A silicon-based composite reagent-reinforced recycled aggregate and its preparation method

Abstract

This invention belongs to the field of aggregate strengthening, specifically relating to a silicon-based composite reagent-strengthened recycled aggregate and its preparation method. The preparation method includes the following steps: crushing and sieving virgin mortar samples, then rinsing to remove impurities to obtain low-quality recycled coarse aggregate; then, under certain conditions, adding lime slurry and surfactant to the low-quality recycled coarse aggregate, stirring, and allowing it to stand, followed by cyclic stirring; then adding water, a hydrophobic agent, silica fume, and fly ash, and maintaining standing for 6–12 hours; finally, immersing in water to remove soluble impurities from the surface of the recycled aggregate, and air-drying to obtain the silicon-based composite reagent-strengthened recycled aggregate. This method, by comprehensively utilizing industrial by-products such as silica fume and fly ash, explores the application potential of industrial waste products in the field of construction solid waste resource utilization, increases resource utilization rate, efficiently utilizes industrial solid waste, and is conducive to resource conservation and the reuse of waste.

Description

Technical Field

[0001] This invention belongs to the field of aggregate strengthening, specifically relating to a silicon-based composite reagent-strengthened recycled aggregate and its preparation method. Technical Background

[0002] Comparison with natural aggregates revealed that recycled aggregates have surface impurities, low strength, microcracks in the surface mortar, and higher water absorption, resulting in inferior quality. Strengthening recycled aggregates with silicon-based composite reagents can not only improve their quality and performance but also fully utilize industrial solid waste, promoting resource conservation and waste reuse, thus demonstrating broad application and development prospects.

[0003] Lime slurry reacts with the surfactant cetyltrimethylammonium bromide (CTAB) to generate nanospheres, which serve as nucleation sites in the pores and microcracks of the mortar surface layer adhering to the recycled aggregate. The formation of these nucleation sites facilitates the subsequent agglomeration and solidification of nano-SiO2 and CTAB, filling the pores and microcracks on the recycled aggregate surface. The lime slurry provides the raw materials for subsequent reactions, accelerating the generation of strength substances and ensuring a more complete reaction.

[0004] Tridecafluorooctyltriethoxysilane, as a hydrophobic agent, can form a hydrophobic film on the surface of recycled aggregate, further blocking the water and ion permeation channels on the mortar surface, thereby reducing water absorption and improving resistance to chloride ion permeation. The use of hydrophobic agents can accelerate the reaction rate of other reagents, thus improving reaction efficiency.

[0005] Silica fume and fly ash are solid wastes emitted during industrial production. They are low-cost, readily available, and possess broad utilization value, making them a valuable industrial waste resource. During the reaction process, silica fume forms nano-SiO2, which agglomerates and solidifies using CTAB particles in the pores and microcracks of mortar attached to the surface of recycled aggregates as nucleation sites, filling these pores and microcracks and resulting in a denser mortar surface structure. The CSH gel generated by the reaction of SiO2, an active component in fly ash, with Ca(OH)2 significantly improves the pore structure of the mortar surface attached to the recycled aggregates, enhancing the density of the mortar surface.

[0006] Existing methods for strengthening recycled aggregates still have the following problems:

[0007] Micro-cracks in recycled aggregates and gaps between residual old mortar and new mortar on the surface can easily cause stress concentration, which is one of the important reasons affecting the strength of recycled aggregates. Insufficient surface bond strength of recycled aggregates leads to decreased crack resistance and increased water absorption, which can adversely affect the performance of recycled aggregates.

[0008] Using chemical reagents to fill the gaps in the transition zone between the new and old mortar on the surface of recycled aggregates, reducing the water absorption and crushing value of the recycled aggregates, increasing their relative apparent density, and enhancing their performance is a current research direction for recycled aggregate concrete. Existing treatment methods are relatively complex, time-consuming, and costly, and there is still room for improvement in terms of strengthening the recycled aggregates. For example, simply using nano-SiO2 solution soaking to strengthen recycled aggregates is not ideal, resulting in low strength and high water absorption.

[0009] Therefore, in order to resolve the contradiction between the strengthening effect of recycled aggregates and the level of treatment, it is necessary to study an environmentally friendly method that is conducive to continuous industrial production with low treatment levels and can effectively achieve the strengthening of recycled aggregates. Summary of the Invention

[0010] The purpose of this invention is to provide a silicon-based composite reagent-enhanced recycled aggregate and its preparation method. This method is environmentally friendly, facilitates continuous industrial production with low processing levels, and can effectively enhance the recycled aggregate.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] This invention provides a method for preparing silicon-based composite reagent-reinforced recycled aggregate, comprising the following steps;

[0013] (1) Use virgin mortar test blocks to crush and produce recycled aggregate. After screening, wash away impurities to obtain low-quality recycled coarse aggregate.

[0014] (2) High-temperature mixing: Under set conditions, lime milk and surfactant are added to low-quality recycled coarse aggregate, stirred and then left to stand, and the mixture is stirred repeatedly.

[0015] (3) Water soaking and strengthening: Water, hydrophobic agent, silica fume and fly ash are added to the low-quality recycled coarse aggregate after step (2), and the aggregate is kept standing for 6 to 12 hours to obtain recycled aggregate;

[0016] (4) Soaking and air drying: Soak the recycled aggregate in water to remove soluble impurities on the surface of the recycled aggregate, and then air dry to obtain silicon-based composite reagent reinforced recycled aggregate.

[0017] Furthermore, in step (1), the water-cement ratio of the virgin mortar test block can be 0.3-0.45, the particle size range during sieving is 5-20mm, and the mass percentage of calcium hydroxide in the lime milk is 40%-60%.

[0018] Furthermore, in step (2), the conditions are set as 90-100℃, pH=13, the volume ratio of the recycled aggregate to lime milk is 5:1-10:1, the surfactant is hexadecyltrimethylammonium bromide, and the amount of surfactant added is 0.9mol / L.

[0019] Furthermore, in step (2), the stirring and then standing is stirred for 90 seconds and then left to stand for 30 seconds, and the number of stirring cycles is 3-6 times.

[0020] Furthermore, in step (3), the mass ratio of water, hydrophobic agent, silica fume and fly ash is 15-30:0.2-0.4:3-6:0.6-1.2; the hydrophobic agent is tridecafluorooctyltriethoxysilane.

[0021] Furthermore, the immersion time in water in step (4) is 0.5-1h.

[0022] The present invention also provides a silicon-based composite reagent-reinforced recycled aggregate prepared using the aforementioned preparation method.

[0023] In this process, cetyltrimethylammonium bromide, used as a surfactant, was concentrated at 0.9 mol / L. Nanoparticles with a diameter of 27 nm were prepared at 90℃ and pH=13, serving as nucleation sites in the pores and microcracks of the recycled aggregate surface mortar. The mixing process was as follows: mixing for 90 seconds, letting stand for 30 seconds, and then repeating the mixing cycle 3–6 times. If the mixing time or number of cycles did not meet the design standards, the formation of nucleation sites for the nanoparticles at the interface between the new and old mortar on the surface of the recycled aggregate would be insufficient, easily leading to unsatisfactory strengthening effects on the deep structure of the aged mortar.

[0024] The hydrophobic agent tridecafluorooctyltriethoxysilane forms a hydrophobic film on the surface of recycled aggregate to reduce its water absorption and improve its resistance to chloride ion penetration. Silica fume forms nano-SiO2, which agglomerates and solidifies using CTAB particles in the pores and microcracks of the mortar attached to the surface of the recycled aggregate as nucleation sites, filling the pores and microcracks and making the mortar surface structure dense. The CSH gel generated by the reaction of SiO2, an active component in fly ash, and Ca(OH)2 can significantly improve the pore structure of the mortar surface attached to the recycled aggregate, further enhancing the density of the mortar surface.

[0025] Immersion washing can effectively remove byproducts generated during the reaction that remain on the surface of recycled aggregates. This immersion washing process is simple, inexpensive, and widely used in industrial production.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Improved performance of recycled aggregates: Under the same conditions of nano-SiO2 concentration, treatment time, and temperature, compared to methods that treat recycled aggregates with nano-SiO2 alone, this method can significantly improve the strengthening effect, increase the apparent density of recycled aggregates, and reduce indicators such as water absorption and crushing value. While achieving the same strengthening effect, the processing level can be significantly reduced.

[0028] 2. Rational utilization of resources: By comprehensively utilizing industrial by-products such as silica fume and fly ash, the application potential of industrial waste products in the field of construction solid waste resource utilization has been explored, increasing resource utilization rate, making efficient use of industrial solid waste, which is conducive to resource conservation and the reuse of waste.

[0029] 3. Simple and easy-to-implement process: Silica fume and fly ash are readily available and inexpensive industrial byproducts. This method is simple and can improve the strength of recycled aggregates, significantly reduce water absorption and crushing value, and can be continuously produced industrially, which is conducive to its widespread application.

[0030] In summary, this method, through the synergistic effect of multiple effective components in a silicon-based composite reagent, effectively strengthens the surface porosity of the aged mortar layer, forming a dense, high-strength, and hydrophobic surface-strengthening layer, thus enhancing the strengthening effect of recycled aggregate adhering to the mortar surface. It can effectively improve the relative apparent density, water absorption, and crushing value of recycled aggregate, thereby improving its performance. Simultaneously, it efficiently utilizes industrial solid waste, possessing advantages such as simple process, environmental friendliness, and continuous production capability, promoting the sustainable utilization of recycled aggregate and holding promise for practical application and widespread adoption. Detailed Implementation

[0031] The following experimental examples and embodiments are used to further illustrate the present invention, but are not limited to the present invention.

[0032] Example 1

[0033] A method for preparing a silicon-based composite reagent to enhance regenerated bone includes the following steps:

[0034] (1) Using virgin mortar test blocks with a water-cement ratio of 0.35 (0.3-0.45 is acceptable), recycled aggregate was produced by crushing with a jaw crusher. After screening, recycled aggregate with a particle size range of 9.5-13.2 mm (5-20 mm is acceptable) was selected. The aggregate was then washed to remove surface dust and other impurities, resulting in clean, low-quality recycled coarse aggregate. The lime slurry was a calcium hydroxide suspension prepared from quicklime and water, with calcium hydroxide comprising 50 wt% (40%-60% is acceptable). The initial apparent density of the recycled aggregate was tested to be 2618 kg / m³. 3 The water absorption rate is 7.265%, and the crushing value is 29.15%.

[0035] (2) High temperature mixing: Under the conditions of 95℃ (90-100℃ is acceptable) and pH=13, add a small amount of lime milk and 0.9mol / L hexadecyltrimethylammonium bromide to the recycled aggregate, stir for 90 seconds and let stand for 30 seconds, and circulate and stir 4 times (3-6 times is acceptable); the volume ratio of recycled aggregate to lime milk is 5:1 (5:1-10:1 is acceptable).

[0036] (3) Water soaking for strengthening: Add 20 parts of water, 0.4 parts of hydrophobic agent: tridecafluorooctyltriethoxysilane, 6 parts of silica fume and 1.2 parts of fly ash, and keep it standing for 8 hours. The proportion of tridecafluorooctyltriethoxysilane in the above raw materials is 0.2 to 0.4 parts, the proportion of water is 15 to 30 parts, the proportion of silica fume is 3 to 6 parts, and the proportion of fly ash is 0.6 to 1.2 parts (all parts by weight).

[0037] (4) Soaking and air drying: Soak in water for 1 hour (0.5-1 hour is acceptable) to remove soluble impurities on the surface of recycled aggregate. After air drying, silicon-based composite reagent reinforced recycled aggregate can be obtained.

[0038] Compared to natural aggregates, reinforced recycled aggregates are more prone to internal and surface damage and cracks due to mechanical breakage and damage accumulation. Residual mortar adhering to the outer surface of recycled aggregates is also a major cause of their poor quality. In the preparation of reinforced recycled aggregates, the synergistic effect of various effective components in the reagents strengthens the surface structure of the mortar layer attached to the recycled aggregates. This creates a dense reinforced layer in the transition zone between the old and new mortar interfaces, forming a new triple-interface transition zone structure of old mortar, reinforced layer, and new mortar. Furthermore, the reinforced layer develops inward along the pores and micro-cracks of the attached mortar surface, exhibiting strong bonding with the old mortar layer. This effectively reduces the water absorption and crushing value of the recycled aggregates, increases their relative apparent density, and thus improves the performance of the recycled aggregates.

[0039] The apparent density of the reinforced recycled aggregate obtained in this embodiment was tested according to the "Test Procedures for Aggregates in Highway Engineering" (JTG E42-2005), and it increased by 1.42% compared with that before reinforcement. The water absorption rate of the reinforced recycled aggregate decreased by 31.67% compared with that before reinforcement. The crushing value of the reinforced recycled aggregate decreased by 26.25% compared with that before reinforcement.

[0040] Example 2

[0041] A method for preparing silicon-based composite reagent-reinforced recycled aggregate includes the following steps:

[0042] (1) Native mortar test blocks with a water-cement ratio of 0.35 were used to produce recycled aggregate using a jaw crusher. After screening, recycled aggregate with a particle size range of 9.5–13.2 mm was selected, and the surface dust and other impurities were washed away to obtain clean, low-quality recycled coarse aggregate. The lime slurry was a calcium hydroxide suspension made from quicklime and water, wherein the calcium hydroxide was 40 wt%.

[0043] (2) High temperature mixing: Under the conditions of 90℃ and pH=13, a small amount of lime milk and 0.9mol / L hexadecyltrimethylammonium bromide are added to the recycled aggregate, stirred for 90 seconds and then left to stand for 30 seconds, and the mixture is stirred 3 times in a cycle; the volume ratio of recycled aggregate to lime milk is 5:1.

[0044] (3) Water soaking for strengthening: Add 30 parts water, 0.4 parts hydrophobic agent: tridecafluorooctyltriethoxysilane, 6 parts silica fume and 1.2 parts fly ash, and keep it standing for 6 hours;

[0045] (4) Soaking and air drying: Soak in water for 1 hour to remove soluble impurities on the surface of recycled aggregate, and air dry to obtain silicon-based composite reagent reinforced recycled aggregate.

[0046] The apparent density of the reinforced recycled aggregate obtained in this embodiment was tested according to the "Test Procedures for Aggregates in Highway Engineering" (JTG E42-2005), and it increased by 1.31% compared with that before reinforcement. The water absorption rate of the reinforced recycled aggregate decreased by 25.13% compared with that before reinforcement. The crushing value of the reinforced recycled aggregate decreased by 23.21% compared with that before reinforcement.

[0047] Example 3

[0048] A method for preparing silicon-based composite reagent-reinforced recycled aggregate includes the following steps:

[0049] (1) Native mortar test blocks with a water-cement ratio of 0.35 were used to produce recycled aggregate using a jaw crusher. After screening, recycled aggregate with a particle size range of 9.5–13.2 mm was selected, and the surface dust and other impurities were washed away to obtain clean, low-quality recycled coarse aggregate. The lime slurry was a calcium hydroxide suspension made from quicklime and water, wherein the calcium hydroxide was 60 wt%.

[0050] (2) High temperature mixing: At 100℃ and pH=13, a small amount of lime milk and 0.9mol / L hexadecyltrimethylammonium bromide were added to the recycled aggregate, stirred for 90 seconds and then allowed to stand for 30 seconds. The mixture was stirred 6 times in a cycle. The volume ratio of recycled aggregate to lime milk was 5:1.

[0051] (3) Water soaking for strengthening: Add 30 parts water, 0.4 parts hydrophobic agent: tridecafluorooctyltriethoxysilane, 6 parts silica fume and 1.2 parts fly ash, and keep it standing for 12 hours;

[0052] (4) Soaking and air drying: Soak in water for 1 hour to remove soluble impurities on the surface of recycled aggregate, and air dry to obtain silicon-based composite reagent reinforced recycled aggregate.

[0053] The apparent density of the reinforced recycled aggregate obtained in this embodiment was tested according to the "Test Procedures for Aggregates in Highway Engineering" (JTG E42-2005), and it increased by 1.51% compared with that before reinforcement. The water absorption rate of the reinforced recycled aggregate decreased by 33.67% compared with that before reinforcement. The crushing value of the reinforced recycled aggregate decreased by 27.65% compared with that before reinforcement.

[0054] Comparative Example 1

[0055] Comparative Example 1 is the recycled aggregate used in step (1) of Examples 1 to 3. The apparent density, water absorption and crushing value of the unreinforced original recycled aggregate were tested.

[0056] Comparative Example 2

[0057] The remaining steps of Comparative Example 2 are the same as those of Example 1, except that the reaction temperature and the volume ratio of recycled aggregate to lime milk are different in step (2).

[0058] In the high-temperature mixing process of Comparative Example 2, a small amount of lime slurry and 0.9 mol / L hexadecyltrimethylammonium bromide were added to the recycled aggregate at 60°C and pH=13. The mixture was stirred for 90 seconds and then allowed to stand for 30 seconds. The mixture was then stirred three times. The volume ratio of recycled aggregate to lime slurry was 8:1.

[0059] The apparent density of the reinforced recycled aggregate increased by 0.32% compared to the unreinforced aggregate. The water absorption rate of the reinforced recycled aggregate decreased by 16.14% compared to the unreinforced aggregate. The crushing value of the reinforced recycled aggregate decreased by 11.55% compared to the unreinforced aggregate.

[0060] Comparative Example 3

[0061] The remaining steps of Comparative Example 3 are the same as those of Example 1, except that the hydrophobic agent, tridecafluorooctyltriethoxysilane, is not used in step (3).

[0062] In the water immersion strengthening treatment step of Comparative Example 3, 30 parts of water, 6 parts of silica fume and 1.2 parts of fly ash were added, and the mixture was kept still for 6 hours.

[0063] The apparent density of the reinforced recycled aggregate increased by 0.86% compared to the unreinforced aggregate. The water absorption rate of the reinforced recycled aggregate decreased by 18.25% compared to the unreinforced aggregate. The crushing value of the reinforced recycled aggregate decreased by 14.67% compared to the unreinforced aggregate.

[0064] To comprehensively examine the effect of silicon-based composite reagent-enhanced recycled aggregate on the performance enhancement of recycled aggregate, this invention refers to the "Test Procedure for Aggregates in Highway Engineering" (JTG E42-2005) to test the apparent density, water absorption rate, and crushing value of the original recycled aggregate (Comparative Example 1), the enhanced recycled aggregates of Examples 1-3, and the enhanced recycled aggregates of Comparative Examples 2-3. The results are shown in Table 1.

[0065] Table 1. Performance of recycled aggregates after enhancement with silicon-based composite reagents

[0066]

[0067] As shown in Examples 1-3 and Comparative Example 1 in Table 1, the reinforced recycled aggregate prepared by the present invention has an increased apparent density and significantly reduced water absorption and crushing value compared to the original aggregate. This is due to the synergistic effect of the effective components in the silicon-based reagent: the initial treatment with lime milk and surfactant CTAB causes CTAB to condense into microparticles in the pores and microcracks of the aged mortar surface, providing nucleation sites for the subsequent silicification reaction and making the reaction easier; silica fume and fly ash react with the minerals, active ingredients and lime milk in the mortar layer to generate new hydration products such as nano-SiO2 and CSH gel around the nucleation sites, filling the surface pore structure of the mortar layer and forming a new dense reinforced layer on the surface of the mortar layer; the use of hydrophobic agents further blocks the water and ion permeation channels on the surface of the mortar layer, thereby further reducing the water absorption rate. Through the synergistic effect of the various effective components in the reagent, a dense reinforced layer structure is formed in the transition zone between the new and old mortar interfaces, creating a new triple interface transition zone structure of old mortar-reinforced layer-new mortar. This structure has strong bonding with the old mortar layer, effectively reducing the water absorption rate and crushing value of recycled aggregates, increasing their relative apparent density, and thus improving the performance of recycled aggregates.

[0068] As can be seen from Example 1 and Comparative Example 2 in Table 1, in the high-temperature mixing step of the recycled aggregate reinforced by the present invention, if the reaction temperature and the volume ratio of recycled aggregate to lime slurry are less than the range provided by the present invention, the reinforcing effect will decrease significantly. This is because during the reaction between lime slurry and CTAB, the number of nanospheres generated by the reaction is insufficient due to the influence of temperature and Ca(OH)2 content. This results in an unsatisfactory transition zone in the pores and microcracks of the mortar surface layer attached to the recycled aggregate, affecting the further reaction with subsequent reagents to form a reinforcing layer structure.

[0069] As shown in Example 1 and Comparative Example 3 in Table 1, the strengthening effect of the recycled aggregate reinforced by the present invention is not significantly improved if a hydrophobic agent is not used during the water soaking strengthening step. This is because without a hydrophobic agent, the surface of the recycled aggregate lacks a hydrophobic film, which cannot effectively reduce the water absorption rate and affects the strengthening result of the recycled aggregate. Therefore, using a hydrophobic agent at the same treatment level can effectively improve the performance of the silicon-based composite reagent-reinforced recycled aggregate.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing silicon-based composite reagent-reinforced recycled aggregate, characterized in that, Includes the following steps; (1) Use virgin mortar test blocks to crush and produce recycled aggregate. After screening, wash away impurities to obtain low-quality recycled coarse aggregate. (2) High-temperature mixing: Under set conditions, lime milk and surfactant are added to low-quality recycled coarse aggregate, stirred and then left to stand, and the mixture is stirred repeatedly. (3) Water soaking and strengthening: Water, hydrophobic agent, silica fume and fly ash are added to the low-quality recycled coarse aggregate after step (2), and the aggregate is kept standing for 6 to 12 hours to obtain recycled aggregate; (4) Soaking and air drying: Soak the recycled aggregate in water to remove soluble impurities on the surface of the recycled aggregate, and then air dry to obtain silicon-based composite reagent reinforced recycled aggregate. In step (2), the conditions are set as 90-100℃ and pH=13, the volume ratio of the recycled aggregate to lime milk is 5:1-10:1, the surfactant is hexadecyltrimethylammonium bromide, and the amount of surfactant added is 0.9mol / L.

2. The preparation method according to claim 1, characterized in that, In step (1), the water-cement ratio of the original mortar test block can be 0.3-0.45, the particle size range during sieving is 5-20mm, and the mass percentage of calcium hydroxide in the lime milk is 40%-60%.

3. The preparation method according to claim 1, characterized in that, In step (2), the stirring and then settling period is 90 seconds after stirring and 30 seconds after settling. The number of times the stirring is repeated is 3-6 times.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of water, hydrophobic agent, silica fume and fly ash is 15-30:0.2-0.4:3-6:0.6-1.2; the hydrophobic agent is tridecafluorooctyltriethoxysilane.

5. The preparation method according to claim 1, characterized in that, The soaking time in water in step (4) is 0.5-1h.

6. Silicon-based composite reagent-reinforced recycled aggregate prepared by the preparation method according to any one of claims 1-5.

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