Environmentally friendly recycled concrete and preparation method thereof

Abstract

This application discloses an environmentally friendly recycled concrete and its preparation method, relating to the field of recycled concrete. The concrete comprises the following components by weight: 70-80 parts cement, 20-30 parts slag powder, 80-100 parts modified recycled coarse aggregate, 120-150 parts gravel, 120-150 parts sand, 30-40 parts water, and 1-2 parts water reducer. The modified recycled coarse aggregate is coated with an organosilicon-modified acrylic resin. The raw materials of the organosilicon-modified acrylic resin include: hydroxyl acrylic resin, epoxy compound with vinyl group, and siloxane compound with silicon hydrogen group. The mass ratio of the hydroxyl acrylic resin, epoxy compound with vinyl group, and siloxane compound with silicon hydrogen group is 100:15-30:20-30. This application can effectively alleviate the problem of reduced concrete strength and impermeability caused by the use of recycled coarse aggregate.

Description

Technical Field

[0001] The present application relates to the field of recycled concrete, and in particular to an environmentally friendly recycled concrete and a preparation method thereof. Background Art

[0002] Recycled concrete is made by partially or completely replacing natural aggregate with recycled aggregate, which is obtained from crushing and processing waste concrete. It offers significant advantages in resource recycling, reducing the environmental impact of construction waste and reducing the need for natural aggregate mining.

[0003] However, recycled aggregates have numerous inherent flaws. Their high porosity and the numerous cracks created during mechanical crushing result in a complex internal pore structure and increased connectivity after curing, significantly compromising the density of recycled concrete. In terms of strength, due to the loose internal structure, its compressive strength and other indicators struggle to reach the same levels as conventional concrete. Regarding impermeability, the numerous pores and cracks provide channels for liquid penetration, making it difficult to effectively prevent liquid intrusion when faced with water pressure. Summary of the Invention

[0004] In order to solve the shortcomings of recycled concrete in strength and impermeability, the present application provides an environmentally friendly recycled concrete and a preparation method thereof.

[0005] In a first aspect, the present application provides an environmentally friendly recycled concrete comprising the following components in parts by weight:

[0006] 70-80 parts of cement, 20-30 parts of slag powder, 80-100 parts of modified recycled coarse aggregate, 120-150 parts of gravel, 120-150 parts of sand, 30-40 parts of water, 1-2 parts of water reducer;

[0007] The surface of the modified recycled coarse aggregate is coated with an organosilicon-modified acrylic resin. The raw materials of the organosilicon-modified acrylic resin include: hydroxy acrylic resin, an epoxy compound with a vinyl group, and a siloxane compound with a silicon hydrogen group. The mass ratio of the hydroxy acrylic resin, the epoxy compound with a vinyl group, and the siloxane compound with a silicon hydrogen group is 100:15-30:20-30.

[0008] In any of the above technical solutions, the preparation method of the organosilicon-modified acrylic resin is as follows:

[0009] Mixing a hydroxy acrylic resin, an epoxy compound having a vinyl group and a double metal cyanide, heating and performing a ring-opening reaction to obtain a vinyl-terminated acrylic resin;

[0010] The vinyl terminated acrylic resin, the siloxane compound having a silane hydrogen group and the platinum catalyst are mixed, and the temperature is raised to carry out a silylation hydrogen addition reaction to obtain an organosilicon modified acrylic resin.

[0011] In any of the above technical solutions, the ring-opening reaction is carried out in propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, propylene glycol methyl ether acetate, propylene glycol methyl ether propionate, propylene glycol ethyl ether propionate, ethylene glycol monoethyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, diethylene glycol ethyl ether acetate or diethylene glycol butyl ether acetate solvent.

[0012] In any of the above technical solutions, the epoxy compound having a vinyl group is selected from glycidyl methacrylate and / or allyl alcohol glycidyl ether.

[0013] In any of the above technical solutions, the siloxane compound having a silicon hydride group is one or a combination of trimethoxysilane, triethoxysilane, and methyldimethoxysilane.

[0014] In any of the above technical solutions, the mass percentage content of hydroxyl groups in the hydroxyl acrylic resin is 2 to 4%.

[0015] In any of the above technical solutions, the temperature of the ring-opening reaction is 105-120°C, and the temperature of the hydrosilylation reaction is 70-90°C.

[0016] The organosilicon-modified acrylic resin attached to the surface of the recycled coarse aggregate in this application can, on the one hand, physically block aggregate pores and, on the other hand, utilize its organosilicon segments to increase the aggregate's hydrophobicity, thereby improving the impermeability of the recycled concrete. Secondly, the resin incorporates siloxane groups, which hydrolyze during the concrete mixing process to produce silanol groups. These groups can cross-link with silanol groups in cement hydration products (such as calcium silicate gel), thereby strengthening the bond between the recycled coarse aggregate and the cementitious material, and thus improving the concrete's strength. Thus, the organosilicon-modified acrylic resin in this application can simultaneously improve the impermeability and strength of recycled concrete.

[0017] It should be noted that in the preparation process of the above-mentioned silicone-modified acrylic resin, the hydroxy acrylic resin and the epoxy compound having a vinyl group are subjected to ring-opening polymerization under the catalysis of double metal cyanide, and unsaturated vinyl groups are introduced into the acrylic resin. Then, a hydrosilylation reaction is carried out with a siloxane compound having a silicon hydrogen group to obtain an acrylic resin having a silicon hydrogen group, thereby achieving cross-linking of the resin with the cement hydration product.

[0018] In any of the above technical solutions, the components further include 0.1 to 0.5% by mass of cement of hydroxycarboxylic acid or hydroxycarboxylate.

[0019] In any of the above technical solutions, the hydroxycarboxylic acid is selected from one or more of citric acid, gluconic acid, and salicylic acid.

[0020] In any of the above technical solutions, the water reducer is a polycarboxylate water reducer.

[0021] The use of the above-mentioned organosilicon-modified acrylic resin will accelerate the crystallization and solidification process of cement hydration products, which is not conducive to the slow growth of crystals to form a stable and dense structure, and reduces the density and strength of concrete. To this end, the present application helps to alleviate the above-mentioned problems by adding the above-mentioned hydroxycarboxylic acid or hydroxycarboxylate.

[0022] In any of the above technical solutions, the slag powder fineness is 400-500m 2 / kg, and the activity index is not less than 70% in 7 days.

[0023] In any of the above technical solutions, the stones are made of continuously graded particles.

[0024] In any of the above technical solutions, the sand is medium sand in zone II with a fineness modulus of 2.3 to 3.0.

[0025] In any of the above technical solutions, the cement is silicate cement.

[0026] In any of the above technical solutions, the particle size of the modified recycled coarse aggregate is 5 to 31.5 mm.

[0027] In a second aspect, the present application provides a method for preparing environmentally friendly recycled concrete, which is obtained by uniformly mixing cement, slag powder, gravel, sand, modified recycled coarse aggregate, water and other raw materials according to any of the above-mentioned recycled concrete ratios.

[0028] In summary, this application has the following beneficial effects:

[0029] This application uses silicone-modified acrylic resin containing siloxane groups to modify the surface of recycled coarse aggregate, which can give the recycled aggregate good hydrophobicity and reactivity, achieve cross-linking reaction with cementitious materials, and effectively compensate for the loss of anti-permeability and strength properties of recycled concrete. DETAILED DESCRIPTION

[0030] Preparation Example

[0031] Preparation Example 1

[0032] A modified recycled coarse aggregate is prepared according to the following steps:

[0033] Silicone modified acrylic resin

[0034] Step 1: Add 800 mL of propylene glycol methyl ether acetate and 1000 g of hydroxylated acrylic resin (hydroxyl content 3%) to a reactor and purge the air from the reactor with nitrogen. Then, add 230 g of glycidyl methacrylate and 30 ppm of double metal cyanide (relative to the total amount of hydroxylated acrylic resin and glycidyl methacrylate) to the reactor. Raise the temperature to 120°C for ring-opening polymerization. The reaction is complete after 8 hours. The reaction product is passed to a rotary evaporator, where the propylene glycol methyl ether acetate and unreacted raw materials are removed under reduced pressure to obtain a vinyl-terminated acrylic resin.

[0035] Step 2: The vinyl-terminated acrylic resin prepared above and 260 g of trimethoxysilane were placed in a reaction kettle and stirred evenly. Then, 50 ppm of divinyltetramethylsiloxane-coordinated platinum catalyst (0.5% platinum content) was added. The temperature was raised to 80°C and the reaction was carried out for 6 hours. After the reaction was completed, the mixture was cooled and the unreacted trimethoxysilane was removed by vacuum to obtain a silicone-modified acrylic resin.

[0036] Preparation of modified recycled coarse aggregate

[0037] Step 3: Take 1000g of silicone-modified acrylic resin and 600g of ethylene glycol monoethyl ether acetate, mix them, and stir for 30 minutes to obtain a resin solution. Immerse the recycled coarse aggregate (5-20mm continuous grading) in the resin solution. After soaking for 3 minutes, filter and dry to obtain modified recycled coarse aggregate.

[0038] Preparation Example 2

[0039] A modified recycled coarse aggregate is prepared according to the following steps:

[0040] Step 1: Add 800 mL of propylene glycol methyl ether acetate and 1000 g of hydroxylated acrylic resin (hydroxyl content 3%) to a reactor and purge the air from the reactor with nitrogen. Then, add 180 g of allyl alcohol glycidyl ether and 30 ppm of double metal cyanide (relative to the total amount of hydroxylated acrylic resin and allyl alcohol glycidyl ether) to the reactor. Raise the temperature to 115°C for ring-opening polymerization. The reaction is complete after 10 hours. The reaction product is passed to a rotary evaporator, and the propylene glycol methyl ether acetate and unreacted raw materials are removed under reduced pressure to obtain a vinyl-terminated acrylic resin.

[0041] Step 2: The vinyl-terminated acrylic resin prepared above and 200 g of trimethoxysilane were placed in a reaction kettle and stirred evenly. Then, 50 ppm of divinyltetramethylsiloxane-coordinated platinum catalyst (0.5% platinum content) was added. The temperature was raised to 85°C and the reaction was carried out for 5 hours. After the reaction was completed, the mixture was cooled and the unreacted trimethoxysilane was removed by vacuum to obtain a silicone-modified acrylic resin.

[0042] Preparation of modified recycled coarse aggregate

[0043] Step 3: Take 1000g of silicone-modified acrylic resin and 600g of ethylene glycol monoethyl ether acetate, mix them, and stir for 30 minutes to obtain a resin solution. Immerse the recycled coarse aggregate (5-20mm continuous grading) in the resin solution. After soaking for 3 minutes, filter and dry to obtain modified recycled coarse aggregate.

[0044] Preparation Example 3

[0045] A modified recycled coarse aggregate is prepared according to the following steps:

[0046] Step 1: Add 800 mL of propylene glycol methyl ether and 1000 g of hydroxylated acrylic resin (hydroxyl content 4%) to a reactor and purge the air from the reactor with nitrogen. Then, add 290 g of glycidyl methacrylate and 30 ppm of double metal cyanide (relative to the total amount of hydroxylated acrylic resin and glycidyl methacrylate) to the reactor. Raise the temperature to 120°C for ring-opening polymerization. The reaction is complete after 8 hours. The reaction product is passed to a rotary evaporator, and the propylene glycol methyl ether and unreacted raw materials are removed under reduced pressure to obtain a vinyl-terminated acrylic resin.

[0047] Step 2: The vinyl-terminated acrylic resin prepared above and 300 g of methyldimethoxysilane were placed in a reaction kettle and stirred evenly. Then, 50 ppm of divinyltetramethylsiloxane-coordinated platinum catalyst (0.5% platinum content) was added. The temperature was raised to 80°C and the reaction was carried out for 6 hours. After the reaction was completed, the mixture was cooled and the unreacted methyldimethoxysilane was removed by vacuum to obtain a silicone-modified acrylic resin.

[0048] Preparation of modified recycled coarse aggregate

[0049] Step 3: Take 1000g of silicone-modified acrylic resin and 600g of ethylene glycol monoethyl ether acetate, mix them, and stir for 30 minutes to obtain a resin solution. Immerse the recycled coarse aggregate (5-20mm continuous grading) in the resin solution. After soaking for 3 minutes, filter and dry to obtain modified recycled coarse aggregate.

[0050] Preparation Example 4

[0051] A modified recycled coarse aggregate is different from Preparation Example 1 in that Step 3 is directly performed without Step 2; and the vinyl terminated acrylic resin obtained in Step 1 is a silicone modified acrylic resin.

[0052] Preparation Example 5

[0053] A modified recycled coarse aggregate is prepared in accordance with Preparation Example 1, wherein the organosilicon-modified acrylic resin prepared in step 2 is replaced by a commercially available organosilicon-modified acrylic resin (acrylic resin SJ-804). Example

[0054] The cement used in the following examples and comparative examples is P.O42.5 cement; the gravel is 5-20 mm continuously graded natural crushed stone with a mud content of 0.8%; the sand is Zone II medium sand with a fineness modulus of 2.6; the slag powder is S95 grade slag powder with a fineness of 400-500 m2 / kg and a 7-day activity index of 95%; and the polycarboxylate water reducer is Sika® ViscoCrete®-530P polycarboxylate water reducer.

[0055] Example 1, an environmentally friendly recycled concrete, weighing 7.6 kg of cement, 2.4 kg of slag powder, 14.2 kg of stone, 9 kg of modified recycled coarse aggregate of Preparation Example 1, 13.6 kg of sand, 1.5 kg of polycarboxylic acid water reducer, 23 g of citric acid, and 3.6 kg of water into a mixer, mixing evenly to obtain the concrete.

[0056] Example 2, an environmentally friendly recycled concrete, weighing 7.0 kg of cement, 2.8 kg of slag powder, 12.5 kg of stone, 10 kg of modified recycled coarse aggregate of Preparation Example 2, 14.3 kg of sand, 1.6 kg of polycarboxylic acid water reducer, 35 g of citric acid, and 4.0 kg of water into a mixer, mixing evenly to obtain the concrete.

[0057] Example 3, an environmentally friendly recycled concrete, weighing 8.0 kg of cement, 2.0 kg of slag powder, 14.6 kg of stone, 8 kg of modified recycled coarse aggregate of Preparation Example 3, 12.5 kg of sand, 1.2 kg of polycarboxylate water reducer, 10 g of sodium citrate, and 3.5 kg of water into a mixer, mixing evenly to obtain the concrete.

[0058] Example 4 is an environmentally friendly recycled concrete, which differs from Example 1 in that citric acid is not added. Comparative Example

[0059] Comparative Example 1 is an environmentally friendly recycled concrete, which differs from Example 1 in that the modified recycled coarse aggregate of Preparation Example 1 is replaced by an equal amount of the modified recycled coarse aggregate of Preparation Example 4.

[0060] Comparative Example 2 is an environmentally friendly recycled concrete, which differs from Example 1 in that the modified recycled coarse aggregate of Preparation Example 1 is replaced by an equal amount of the modified recycled coarse aggregate of Preparation Example 5.

[0061] Performance testing

[0062] Test 1: Determine the 7-day and 28-day compressive strengths of recycled concrete according to GB / T 17671-2021, Test Method for Strength of Cement Mortar (ISO Method). Calculate the arithmetic mean of the compressive strengths of the six specimens as the average compressive strength for the group.

[0063] Test 2: The penetration height of concrete specimens was measured according to the "Water Penetration Resistance Test - Water Penetration Height Method" in GB / T 50082-2009 to characterize the water penetration resistance of recycled concrete. The water pressure was generally maintained at a constant 1.2 ± 0.05 MPa for 24 hours before the test was terminated. The specimen was removed and split in half along its longitudinal section. Once the water mark was clearly visible, it was traced with Chinese ink to form the water penetration profile. The water penetration height was then measured along ten lines using a trapezoidal glass plate to an accuracy of 1 mm. The arithmetic mean of the water penetration heights at these ten measurement points was taken as the water penetration height for the specimen. The arithmetic mean of the water penetration heights of the six specimens was then calculated as the average water penetration height for the group of specimens.

[0064] Table 1. Test results

[0065]

[0066] Results Analysis: Compared to Comparative Examples 1-2, which used commercially available or ungrafted silicone-modified acrylic resins, Examples 1-4, which used the silicone-modified acrylic resins of the present application, exhibited higher compressive strength and lower penetration heights, demonstrating that Examples 1-4 exhibited superior strength and impermeability. This may be due to the fact that the siloxane groups in the silicone-modified acrylic resins of the present application, upon hydrolysis, can generate silanol groups, which react and cross-link with the silanol groups in cement hydration products, thereby improving the strength and density of the recycled coarse aggregate and the internal structure of the concrete. Furthermore, the siloxane-silicon chains formed by the reaction possess excellent hydrophobicity, contributing to improved impermeability.

[0067] Compared to Examples 1-3, the recycled concrete of Example 4 exhibited superior initial strength (7-day compressive strength), but exhibited inferior late-stage strength (28-day compressive strength) and impermeability. This may be due to the siloxane groups in the silicone-modified acrylic resin accelerating the crystallization and solidification of the hydration products during the initial hydration phase, hindering the formation of a dense and stable crystal structure and potentially inducing the formation of thermal cracks, leading to the aforementioned consequences. The hydroxypropionic acid or hydroxypropionic acid salt added in Examples 1-3 may inhibit the accelerating effect of the modified resin through steric hindrance and / or electrostatic effects.

[0068] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An environmentally friendly recycled concrete, characterized in that: The composition comprises the following components in parts by weight: 70-80 parts of cement, 20-30 parts of slag powder, 80-100 parts of modified recycled coarse aggregate, 120-150 parts of gravel, 120-150 parts of sand, 30-40 parts of water, 1-2 parts of water reducer, 0.1-0.5% of the mass of cement hydroxycarboxylic acid or hydroxycarboxylate; The surface of the modified recycled coarse aggregate is coated with an organosilicon-modified acrylic resin. The raw materials of the organosilicon-modified acrylic resin include: hydroxy acrylic resin, an epoxy compound with a vinyl group, and a siloxane compound with a silicon hydrogen group. The mass ratio of the hydroxy acrylic resin, the epoxy compound with a vinyl group, and the siloxane compound with a silicon hydrogen group is 100:15-30:20-30.

2. The concrete according to claim 1, characterized in that The preparation method of the organosilicon-modified acrylic resin is as follows: Mixing a hydroxy acrylic resin, an epoxy compound having a vinyl group and a double metal cyanide, heating and performing a ring-opening reaction to obtain a vinyl-terminated acrylic resin; The vinyl terminated acrylic resin, the siloxane compound having a silane hydrogen group and the platinum catalyst are mixed, and the temperature is raised to carry out a silylation hydrogen addition reaction to obtain an organosilicon modified acrylic resin.

3. The concrete according to claim 1, characterized in that The epoxy compound having a vinyl group is selected from glycidyl methacrylate and / or allyl alcohol glycidyl ether.

4. The concrete according to claim 1, characterized in that The siloxane compound having a silicon hydrogen group is one or a combination of trimethoxysilane, triethoxysilane and methyldimethoxysilane.

5. The concrete according to claim 1, characterized in that The mass percentage content of hydroxyl groups in the hydroxyl acrylic resin is 2-4%.

6. The concrete according to claim 2, characterized in that The temperature of the ring-opening reaction is 105-120°C, and the temperature of the hydrosilylation reaction is 70-90°C.

7. The concrete according to claim 1, characterized in that The water reducer is a polycarboxylate water reducer.

8. The concrete according to claim 1, characterized in that The slag powder has a fineness of 400 to 500 m2 / kg and a 7d activity index of not less than 70%.

9. A method for preparing environmentally friendly recycled concrete, characterized in that: The recycled concrete is prepared by uniformly mixing cement, slag powder, gravel, sand, modified recycled coarse aggregate, water and other raw materials according to the mix ratio of any one of claims 1 to 8.

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