Low-carbon anti-crack concrete and preparation method thereof

Abstract

The invention discloses low-carbon anti-crack concrete and a preparation method thereof, belongs to the technical field of concrete processing, and is used for solving the technical problem that the anti-crack performance and the mechanical performance of concrete in the prior art need to be further improved. The preparation method comprises the following steps: injecting a concrete precursor into a plastic test mold, putting the plastic test mold on a vibration table, and vibrating for 1-2 minutes, and curing to obtain the anti-crack concrete. The preparation method comprises the following steps: preparing modified composite fibers, modified epoxy resin and modified recycled coarse aggregate as reinforcing materials of concrete, preparing a concrete precursor together with recycled fine aggregate, fly ash, cement, a curing agent and an auxiliary additive, injecting the concrete precursor into a plastic test mold, vibrating to remove bubbles, and curing to obtain the anti-crack concrete. The anti-cracking performance of the concrete is improved, and the mechanical performance and the high-temperature resistance of the concrete are also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete processing, and particularly relates to a low-carbon crack-resistant concrete and a preparation method thereof. Background Art

[0002] In concrete production, if construction waste can be recycled and recycled aggregates are used to replace natural aggregates to prepare concrete products, it can not only save material costs, but also reduce greenhouse gas emissions and non-renewable energy consumption. However, compared with natural aggregates, the recycled aggregates formed after crushing and screening of construction waste also have problems in their own properties. Their crushing index is relatively large, the porosity is relatively large, and the apparent density is relatively small. The quality of recycled aggregates will directly affect the mechanical properties and durability of recycled concrete products.

[0003] In the prior art, the reason why the performance of concrete prepared with recycled aggregates is poor is mainly that the recycled aggregates are attached with old cement mortar on their surfaces. Their porosity is relatively high and they contain unhydrated cement particles, resulting in a large number of microcracks and defects inside the aggregates. The hydration products in the old mortar break during the crushing process, forming an irregular interfacial transition zone, weakening the bonding force between the aggregates and the new cement paste. In addition, adding epoxy resin to improve the mechanical properties of concrete, due to the poor compatibility between epoxy resin and the inorganic materials of concrete, it is difficult to fully bond with the surface of recycled aggregates, thus affecting the mechanical properties of concrete. Moreover, there may be an incomplete curing phenomenon during the curing process of epoxy resin, which will also lead to insufficient mechanical properties and crack resistance of concrete.

[0004] In view of the technical defects in this regard, a solution is proposed now. Summary of the Invention

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

[0006] The purpose of the present invention can be achieved by the following technical solutions: A low-carbon crack-resistant concrete, comprising the following raw materials in parts by weight: 3-5 parts of modified composite fiber, 50-60 parts of recycled fine aggregate, 5-6 parts of fly ash, 32-45 parts of cement, 10-15 parts of modified epoxy resin, 90-100 parts of modified recycled coarse aggregate, 8-12 parts of curing agent, and 7-13 parts of auxiliary additive.

[0007] Furthermore, the recycled fine aggregate is recycled rubber particles, the curing agent is 4,4-diaminodiphenylmethane, the auxiliary additives are water reducer, air-entraining agent, dispersant, viscosity regulator and defoaming agent, which are composed according to the mass ratio of 100:10:300:5:1. The water reducer is polycarboxylate water reducer, the air-entraining agent is one or both of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate, the dispersant is deionized water, the viscosity regulator is hydroxypropyl methyl cellulose ether, and the defoaming agent is one or both 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 kettle, immerse them at room temperature for 20 - 24h, and then dry to obtain alkalized recycled coarse aggregate;

[0010] The reaction principle for the preparation of alkalized recycled coarse aggregate is as follows:

[0011] During the reaction process, the saturated calcium hydroxide solution will penetrate into the pores and microcracks of the recycled coarse aggregate. During the subsequent drying process, the water evaporates, and calcium hydroxide recrystallizes to fill the cracks and pores generated during the crushing of the recycled coarse aggregate. Moreover, the recycled coarse aggregate is attached with old cement mortar, containing substances such as unhydrated tricalcium silicate and dicalcium silicate. Calcium hydroxide reacts with tricalcium silicate and dicalcium silicate to undergo an alkali activation reaction, generating new hydrated calcium silicate gel, enhancing the performance of the interfacial transition zone of the aggregate, and obtaining alkalized recycled coarse aggregate.

[0012] A2. Place the alkalized recycled coarse aggregate in a reaction kettle and carry out vacuum carbonization to obtain carbonized recycled coarse aggregate;

[0013] The reaction principle for the preparation of carbonized recycled coarse aggregate is as follows:

[0014] During the reaction process, calcium hydroxide reacts with carbon dioxide to form calcium carbonate, filling the cracks and pores generated during the crushing of the recycled coarse aggregate.

[0015] A3. Place the carbonized recycled coarse aggregate, deionized water and nano-silica sol in a reaction kettle, immerse them at room temperature for 24 - 36h, and then dry to obtain modified recycled coarse aggregate.

[0016] The reaction principle for the preparation of modified recycled coarse aggregate is as follows:

[0017] During the reaction process, the particle size of nano-silica in the nano-silica sol is relatively small, which 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 construction gravel with a size of 4.7 - 5.2 mm and construction gravel with a size of 5.3 - 9.7 mm in a mass ratio of 1:1, and the dosage ratio of the recycled coarse aggregate to the saturated calcium hydroxide solution is 100 - 150 g: 2000 - 3000 mL; in step A2, the operation steps of vacuum carbonization include: using a vacuum pump to pump the reaction kettle to -0.05 MPa, continuously introducing carbon dioxide for 20 - 24 h, after the reaction is completed, reducing the pressure to 0 MPa, and discharging carbon dioxide; in step A3, the dosage ratio of the carbonized recycled coarse aggregate, deionized water, and nano-silica sol is 150 - 200 g: 1000 - 1500 mL: 30 - 45 mL.

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

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

[0021] B2. Place the basalt fiber dispersion and sodium hydroxide solution in a reaction kettle, stir for 25 - 45 min, and perform post-treatment to obtain pretreated basalt fiber;

[0022] The reaction principle for the preparation of the pretreated basalt fiber is as follows:

[0023] During the reaction process, the basalt fiber is mainly composed of silicon dioxide and alumina. Sodium hydroxide reacts chemically with the silicon dioxide and alumina on the surface of the basalt fiber to form soluble silicate and aluminate. These salts are removed by washing with ethanol and deionized water in the post-treatment step, and sodium hydroxide reacts with the silicon oxygen on the surface of the basalt fiber to form silanol groups, obtaining pretreated basalt fiber with increased reaction sites.

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

[0025] The reaction principle for the preparation of the modified composite fiber is as follows:

[0026] During the reaction process, the siloxane bond of KH-550 is hydrolyzed by deionized water into silanol groups, which further undergo a condensation reaction with the hydroxyl groups on the surface of the pretreated basalt fiber and the recycled glass fiber to obtain the modified composite fiber.

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

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

[0029] C1. Place 4-tolylboronic acid, KH-560, deionized water, and 1,2-dichloroethane in a reaction kettle protected by a nitrogen atmosphere, heat up to 50 - 60 °C, keep the temperature for reaction for 4 - 8 h, and carry out post-treatment to obtain intermediate I;

[0030] The preparation reaction formula of intermediate I is:

[0031]

[0032] The preparation reaction principle of intermediate I is:

[0033] During the reaction process, the siloxane bond in KH-560 is hydrolyzed into silanol, and the silanol further undergoes a condensation reaction with phenylboronic acid to obtain intermediate I.

[0034] C2. Place intermediate I, bisphenol A epoxy resin, and ethanol in a reaction kettle protected by a nitrogen atmosphere, add a dilute hydrochloric acid solution to adjust the pH to 6 ± 0.5, heat up to 45 - 55 °C, keep the temperature for reaction for 2 - 4 h, and carry out post-treatment to obtain modified epoxy resin.

[0035] The preparation reaction formula of the modified epoxy resin is:

[0036]

[0037] In the formula:

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

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

[0040] Furthermore, in step C1, the dosage ratio of 4-tolylboronic acid, 3-mercaptopropyltriethoxysilane, deionized water, and 1,2-dichloroethane is 100 - 150 g: 50 - 60 g: 10 - 15 mL: 1000 - 1500 mL. The post-treatment steps include: after the reaction is completed, wait for the reaction solution to cool to room temperature, perform suction filtration, transfer the filtrate to a rotary evaporator at a temperature of 50 - 60 °C, and rotate and evaporate until no liquid is collected to obtain intermediate I; in step C2, the concentration of the dilute hydrochloric acid solution is 0.5 - 1 mol / L, and the dosage ratio of intermediate I, bisphenol A epoxy resin, and ethanol is 200 - 250 g: 400 - 500 g: 5000 - 5500 mL. The post-treatment step is: after the reaction is completed, add ethanol to the reaction solution, heat up to 60 - 70 °C, and perform vacuum distillation until no liquid is collected to obtain the modified epoxy resin.

[0041] Furthermore, a preparation method of a 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 stirring kettle, mix evenly, add the modified epoxy resin and modified recycled coarse aggregate, stir for 1 - 3 min, add the curing agent and auxiliary additive, and stir for 3 - 5 min to obtain a concrete precursor;

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

[0044] Furthermore, in step S2, the curing step includes: place the vibrated plastic test mold in a curing room at a temperature of 20 - 22 °C, cover it with a plastic film, let it stand for 20 - 24 h, demold, soak it in water at room temperature for 20 - 24 h, and air dry to obtain the crack-resistant concrete.

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

[0046] 1. The low-carbon crack-resistant concrete prepared by the present invention is obtained by preparing modified composite fibers, modified epoxy resin and modified recycled coarse aggregate as the reinforcing materials of the concrete, and jointly preparing a concrete precursor with recycled fine aggregate, fly ash, cement, curing agent and auxiliary additives. The concrete precursor is injected into a plastic test mold, vibrated to remove air bubbles, and cured to obtain the crack-resistant concrete. The present invention processes the recycled coarse aggregate with saturated calcium hydroxide solution, carbon dioxide carbonization and nano-silica sol respectively to obtain the modified recycled coarse aggregate. The saturated calcium hydroxide solution will penetrate into the pores and micro-cracks of the recycled coarse aggregate. During the subsequent drying process, the water evaporates, and calcium hydroxide recrystallizes to fill the cracks and pores generated during the crushing of the recycled coarse aggregate. Moreover, the recycled coarse aggregate is attached with old cement mortar, containing substances such as unhydrated tricalcium silicate and dicalcium silicate. Calcium hydroxide reacts with tricalcium silicate and dicalcium silicate to generate alkali-activated reaction, forming new hydrated calcium silicate gel, enhancing the performance of the interfacial transition zone of the aggregate, improving the mechanical properties and crack resistance of the crack-resistant concrete. And calcium hydroxide reacts with carbon dioxide to generate calcium carbonate, filling the cracks and pores generated during the crushing of the recycled coarse aggregate. At the same time, nano-silica particles can act as nuclei, playing a nucleation role, providing active sites for clinker ions to adhere around the nanoparticles, helping to promote the further hydration development of cement, accelerating the cement hydration process, improving the mechanical strength of the concrete. During the carbonization operation, the content of carbon dioxide in the environment is reduced, improving the low-carbon environmental protection of the concrete.

[0047] 2. The present invention obtains a basalt fiber dispersion with good dispersibility by boiling basalt fiber at high temperature. It is further treated with sodium hydroxide to remove surface impurities, increasing the surface roughness of the modified composite fiber. When the concrete is stressed, the modified composite fiber is subjected to greater friction during the pulling-out process, causing greater tensile stress to be generated inside the concrete material, delaying the deformation of the concrete. The pretreated basalt fiber and recycled glass fiber are modified with 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, reacting with the cement mortar matrix to form hydrates, making the interface between the cement mortar and the composite fiber more dense. And the amino group reacts with the epoxy group of the modified epoxy resin during the preparation of the concrete to form chemical bonding, improving the curing degree of the concrete, strengthening the mechanical properties and crack resistance of the concrete.

[0048] 3. In the present invention, bisphenol A epoxy resin and a silane coupling agent containing a silicon-oxygen bond are grafted together to prepare a modified epoxy resin. The epoxy groups in the modified epoxy resin can form chemical bonds with the amino groups on the surface of the modified composite fibers, 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 a relatively 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 rings in the modified epoxy resin are rigid structures, which together with the Si-O-B-O flexible chain segments improve the strength and toughness of the concrete. In the present invention, recycled glass fibers are used to prepare modified composite fibers, and recycled fine aggregates and recycled coarse aggregates are used to prepare crack-resistant concrete, reducing the dependence on natural aggregates and reducing the carbon emissions generated during the mining, transportation, and processing of natural aggregates. At the same time, the use of recycled aggregates helps to reduce the accumulation of construction waste, avoid waste concrete from entering landfills or waste yards, reduce the environmental burden of waste, and improve the low-carbon environmental protection of the concrete. Detailed implementation mode

[0049] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0050] The polycarboxylate water reducer used in the present invention is purchased from Nanjing Xinyi Synthetic Technology Co., Ltd., and the bulk density is

[0051] 400 - 700 kg / m 3 , and the model is 1903;

[0052] The bisphenol A epoxy resin used in the present invention is purchased from Shandong Qiansheng Chemical Co., Ltd., and the grade is E51;

[0053] The cement used in the present invention is purchased from Jiaozuo Qianye Cement Co., Ltd., and the model is P.O42.5 Portland cement;

[0054] The recycled rubber particles used in the present invention are purchased from Hebei Runhuabang New Material Technology Co., Ltd., and the specification is 0.35 - 0.50 mm;

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

[0056] Example 1

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

[0058] S1. Preparation of Modified Recycled Coarse Aggregate

[0059] Mix 4.7 - 5.2 mm construction crushed stones as recycled coarse aggregate and 5.3 - 9.7 mm construction crushed stones evenly by mass ratio of 1:1 to obtain recycled coarse aggregate;

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

[0061] Place the alkalized recycled coarse aggregate in a reaction kettle, use a vacuum pump to pump the reaction kettle to -0.05 MPa, continuously introduce carbon dioxide for 20 h, after the reaction is completed, reduce the pressure to 0 MPa, and discharge carbon dioxide to obtain carbonized recycled coarse aggregate;

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

[0063] S2. Preparation of Modified Composite Fiber

[0064] Weigh: 100 g of basalt fiber and 1000 mL of deionized water, place them in a reaction kettle, heat up to 100 °C, stir at a speed of 200 r / min for 1 h, and dry to obtain basalt fiber dispersion;

[0065] Weigh: 150 g of basalt fiber dispersion and 1000 mL of 15 wt% sodium hydroxide solution, place them in a reaction kettle, stir for 25 min, after the reaction is completed, filter by suction, wash the filter cake once with ethanol and deionized water, transfer it to a drying oven at 95 °C, and dry to constant weight to obtain pretreated basalt fiber;

[0066] Weigh: 200 g of pretreated basalt fiber, 100 g of recycled glass fiber, 50 g of KH - 550, 50 mL of deionized water and 800 mL of ethanol, place them in a reaction kettle, heat up to 50 °C, keep the temperature for reaction for 30 min, after the reaction is completed, filter by suction, wash the filter cake once with ethanol and pure water, transfer it to a drying oven at 95 °C, and dry to constant weight to obtain modified composite fiber.

[0067] S3. Preparation of Modified Epoxy Resin

[0068] Weigh: 100 g of 4 - tolylboronic acid, 50 g of KH - 560, 10 mL of deionized water and 1000 mL of 1,2 - dichloroethane, place them in a reaction kettle under nitrogen atmosphere protection, heat up to 50 °C, keep the temperature for reaction for 4 h, after the reaction is completed, wait for the reaction solution to cool to room temperature, filter by suction, transfer the filtrate to a rotary evaporator at 50 °C, and rotary evaporate until no liquid is collected to obtain intermediate Ⅰ;

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

[0070] S4. Prepare crack-resistant concrete

[0071] Mix polycarboxylate superplasticizer, sodium dodecyl sulfate, deionized water, hydroxypropyl methylcellulose ether and polydimethylsiloxane evenly according to the mass ratio of 100:10:300:5:1 to obtain an auxiliary additive;

[0072] Weigh by weight: 3 parts of modified composite fiber, 50 parts of recycled rubber particles, 5 parts of fly ash and 32 parts of cement, place them in a stirring kettle, mix evenly, add 10 parts of modified epoxy resin and 90 parts of modified recycled coarse aggregate, stir for 1 min, add 8 parts of curing agent and 7 parts of auxiliary additive, and stir for 3 min to obtain a concrete precursor;

[0073] Inject the concrete precursor into a plastic test mold, place it on a vibrating table, vibrate for 1 min, place the vibrated plastic test mold in a curing room at 20 °C, cover it with a plastic film, let it stand for 20 h, demold it, soak it in water at room temperature for 20 h, and air dry it to obtain crack-resistant concrete.

[0074] Example 2

[0075] This example provides a preparation method of low-carbon crack-resistant concrete, including the following steps:

[0076] S1. Prepare modified recycled coarse aggregate

[0077] Mix construction gravel with a particle size of 4.7 - 5.2 mm and construction gravel with a particle size of 5.3 - 9.7 mm evenly according to the mass ratio of 1:1 to obtain recycled coarse aggregate;

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

[0079] Place the alkalized recycled coarse aggregate in a reaction kettle, use a vacuum pump to pump the reaction kettle to -0.05 MPa, continuously introduce carbon dioxide for 22 h, after the reaction is completed, reduce the pressure to 0 MPa, and discharge carbon dioxide to obtain carbonized recycled coarse aggregate;

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

[0081] S2. Preparation of modified composite fibers

[0082] Weigh: 110 g of basalt fibers and 1250 mL of deionized water and place them in a reaction kettle. Heat up to 100 °C and stir at a speed of 225 r / min for 1 h. Then dry to obtain a basalt fiber dispersion;

[0083] Weigh: 165 g of basalt fiber dispersion and 1250 mL of 17 wt% sodium hydroxide solution and place them in a reaction kettle. Stir for 30 min. After the reaction is completed, perform suction filtration. Wash the filter cake twice with ethanol and deionized water, and transfer it to a drying oven at 100 °C and dry to constant weight to obtain pretreated basalt fibers;

[0084] Weigh: 210 g of pretreated basalt fibers, 125 g of recycled glass fibers, 55 g of KH-550, 70 mL of deionized water and 900 mL of ethanol and place them in a reaction kettle. Heat up to 55 °C and keep the temperature for reaction for 45 min. After the reaction is completed, perform suction filtration. Wash the filter cake twice with ethanol and pure water, and transfer it to a drying oven at 100 °C and dry to constant weight to obtain modified composite fibers.

[0085] S3. Preparation of modified epoxy resin

[0086] Weigh: 125 g of 4-tolueneboronic acid, 55 g of KH-560, 13 mL of deionized water and 1250 mL of 1,2-dichloroethane and place them in a reaction kettle protected by a nitrogen atmosphere. Heat up to 55 °C and keep the temperature for reaction for 6 h. After the reaction is completed, wait for the reaction solution to cool to room temperature, perform suction filtration. Transfer the filtrate to a rotary evaporator at 55 °C and evaporate until no liquid is collected to obtain intermediate Ⅰ;

[0087] Weigh: 225 g of intermediate Ⅰ, 450 g of bisphenol A epoxy resin and 5250 mL of ethanol and place them in a reaction kettle protected by a nitrogen atmosphere. Add 0.7 mol / L dilute hydrochloric acid to adjust the pH to 6.2. Heat up to 50 °C and keep the temperature for reaction for 3 h. After the reaction is completed, add ethanol to the reaction solution, heat up to 65 °C and perform vacuum distillation until no liquid is collected to obtain modified epoxy resin.

[0088] S4. Preparation of crack-resistant concrete

[0089] Mix polycarboxylate water reducer, sodium dodecyl sulfate, deionized water, hydroxypropyl methylcellulose ether and polydimethylsiloxane evenly according to the mass ratio of 100:10:300:5:1 to obtain an auxiliary additive;

[0090] Weigh by parts by weight: 4 parts of modified composite fiber, 55 parts of recycled rubber particles, 5.5 parts of fly ash, and 38 parts of cement, place them in a stirring kettle, mix evenly, add 13 parts of modified epoxy resin and 95 parts of modified recycled coarse aggregate, stir for 2 min, add 10 parts of curing agent and 10 parts of auxiliary additive, stir for 4 min to obtain a concrete precursor;

[0091] Inject the concrete precursor into a plastic test mold, place it on a vibrating table, vibrate for 1 min, place the vibrated plastic test mold in a curing room at a temperature of 21 °C, cover it with a plastic film, let it stand for 22 h, demold, soak it in water at room temperature for 22 h, and dry it to obtain crack-resistant concrete.

[0092] Example 3

[0093] This example provides a preparation method for low-carbon crack-resistant concrete, which includes the following steps:

[0094] S1. Prepare modified recycled coarse aggregate

[0095] Mix 4.7 - 5.2 mm construction gravel and 5.3 - 9.7 mm construction gravel as recycled coarse aggregate evenly by a mass ratio of 1:1 to obtain recycled coarse aggregate;

[0096] Weigh: 150 g of recycled coarse aggregate and 3000 mL of saturated calcium hydroxide solution, place them in a reaction kettle, impregnate at room temperature for 24 h, and dry to obtain alkalized recycled coarse aggregate;

[0097] Place the alkalized recycled coarse aggregate in a reaction kettle, use a vacuum pump to pump the reaction kettle to -0.05 MPa, continuously introduce carbon dioxide for 24 h, after the reaction is completed, reduce the pressure to 0 MPa, and discharge carbon dioxide to obtain carbonized recycled coarse aggregate;

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

[0099] S2. Prepare modified composite fiber

[0100] Weigh: 120 g of basalt fiber and 1500 mL of deionized water, place them in a reaction kettle, heat up to 100 °C, stir at a speed of 250 r / min for 1.5 h, and dry to obtain a basalt fiber dispersion;

[0101] Weigh: 180 g of basalt fiber dispersion and 1500 mL of 20 wt% sodium hydroxide solution, place them in a reaction kettle, stir for 45 min, after the reaction is completed, filter by suction, wash the filter cake with ethanol and deionized water twice, transfer it to a drying oven at a temperature of 105 °C, and dry to constant weight to obtain pretreated basalt fiber;

[0102] Weigh: 220 g of pretreated basalt fiber, 150 g of recycled glass fiber, 60 g of KH-550, 80 mL of deionized water and 1000 mL of ethanol, place them in a reaction kettle, heat up to 60 °C, keep the temperature for reaction for 60 min. After the reaction is completed, perform suction filtration, wash the filter cake twice with ethanol and pure water, transfer it to a drying oven at 105 °C, and dry it to constant weight to obtain the modified composite fiber.

[0103] S3. Prepare the modified epoxy resin

[0104] Weigh: 150 g of 4-tolylboronic acid, 60 g of KH-560, 15 mL of deionized water and 1500 mL of 1,2-dichloroethane, place them in a reaction kettle protected by a nitrogen atmosphere, heat up to 60 °C, keep the temperature for reaction for 8 h. After the reaction is completed, wait for the reaction solution to cool to room temperature, perform suction filtration, transfer the filtrate to a rotary evaporator at 60 °C, and rotate and evaporate until no liquid is produced to obtain Intermediate I;

[0105] Weigh: 250 g of Intermediate I, 500 g of bisphenol A epoxy resin and 5500 mL of ethanol, place them in a reaction kettle protected by a nitrogen atmosphere, add 1 mol / L dilute hydrochloric acid to adjust the pH to 6.1, heat up to 55 °C, keep the temperature for reaction for 4 h. After the reaction is completed, add ethanol to the reaction solution, heat up to 70 °C, and perform vacuum distillation until no liquid is produced to obtain the modified epoxy resin.

[0106] S4. Prepare the crack-resistant concrete

[0107] Mix the polycarboxylate water reducer, sodium dodecyl sulfate, deionized water, hydroxypropyl methylcellulose ether and polydimethylsiloxane evenly according to the mass ratio of 100:10:300:5:1 to obtain the auxiliary additive;

[0108] Weigh by weight: 5 parts of modified composite fiber, 60 parts of recycled rubber particles, 6 parts of fly ash and 45 parts of cement, place them in a stirring kettle, mix evenly, add 15 parts of modified epoxy resin and 100 parts of modified recycled coarse aggregate, stir for 3 min, add 12 parts of curing agent and 13 parts of auxiliary additive, and stir for 5 min to obtain the concrete precursor;

[0109] Inject the concrete precursor into a plastic test mold, place it on a vibrating table, vibrate for 2 min, place the vibrated plastic test mold in a curing room at 22 °C, cover it with a plastic film, let it stand for 24 h, demold it, soak it in water at room temperature for 24 h, and air dry it to obtain the crack-resistant concrete.

[0110] Comparative Example 1

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

[0112] Comparative Example 2

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

[0114] Comparative Example 3

[0115] The difference between this comparative example and Example 2 is that when preparing crack-resistant concrete in step S4, step S3 is cancelled, and bisphenol A epoxy resin in step S3 is used to replace the modified epoxy resin in equal amount.

[0116] Performance test:

[0117] Referring to the standard GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", 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 after 28 days of solidification were tested;

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

[0119] Table 1. Performance test table of each specimen

[0120]

[0121] Data analysis:

[0122] By comparing and analyzing the data in Table 1 above, it can be seen that the flexural strength of the low-carbon crack-resistant concrete prepared by the present invention is 13.12 MPa, the compressive strength is 61.62 MPa, the splitting tensile strength is 5.74 MPa, the linear expansion coefficient is 8.54×10 -6 ×℃ -1 and the wear loss after 45 cycle rotations is 1.58 kg·m 2 ;

[0123] By comparing the data of Comparative Example 1 and Example 2, it is found that the flexural strength, compressive strength and splitting tensile strength of the low-carbon crack-resistant concrete prepared in Comparative Example 1 all decrease, and the wear amount increases after 45 cycles. This shows that in the present invention, the recycled coarse aggregate is treated with saturated calcium hydroxide solution, carbon dioxide carbonization and nano-silica sol respectively to obtain a modified recycled coarse aggregate. The saturated calcium hydroxide solution will penetrate into the pores and microcracks of the recycled coarse aggregate. During the subsequent drying process, the water evaporates, and calcium hydroxide recrystallizes to fill the cracks and pores generated during the crushing of the recycled coarse aggregate. Moreover, the recycled coarse aggregate is attached with old cement mortar, containing substances such as unhydrated tricalcium silicate and dicalcium silicate. Calcium hydroxide reacts with tricalcium silicate and dicalcium silicate to generate a new hydrated calcium silicate gel, enhancing the performance of the interfacial transition zone of the aggregate and improving the mechanical properties and crack resistance of the crack-resistant concrete. At the same time, calcium hydroxide reacts with carbon dioxide to generate calcium carbonate, filling the cracks and pores generated during the crushing of the recycled coarse aggregate. Meanwhile, nano-silica particles can act as nuclei, playing a nucleation role and providing active sites for the attachment of clinker ions around the nanoparticles, which helps to promote the further hydration development of cement, accelerate the cement hydration process and improve the mechanical strength of the concrete;

[0124] By comparing the data of Comparative Example 2 and Example 2, it is found that the flexural strength, compressive strength and splitting tensile strength of the low-carbon crack-resistant concrete prepared in Comparative Example 1 all decrease, and the wear amount increases after 45 cycles. This shows that in the present invention, the basalt fiber is boiled in high-temperature water to obtain a basalt fiber dispersion with good dispersibility, which is further treated with sodium hydroxide to remove surface impurities and increase the surface roughness of the modified composite fiber. When the concrete is stressed, the modified composite fiber is subjected to greater friction during the pulling-out process, resulting in greater tensile stress inside the concrete material and delaying the deformation of the concrete. The pretreated basalt fiber and recycled glass fiber are modified with a silane coupling agent. The amino group of the silane coupling agent is a hydrophilic group, and the presence of the hydrophilic amino group will attract more free water around the modified composite fiber, reacting with the cement mortar matrix to form a hydrate, making the interface between the cement mortar and the composite fiber more dense. Moreover, the amino group reacts with the epoxy group of the modified epoxy resin during the preparation of the concrete to form a chemical bond, improving the curing degree of the concrete and enhancing the mechanical properties and crack resistance of the concrete;

[0125] By comparing the data of Comparative Example 3 and Example 2, it is found that the flexural strength, compressive strength and splitting tensile strength of the low-carbon crack-resistant concrete prepared in Comparative Example 1 all decrease, and the linear expansion coefficient and the wear amount after 45 cycles increase. This shows that in the present invention, bisphenol A epoxy resin and a silane coupling agent containing a silicon-oxygen bond are grafted together to prepare a modified epoxy resin. The epoxy groups in the modified epoxy resin can form chemical bonding 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 bond introduced in the modified epoxy resin has a relatively high bond energy, which can delay the thermal decomposition process of the epoxy resin, further improving the high-temperature resistance of the concrete. The benzene ring in the modified epoxy resin is a rigid structure, which together with the Si-O-B-O flexible chain segment improves the strength and toughness of the concrete.

[0126] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A low-carbon crack-resistant concrete, characterized in that: The raw material composition includes the following parts by weight: 3-5 parts of modified composite fiber, 50-60 parts of recycled fine aggregate, 5-6 parts of fly ash, 32-45 parts of cement, 10-15 parts of modified epoxy resin, 90-100 parts of modified recycled coarse aggregate, 8-12 parts of curing agent and 7-13 parts of auxiliary additives.

2. A low-carbon crack-resistant concrete according to claim 1, characterized in that: The recycled fine aggregate is recycled rubber particles, the curing agent is 4,4-diaminodiphenylmethane, the auxiliary additives are a water reducer, an air entraining agent, a dispersant, a viscosity regulator and a defoamer in a mass ratio of 100:10:300:5:1, the water reducer is a polycarboxylic acid water reducer, the air entraining agent is one or two of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate, the dispersant is deionized water, the viscosity regulator is hydroxypropyl methylcellulose ether, and the defoamer is one or two of polydimethylsiloxane and tributyl phosphate.

3. A low-carbon crack-resistant concrete according to claim 1, characterized in that: The modified recycled coarse aggregate is prepared by the following steps: A1. Place the recycled coarse aggregate and saturated calcium hydroxide solution in a reactor, soak at room temperature for 20-24 hours, and dry to obtain alkalized recycled coarse aggregate; A2, placing the alkalized regenerated coarse aggregate in a reactor and vacuum carbonizing it to obtain carbonized regenerated coarse aggregate; A3. Place carbonized recycled coarse aggregate, deionized water and nano-silica sol in a reactor, immerse at room temperature for 24-36 hours, and dry to obtain modified recycled coarse aggregate.

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

5. The low-carbon crack-resistant concrete according to claim 1, characterized in that: The modified composite fiber is prepared by the following steps: B1. Place basalt fiber and deionized water in a reaction kettle, heat to 100°C, stir at a speed of 200-250 r / min for 1-1.5 h, and dry to obtain a basalt fiber dispersion; B2, placing the basalt fiber dispersion and the sodium hydroxide solution in a reaction kettle, stirring for 25-45 minutes, and post-treating to obtain pretreated basalt fiber; B3. Place the pretreated basalt fiber, regenerated glass fiber, KH-550, deionized water and ethanol in a reactor, heat to 50-60° C., keep the temperature for 30-60 minutes, and post-treat to obtain a modified composite fiber.

6. A low-carbon crack-resistant concrete according to claim 5, characterized in that: In step B1, the dosage ratio of the basalt fiber and deionized water is 100-120g:1000-1500mL; in step B2, the concentration of the sodium hydroxide is 15-20wt%, and the dosage ratio of the basalt fiber dispersion and the sodium hydroxide solution is 150-180g:1000-1500mL; in step B3, the dosage ratio of the pretreated basalt fiber, the regenerated glass fiber, KH-550, the deionized water and the ethanol is 200-220g:100-150g:50-60g:50-80mL:800-1000mL.

7. The low-carbon crack-resistant concrete according to claim 1, characterized in that: The modified epoxy resin is prepared by the following steps: C1. Place 4-tolueneboric acid, KH-560, deionized water and 1,2-dichloroethane in a reactor protected by nitrogen atmosphere, heat to 50-60°C, keep warm for 4-8h, and post-treat to obtain intermediate I; C2. Place intermediate I, bisphenol A epoxy resin and ethanol in a reactor protected by nitrogen atmosphere, add dilute hydrochloric acid solution to adjust the pH to 6±0.5, raise the temperature to 45-55°C, keep the temperature for reaction for 2-4h, and post-treat to obtain modified epoxy resin.

8. The low-carbon crack-resistant concrete according to claim 7, characterized in that: In step C1, the amount ratio of 4-tolueneboric acid, 3-mercaptopropyltriethoxysilane, deionized water and 1,2-dichloroethane is 100g:50-60g:10-15mL:1000-1500mL; in step C2, the concentration of dilute hydrochloric acid is 0.5-1mol / L, and the amount ratio of intermediate I, bisphenol A type epoxy resin and ethanol is 200-250g:400-500g:5000-5500mL.

9. A method for preparing low-carbon crack-resistant concrete according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Place the modified composite fiber, recycled fine aggregate, fly ash and cement in a stirring tank, mix them evenly, add the modified epoxy resin and the modified recycled coarse aggregate, stir for 1-3 minutes, add the curing agent and auxiliary additives, stir for 3-5 minutes, and obtain a concrete precursor; S2. Inject the concrete precursor into a plastic test mold, place it on a vibration table, vibrate for 1-2 minutes, and cure to obtain crack-resistant concrete.

10. The method for preparing low-carbon crack-resistant concrete according to claim 9, characterized in that: In step S2, the curing step includes: placing the vibrated plastic test mold in a curing room at a temperature of 20-22°C, covering it with a plastic film, leaving it to stand for 20-24 hours, demoulding it, soaking it in room temperature water for 20-24 hours, and drying it to obtain crack-resistant concrete.

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