ion solution and improve the concrete's resistance to chloride ion diffusion (RCM value reduction), making it suitable for structures with high durability requirements such as marine concrete and bridge concrete. However, the hydrophobic properties of sodium methyl silicate itself will have a negative impact on the hydration rate and time of the cementitious material in the concrete, ultimately leading to a reduction in concrete strength.

[0028] The present invention is different from the conventional internal addition method of sodium methyl silicate. It adopts the method of ball milling composite mineral admixtures (fly ash, silica fume and slag powder) with sodium methyl silicate powder, so that sodium methyl silicate is coated on the surface of the mineral admixture. The ground powder has the hydrophobic property of sodium methyl silicate while maintaining the original reactivity. At the same time, the composite mineral admixture can effectively reduce the strength reduction caused by the inhibition of hydration of sodium methyl silicate. The powder is refined after ball milling, which can reduce the porosity of concrete, form a denser microstructure, and reduce the penetration rate of chloride ions. In addition, the components after ball milling are evenly distributed, which can ensure the uniformity of concrete.

[0029] The present invention adopts recycled fine aggregate to completely replace natural sand to prepare concrete, which plays a significant role in alleviating the current shortage of river sand, protecting the environment, and solving the problem of accumulation of construction waste.

[0030] Compared with the prior art, the invention has the following beneficial effects: the invention improves the internal mixing method of sodium methyl silicate, and adopts a combination of multiple mineral admixtures to offset the negative effects of sodium methyl silicate on the hydration rate and degree of cementitious materials. Sodium methyl silicate and composite mineral admixtures show good synergistic effects. The use of recycled fine aggregate reduces costs and is very environmentally friendly. The prepared waterproof and chloride-resistant recycled fine aggregate concrete has a compressive strength of ≥55.6MPa, a permeability pressure of ≥1.8MPa, and a non-steady-state chloride ion rapid migration coefficient (RCM) of ≤2.2×10 -12 m 2 / s. Good construction performance: slump ≥ 180mm. The waterproof and chloride-resistant recycled fine aggregate concrete is suitable for use as structural concrete in chloride-corrosion environments. DETAILED DESCRIPTION

[0031] The present invention is described in detail below. The present invention tests the slump of recycled fine aggregate concrete according to GB / T50080-2016 "Standard for Test Methods for Performance of Ordinary Concrete Mixtures", tests the 28d compressive strength of recycled fine aggregate concrete according to GB / T50081-2019 "Standard for Test Methods for Mechanical Properties of Ordinary Concrete", and tests the impermeability grade and RCM of concrete according to GB / T50082-2024 "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete".

[0032] In the following embodiments and comparative examples, the raw materials used are: P.O52.5 ordinary Portland cement; Class II natural coarse aggregate specified in GB / T14685-2022, with a particle size of 4.75-31.5 mm; Class III recycled fine aggregate specified in GB / T25176-2010, with a particle size of 0.15-4.75 mm and an average particle size of 2.43 μm, Class I silicon powder; Class I fly ash; S105 grade granulated blast furnace slag powder; white powdery solid sodium methyl silicate, with a purity of 98%, a pH of 13±1, and an alkali content of 29%.

[0033] Embodiment 1:

[0034] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 352 parts of cement, 76 parts of fly ash, 26 parts of silica fume, 52 parts of slag powder, 6.4 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0035] S2: Put the fly ash, silica ash, slag powder and sodium methyl silicate powder weighed in S1 into a planetary ball mill, with 6-15mm agate balls and the volume of the raw materials each accounting for one-third of the volume of the corundum tank, and ball mill at a speed of 200rpm for 1.5h.

[0036] S3: Add recycled fine aggregate, coarse aggregate and 30% of water into the mixer and mix at 90 rpm for 60 s.

[0037] S4: Add cement and ball-milled composite powder into the mixer, stir at 90 rpm for 30 seconds, continue to start the mixer, slowly add 70% of water and water reducing agent during the stirring process, and stir at 90 rpm for 60 seconds.

[0038] S5: After the mixing is completed, the concrete is molded and demolded after 24 hours for curing to obtain waterproof and chloride-resistant recycled fine aggregate concrete.

[0039] Embodiment 2:

[0040] S1: Weigh the following raw materials in parts by weight: 520 parts of recycled fine aggregate, 1100 parts of natural coarse aggregate, 364 parts of cement, 72 parts of fly ash, 21 parts of silica fume, 48 parts of slag powder, 8.0 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0041] S2: Same as Example 1.

[0042] S3: Same as Example 1.

[0043] S4: Same as Example 1.

[0044] S5: Same as Example 1.

[0045] Embodiment 3:

[0046] S1: Weigh the following raw materials in parts by weight: 552 parts of recycled fine aggregate, 1130 parts of natural coarse aggregate, 338 parts of cement, 80 parts of fly ash, 32 parts of silica fume, 56 parts of slag powder, 4.8 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0047] S2: Same as Example 1.

[0048] S3: Same as Example 1.

[0049] S4: Same as Example 1.

[0050] S5: Same as Example 1.

[0051] Comparative Example 1:

[0052] S1: Same as Example 1;

[0053] S2: Dissolve sodium methyl silicate in 70% mixing water and stir manually for 30 seconds.

[0054] S3: Add recycled fine aggregate, coarse aggregate and 30% of water into the mixer and mix at 90 rpm for 60 s.

[0055] S4: Add cement, fly ash, silica fume and slag powder into the mixer, stir at 90 rpm for 30 s, continue to start the mixer, slowly add the sodium methyl silicate aqueous solution and water reducing agent obtained in S2 during the stirring process, and stir at 90 rpm for 60 s.

[0056] S5: After the mixing is completed, the concrete is molded and demolded after 24 hours for curing to obtain waterproof and chloride-resistant recycled fine aggregate concrete.

[0057] Comparative Example 2:

[0058] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 352 parts of cement, 76 parts of fly ash, 26 parts of silica fume, 52 parts of slag powder, 3 parts of water reducer, and 168 parts of water;

[0059] S2: Add recycled fine aggregate, coarse aggregate and 30% of water into a mixer and mix at 90 rpm for 60 s.

[0060] S3: Add cement, fly ash, silica fume and slag powder into the mixer, stir at 90 rpm for 30 seconds, continue to start the mixer, slowly add 70% of water and water reducing agent during the stirring process, and stir at 90 rpm for 60 seconds.

[0061] S4: After the mixing is completed, the concrete is molded and demolded after 12 hours for curing to obtain waterproof and chloride-resistant recycled fine aggregate concrete.

[0062] Comparative Example 3:

[0063] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 352 parts of cement, 76 parts of fly ash, 26 parts of silica fume, 52 parts of slag powder, 3 parts of water reducer, and 168 parts of water;

[0064] S2: Put fly ash, silica ash and slag powder into a planetary ball mill and mill at 200 rpm for 1.5 hours. The volume of 6-15 mm agate balls and raw materials in the ball mill each accounts for one third of the volume of the corundum tank.

[0065] S3: Add recycled fine aggregate, coarse aggregate and 30% of water into the mixer and mix at 90 rpm for 60 s.

[0066] S4: Add cement and ball-milled composite powder into the mixer, stir at 90 rpm for 30 seconds, continue to start the mixer, slowly add 70% of water and water reducing agent during the stirring process, and stir at 90 rpm for 60 seconds.

[0067] S5: After the mixing is completed, the concrete is molded and demolded after 12 hours for curing to obtain a waterproof and chloride-resistant recycled fine aggregate concrete.

[0068] Comparative Example 4:

[0069] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 352 parts of cement, 76 parts of fly ash, 26 parts of silica fume, 52 parts of slag powder, 12 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0070] S2: Same as Example 1.

[0071] S3: Same as Example 1.

[0072] S4: Same as Example 1.

[0073] S5: Same as Example 1.

[0074] Comparative Example 5:

[0075] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 355 parts of cement, 151 parts of fly ash, 6.4 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0076] S2: Put fly ash and sodium methyl silicate powder into a planetary ball mill and mill at 200 rpm for 1.5 hours. The volume of 6-15 mm agate balls and raw materials in the ball mill each accounts for one third of the volume of the corundum tank.

[0077] S3: Same as Example 1.

[0078] S4: Same as Example 1.

[0079] S5: Same as Example 1.

[0080] Comparative Example 6:

[0081] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 455 parts of cement, 51 parts of silica fume, 6.4 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0082] S2: Put silica fume and sodium methyl silicate powder into a planetary ball mill and mill at 200 rpm for 1.5 h.

[0083] S3: Same as Example 1.

[0084] S4: Same as Example 1.

[0085] S5: Same as Example 1.

[0086] Comparative Example 7:

[0087] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 430 parts of cement, 76 parts of slag powder, 6.4 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0088] S2: Put the slag powder and sodium methyl silicate powder into a planetary ball mill and mill them at 200 rpm for 1.5 hours. The volume of 6-15 mm agate balls and raw materials in the ball mill each accounts for one third of the volume of the corundum tank.

[0089] S3: Same as Example 1.

[0090] S4: Same as Example 1.

[0091] S5: Same as Example 1.

[0092] Comparative Example 8

[0093] S1: Weigh the following raw materials in parts by weight: 534 parts of recycled fine aggregate, 1119 parts of natural coarse aggregate, 430 parts of cement, 76 parts of fly ash, 76 parts of slag powder, 6.4 parts of sodium methyl silicate powder, 3 parts of water reducer, and 168 parts of water;

[0094] S2: Place fly ash, slag powder and sodium methyl silicate powder into a planetary ball mill and mill at 200 rpm for 1.5 h.

[0095] S3: Same as Example 1.

[0096] S4: Same as Example 1.

[0097] S5: Same as Example 1.

[0098] Table 1 Content of each component of concrete in the embodiment and comparative example

[0099] natural coarse aggregate Recycled fine aggregate cement Fly ash Silica Fume Slag powder Sodium Methyl Silicate Whether ball milling Example 1 1119 534 352 76 26 52 6.4 yes Example 2 1110 520 364 72 21 48 8.0 yes Example 3 1130 552 338 80 32 56 4.8 yes Comparative Example 1 1119 534 352 76 26 52 6.4 no Comparative Example 2 1119 534 352 76 26 52 0 no Comparative Example 3 1119 534 352 76 26 52 0 yes Comparative Example 4 1119 534 352 76 26 52 12 yes Comparative Example 5 1119 534 355 151 0 0 6.4 yes Comparative Example 6 1119 534 455 0 51 0 6.4 yes Comparative Example 7 1119 534 355 0 0 151 6.4 yes Comparative Example 8 1119 534 355 76 0 76 6.4 yes

[0100] Among them, in comparative examples 5-7, the dosages of fly ash, silica fume and slag powder are 30%, 10% and 30% (conventional dosage in engineering) of the total amount of cementitious materials (506 parts), respectively.

[0101] Table 2 Mechanical properties and chloride corrosion resistance of concrete

[0102]

[0103] It can be seen from the test results of Examples 1-3 and Tables 1 and 2 that the waterproof and chloride-resistant recycled fine aggregate concrete prepared by the present invention uses 100% recycled fine aggregate to replace natural sand, has a 28d compressive strength of more than 55.6 MPa, a water-resistant grade of P18 and above, RCM≤2.2, a slump of more than 180 mm, and has good mechanical properties, water-resistant properties, chloride-resistant properties and working performance, among which Example 1 has the best comprehensive performance.

[0104] It can be seen from the test results of comparative examples 1-3 and comparative examples 3-4 that with the increase of the amount of sodium methyl silicate, the 28d compressive strength of the concrete prepared by the present invention shows a trend of first increasing and then decreasing. The strength is highest when the amount of sodium methyl silicate is 6.4 parts. It can be seen that in order to ensure the strength of the concrete, the amount of sodium methyl silicate should not exceed 8.0 parts. After sodium methyl silicate is added to the concrete, methyl silicate alcohol is generated and dehydrated and condensed, which has the effect of micro-expansion and filling pores, and can participate in the hydration reaction to generate a highly dense CSH gel. In addition, the alkalinity of sodium methyl silicate can be used as an alkaline stimulator to promote the formation of hydrated aluminum silicate gel, enhance the bonding force between cement and aggregate, improve the interface transition zone, and enhance the overall strength of concrete. Excessive dosage will lead to the formation of a thicker layer of hydrophobic film on the surface of the cementitious material particles, reduce the wetting effect of water on the particles, and make the hydration reaction insufficient. In addition, excessive micro-expansion caused by excessive dosage will also cause micro-cracks in the concrete and reduce its strength.

[0105] Comparing the test results of Examples 1-3 and Comparative Examples 3-4, it can be seen that sodium methyl silicate can increase the impermeability grade of concrete by 120% and reduce RCM by 49%. 3 ) has extremely strong hydrophobicity, and the Si-O bond at the other end of the methyl group has strong polarity, which makes the hydrophobic film adsorbed on the matrix and pore surface, resulting in anti-capillary phenomenon. While adding fly ash, silica fume and slag powder to increase the overall density of concrete, sodium methyl silicate makes the concrete achieve the effect of "cracking but not water seepage". Chloride salt erosion relies on solution to penetrate into the interior of the concrete, and the hydrophobic film largely prevents liquid from entering the concrete matrix, thereby improving the concrete's resistance to chloride salt erosion.

[0106] Comparative Examples 1-3 and Comparative Examples 1-4 show that sodium methyl silicate reduces the slump of concrete, and fly ash and slag powder can improve the workability of concrete and reduce the decline in slump. When the sodium methyl silicate powder is added in an amount of 6.4 parts, the slump of the concrete after ball milling and without ball milling is reduced by 10 mm and 15 mm respectively compared with the concrete with a dosage of 0; if the cementitious material and sodium methyl silicate powder are ball milled, the slump of the concrete with a sodium methyl silicate dosage of 12 parts is reduced by 60 mm compared with the concrete with a dosage of 0. Sodium methyl silicate has a certain hydrophobicity. After being added, it will form a hydrophobic film on the surface of cement particles, reduce the wettability of cement particles, and make it difficult for water to fully wet the cementitious material, thereby resulting in reduced fluidity and a decrease in slump. In addition, sodium methyl silicate can reduce the fluidity of free water inside concrete and increase the consistency of the mixture. To ensure the slump of concrete, the amount of sodium methyl silicate powder should not exceed 8.0 parts.

[0107] By comparing the test results of Example 1 and Comparative Examples 1-3, it can be seen that ball milling can greatly improve the strength, impermeability and chloride salt corrosion resistance of concrete. The strength of Example 1 is 11% higher than that of Comparative Example 1, the impermeability grade is 47% higher, and the RCM is reduced by 37%; the strength of Comparative Example 3 is 6% higher than that of Comparative Example 2, the impermeability grade is 20% higher, and the RCM is reduced by 11%. After ball milling, the powder particles are refined, the specific surface area is increased, the volcanic ash activity and potential hydration activity are improved, so that it can react with the hydration products (such as Ca(OH) 2 ) reaction to generate additional CSH gel, thereby improving the early strength of concrete and compensating for the low early activity of fly ash and slag powder. In addition, ball milling can coat the surface of the mineral admixture with a layer of sodium methyl silicate, which is helpful for the dispersion of sodium methyl silicate and avoids the problem of low concrete strength and high porosity caused by the agglomeration of sodium methyl silicate in some areas. In addition, coating the surface of the mineral admixture with a layer of sodium methyl silicate helps to utilize the high hydration activity of the mineral admixture to offset the problems of slow hydration and incomplete hydration of the cementitious material caused by the hydrophobicity of sodium methyl silicate, and further improve the density. The present invention combines the high hydration activity of the mineral admixture to increase the density with the hydrophobicity of sodium methyl silicate to form a good synergistic effect.

[0108] Comparing the test results of Example 1 and Comparative Examples 5-7, it can be seen that, compared with the ball milling effect of a single mineral admixture, ball milling the composite mineral admixture and sodium methyl silicate can make the concrete obtain better performance. The strength of Example 1 is 11%, 17% and 9% higher than that of Comparative Examples 5-7, respectively, the impermeability grade is 38%, 47% and 29% higher, respectively, and the RCM is reduced by 32%, 38% and 27%, respectively. The silica fume particles are fine, and it is difficult for sodium methyl silicate to coat its surface, while the fly ash and slag powder particles are coarse, and the sodium methyl silicate coating effect is good. In addition, fly ash and slag powder have a higher aluminum content, and the alkalinity of sodium methyl silicate can be used as an alkaline activator to improve the performance of concrete. The slag powder particles are irregular in shape and have a better coating effect than fly ash. Therefore, the performance of Comparative Example 7 is the best, followed by Comparative Example 5, and the worst is Comparative Example 6. Silica fume has strong activity, which can promote hydration well and reduce the negative effects of the hydrophobicity of sodium methyl silicate. Silica fume has the strongest activity, followed by slag powder, and fly ash has the weakest activity. The three complement each other in terms of activity and promote the hydration process. Therefore, sodium methyl silicate and composite mineral admixtures produce a good synergistic effect when ball-milled, and the performance of concrete is greatly improved.

[0109] Comparing the test results of Example 1 and Comparative Example 8, it can be seen that when sodium methyl silicate is added, different from adding only fly ash and slag powder, adding silica fume on this basis can significantly improve the strength, impermeability and chloride salt corrosion resistance of concrete. The 28d compressive strength and impermeability of Example 1 are respectively improved by 17% and 29% compared with Comparative Example 1, and the RCM value is reduced by 44%. Sodium methyl silicate is a hydrophobic material and has an inhibitory effect on the hydration of cement-based materials. The volcanic ash activity of fly ash and slag powder is weak and is not enough to promote the formation of concrete hydration products. Silica fume has the characteristics of fine particles and high activity, which helps to fill pores, reduce porosity, enhance density, and improve early strength and impermeability. In addition, silica fume, fly ash and slag powder can form a good "particle size filling effect", form a good filling skeleton, and enhance density.

[0110] Ball-milling sodium methyl silicate with composite mineral admixtures and then adding them into concrete is a new idea for the application of sodium methyl silicate. The present invention fully combines two ideas for enhancing the waterproof, anti-corrosion and durable performance of concrete: increasing density and hydrophobic modification. Based on the embodiments and comparative examples, sodium methyl silicate is applied to the surface of the mineral admixture using a ball mill and fully dispersed, which can greatly reduce the negative impact of the hydrophobicity of sodium methyl silicate on the hydration of cementitious materials by the mineral admixture, make the concrete hydrophobic by using sodium methyl silicate, increase the water repellent effect of the concrete, use the dehydration condensation micro-expansion of sodium methyl silicate to fill the pores, and use sodium methyl silicate as an alkaline activator to promote the generation of more cementitious products, which can greatly improve the strength and durability of the concrete.

[0111] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A waterproof, chloride-resistant recycled fine aggregate concrete and a preparation method thereof, characterized in that: The steps include: S1: Weigh the following raw materials: natural coarse aggregate, recycled fine aggregate, cement, fly ash, silica fume, slag powder, water, water reducing agent, sodium methyl silicate powder; S2: putting fly ash, silica ash, slag powder and sodium methyl silicate powder into a ball mill and grinding them to obtain composite powder; S3: Add recycled fine aggregate, coarse aggregate and part of water into a mixer for mixing; S4: adding cement and composite powder into a mixer and mixing; S5: Add the remaining water and water reducing agent into the mixer and stir; S6: After the mixing is completed, the concrete is molded, demolded and cured to obtain a waterproof and chloride-resistant recycled fine aggregate concrete.

2. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The mass parts of the raw materials in step S1 are as follows: 1110-1130 parts of natural coarse aggregate, 520-552 parts of recycled fine aggregate, 338-364 parts of cement, 72-80 parts of fly ash, 21-32 parts of silica fume, 48-56 parts of slag powder, 168 parts of water, 3 parts of water reducer, and 4.8-8.0 parts of sodium methyl silicate powder.

3. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The cementitious material includes cement, fly ash, slag powder and silica fume in a mass ratio of 13:3:2:1; the mass ratio of water to cementitious material is 0.33; and the mass ratio of the total mass of natural coarse aggregate and recycled fine aggregate to cementitious material is 3.

3.

4. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The physical properties of the natural coarse aggregate conform to Class II crushed stone and above in GB / T14685-2022, with a particle size of 4.75-31.5 mm.

5. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The physical properties of the recycled fine aggregate meet the requirements of Class III and above as specified in GB / T25176-2010, and the particle size is 0.15-4.75 mm.

6. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The cement is PO52.5 ordinary Portland cement; the fly ash is Class I fly ash; the slag powder is S105 granulated blast furnace slag powder; the silica ash is Class I with an average particle size of 2.43 μm.

7. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The sodium methyl silicate is a white powdery solid with a purity of 98%, a pH of 13±1, and an alkali content of 29%.

8. The method for preparing waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid high efficiency water reducing agent with a water reducing efficiency of 40%.

9. The method for preparing the air-proof, waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The ratio of the total mass of the fly ash, silica ash and slag powder to the mass of the sodium methyl silicate powder is 18-35.

10. The method for preparing the air-proof, waterproof and chloride-resistant recycled fine aggregate concrete according to claim 1, characterized in that: The ball milling speed is 200 rpm, and the time is 1.5 to 2 hours.

Images