A solid waste-based recycled concrete and its preparation method

Abstract

This invention discloses a solid waste-based recycled concrete and its preparation method, belonging to the field of building materials technology. Addressing the shortcomings of traditional recycled coarse aggregates from waste concrete sources—high water absorption, high porosity, low strength, and the formation of a complex microstructure and exceptionally weak bond between the aggregate and mortar interface during pouring, leading to low-performance recycled concrete—this invention proposes a strengthening scheme involving acid leaching of the recycled coarse aggregate followed by vacuum impregnation with a nano-silica epoxy emulsion. Through the synergistic strengthening of acid leaching and vacuum impregnation with the nano-silica epoxy emulsion, the strength of the recycled coarse aggregate is significantly improved, its water absorption and porosity are reduced, and the interface transition zone between the recycled coarse aggregate and mortar in the recycled concrete prepared from it is improved. The recycled coarse aggregate strengthening scheme provided by this invention is simple, and the prepared recycled concrete exhibits high strength and good impermeability, demonstrating promising prospects for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a solid waste-based recycled concrete and its preparation method. Background Technology

[0002] Recycled aggregate concrete technology is one of the most common and direct ways to utilize construction waste. However, compared with natural aggregate concrete, recycled aggregate concrete has obvious performance deficiencies. The main reason is that the surface of recycled coarse aggregate is covered with old mortar, which has defects such as strong water absorption, high porosity, and low strength. During pouring, a complex microstructure and abnormally weak bonding performance of aggregate-mortar interface transition zone (ITZ) is formed between recycled coarse aggregate and new mortar, resulting in a reduction in the performance of recycled aggregate concrete.

[0003] Currently, performance enhancement technologies for recycled concrete mainly focus on modifying recycled aggregates, including physical and chemical methods. Physical strengthening involves using mechanical equipment to reprocess simply crushed recycled aggregates without altering their microstructure and phase properties, removing cement mortar adhering to the surface and weakly bonded particle edges. Chemical strengthening involves using chemical reagents to alter the microstructure and phase properties of the inert gas (ITZ) of recycled aggregates, thereby modifying and strengthening the ITZ. While there is considerable research on strengthening methods for recycled aggregates, with varying principles, most are cumbersome and costly, hindering their widespread engineering application. Summary of the Invention

[0004] The purpose of this invention is to provide a solid waste-based recycled concrete and its preparation method. By using pulverized waste concrete as recycled coarse aggregate and strengthening it, not only is the porosity of the recycled coarse aggregate reduced, improving the impermeability of the resulting recycled concrete, but the strength of the recycled coarse aggregate is also enhanced, and the interfacial transition zone between the recycled coarse aggregate and mortar is improved, significantly improving the performance of the recycled concrete. The raw materials used in this invention are common and inexpensive, and the strengthening effect on recycled coarse aggregate is excellent, possessing broad prospects for widespread application.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention is to provide a method for strengthening recycled coarse aggregate, comprising the following steps:

[0007] The recycled coarse aggregate from waste concrete is impregnated in oxalic acid solution and drained, then vacuum impregnated in nano-silica epoxy emulsion, removed and cured to complete the strengthening of the recycled coarse aggregate.

[0008] This invention first uses oxalic acid to impregnate recycled coarse aggregate, aiming to allow the nano-silica epoxy emulsion to better penetrate the recycled coarse aggregate. The nano-silica epoxy emulsion is chosen as the reinforcing solution because, on the one hand, the nano-silica and the cured epoxy resin can effectively increase the strength of the recycled coarse aggregate; on the other hand, the film formed by the nano-silica epoxy emulsion on the surface of the recycled coarse aggregate can also enhance the impermeability of the recycled coarse aggregate, and can better adhere to concrete mortar, enhance the interfacial transition zone, and produce high-performance concrete.

[0009] Preferably, the particle size of the recycled coarse aggregate is 5-25 mm.

[0010] Preferably, the concentration of the oxalic acid solution is 1 to 1.5 mol / L.

[0011] Preferably, the vacuum degree of the vacuum impregnation is 0.05 to 0.08 MPa, and the time is 30 to 60 minutes.

[0012] Preferably, the nano-silica epoxy emulsion contains 5-12 wt.% nano-silica, has a water content of 10-20 wt.%, and the mass ratio of epoxy resin, curing agent, and emulsifier is 2:1-1.5:1-1.5.

[0013] Optionally, the epoxy resin in the nano-silica epoxy emulsion is bisphenol A type epoxy resin, the curing agent is isophorone diamine (IPDA), and the emulsifier is sodium dodecylbenzene sulfonate.

[0014] The second technical solution of the present invention provides a recycled coarse aggregate prepared according to the above-mentioned method for strengthening recycled coarse aggregate.

[0015] The third technical solution of the present invention provides a solid waste-based recycled concrete, which, by mass parts, comprises: 25-35 parts of composite cementitious material, 40-60 parts of the above-mentioned recycled coarse aggregate, 15-25 parts of fine aggregate, 0.3-0.8 parts of water-reducing agent, and 8-12 parts of water; the composite cementitious material is obtained by mixing cement, fly ash, and alkali activator in a mass ratio of 7:2:1.

[0016] Preferably, the alkaline activator is a mixture of sodium silicate and sodium hydroxide in a mass ratio of 3:1.

[0017] Preferably, the fine aggregate is river sand or manufactured sand with a fineness modulus of 2.6 to 3.0.

[0018] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of not less than 20%.

[0019] Fourth technical solution of the present invention: A method for preparing the above-mentioned solid waste-based recycled concrete, comprising the following steps:

[0020] Cement, fly ash, and alkali activator are mixed evenly, then mixed evenly with recycled coarse and fine aggregates, and finally water and water-reducing agent are added and stirred evenly to obtain solid waste-based recycled concrete.

[0021] The beneficial technical effects of the present invention are as follows:

[0022] This invention addresses the shortcomings of traditional recycled coarse aggregates from waste concrete sources, which are characterized by high water absorption, high porosity, low strength, and a complex microstructure and exceptionally weak bond between the aggregate and mortar in the aggregate-mortar interface transition zone during pouring, leading to low performance in the prepared recycled concrete. The invention proposes a strengthening scheme involving acid leaching of the recycled coarse aggregate followed by vacuum impregnation with a nano-silica epoxy emulsion. Through the synergistic strengthening of acid leaching and vacuum impregnation with the nano-silica epoxy emulsion, the strength of the recycled coarse aggregate is significantly improved, its water absorption and porosity are reduced, and the interface transition zone between the recycled coarse aggregate and the mortar in the recycled concrete prepared using it as a raw material is improved.

[0023] The recycled coarse aggregate strengthening scheme provided by this invention is simple, and the recycled concrete prepared has high strength and good impermeability. This scheme has good prospects for promotion and application. Detailed Implementation

[0024] With the acceleration of urbanization, a large amount of construction waste is generated, of which waste concrete accounts for a significant proportion. Traditional disposal methods, such as landfill, not only occupy land but also pollute the environment. Crushing and screening waste concrete and using it as recycled coarse aggregate in the preparation of new concrete is an effective way to realize the resource utilization of construction waste.

[0025] Waste concrete, as a recycled coarse aggregate, has significant advantages in the construction field, mainly in the following aspects:

[0026] 1. Resource conservation and recycling

[0027] Reduce the consumption of natural resources: Recycled coarse aggregates can replace natural sand and gravel, reducing the demand for mining non-renewable resources (such as natural gravel and rock) and alleviating the pressure of resource depletion.

[0028] Construction waste recycling: Waste concrete accounts for 30% to 50% of the total construction waste. Recycling can significantly reduce landfill volume and improve resource recycling efficiency.

[0029] 2. Environmental protection

[0030] Reduce carbon emissions: Compared to mining and transporting natural aggregates, the production of recycled coarse aggregates consumes less energy and emits less carbon (studies show that it can reduce the carbon footprint by about 20% to 30%).

[0031] Reduce land occupation and pollution: Avoid the damage to soil, groundwater and ecological environment caused by construction waste landfill, and alleviate the problem of "garbage surrounding the city".

[0032] 3. Economic benefits

[0033] Cost advantage: The production cost of recycled coarse aggregate is usually lower than that of natural aggregate (especially in areas with scarce natural resources or long transportation distances).

[0034] 4. Applicability of technical performance

[0035] Meeting the needs of medium and low strength: Recycled coarse aggregate can be used in non-structural or low-strength concrete (such as roadbed, floor, and infill layers), and its performance can be further improved by optimizing the mix proportion or pretreatment (such as strengthening and removing impurities).

[0036] When mixed with natural aggregates: When partially replacing natural aggregates (e.g., 30% to 50%), the mechanical properties of concrete (compressive strength, durability) can still meet the engineering requirements.

[0037] 5. Promote sustainable development

[0038] Compliant with green building standards: Certification systems such as LEED and BREEAM encourage the use of recycled materials and improve the environmental rating of projects.

[0039] Promoting a circular economy: forming a closed-loop model of "demolition-regeneration-new construction" to help the construction industry transform towards low carbon.

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0041] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0043] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0044] In the embodiments of this invention, "parts" refers to parts by mass.

[0045] Example 1

[0046] Preparation of solid waste-based recycled concrete:

[0047] (1) The waste concrete from the construction site is manually crushed and then fed into a jaw concrete crusher to screen out particles with a particle size of 5-25mm. The screened particles are then immersed in an oxalic acid solution with a concentration of 1mol / L for 24 hours and then taken out and drained.

[0048] (2) Take 100 parts of bisphenol A epoxy resin and 20 parts of nano silica and stir evenly. Then add 50 parts of curing agent IPDA and stir evenly. Then add sodium dodecylbenzene sulfonate emulsifier and stir evenly. Then slowly add 40 parts of water while performing high-speed shearing to obtain nano silica epoxy emulsion.

[0049] (3) Add the granules after acid leaching in step (1) to the nano-silica epoxy emulsion prepared in step (2), immerse them under a vacuum of 0.08 MPa for 60 min, take them out and solidify them to obtain modified recycled coarse aggregate.

[0050] (4) Take 70 parts of PO42.5 cement and fly ash (specific surface area 650 m²). 2 Mix 20 parts of sodium silicate and 2.5 parts of sodium hydroxide evenly, then add 200 parts of modified recycled coarse aggregate and 80 parts of manufactured sand with a fineness modulus of 2.6, mix evenly, and finally add 3 parts of polycarboxylate superplasticizer (water reduction rate 25%) and 40 parts of water, mix evenly to obtain solid waste-based recycled concrete.

[0051] Example 2

[0052] Preparation of solid waste-based recycled concrete:

[0053] (1) The waste concrete from the construction site is manually crushed and then fed into a jaw concrete crusher to screen out particles with a particle size of 5-25mm. The screened particles are then immersed in an oxalic acid solution with a concentration of 1mol / L for 24 hours and then taken out and drained.

[0054] (2) Take 100 parts of bisphenol A type epoxy resin and 18 parts of nano silica and stir evenly. Then add 50 parts of curing agent IPDA and stir evenly. Then add sodium dodecylbenzene sulfonate emulsifier and stir evenly. Then slowly add 40 parts of water while performing high-speed shearing to obtain nano silica epoxy emulsion.

[0055] (3) Add the granules after acid leaching in step (1) to the nano-silica epoxy emulsion prepared in step (2), immerse them under a vacuum of 0.08 MPa for 60 min, take them out and solidify them to obtain modified recycled coarse aggregate.

[0056] (4) Take 70 parts of PO42.5 cement and fly ash (specific surface area 650 m²). 2 Mix 20 parts of sodium silicate and 2.5 parts of sodium hydroxide evenly, then add 180 parts of modified recycled coarse aggregate and 75 parts of manufactured sand with a fineness modulus of 2.6, mix evenly, and finally add 3 parts of polycarboxylate superplasticizer (water reduction rate 25%) and 38 parts of water, mix evenly to obtain solid waste-based recycled concrete.

[0057] Comparative Example 1

[0058] Preparation of solid waste-based recycled concrete (acid leaching process omitted compared to Example 1):

[0059] (1) The waste concrete from the construction site is manually crushed and then fed into a jaw concrete crusher to screen out particles with a particle size of 5 to 25 mm.

[0060] (2) Take 100 parts of bisphenol A epoxy resin and 20 parts of nano silica and stir evenly. Then add 50 parts of curing agent IPDA and stir evenly. Then add sodium dodecylbenzene sulfonate emulsifier and stir evenly. Then slowly add 40 parts of water while performing high-speed shearing to obtain nano silica epoxy emulsion.

[0061] (3) Add the particles screened in step (1) to the nano-silica epoxy emulsion prepared in step (2), immerse it under a vacuum of 0.08 MPa for 60 min, take it out and solidify it to obtain modified recycled coarse aggregate.

[0062] (4) Take 70 parts of PO42.5 cement and fly ash (specific surface area 650 m²). 2 Mix 20 parts of sodium silicate and 2.5 parts of sodium hydroxide evenly, then add 200 parts of modified recycled coarse aggregate and 80 parts of manufactured sand with a fineness modulus of 2.6, mix evenly, and finally add 3 parts of polycarboxylate superplasticizer (water reduction rate 25%) and 40 parts of water, mix evenly to obtain solid waste-based recycled concrete.

[0063] Comparative Example 2

[0064] Preparation of solid waste-based recycled concrete (compared to Example 1, the addition of nano-silica is omitted):

[0065] (1) The waste concrete from the construction site is manually crushed and then fed into a jaw concrete crusher to screen out particles with a particle size of 5-25mm. The screened particles are then immersed in an oxalic acid solution with a concentration of 1mol / L for 24 hours and then taken out and drained.

[0066] (2) Take 100 parts of bisphenol A type epoxy resin and 50 parts of curing agent IPDA, stir evenly, add sodium dodecylbenzene sulfonate emulsifier, stir evenly, then slowly add 40 parts of water while performing high-speed shearing to obtain epoxy emulsion.

[0067] (3) Add the granules after acid leaching in step (1) to the epoxy emulsion prepared in step (2), immerse them under a vacuum of 0.08 MPa for 60 min, take them out and cure them to obtain modified recycled coarse aggregate.

[0068] (4) Take 70 parts of PO42.5 cement and fly ash (specific surface area 650 m²). 2 Mix 20 parts of sodium silicate and 2.5 parts of sodium hydroxide evenly, then add 200 parts of modified recycled coarse aggregate and 80 parts of manufactured sand with a fineness modulus of 2.6, mix evenly, and finally add 3 parts of polycarboxylate superplasticizer (water reduction rate 25%) and 40 parts of water, mix evenly to obtain solid waste-based recycled concrete.

[0069] Comparative Example 3

[0070] Preparation of solid waste-based recycled concrete:

[0071] (1) Waste concrete from construction sites is manually crushed and then fed into a jaw concrete crusher to screen out particles with a particle size of 5-25mm to obtain recycled coarse aggregate.

[0072] (2) Take 70 parts of PO42.5 cement and fly ash (specific surface area 650 m²). 2 Mix 20 parts of recycled coarse aggregate ( / kg), 7.5 parts of sodium silicate and 2.5 parts of sodium hydroxide evenly, then add 200 parts of recycled coarse aggregate and 80 parts of manufactured sand with a fineness modulus of 2.6, mix evenly, and finally add 3 parts of polycarboxylate superplasticizer (water reduction rate 25%) and 40 parts of water, mix evenly to obtain solid waste-based recycled concrete.

[0073] The 28-day compressive strength of the solid waste-based recycled concrete prepared in Examples 1-2 and Comparative Examples 1-3 was determined according to GB / T 50081-2002, and the results are shown in Table 1. The 28-day chloride ion diffusion coefficient m of the solid waste-based recycled concrete prepared in Examples 1-2 and Comparative Examples 1-3 was determined according to GB / T 31289-2014. 2 / s, the measurement results are shown in Table 1.

[0074] Table 1. Results of strength and impermeability tests of recycled concrete

[0075] 28-day compressive strength (MPa) <![CDATA[28d chloride ion diffusion coefficient m 2 / s]]> Example 1 48.5 <![CDATA[6.84×10 -12 ]]> Example 2 47.4 <![CDATA[6.35×10 -12 ]]> Comparative Example 1 44.1 <![CDATA[1.36×10 -11 ]]> Comparative Example 2 42.2 <![CDATA[1.07×10 -11 ]]> Comparative Example 3 32.1 <![CDATA[3.96×10 -11 ]]>

[0076] As can be seen from Table 1, the recycled coarse aggregate strengthening method provided by the present invention can improve the strength and impermeability of the recycled concrete prepared therefrom. The acid washing and nano-silica epoxy emulsion impregnation of the present invention have a synergistic effect.

[0077] The water absorption, crushing value, and porosity of the recycled coarse aggregate or modified recycled coarse aggregate used in the preparation of solid waste-based recycled concrete in Examples 1-2 and Comparative Examples 1-3 were determined, and the results are shown in Table 2.

[0078] Among them, water absorption rate is the proportion of weight gain of coarse aggregate after water absorption, crushing value is determined by crushing value tester, and porosity is determined by vacuum adsorption method.

[0079] The crushing value determination procedure is as follows: Level the sample surface inside the cylinder, install the pressure head, place it on the testing machine, and uniformly apply a load of 200 kN within 160-300 s, stabilize for 5 s, then unload and remove the testing cylinder. Pour out the sample from the cylinder and weigh its mass (m0). Use a 2.50 mm diameter square hole sieve to remove the crushed fine particles, and weigh the sample mass remaining on the sieve (m1). Crushing value (%) = (m0-m1) / m0 × 100%.

[0080] Table 2 Results of determination of water absorption, crushing value and porosity of coarse aggregate

[0081] Water absorption rate % Crushing value % Porosity % Example 1 8.3 11.3 7.3 Example 2 8.6 12.1 7.5 Comparative Example 1 9.9 14.2 8.9 Comparative Example 2 9.3 13.7 8.6 Comparative Example 3 13.4 24.2 15.9

[0082] As can be seen from Table 2, acid leaching followed by impregnation with nano-silica epoxy emulsion can significantly reduce the water absorption and porosity of recycled coarse aggregate and improve its strength. The nano-silica in the nano-silica epoxy emulsion has a positive effect on reducing the water absorption and porosity of recycled coarse aggregate and improving its strength. Whether acid leaching is performed before impregnating the recycled coarse aggregate with nano-silica epoxy emulsion has a significant impact on the water absorption, porosity and strength of the recycled coarse aggregate.

[0083] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for strengthening recycled coarse aggregate, characterized in that, Includes the following steps: The recycled coarse aggregate from the waste concrete source is impregnated in oxalic acid solution and drained, then vacuum impregnated in nano-silica epoxy emulsion, taken out and cured to complete the strengthening of the recycled coarse aggregate. The concentration of the oxalic acid solution is 1–1.5 mol / L; The nano-silica epoxy emulsion contains 5-12 wt.% nano-silica, has a water content of 10-20 wt.%, and the mass ratio of epoxy resin, curing agent, and emulsifier is 2:1-1.5:1-1.

5.

2. The method for strengthening recycled coarse aggregate according to claim 1, characterized in that, The particle size of the recycled coarse aggregate is 5-25 mm.

3. The method for strengthening recycled coarse aggregate according to claim 1, characterized in that, The vacuum impregnation process involves a vacuum level of 0.05–0.08 MPa and a time of 30–60 min.

4. A recycled coarse aggregate prepared by a strengthening method according to any one of claims 1 to 3.

5. A solid waste-based recycled concrete, characterized in that, The components, by mass parts, include: 25-35 parts of composite cementitious material, 40-60 parts of recycled coarse aggregate as described in claim 4, 15-25 parts of fine aggregate, 0.3-0.8 parts of water-reducing agent, and 8-12 parts of water; the composite cementitious material is obtained by mixing cement, fly ash, and alkali activator in a mass ratio of 7:2:

1.

6. The solid waste-based recycled concrete according to claim 5, characterized in that, The alkali activator is a mixture of sodium silicate and sodium hydroxide in a mass ratio of 3:1; and / or, the fine aggregate is river sand or manufactured sand with a fineness modulus of 2.6 to 3.0; and / or, the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of not less than 20%.

7. A method for preparing solid waste-based recycled concrete as described in claim 5 or 6, characterized in that, Includes the following steps: Cement, fly ash, and alkali activator are mixed evenly, then mixed evenly with recycled coarse and fine aggregates, and finally water and water-reducing agent are added and stirred evenly to obtain solid waste-based recycled concrete.