Low-carbon anti-cracking concrete and preparation method thereof

Abstract

The application discloses a kind of low-carbon anti-crack concrete and preparation method thereof, belong to concrete processing technical field, to solve the technical problem that the crack resistance and mechanical properties of prior art concrete need to be further improved, the application includes the following steps: concrete precursor is injected into plastic test mold, be placed on vibration table, vibration 1-2min, maintenance, obtain anti-crack concrete;The application is prepared by modified composite fiber, modified epoxy resin and modified recycled coarse aggregate as the reinforcing material of concrete, which is prepared together with recycled fine aggregate, fly ash, cement, curing agent and auxiliary additive to obtain concrete precursor, the concrete precursor is injected into plastic test mold, vibration bubble is exhausted, maintenance, obtain anti-crack concrete, not only improve the crack resistance of concrete, but also improve its mechanical properties and high temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of concrete processing technology, specifically to a low-carbon, crack-resistant concrete and its preparation method. Background Technology

[0002] If construction waste can be recycled in concrete production, using recycled aggregates to replace natural aggregates in concrete production can not only save material costs, but also reduce greenhouse gas emissions and non-renewable energy consumption. However, compared with natural aggregates, recycled aggregates formed after crushing and screening construction waste also have their own performance problems. They have a larger crushing index, larger porosity, and smaller apparent density. The performance of recycled aggregates will directly affect the mechanical properties and durability of recycled concrete products.

[0003] In existing technologies, the poor performance of concrete prepared using recycled aggregates is mainly due to the presence of old cement mortar adhering to the surface of the recycled aggregates. This old mortar has high porosity and contains unhydrated cement particles, resulting in numerous microcracks and defects within the aggregates. The hydration products in the old mortar fracture during the crushing process, forming irregular interface transition zones that weaken the bond between the aggregates and the new cement paste. Furthermore, the addition of epoxy resin to improve the mechanical properties of concrete is problematic because epoxy resin has poor compatibility with the inorganic materials in concrete, making it difficult to fully bond with the surface of the recycled aggregates. This also affects the mechanical properties of the concrete. Incomplete curing of epoxy resin during the curing process can also lead to insufficient mechanical properties and crack resistance of the concrete.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a low-carbon, crack-resistant concrete and its preparation method, which addresses the technical problem that the crack resistance and mechanical properties of concrete in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a low-carbon crack-resistant concrete, comprising the following raw material components by weight: 3-5 parts modified composite fiber, 50-60 parts recycled fine aggregate, 5-6 parts fly ash, 32-45 parts cement, 10-15 parts modified epoxy resin, 90-100 parts modified recycled coarse aggregate, 8-12 parts curing agent and 7-13 parts auxiliary additives.

[0007] Furthermore, the recycled fine aggregate is recycled rubber granules, the curing agent is 4,4-diaminodiphenylmethane, and the auxiliary additives are water-reducing agent, air-entraining agent, dispersant, viscosity modifier, and defoamer in a mass ratio of 100:10:300:5:1. The water-reducing agent is a polycarboxylate water-reducing agent, the air-entraining agent is one or two of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate, the dispersant is deionized water, the viscosity modifier is hydroxypropyl methylcellulose ether, and the defoamer is one or two of polydimethylsiloxane and tributyl phosphate.

[0008] Furthermore, the modified recycled coarse aggregate is prepared by the following steps:

[0009] A1. Place the recycled coarse aggregate and saturated calcium hydroxide solution in a reaction vessel, soak at room temperature for 20-24 hours, and dry to obtain alkalized recycled coarse aggregate;

[0010] The reaction principle for preparing alkali-treated recycled coarse aggregate is as follows:

[0011] During the reaction, the saturated calcium hydroxide solution penetrates into the pores and microcracks of the recycled coarse aggregate. In the subsequent drying process, the water evaporates, and the calcium hydroxide recrystallizes, filling the cracks and pores generated during the crushing process of the recycled coarse aggregate. The recycled coarse aggregate is also covered with old cement mortar containing unhydrated tricalcium silicate and dicalcium silicate. The calcium hydroxide reacts with the tricalcium silicate and dicalcium silicate in an alkaline-activated reaction to generate new hydrated calcium silicate gel, which enhances the interfacial transition zone properties of the aggregate, resulting in alkali-treated recycled coarse aggregate.

[0012] A2. Place the alkali-treated recycled coarse aggregate in a reactor and carbonize it under vacuum to obtain carbonized recycled coarse aggregate;

[0013] The reaction principle for preparing carbonized recycled coarse aggregate is as follows:

[0014] During the reaction, calcium hydroxide reacts with carbon dioxide to produce calcium carbonate, which fills the cracks and pores generated in the recycled coarse aggregate during the crushing process.

[0015] A3. Place carbonized recycled coarse aggregate, deionized water and nano silica sol in a reactor, soak at room temperature for 24-36 hours, and dry to obtain modified recycled coarse aggregate.

[0016] The reaction principle for preparing modified recycled coarse aggregate is as follows:

[0017] During the reaction, the small particle size of the nano-silica in the nano-silica sol can further fill the tiny pores of the carbonized recycled coarse aggregate to obtain modified recycled coarse aggregate.

[0018] Further, in step A1, the recycled coarse aggregate is composed of 4.7-5.2mm and 5.3-9.7mm building crushed stone in a mass ratio of 1:1, and the ratio of the recycled coarse aggregate to the saturated calcium hydroxide solution is 100-150g:2000-3000mL; in step A2, the vacuum carbonization operation includes: using a vacuum pump to evacuate the reactor to -0.05MPa, continuously introducing carbon dioxide for 20-24h, and after the reaction is completed, reducing the pressure to 0MPa and discharging the carbon dioxide; in step A3, the ratio of the carbonized recycled coarse aggregate, deionized water, and nano-silica sol is 150-200g:1000-1500mL:30-45mL.

[0019] Furthermore, the modified composite fiber is prepared by the following steps:

[0020] B1. Place basalt fiber and deionized water in a reaction vessel, heat to 100℃, stir at 200-250 r / min for 1-1.5 h, and dry to obtain basalt fiber dispersion;

[0021] B2. Place the basalt fiber dispersion and sodium hydroxide solution in a reaction vessel, stir for 25-45 minutes, and then process to obtain pretreated basalt fibers.

[0022] The reaction principle for preparing pretreated basalt fibers is as follows:

[0023] During the reaction, basalt fibers are mainly composed of silicon dioxide and aluminum oxide. Sodium hydroxide reacts chemically with the silicon dioxide and aluminum oxide on the surface of basalt fibers to generate soluble silicates and aluminates. These salts are removed by washing with ethanol and deionized water in the post-treatment step. Sodium hydroxide also reacts with the silicon oxide on the surface of basalt fibers to generate silanol groups, resulting in pretreated basalt fibers with increased reaction sites.

[0024] B3. Place pretreated basalt fiber, recycled glass fiber, KH-550, deionized water and ethanol in a reaction vessel, heat to 50-60℃, keep the temperature for 30-60 min, and then perform post-treatment to obtain modified composite fiber.

[0025] The preparation reaction principle of modified composite fibers is as follows:

[0026] During the reaction, the silicon-oxygen bonds of KH-550 are hydrolyzed by deionized water into silanol groups, which further undergo condensation reactions with the hydroxyl groups on the surfaces of pretreated basalt fibers and recycled glass fibers to obtain modified composite fibers.

[0027] Further, in step B1, the ratio of basalt fiber to deionized water is 100-120g:1000-1500mL; in step B2, the concentration of sodium hydroxide is 15-20wt%, and the ratio of basalt fiber dispersion to sodium hydroxide solution is 150-180g:1000-1500mL. The post-treatment steps include: after the reaction is complete, filtration is performed, the filter cake is washed 1-2 times with ethanol and deionized water, and then transferred to a drying oven at a temperature of 95-105℃. The pretreated basalt fiber is obtained by drying to constant weight. In step B3, the ratio of the pretreated basalt fiber, recycled glass fiber, KH-550, deionized water and ethanol is 200-220g:100-150g:50-60g:50-80mL:800-1000mL. The post-treatment steps include: after the reaction is completed, the filter cake is washed with ethanol and pure water 1-2 times, transferred to a drying oven at 95-105℃, and dried to constant weight to obtain modified composite fiber.

[0028] Furthermore, the modified epoxy resin is prepared by the following steps:

[0029] C1. Place 4-tolueneboronic acid, KH-560, deionized water and 1,2-dichloroethane in a reaction vessel under nitrogen atmosphere protection, heat to 50-60℃, keep the reaction at this temperature for 4-8h, and then process to obtain intermediate I.

[0030] The reaction formula for the preparation of intermediate I is as follows:

[0031]

[0032] The reaction principle for the preparation of intermediate I is as follows:

[0033] During the reaction, the silicon-oxygen bonds in KH-560 hydrolyze into silanols, which then undergo a condensation reaction with phenylboronic acid to obtain intermediate I.

[0034] C2. Intermediate I, bisphenol A epoxy resin and ethanol are placed in a reaction vessel under nitrogen atmosphere protection, dilute hydrochloric acid solution is added to adjust the pH to 6±0.5, the temperature is raised to 45-55℃, and the reaction is maintained for 2-4 hours. The modified epoxy resin is obtained after post-treatment.

[0035] The preparation reaction formula for modified epoxy resin is as follows:

[0036]

[0037] In the formula:

[0038] The preparation reaction principle of modified epoxy resin is as follows:

[0039] During the reaction, in an acidic environment, the epoxy group of intermediate I and the hydroxyl group in bisphenol A epoxy resin undergo a nucleophilic addition reaction to obtain the modified epoxy resin.

[0040] Further, in step C1, the ratio of 4-tolueneboronic acid, 3-mercaptopropyltriethoxysilane, deionized water, and 1,2-dichloroethane is 100-150g:50-60g:10-15mL:1000-1500mL. The post-processing step includes: after the reaction is completed, the reaction solution is cooled to room temperature, filtered, and the filtrate is transferred to a rotary evaporator at a temperature of 50-60℃ and evaporated until no liquid is collected to obtain intermediate I. In step C2, the concentration of the dilute hydrochloric acid solution is 0.5-1mol / L, and the ratio of intermediate I, bisphenol A epoxy resin, and ethanol is 200-250g:400-500g:5000-5500mL. The post-processing step is: after the reaction is completed, ethanol is added to the reaction solution, the temperature is raised to 60-70℃, and the solution is distilled under reduced pressure until no liquid is collected to obtain modified epoxy resin.

[0041] Furthermore, a method for preparing low-carbon, crack-resistant concrete includes the following steps:

[0042] S1. Place the modified composite fiber, recycled fine aggregate, fly ash and cement in a mixing tank, mix evenly, add the modified epoxy resin and modified recycled coarse aggregate, stir for 1-3 minutes, add the curing agent and auxiliary additives, stir for 3-5 minutes to obtain the concrete precursor.

[0043] S2. Inject the concrete precursor into a plastic mold, place it on a vibration table, vibrate for 1-2 minutes, and cure to obtain crack-resistant concrete.

[0044] Furthermore, in step S2, the curing step includes: placing the vibrated plastic mold in a curing room at a temperature of 20-22℃, covering it with a plastic film, letting it stand for 20-24 hours, demolding it, soaking it in room temperature water for 20-24 hours, and drying it to obtain crack-resistant concrete.

[0045] The present invention has the following beneficial effects:

[0046] 1. The low-carbon, crack-resistant concrete prepared by this invention involves preparing modified composite fibers, modified epoxy resin, and modified recycled coarse aggregate as reinforcing materials for concrete. These are then combined with recycled fine aggregate, fly ash, cement, curing agent, and auxiliary additives to prepare a concrete precursor. The concrete precursor is injected into a plastic mold, vibrated to remove air bubbles, and cured to obtain crack-resistant concrete. This invention also involves treating the recycled coarse aggregate with saturated calcium hydroxide solution, carbon dioxide carbonation, and nano-silica sol to obtain modified recycled coarse aggregate. The saturated calcium hydroxide solution penetrates into the pores and microcracks of the recycled coarse aggregate. During subsequent drying, the moisture evaporates, and the calcium hydroxide recrystallizes, filling the cracks and pores generated during the crushing process of the recycled coarse aggregate. Furthermore, the recycled coarse aggregate is coated with... The recycled cement mortar contains unhydrated tricalcium silicate and dicalcium silicate, among other substances. Calcium hydroxide reacts with tricalcium silicate and dicalcium silicate in an alkaline-activated reaction to generate new hydrated calcium silicate gel, enhancing the interfacial transition zone properties of the aggregate and improving the mechanical and crack-resistant properties of the concrete. Furthermore, calcium hydroxide reacts with carbon dioxide to generate calcium carbonate, filling the cracks and pores generated during the crushing process of the recycled coarse aggregate. At the same time, nano-silica particles can act as nuclei, providing active sites for clinker ions to adhere around the nanoparticles, which helps promote further hydration of cement, accelerates the cement hydration process, and improves the mechanical strength of the concrete. During the carbonation process, the carbon dioxide content in the environment is reduced, improving the low-carbon and environmentally friendly nature of the concrete.

[0047] 2. This invention involves boiling basalt fibers in water at high temperatures to obtain a well-dispersed basalt fiber dispersion. This dispersion is further treated with sodium hydroxide to remove surface impurities, increasing the surface roughness of the modified composite fibers. Under concrete stress, the modified composite fibers experience greater friction during pull-out, resulting in greater tensile stress within the concrete material and delaying deformation. The pretreated basalt fibers and recycled glass fibers are modified using a silane coupling agent. The amino groups in the silane coupling agent are hydrophilic, attracting more free water around the modified composite fibers. This water reacts with the cement mortar matrix to form hydrates, making the interface between the cement mortar and the composite fibers more compact. Furthermore, the amino groups react with the epoxy groups of the modified epoxy resin during concrete preparation, forming chemical bonds that improve the curing degree of the concrete and enhance its mechanical and crack resistance.

[0048] 3. This invention prepares a modified epoxy resin by grafting bisphenol A type epoxy resin and a silane coupling agent containing silicon-oxygen bonds. The epoxy groups in the modified epoxy resin can form chemical bonds with the amino groups on the surface of the modified composite fiber, enhancing the interfacial bonding force between the epoxy resin and the concrete matrix. At the same time, the silicon-oxygen bonds introduced into the modified epoxy resin have high bond energy, which can delay the thermal decomposition process of the epoxy resin and further improve the high-temperature resistance of the concrete. The benzene ring in the modified epoxy resin has a rigid structure, which, together with the Si-OBO flexible chain segment, improves the strength and toughness of the concrete. This invention uses recycled glass fiber to prepare modified composite fiber, recycled fine aggregate, and recycled coarse aggregate to prepare crack-resistant concrete, reducing the dependence on natural aggregate and reducing the carbon emissions generated during the mining, transportation, and processing of natural aggregate. At the same time, the use of recycled aggregate helps to reduce the accumulation of construction waste, avoid waste concrete entering landfills or waste sites, reduce the environmental burden of waste, and improve the low-carbon and environmentally friendly nature of concrete. Detailed Implementation

[0049] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] The polycarboxylate superplasticizer used in this invention was purchased from Nanjing Xinyi Synthetic Technology Co., Ltd., and its bulk density is [not specified].

[0051] 400-700kg / m 3 Model number 1903;

[0052] The bisphenol A type epoxy resin used in this invention was purchased from Shandong Qiansheng Chemical Co., Ltd., and its grade is E51.

[0053] The cement used in this invention was purchased from Jiaozuo Qianye Cement Co., Ltd., and the type is P.O42.5 silicate cement;

[0054] The recycled rubber granules used in this invention were purchased from Hebei Runhuabang New Material Technology Co., Ltd., with a specification of 0.35-0.50mm;

[0055] The fly ash used in this invention was purchased from Lingshou County Laipeng Mineral Products Business Department, and its density is 2000 g / cm³.

[0056] Example 1

[0057] This embodiment provides a method for preparing low-carbon, crack-resistant concrete, including the following steps:

[0058] S1. Preparation of modified recycled coarse aggregate

[0059] The recycled coarse aggregate is obtained by mixing 4.7-5.2mm and 5.3-9.7mm building crushed stone at a mass ratio of 1:1.

[0060] Weigh 100g of recycled coarse aggregate and 2000mL of saturated calcium hydroxide solution and place them in a reaction vessel. Soak at room temperature for 20h and dry to obtain alkalized recycled coarse aggregate.

[0061] The alkalized recycled coarse aggregate was placed in a reactor, and the reactor was evacuated to -0.05 MPa using a vacuum pump. Carbon dioxide was continuously introduced for 20 hours. After the reaction was completed, the pressure was reduced to 0 MPa, and the carbon dioxide was discharged to obtain carbonized recycled coarse aggregate.

[0062] Weigh out 150g of carbonized recycled coarse aggregate, 1000mL of deionized water and 30-45mL of nano-silica sol, place them in a reaction vessel, soak at room temperature for 24h, and dry to obtain modified recycled coarse aggregate.

[0063] S2, Preparation of modified composite fibers

[0064] Weigh 100g of basalt fiber and 1000mL of deionized water and place them in a reaction vessel. Heat the mixture to 100℃ and stir at 200r / min for 1h. Dry the mixture to obtain a basalt fiber dispersion.

[0065] Weigh 150g of basalt fiber dispersion and 1000mL of 15wt% sodium hydroxide solution and place them in a reaction vessel. Stir for 25min. After the reaction is complete, filter the mixture and wash the filter cake once with ethanol and deionized water. Transfer the cake to a drying oven at 95℃ and dry it to constant weight to obtain pretreated basalt fiber.

[0066] Weigh out 200g of pretreated basalt fiber, 100g of recycled glass fiber, 50g of KH-550, 50mL of deionized water and 800mL of ethanol and place them in a reaction vessel. Heat to 50℃ and keep the temperature for 30min. After the reaction is complete, filter the mixture. Wash the filter cake once with ethanol and pure water and transfer it to a drying oven at 95℃. Dry it to constant weight to obtain modified composite fiber.

[0067] S3. Preparation of modified epoxy resin

[0068] Weigh out 100g of 4-tolueneboronic acid, 50g of KH-560, 10mL of deionized water and 1000mL of 1,2-dichloroethane and place them in a reaction vessel under nitrogen atmosphere protection. Heat to 50℃ and keep the temperature for 4h. After the reaction is completed, wait for the reaction solution to cool to room temperature, filter, and transfer the filtrate to a rotary evaporator at 50℃. Evaporate until no liquid is collected to obtain intermediate I.

[0069] Weigh 200g of intermediate I, 400g of bisphenol A epoxy resin and 5000mL of ethanol and place them in a reaction vessel under nitrogen atmosphere protection. Add 0.5mol / L dilute hydrochloric acid to adjust the pH to 6.3, heat to 45℃ and keep the temperature for 2h. After the reaction is complete, add ethanol to the reaction solution, heat to 60℃, and distill under reduced pressure until no liquid is collected to obtain the modified epoxy resin.

[0070] S4. Preparation of crack-resistant concrete

[0071] Polycarboxylate superplasticizer, sodium dodecyl sulfate, deionized water, hydroxypropyl methylcellulose ether and polydimethylsiloxane were mixed evenly in a mass ratio of 100:10:300:5:1 to obtain auxiliary additives.

[0072] Weigh out the following by weight: 3 parts modified composite fiber, 50 parts recycled rubber granules, 5 parts fly ash and 32 parts cement, place them in a mixing tank, mix evenly, add 10 parts modified epoxy resin and 90 parts modified recycled coarse aggregate, stir for 1 minute, add 8 parts curing agent and 7 parts auxiliary additives, stir for 3 minutes to obtain concrete precursor.

[0073] The concrete precursor was injected into a plastic mold, placed on a vibration table, and vibrated for 1 minute. The vibrated plastic mold was then placed in a curing room at 20°C, covered with a plastic film, and left to stand for 20 hours. After demolding, the mold was immersed in room temperature water for 20 hours and then dried to obtain crack-resistant concrete.

[0074] Example 2

[0075] This embodiment provides a method for preparing low-carbon, crack-resistant concrete, including the following steps:

[0076] S1. Preparation of modified recycled coarse aggregate

[0077] The recycled coarse aggregate is obtained by mixing 4.7-5.2mm and 5.3-9.7mm building crushed stone at a mass ratio of 1:1.

[0078] Weigh 125g of recycled coarse aggregate and 2500mL of saturated calcium hydroxide solution and place them in a reaction vessel. Soak at room temperature for 22h and dry to obtain alkalized recycled coarse aggregate.

[0079] The alkalized recycled coarse aggregate was placed in a reactor, and the reactor was evacuated to -0.05 MPa using a vacuum pump. Carbon dioxide was continuously introduced for 22 hours. After the reaction was completed, the pressure was reduced to 0 MPa, and the carbon dioxide was discharged to obtain carbonized recycled coarse aggregate.

[0080] Weigh out 170g of carbonized recycled coarse aggregate, 1250mL of deionized water and 40mL of nano-silica sol and place them in a reaction vessel. Soak at room temperature for 30h and dry to obtain modified recycled coarse aggregate.

[0081] S2, Preparation of modified composite fibers

[0082] Weigh 110g of basalt fiber and 1250mL of deionized water and place them in a reaction vessel. Heat the mixture to 100℃ and stir at 225r / min for 1h. Dry the mixture to obtain a basalt fiber dispersion.

[0083] Weigh 165g of basalt fiber dispersion and 1250mL of 17wt% sodium hydroxide solution and place them in a reaction vessel. Stir for 30min. After the reaction is complete, filter the mixture and wash the filter cake twice with ethanol and deionized water. Transfer the cake to a drying oven at 100℃ and dry it to constant weight to obtain pretreated basalt fiber.

[0084] Weigh out 210g of pretreated basalt fiber, 125g of recycled glass fiber, 55g of KH-550, 70mL of deionized water and 900mL of ethanol and place them in a reaction vessel. Heat to 55℃ and keep the temperature for 45min. After the reaction is complete, filter the mixture. Wash the filter cake twice with ethanol and pure water. Transfer it to a drying oven at 100℃ and dry it to constant weight to obtain modified composite fiber.

[0085] S3. Preparation of modified epoxy resin

[0086] Weigh out 125g of 4-tolueneboronic acid, 55g of KH-560, 13mL of deionized water and 1250mL of 1,2-dichloroethane and place them in a reaction vessel under nitrogen atmosphere protection. Heat to 55℃ and keep the temperature for 6h. After the reaction is completed, wait for the reaction solution to cool to room temperature, filter, and transfer the filtrate to a rotary evaporator at 55℃. Evaporate until no liquid is collected to obtain intermediate I.

[0087] Weigh 225g of intermediate I, 450g of bisphenol A epoxy resin and 5250mL of ethanol and place them in a reaction vessel under nitrogen atmosphere protection. Add 0.7mol / L dilute hydrochloric acid to adjust the pH to 6.2, heat to 50℃ and keep the temperature for 3h. After the reaction is completed, add ethanol to the reaction solution, heat to 65℃, and distill under reduced pressure until no liquid is collected to obtain the modified epoxy resin.

[0088] S4. Preparation of crack-resistant concrete

[0089] Polycarboxylate superplasticizer, sodium dodecyl sulfate, deionized water, hydroxypropyl methylcellulose ether and polydimethylsiloxane were mixed evenly in a mass ratio of 100:10:300:5:1 to obtain auxiliary additives.

[0090] Weigh out the following by weight: 4 parts modified composite fiber, 55 parts recycled rubber granules, 5.5 parts fly ash and 38 parts cement, place them in a mixing tank, mix evenly, add 13 parts modified epoxy resin and 95 parts modified recycled coarse aggregate, stir for 2 minutes, add 10 parts curing agent and 10 parts auxiliary additives, stir for 4 minutes to obtain concrete precursor.

[0091] The concrete precursor was injected into a plastic mold, placed on a vibration table, and vibrated for 1 minute. The vibrated plastic mold was then placed in a curing room at 21°C, covered with a plastic film, and left to stand for 22 hours. After demolding, the mold was immersed in room temperature water for 22 hours and then dried to obtain crack-resistant concrete.

[0092] Example 3

[0093] This embodiment provides a method for preparing low-carbon, crack-resistant concrete, including the following steps:

[0094] S1. Preparation of modified recycled coarse aggregate

[0095] The recycled coarse aggregate is obtained by mixing 4.7-5.2mm and 5.3-9.7mm building crushed stone at a mass ratio of 1:1.

[0096] Weigh out 150g of recycled coarse aggregate and 3000mL of saturated calcium hydroxide solution and place them in a reaction vessel. Soak at room temperature for 24h and dry to obtain alkalized recycled coarse aggregate.

[0097] The alkalized recycled coarse aggregate was placed in a reactor, and the reactor was evacuated to -0.05 MPa using a vacuum pump. Carbon dioxide was continuously introduced for 24 hours. After the reaction was completed, the pressure was reduced to 0 MPa, and the carbon dioxide was discharged to obtain carbonized recycled coarse aggregate.

[0098] Weigh 200g of carbonized recycled coarse aggregate, 1500mL of deionized water and 45mL of nano-silica sol and place them in a reaction vessel. Soak at room temperature for 36h and dry to obtain modified recycled coarse aggregate.

[0099] S2, Preparation of modified composite fibers

[0100] Weigh 120g of basalt fiber and 1500mL of deionized water and place them in a reaction vessel. Heat the mixture to 100℃ and stir at 250r / min for 1.5h. Dry the mixture to obtain a basalt fiber dispersion.

[0101] Weigh 180g of basalt fiber dispersion and 1500mL of 20wt% sodium hydroxide solution and place them in a reaction vessel. Stir for 45min. After the reaction is complete, filter the mixture and wash the filter cake twice with ethanol and deionized water. Transfer the cake to a drying oven at 105℃ and dry it to constant weight to obtain pretreated basalt fiber.

[0102] Weigh out 220g of pretreated basalt fiber, 150g of recycled glass fiber, 60g of KH-550, 80mL of deionized water and 1000mL of ethanol and place them in a reaction vessel. Heat to 60℃ and keep the temperature for 60min. After the reaction is complete, filter the mixture. Wash the filter cake twice with ethanol and pure water. Transfer it to a drying oven at 105℃ and dry it to constant weight to obtain modified composite fiber.

[0103] S3. Preparation of modified epoxy resin

[0104] Weigh out 150g of 4-tolueneboronic acid, 60g of KH-560, 15mL of deionized water and 1500mL of 1,2-dichloroethane and place them in a reaction vessel under nitrogen atmosphere protection. Heat to 60℃ and keep the temperature for 8h. After the reaction is completed, wait for the reaction solution to cool to room temperature, filter, and transfer the filtrate to a rotary evaporator at 60℃. Evaporate until no liquid is collected to obtain intermediate I.

[0105] Weigh 250g of intermediate I, 500g of bisphenol A epoxy resin and 5500mL of ethanol and place them in a reaction vessel under nitrogen atmosphere protection. Add 1mol / L dilute hydrochloric acid to adjust the pH to 6.1, heat to 55℃ and keep the temperature for 4h. After the reaction is complete, add ethanol to the reaction solution, heat to 70℃, and distill under reduced pressure until no liquid is collected to obtain the modified epoxy resin.

[0106] S4. Preparation of crack-resistant concrete

[0107] Polycarboxylate superplasticizer, sodium dodecyl sulfate, deionized water, hydroxypropyl methylcellulose ether and polydimethylsiloxane were mixed evenly in a mass ratio of 100:10:300:5:1 to obtain auxiliary additives.

[0108] Weigh out the following by weight: 5 parts of modified composite fiber, 60 parts of recycled rubber granules, 6 parts of fly ash and 45 parts of cement and place them in a mixing tank. Mix them evenly, add 15 parts of modified epoxy resin and 100 parts of modified recycled coarse aggregate, stir for 3 minutes, add 12 parts of curing agent and 13 parts of auxiliary additives, stir for 5 minutes to obtain concrete precursor.

[0109] The concrete precursor was injected into a plastic mold, placed on a vibration table, and vibrated for 2 minutes. The vibrated plastic mold was then placed in a curing room at 22°C, covered with a plastic film, left to stand for 24 hours, demolded, and soaked in room temperature water for 24 hours. After drying, crack-resistant concrete was obtained.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 2 is that step S1 omits the preparation of modified recycled coarse aggregate, while in step S4, when preparing crack-resistant concrete, the recycled coarse aggregate from step S1 is used to replace the modified recycled coarse aggregate in an equal amount.

[0112] Comparative Example 2

[0113] The difference between this comparative example and Example 2 is that step S2 is omitted when preparing crack-resistant concrete in step S4, and modified composite fibers are not added in step S4.

[0114] Comparative Example 3

[0115] The difference between this comparative example and Example 2 is that, in step S4, when preparing crack-resistant concrete, step S3 is omitted, and the modified epoxy resin is replaced with an equal amount of bisphenol A type epoxy resin in step S3.

[0116] Performance testing:

[0117] The flexural strength, compressive strength, splitting tensile strength, and abrasion resistance of the crack-resistant concrete prepared in Examples 1-3 and Comparative Examples 1-3 were tested after 28 days of curing, in accordance with the standard GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0118] The high-temperature resistance of the crack-resistant concrete prepared in Examples 1-3 and Comparative Examples 1-3 after 28 days of curing was determined in accordance with the standard GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The specific test results are shown in Table 1.

[0119] Table 1. Performance Test Table for Each Sample

[0120]

[0121] Data Analysis:

[0122] Comparative analysis of the data in Table 1 shows that the low-carbon, crack-resistant concrete prepared by this invention has a flexural strength of 13.12 MPa, a compressive strength of 61.62 MPa, a splitting tensile strength of 5.74 MPa, and a linear expansion coefficient of 8.54 × 10⁻⁶ MPa. -6 ×℃ -1 After 45 cycles, the wear amount is 1.58 kg·m. 2 ;

[0123] Comparing the data from Comparative Example 1 and Example 2, it was found that the flexural strength, compressive strength, and splitting tensile strength of the low-carbon crack-resistant concrete prepared in Comparative Example 1 all decreased, and the wear amount increased after 45 cycles. This indicates that the present invention obtains modified recycled coarse aggregate by treating it with saturated calcium hydroxide solution, carbon dioxide carbonization, and nano-silica sol. The saturated calcium hydroxide solution penetrates into the pores and microcracks of the recycled coarse aggregate. During the subsequent drying process, the water evaporates, and the calcium hydroxide recrystallizes, filling the cracks and pores generated during the crushing process of the recycled coarse aggregate. Furthermore, the recycled coarse aggregate is coated with old cement mortar. It contains unhydrated tricalcium silicate and dicalcium silicate, etc. Calcium hydroxide reacts with tricalcium silicate and dicalcium silicate in an alkaline-activated reaction to generate new hydrated calcium silicate gel, which enhances the interfacial transition zone performance of aggregates and improves the mechanical and crack-resistant properties of crack-resistant concrete. Calcium hydroxide also reacts with carbon dioxide to generate calcium carbonate, which fills the cracks and pores generated during the crushing process of recycled coarse aggregates. At the same time, nano-silica particles can act as cores, playing a nucleation role and providing active sites for clinker ions to attach around the nanoparticles, which helps to promote further hydration of cement, accelerates the cement hydration process, and improves the mechanical strength of concrete.

[0124] By comparing the data of Comparative Example 2 and Example 2, it was found that the flexural strength, compressive strength, and splitting tensile strength of the low-carbon crack-resistant concrete prepared in Comparative Example 1 all decreased, and the wear amount increased after 45 cycles. This indicates that the present invention obtains a well-dispersed basalt fiber dispersion by boiling basalt fibers in high temperature water. The dispersion is further treated with sodium hydroxide to remove surface impurities and increase the surface roughness of the modified composite fiber. When the concrete is under stress, the modified composite fiber is subjected to greater friction during the pull-out process, which causes greater tensile stress to be generated inside the concrete material, thus delaying the deformation of the concrete. The pretreated basalt fiber and recycled glass fiber are modified by using a silane coupling agent. The amino group of the silane coupling agent is a hydrophilic group. The presence of the hydrophilic amino group will attract more free water around the modified composite fiber, react with the cement mortar matrix to form a hydrate, making the interface between the cement mortar and the composite fiber more compact. In addition, the amino group reacts with the epoxy group of the modified epoxy resin during the preparation of concrete to form a chemical bond, which improves the curing degree of the concrete and enhances the mechanical properties and crack resistance of the concrete.

[0125] Comparing the data from Comparative Example 3 and Example 2, it was found that the flexural strength, compressive strength, and splitting tensile strength of the low-carbon crack-resistant concrete prepared in Comparative Example 1 all decreased, while the linear expansion coefficient and wear after 45 cycles increased. This indicates that the present invention prepares a modified epoxy resin by grafting bisphenol A type epoxy resin and a silane coupling agent containing silicon-oxygen bonds together. The epoxy groups in the modified epoxy resin can form chemical bonds with the amino groups on the surface of the modified composite fiber, enhancing the interfacial bonding force between the epoxy resin and the concrete matrix. At the same time, the silicon-oxygen bonds introduced into the modified epoxy resin have high bond energy, which can delay the thermal decomposition process of the epoxy resin and further improve the high-temperature resistance of the concrete. The benzene ring in the modified epoxy resin has a rigid structure, which, together with the Si-OBO flexible segments, improves the strength and toughness of the concrete.

[0126] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low-carbon, crack-resistant concrete, characterized in that, It comprises the following raw materials in parts by weight: 3-5 parts modified composite fiber, 50-60 parts recycled fine aggregate, 5-6 parts fly ash, 32-45 parts cement, 10-15 parts modified epoxy resin, 90-100 parts modified recycled coarse aggregate, 8-12 parts curing agent and 7-13 parts auxiliary additives. The modified recycled coarse aggregate is prepared by the following steps: A1. Place the recycled coarse aggregate and saturated calcium hydroxide solution in a reaction vessel, soak at room temperature for 20-24 hours, and dry to obtain alkalized recycled coarse aggregate; A2. Place the alkali-treated recycled coarse aggregate in a reactor and carbonize it under vacuum to obtain carbonized recycled coarse aggregate; A3. Place carbonized recycled coarse aggregate, deionized water and nano silica sol in a reaction vessel, soak at room temperature for 24-36 hours, and dry to obtain modified recycled coarse aggregate; The modified composite fiber is prepared by the following steps: B1. Place basalt fiber and deionized water in a reaction vessel, heat to 100℃, stir at 200-250 r / min for 1-1.5 h, and dry to obtain basalt fiber dispersion; B2. Place the basalt fiber dispersion and sodium hydroxide solution in a reaction vessel, stir for 25-45 minutes, and then process to obtain pretreated basalt fibers. B3. Place pretreated basalt fiber, recycled glass fiber, KH-550, deionized water and ethanol in a reaction vessel, heat to 50-60℃, keep the temperature for 30-60 min, and then process to obtain modified composite fiber. The modified epoxy resin is prepared by the following steps: C1. Place 4-tolueneboronic acid, KH-560, deionized water and 1,2-dichloroethane in a reaction vessel under nitrogen atmosphere protection, heat to 50-60℃, keep the reaction at this temperature for 4-8h, and then process to obtain intermediate I. C2. Intermediate I, bisphenol A epoxy resin and ethanol are placed in a reaction vessel under nitrogen atmosphere protection, dilute hydrochloric acid solution is added to adjust the pH to 6±0.5, the temperature is raised to 45-55℃, and the reaction is maintained for 2-4 hours. The modified epoxy resin is obtained after post-treatment.

2. The low-carbon, crack-resistant concrete according to claim 1, characterized in that, The recycled fine aggregate is recycled rubber granules, the curing agent is 4,4-diaminodiphenylmethane, and the auxiliary additives are water-reducing agent, air-entraining agent, dispersant, viscosity modifier and defoamer in a mass ratio of 100:10:300:5:

1. The water-reducing agent is a polycarboxylate water-reducing agent, the air-entraining agent is one or two of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate, the dispersant is deionized water, the viscosity modifier is hydroxypropyl methylcellulose ether, and the defoamer is one or two of polydimethylsiloxane and tributyl phosphate.

3. The low-carbon, crack-resistant concrete according to claim 1, characterized in that, In step A1, the recycled coarse aggregate is composed of 4.7-5.2mm and 5.3-9.7mm building crushed stone in a mass ratio of 1:1, and the ratio of recycled coarse aggregate to saturated calcium hydroxide solution is 100-150g:2000-3000mL; In step A2, the vacuum carbonization operation includes: evacuating the reactor to -0.05MPa using a vacuum pump, continuously introducing carbon dioxide for 20-24h, and after the reaction is completed, reducing the pressure to 0MPa and discharging the carbon dioxide; In step A3, the ratio of carbonized recycled coarse aggregate, deionized water, and nano-silica sol is 150-200g:1000-1500mL:30-45mL.

4. The low-carbon, crack-resistant concrete according to claim 1, characterized in that, In step B1, the ratio of basalt fiber to deionized water is 100-120g:1000-1500mL; in step B2, the concentration of sodium hydroxide is 15-20wt%, and the ratio of basalt fiber dispersion to sodium hydroxide solution is 150-180g:1000-1500mL; in step B3, the ratio of pretreated basalt fiber, recycled glass fiber, KH-550, deionized water, and ethanol is 200-220g:100-150g:50-60g:50-80mL:800-1000mL.

5. The low-carbon, crack-resistant concrete according to claim 1, characterized in that, In step C1, the ratio of 4-tolueneboric acid, KH-560, deionized water, and 1,2-dichloroethane is 100g:50-60g:10-15mL:1000-1500mL; in step C2, the concentration of the dilute hydrochloric acid is 0.5-1mol / L, and the ratio of intermediate I, bisphenol A epoxy resin, and ethanol is 200-250g:400-500g:5000-5500mL.

6. A method for preparing low-carbon, crack-resistant concrete as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Place the modified composite fiber, recycled fine aggregate, fly ash and cement in a mixing tank, mix evenly, add the modified epoxy resin and modified recycled coarse aggregate, stir for 1-3 minutes, add the curing agent and auxiliary additives, stir for 3-5 minutes to obtain the concrete precursor. S2. Inject the concrete precursor into a plastic mold, place it on a vibration table, vibrate for 1-2 minutes, and cure to obtain crack-resistant concrete.

7. The method for preparing low-carbon, crack-resistant concrete according to claim 6, characterized in that, In step S2, the curing step includes: placing the vibrated plastic mold in a curing room at a temperature of 20-22℃, covering it with a plastic film, letting it stand for 20-24 hours, demolding it, soaking it in room temperature water for 20-24 hours, and drying it to obtain crack-resistant concrete.

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