Recycled aggregate concrete and preparation method thereof

Abstract

The present invention provides a recycled aggregate concrete and a preparation method thereof, comprising the following components by weight: 280-300 parts of cement, 160-180 parts of water, 120-170 parts of fly ash, 140-200 parts of modified rubber, 120-160 parts of construction waste, 30-45 parts of a water reducer, and 20-30 parts of a mineral admixture. The present invention selects a scientifically proportioned combination of cement, fly ash, modified rubber, construction waste, water reducer, water, and mineral admixtures. The resulting recycled aggregate concrete exhibits a flexural strength of 3.36-3.57 MPa and a splitting strength of 1.96-2.40 MPa at 28 days of age, indicating excellent flexural and splitting strengths, as well as good toughness and deformation properties. After 100 freeze-thaw cycles, the mass loss rate of the specimen does not exceed 5%, meeting the failure standard, and exhibits good frost resistance, meeting the requirements.

Description

Technical Field

[0001] The present invention relates to the field of concrete, in particular to recycled aggregate concrete and a preparation method thereof. Background Art

[0002] Concrete is one of the most widely used civil engineering materials in modern building structures. It has evolved from a single-property building material to a multi-property building material. Different types of concrete have different performance requirements depending on the specific engineering application, leading to the development of various types of concrete. Self-compacting concrete, for example, offers advantages such as good fluidity, a short construction cycle, and low cost, making it an excellent choice for complex structural engineering applications.

[0003] With the overuse of building materials, research on recycled concrete has become a hot topic. This involves manually crushing, cleaning, and grading waste concrete, using it as aggregate. This is then mixed with a specific proportion and grade to partially or completely replace natural aggregates like sand and gravel, and then made into concrete. Recycled concrete can effectively alleviate the overuse of natural aggregates like sand and gravel, while also reducing the environmental impact of construction waste.

[0004] Recycled aggregate is made from waste concrete from construction waste through crushing, screening, cleaning, and drying. Its surface is rough, porous, and angular, resulting in a loose structure and harmful pores and microcracks within the recycled aggregate. When used in concrete, this results in high porosity and water absorption. Consequently, these inherent defects in recycled aggregate lead to unsatisfactory mechanical and durability properties in recycled concrete. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a recycled aggregate concrete and a preparation method thereof, which can effectively alleviate the excessive use of natural aggregates such as sand and gravel and reduce the harm of construction waste to the environment.

[0006] The technical solution of the present invention is achieved as follows:

[0007] A recycled aggregate concrete comprises the following components in parts by weight: 280-300 parts of cement, 160-180 parts of water, 120-170 parts of fly ash, 140-200 parts of modified rubber, 120-160 parts of construction waste, 30-45 parts of water reducing agent and 20-30 parts of mineral admixture.

[0008] Further description, the following components are included in parts by weight: 290 parts of cement, 170 parts of water, 140 parts of fly ash, 180 parts of modified rubber, 140 parts of construction waste, 32 parts of water reducing agent and 25 parts of mineral admixture.

[0009] Further explanation, the preparation method of the modified rubber includes: adding polyamic acid, acetic anhydride and methyl pyrrolidone into rubber, reacting with inert gas, and vacuum drying to obtain the modified rubber.

[0010] It is further described that the mass ratio of the rubber, polyamic acid, acetic anhydride and methyl pyrrolidone is 1:1:0.6-0.8:0.4-0.5; the temperature of the inert gas reaction is 180-200°C, and the time of the inert gas reaction is 1-2 hours; and the vacuum drying is performed until the moisture content is less than 10%.

[0011] It is further explained that the construction waste is selected from at least one of discarded concrete blocks, bricks, and asphalt blocks;

[0012] The water reducer is a polycarboxylate water reducer;

[0013] The mineral admixture is at least one of volcanic ash, industrial waste talc powder, and shale ash mixture.

[0014] Further description includes the following steps: mixing cement, water, fly ash, modified rubber and construction waste, adding water reducing agent and mineral admixture, and ball milling to obtain recycled aggregate concrete.

[0015] It is further specified that the ball milling temperature is 80-90° C. and the ball milling time is 30-40 min.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention selects cement, fly ash, modified rubber, construction waste, water reducer, water and mineral admixtures in a scientific proportion, and the obtained recycled aggregate concrete has a flexural strength of 3.36-3.57 MPa and a splitting strength of 1.96-2.40 MPa at the age of 28 days, indicating that it has excellent flexural strength and splitting strength, and good toughness and deformation performance.

[0018] After 100 freeze-thaw cycles, the mass loss rate of the recycled aggregate concrete obtained by the present invention does not exceed 5%, reaching the destruction standard, and has good antifreeze performance, meeting the requirements.

[0019] In addition, the present invention selects modified rubber as the raw material of recycled aggregate concrete. The modified rubber is conducive to enhancing its compatibility with cement particles, helping to improve and improve the microstructure of concrete, and making the concrete transition to a durable fine-grained macrostructure, thereby improving the durability of the recycled concrete; when adding fly ash to improve the early flexural strength and splitting strength of the recycled concrete, adding a certain amount of mineral admixtures can better react with the cement paste, and the modified rubber powder cannot react with the cement paste. It can fill the microcracks in the microstructure of the concrete, and the modified rubber powder is added to the concrete by ball milling, the pore structure is improved, and the density and durability of the recycled concrete are increased. DETAILED DESCRIPTION

[0020] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0021] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0022] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0023] The shale ash of the present invention is selected from the shale ash of the oil shale boiling furnace power plant.

[0024] Example 1

[0025] A recycled aggregate concrete comprises the following components in parts by weight: 290 parts of cement, 170 parts of water, 140 parts of fly ash, 180 parts of modified rubber, 140 parts of waste bricks, 32 parts of polycarboxylate water reducer and 25 parts of shale ash.

[0026] The preparation method of the modified rubber comprises: adding polyamic acid, acetic anhydride and methyl pyrrolidone to rubber in a mass ratio of 1:1:0.7:0.4, reacting at 190°C in an inert gas for 1.5 hours, and vacuum drying until the moisture content is less than 10% to obtain the modified rubber.

[0027] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, modified rubber and bricks are mixed, polycarboxylic acid water reducer and shale ash are added, and ball milling is performed at 85° C. for 35 minutes to obtain the recycled aggregate concrete.

[0028] Example 2

[0029] A recycled aggregate concrete comprises the following components in parts by weight: 300 parts of cement, 180 parts of water, 170 parts of fly ash, 200 parts of modified rubber, 160 parts of waste concrete blocks, 45 parts of polycarboxylate water reducer and 30 parts of industrial waste talc.

[0030] The preparation method of the modified rubber comprises: adding polyamic acid, acetic anhydride and methyl pyrrolidone to rubber in a mass ratio of 1:1:0.8:0.5, reacting at 200°C in an inert gas atmosphere for 2 hours, and vacuum drying until the moisture content is less than 10% to obtain the modified rubber.

[0031] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, modified rubber and concrete blocks are mixed, polycarboxylate water reducer and industrial waste talc are added, and ball milling is performed at 90° C. for 40 minutes to obtain the recycled aggregate concrete.

[0032] Example 3

[0033] A recycled aggregate concrete comprises the following components in parts by weight: 280 parts of cement, 160 parts of water, 120 parts of fly ash, 140 parts of modified rubber, 120 parts of waste concrete blocks, 30 parts of polycarboxylate water reducer and 20 parts of volcanic ash.

[0034] The preparation method of the modified rubber comprises: adding polyamic acid, acetic anhydride and methyl pyrrolidone to rubber in a mass ratio of 1:1:0.6:0.4, reacting at 180°C in an inert gas atmosphere for 1 hour, and vacuum drying until the moisture content is less than 10% to obtain the modified rubber.

[0035] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, modified rubber and concrete blocks are mixed, polycarboxylic acid water reducer and volcanic ash are added, and ball milling is performed at 80° C. for 30 minutes to obtain the recycled aggregate concrete.

[0036] Test Example 1-Basic Properties of Concrete

[0037] The 28-day flexural strength and splitting strength of recycled aggregate concrete were measured according to the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GBT 50081-2019). The standard specimen dimensions for flexural strength are 150 mm × 150 mm × 550 mm, and the standard specimen dimensions for splitting strength are 150 mm × 150 mm × 150 mm. The mechanical properties of the recycled aggregate concretes in Examples 1-3 are shown in Table 1 below.

[0038] Table 1 Flexural strength and splitting strength of recycled aggregate concrete

[0039] project Flexural strength / MPa Splitting strength / MPa Example 1 3.36 2.40 Example 2 3.48 1.96 Example 3 3.57 2.38

[0040] As can be seen from the above table, the flexural strength of the recycled aggregate concrete obtained by the present invention at the age of 28 days is 3.36-3.57 MPa, and the splitting strength is 1.96-2.40 MPa, indicating that the recycled aggregate concrete obtained by selecting a scientifically proportioned cement, fly ash, modified rubber, construction waste, water reducer, water and mineral admixtures has excellent flexural strength and splitting strength, and good toughness and deformation properties.

[0041] Test Example 2-Concrete Durability

[0042] According to the Ministry of Housing and Urban-Rural Development of the People's Republic of China, GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (China Building Industry Press 2009), the rapid freezing method is used to determine the frost resistance of concrete. The concrete specimen is immersed in water for 4 days, the water is wiped off, and the initial weight of the specimen is weighed m0. The specimen is placed in a specimen box with the specimen located in the center of the specimen box. The specimen box is placed in the specimen rack in the freeze-thaw chamber and tap water is injected into the specimen box. During the entire test process, the liquid level is ensured to be at least 5mm above the specimen. The parameters of the rapid freeze-thaw test are set according to the requirements, and the mass of the specimen is measured every 25 freeze-thaw cycles. i , until 100 freeze-thaw cycles are reached or the specimen is destroyed.

[0043] The mass loss rate of the specimen is △m=(m0-m i ) / m0×100%, where △m is the mass loss rate after a certain number of freeze-thaw cycles (%), m0 is the mass of the specimen before freeze-thaw (kg), and m i is the mass of the specimen after i freeze-thaw cycles (kg).

[0044] Table 2 Durability test of recycled aggregate concrete

[0045]

[0046] As can be seen from the above table, after 100 freeze-thaw cycles, the mass loss rate of the recycled aggregate concrete obtained by the present invention did not exceed 5%, meeting the failure standard, indicating that the recycled aggregate concrete prepared by the present invention using cement, fly ash, modified rubber, construction waste, water reducer, water and mineral admixtures has good frost resistance and meets the requirements.

[0047] Example 4

[0048] A recycled aggregate concrete comprises the following components in parts by weight: 280 parts of cement, 160 parts of water, 120 parts of fly ash, 140 parts of modified rubber, 120 parts of waste concrete blocks, 30 parts of polycarboxylate water reducer and 20 parts of volcanic ash.

[0049] The preparation method of the modified rubber comprises: adding polyamic acid, acetic anhydride and methyl pyrrolidone to rubber in a mass ratio of 1:1:0.6:0.4, reacting at 180°C in an inert gas atmosphere for 1 hour, and vacuum drying until the moisture content is less than 10% to obtain the modified rubber.

[0050] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, modified rubber and concrete blocks are mixed, polycarboxylic acid water reducer and volcanic ash are added, and the mixture is sheared at 6000 rpm / min for 30 minutes to obtain the recycled aggregate concrete.

[0051] After testing, it was found that when the number of freeze-thaw cycles was 100, the mass loss rate of the recycled aggregate concrete specimen was 2.86%.

[0052] Example 5

[0053] A recycled aggregate concrete comprises the following components in parts by weight: 280 parts of cement, 160 parts of water, 120 parts of fly ash, 140 parts of modified rubber, 120 parts of waste concrete blocks, 30 parts of polycarboxylate water reducer and 20 parts of volcanic ash.

[0054] The preparation method of the modified rubber comprises: soaking the rubber in a sodium hydroxide solution at a volume ratio of 1:2.5 for 24 hours, taking out the rubber and vacuum drying it, immersing it in a potassium permanganate solution at 60°C for 30 minutes, adding hydrogen peroxide until the pH of the system reaches 5.0, continuing to soak for 2 hours, adjusting the pH of the system to 8.0, adding urea, soaking it at 90°C for 30 minutes, rinsing and drying it to obtain the modified rubber.

[0055] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, modified rubber and concrete blocks are mixed, polycarboxylic acid water reducer and volcanic ash are added, and the mixture is sheared at 6000 rpm / min for 30 minutes to obtain the recycled aggregate concrete.

[0056] After testing, it was found that when the number of freeze-thaw cycles was 100, the mass loss rate of the recycled aggregate concrete specimen was 2.56%.

[0057] Comparative Example 1

[0058] A recycled aggregate concrete comprises the following components in parts by weight: 280 parts of cement, 160 parts of water, 120 parts of fly ash, 60 parts of modified rubber, 120 parts of waste concrete blocks, 30 parts of polycarboxylate water reducer and 20 parts of volcanic ash.

[0059] The preparation method of the modified rubber comprises: adding polyamic acid, acetic anhydride and methyl pyrrolidone to rubber in a mass ratio of 1:1:0.6:0.4, reacting at 180°C in an inert gas atmosphere for 1 hour, and vacuum drying until the moisture content is less than 10% to obtain the modified rubber.

[0060] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, modified rubber and concrete blocks are mixed, polycarboxylic acid water reducer and volcanic ash are added, and ball milling is performed at 80° C. for 30 minutes to obtain the recycled aggregate concrete.

[0061] After testing, it was found that when the number of freeze-thaw cycles reached 100 times, the recycled aggregate concrete specimen could not maintain the specimen properties and had been damaged, indicating that modified rubber can improve the frost resistance of concrete, and the optimal addition amount should reach more than 140 parts.

[0062] Comparative Example 2

[0063] A recycled aggregate concrete comprises the following components in parts by weight: 280 parts of cement, 160 parts of water, 120 parts of fly ash, 140 parts of 40-mesh waste rubber, 120 parts of waste concrete blocks, 30 parts of polycarboxylate water reducer and 20 parts of volcanic ash.

[0064] The preparation method of the recycled aggregate concrete is as follows: cement, water, fly ash, waste rubber and concrete blocks are mixed, polycarboxylic acid water reducer and volcanic ash are added, and ball milling is performed at 80° C. for 30 minutes to obtain the recycled aggregate concrete.

[0065] After testing, it was found that when the number of freeze-thaw cycles reached 75 times, the recycled aggregate concrete specimen could not maintain the specimen properties and had been damaged. The modified rubber is beneficial to enhance its compatibility with cement particles, helps to improve and improve the microstructure of concrete, and makes the concrete transition to a durable fine-grained macrostructure, thereby improving the durability of recycled concrete.

[0066] At the same time, when adding fly ash to improve the early flexural strength and splitting strength of recycled concrete, adding a certain amount of mineral admixtures (volcanic ash, industrial waste talc or shale ash mixture) can better react with cement paste, and modified rubber powder cannot react with cement paste. It can fill the microcracks in the microstructure of concrete, and by ball milling, the modified rubber powder is added to the concrete, the pore structure is improved, and the density and durability of the recycled concrete are increased.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A recycled aggregate concrete, characterized in that: The invention comprises the following components in parts by weight: 280-300 parts of cement, 160-180 parts of water, 120-170 parts of fly ash, 140-200 parts of modified rubber, 120-160 parts of construction waste, 30-45 parts of water reducing agent and 20-30 parts of mineral admixture; The preparation method of the modified rubber comprises: adding polyamic acid, acetic anhydride and methyl pyrrolidone into rubber, reacting with inert gas, and vacuum drying to obtain the modified rubber; The mass ratio of the rubber, polyamic acid, acetic anhydride and methyl pyrrolidone is 1:1:0.6-0.8:0.4-0.5; the temperature of the inert gas reaction is 180-200° C., and the time of the inert gas reaction is 1-2 hours; and the vacuum drying is performed until the moisture content is less than 10%.

2. A recycled aggregate concrete according to claim 1, characterized in that: The invention comprises the following components in parts by weight: 290 parts of cement, 170 parts of water, 140 parts of fly ash, 180 parts of modified rubber, 140 parts of construction waste, 32 parts of water reducing agent and 25 parts of mineral admixture.

3. A recycled aggregate concrete according to claim 1 or 2, characterized in that: The construction waste is selected from at least one of discarded concrete blocks, bricks, and asphalt blocks; The water reducer is a polycarboxylate water reducer; The mineral admixture is at least one of volcanic ash, industrial waste talc powder, and shale ash mixture.

4. The method for preparing recycled aggregate concrete according to any one of claims 1 to 3, wherein: The method comprises the following steps: mixing cement, water, fly ash, modified rubber and construction waste, adding a water reducing agent and mineral admixtures, and ball milling to obtain recycled aggregate concrete.

5. A method for preparing recycled aggregate concrete according to claim 4, characterized in that: The ball milling temperature is 80-90° C., and the ball milling time is 30-40 minutes.

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