Impact-resistant concrete with full recycled coarse aggregate and fiber and preparation process thereof

Abstract

The application relates to the technical field of building materials, in particular to a full-recycled coarse aggregate and fiber composite impact-resistant concrete and a preparation process, which comprises the following components: cement 389-393 parts, river sand 785-793 parts, recycled concrete aggregate 1085-1095 parts, water reducing agent 5.863-5.867 parts, nylon fiber 1.13-1.19 parts, steel fiber 31.1-31.7 parts and tap water 160-200 parts. The full-recycled coarse aggregate is combined with the nylon fiber and the steel fiber in a specific proportion, and the dosage of the cementing material, the aggregate and the water reducing agent is optimized, so that the building solid waste is recycled, the consumption of the natural aggregate is reduced, the integrity and the toughness of the recycled concrete matrix are improved, the generation and the expansion of the micro cracks under the impact load are effectively inhibited, the defects of the traditional recycled concrete, such as the brittleness and the insufficient impact resistance, are improved, and the concrete has better compressive resistance, tensile resistance and impact resistance mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to an impact-resistant concrete made of fully recycled coarse aggregate and fiber composite and its preparation process. Background Technology

[0002] With the rapid development of the construction industry, the amount of construction waste is increasing year by year, of which waste concrete accounts for a very high proportion. This not only wastes resources but also causes serious environmental pollution problems. Using waste concrete to prepare recycled coarse aggregate and use it in concrete production is an effective way to achieve resource recycling, reduce raw material costs, and reduce environmental pollution.

[0003] However, traditional recycled aggregate concrete suffers from poor mechanical properties, especially impact resistance, due to the rough surface, high porosity, and high water absorption of recycled aggregates. It is a typical brittle material and is prone to brittle failure when subjected to dynamic loads such as earthquakes, explosions, and impacts, which severely limits its application in building structures.

[0004] Therefore, based on the above situation, we propose an impact-resistant concrete composed of fully recycled coarse aggregate and fiber, and its preparation process to solve the above problems. Summary of the Invention

[0005] This invention provides an impact-resistant concrete composed of fully recycled coarse aggregate and fiber, and its preparation process, to solve the problems in the prior art.

[0006] The technical problem solved by this invention is achieved by the following technical solution: A fully recycled coarse aggregate and mixed fiber composite modified impact-resistant concrete, wherein the fully recycled coarse aggregate and fiber composite impact-resistant concrete comprises the following raw materials in parts by weight: Cement, 389-393 parts; River sand, 785-793 parts; Recycled concrete aggregate, 1085-1095 parts; Water-reducing agent, 5.863-5.867 parts; Nylon fiber, 1.13-1.19 parts; Steel fiber, 31.1-31.7 parts; Tap water, 160-200 servings.

[0007] Preferably, the fully recycled coarse aggregate and fiber composite impact-resistant concrete comprises the following parts by weight of raw materials: Cement, 391 parts; River sand, 789 portions; 1090 parts of recycled concrete aggregate; Water-reducing agent, 5.865 parts; Nylon fiber, 1.16 parts; Steel fiber, 31.4 parts; 180 portions of tap water.

[0008] Preferably, the water-reducing agent is a polycarboxylate high-performance water-reducing agent.

[0009] Preferably, the river sand has a particle size of 0mm-5mm and a fineness modulus of 2.9-3.0.

[0010] Preferably, the nylon fiber has a length of 12-20 mm, and the steel fiber is a copper-plated steel fiber with a length of 15-25 mm.

[0011] A process for preparing impact-resistant concrete composed of fully recycled coarse aggregate and fiber includes the following steps: S1: Weigh the raw materials according to the proportion, dry mix the cement and river sand for 25-35 seconds using a pre-wetting concrete mixer, then add the recycled concrete coarse aggregate and continue to dry mix for 25-35 seconds until evenly mixed; S2: Add nylon fibers and steel fibers to the mixer in batches and disperse them, and dry mix until the fibers are evenly dispersed; S3: Add water and water-reducing agent to the mixture obtained in step S2, and stir until the mixture is uniform to obtain concrete mixture; S4: Pour the concrete mixture into shape and cure it.

[0012] Preferably, in step S2, the total dry mixing time of the nylon fiber and the steel fiber is not less than 2 minutes.

[0013] Preferably, in step S3, the wet mixing time after adding water and water-reducing agent is 2.5-3.5 minutes.

[0014] Preferably, in step S4, the curing conditions are: temperature 20±2℃, relative humidity not less than 95%, and curing period not less than 28 days.

[0015] The beneficial effects of this invention are as follows: by limiting the composite of fully recycled coarse aggregate with a specific ratio of nylon fiber and steel fiber, and by optimizing the dosage of cementitious materials, aggregates and water-reducing agents, the invention achieves resource utilization of construction solid waste and reduces the consumption of natural aggregates, while improving the integrity and toughness of the recycled concrete matrix. It effectively inhibits the generation and propagation of microcracks under impact loads, improves the defects of traditional recycled concrete such as high brittleness and insufficient impact resistance, and makes the concrete have better compressive, tensile and impact mechanical properties, making it suitable for earthquake-resistant, explosion-proof and other protective engineering projects. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the preparation process provided by the present invention. Detailed Implementation

[0018] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments and performance test data.

[0019] An impact-resistant concrete composed of fully recycled coarse aggregate and fiber, comprising the following raw materials in parts by weight, with the selection criteria and functions of each raw material as follows: 389-393 parts cement, 785-793 parts river sand, 1085-1095 parts recycled concrete aggregate, 5.863-5.867 parts water-reducing agent, 1.13-1.19 parts nylon fiber, 31.1-31.7 parts steel fiber, and 160-200 parts tap water; The preferred impact-resistant concrete composed of fully recycled coarse aggregate and fiber composite includes the following raw materials by weight: 391 parts cement, 789 parts river sand, 1090 parts recycled concrete aggregate, 5.865 parts water-reducing agent, 1.16 parts nylon fiber, 31.4 parts steel fiber, and 180 parts tap water; Weigh each raw material according to the preferred proportions shown in the table below (unit: kg / m³).

[0020] Specifically, recycled aggregate concrete suffers from poor mechanical properties, especially impact resistance, due to the rough surface, high porosity, and high water absorption of recycled aggregates, making it prone to brittle fracture. Based on this, the present invention addresses these technical pain points by precisely selecting each raw material component, optimizing the proportion design, and using a composite reinforcement technique of nylon fiber and steel fiber. At the same time, it realizes the resource utilization of construction solid waste, taking into account both environmental protection and engineering practicality.

[0021] Preferably, P.O42.5 grade ordinary Portland cement can be used, whose performance strictly complies with GB 175-2023 "General Portland Cement" standard. Its cement hydration reaction is sufficient and its strength development is stable. As the core of concrete cementitious material, it can effectively fill the gaps of recycled aggregate, improve the problems of rough surface and weak interfacial bonding of recycled aggregate, provide basic mechanical support for concrete, and reduce the risk of brittle failure due to insufficient cementitious strength. Preferably, the river sand can be medium sand with a particle size of 0mm-5mm and a fineness modulus of 2.9-3.0, which conforms to the GB / T 14684-2022 standard for construction sand. River sand with this fineness modulus and particle size range belongs to the medium sand type with a slightly coarser texture. The gradation is continuous and reasonable, which can meet the gradation requirements of recycled concrete aggregate, fully fill the pores between recycled aggregates, reduce the adverse effects of high porosity of recycled aggregates, enhance the workability and density of concrete mixtures, improve the overall structural stability of concrete, and reduce the crack initiation points under impact loads. Preferably, the recycled concrete aggregate can be made from waste concrete after the demolition of concrete buildings by crushing with a crusher and grading with a vibrating screen. The particle size is controlled at 5-20mm, the apparent density is 2660kg / m³, the crushing value is 21.4%, the water absorption rate is 5.8%, and the mud content is 1.9%. Its performance meets the requirements for the application of recycled aggregate concrete. This invention uses fully recycled coarse aggregate to replace natural coarse aggregate, which not only realizes the resource utilization of construction solid waste and reduces the environmental pressure caused by the mining of natural aggregate and solid waste landfill, but also reduces the negative impact of the defects of recycled aggregate itself on the performance of concrete by strictly controlling its particle size, crushing value and mud content, thus taking into account both environmental protection value and engineering reliability.

[0022] Preferably, the water-reducing agent can be a polycarboxylate high-performance water-reducing agent, which conforms to the GB / T 8076-2025 standard "Concrete Admixtures". Targeting the high water absorption of recycled aggregates, this water-reducing agent can effectively reduce the water-cement ratio of concrete. While reducing the amount of tap water used, it ensures that the concrete mixture has good fluidity and workability, reduces the dryness and pouring difficulties caused by water absorption of recycled aggregates, and thus reduces internal pores and defects in concrete, improving interfacial bonding strength and overall density.

[0023] Preferably, nylon fiber and steel fiber are the core components of this invention for solving the poor impact resistance of recycled concrete. The nylon fiber is controlled at a length of 12-20mm, which has the characteristics of good flexibility and high elongation. It can inhibit the initiation and early propagation of micro-cracks inside the concrete, and can especially improve the weak link at the interface between recycled aggregate and cement matrix. The steel fiber is selected as copper-plated steel fiber with a length of 15-25mm. It has high strength and high modulus, which can effectively resist macro-impact loads and prevent crack penetration and propagation. When the two work together, the nylon fiber is responsible for micro-crack prevention, and the steel fiber is responsible for macro-impact resistance. The fiber length is matched with the particle size of recycled aggregate, which can bridge the gaps between aggregates to form a three-dimensional crack-prevention network. This changes the failure mode of traditional brittle fracture of recycled concrete and improves the impact toughness and crack resistance of concrete. At the same time, by optimizing the ratio of the two fibers, the problems of insufficient toughness and easy agglomeration of single fiber reinforcement can be avoided, taking into account the mechanical properties of concrete and construction convenience.

[0024] Furthermore, this invention also provides a process for preparing impact-resistant concrete composed of fully recycled coarse aggregate and fiber, comprising the following steps: S1: Weigh each raw material according to the proportion. First, pre-wet the concrete mixer to eliminate the adsorption interference on the inner wall. Add cement and river sand into the mixer and dry mix for 25-35 seconds to achieve uniform coating of cementitious materials and fine aggregates. Then add recycled concrete aggregates and continue to dry mix for 25-35 seconds to obtain a premixed material in which coarse and fine aggregates and cementitious materials are fully mixed. The dry mixing time is preferably 30 seconds. S2: Add nylon fibers and steel fibers to the premixed material in batches and in a dispersed manner, with an interval of no less than 15 seconds between each batch, so that the nylon fibers and steel fibers are evenly mixed in the material, reducing the phenomenon of fiber agglomeration. After the material is added, continue to dry mix for a total dry mixing time of no less than 2 minutes, so as to achieve a three-dimensional random distribution of fibers in the material without agglomeration. S3: Premix tap water and water-reducing agent to prepare a composite aqueous solution, inject it into step S2 at a uniform speed to obtain a mixture, stir for no less than 3 minutes until a homogeneous, stable, lump-free, and workable concrete mixture is formed. S4: The concrete mixture is poured into a mold of a pre-set size, and after being vibrated to remove internal air bubbles, it is left to stand at room temperature for 24 hours to complete the initial setting. Then it is transferred to a curing environment for curing to obtain the finished product.

[0025] Preferably, in S4, the curing conditions are: temperature 20±2℃, relative humidity not less than 95%, and curing age not less than 28 days. This temperature range is suitable for the hydration reaction of concrete, ensuring sufficient cement hydration to generate enough hydrated calcium silicate gel to fill the pores of recycled aggregate and strengthen interfacial bonding. It also avoids the adverse effects of excessively high or low temperatures on performance. Excessively high temperatures lead to overly rapid hydration, causing heat accumulation inside the concrete and increasing the risk of temperature cracks. Conversely, excessively low temperatures result in slow hydration, slow strength development, and affect the bond strength between fibers and the cement matrix, ultimately leading to a decrease in impact resistance. This temperature also complies with GB / T The standard curing temperature requirements in 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" ensure the accuracy and comparability of performance test results. The core purpose of the humidity requirements is to prevent excessive water loss from the concrete surface, especially considering the high water absorption rate of recycled aggregates in this solution. Recycled aggregates will still slowly absorb water during curing. If the ambient humidity is insufficient, the surface moisture will evaporate rapidly, leading to surface shrinkage and cracking. Furthermore, excessive extraction of internal moisture results in incomplete cement hydration, which not only reduces the overall strength of the concrete but also exacerbates the weakness of the interface between recycled aggregates and the cement matrix, making it prone to fracture at the interface during impact. Therefore, ensuring the surface moisture of the concrete is protected is crucial. Maintaining a consistently moist state ensures continuous and thorough cement hydration, enhancing concrete density and interfacial bonding strength, thus laying the foundation for impact resistance. The development of concrete strength and toughness is a gradual process. Furthermore, 28 days is the industry-recognized standard curing age for concrete. At this point, the cement hydration reaction is essentially complete, the strength reaches the design standard value, and the bond between fibers and the cement matrix tends to stabilize. The compressive, tensile, and impact resistance properties of the concrete can all reach their optimal state. A sufficiently long curing age ensures that fibers and hydration products are fully integrated. If the curing age is insufficient, the concrete strength will not be fully developed, the synergistic reinforcing effect of the fibers cannot be fully utilized, and brittle failure during impact is likely to occur.

[0026] The prepared concrete specimens were subjected to compressive strength, splitting tensile strength, flexural strength, drop hammer impact, and split Hopkinson bar tests. The results showed that the 28-day cubic compressive strength reached 52.3 MPa ± 2.67 MPa; the splitting tensile strength reached 6.23 MPa ± 1.61 MPa; the flexural strength was 5.74 MPa ± 1.24 MPa; and the drop hammer impact energy was 9810 J ± 2948 J. The specimens maintained their original shape, with only minor surface cracks. Under different strain rates, the dynamic compressive strength was greater than 60 MPa. The specimens exhibited excellent energy absorption under impact loads and significant toughness. They demonstrated clear advantages in splitting tensile strength, flexural strength, and especially impact resistance (drop hammer impact energy), proving that the composite of nylon fiber and steel fiber produces a more synergistic reinforcing effect, effectively improving the brittleness of concrete and enhancing its toughness and energy absorption capacity under impact loads. Specific mechanical property tests of the concrete specimens are shown in the table below.

[0027] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An impact-resistant concrete composed of fully recycled coarse aggregate and fiber, characterized in that, The fully recycled coarse aggregate and fiber composite impact-resistant concrete comprises the following raw materials in parts by weight: Cement, 389-393 parts; River sand, 785-793 parts; Recycled concrete aggregate, 1085-1095 parts; Water-reducing agent, 5.863-5.867 parts; Nylon fiber, 1.13-1.19 parts; Steel fiber, 31.1-31.7 parts; Tap water, 160-200 servings.

2. The impact-resistant concrete made of fully recycled coarse aggregate and fiber composite according to claim 1, characterized in that, The preferred impact-resistant concrete composed of fully recycled coarse aggregate and fiber composite comprises the following raw materials in parts by weight: Cement, 391 parts; River sand, 789 portions; 1090 parts of recycled concrete aggregate; Water-reducing agent, 5.865 parts; Nylon fiber, 1.16 parts; Steel fiber, 31.4 parts; 180 portions of tap water.

3. The impact-resistant concrete made of fully recycled coarse aggregate and fiber composite according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-performance water-reducing agent.

4. The impact-resistant concrete made of fully recycled coarse aggregate and fiber composite according to claim 1, characterized in that, The river sand has a particle size of 0mm-5mm and a fineness modulus of 2.9-3.

0.

5. The impact-resistant concrete modified with fully recycled coarse aggregate and mixed fiber as described in claim 1, characterized in that, The nylon fiber has a length of 12-20 mm, and the steel fiber is a copper-plated steel fiber with a length of 15-25 mm.

6. The process for preparing impact-resistant concrete using a composite of fully recycled coarse aggregate and fiber as described in claim 1, characterized in that, Includes the following steps: S1: Weigh the raw materials according to the proportion, dry mix the cement and river sand for 25-35 seconds using a pre-wetted concrete mixer, then add the recycled concrete coarse aggregate and continue to dry mix for 25-35 seconds until evenly mixed; S2: Add nylon fibers and steel fibers to the mixer in batches and disperse them, and dry mix until the fibers are evenly dispersed; S3: Add water and water-reducing agent to the mixture obtained in step S2, and stir until the mixture is uniform to obtain concrete mixture; S4: Pour the concrete mixture into shape and cure it.

7. The process for preparing impact-resistant concrete using a fully recycled coarse aggregate and fiber composite according to claim 6, characterized in that, In step S2, the total dry mixing time of the nylon fiber and steel fiber is not less than 2 minutes.

8. The process for preparing impact-resistant concrete using a fully recycled coarse aggregate and fiber composite according to claim 6, characterized in that, In step S3, the wet mixing time after adding water and water-reducing agent is no less than 3 minutes.

9. The process for preparing impact-resistant concrete using a composite of fully recycled coarse aggregate and fiber as described in claim 6, characterized in that, In S4, the curing conditions are: temperature 20±2℃, relative humidity not less than 95%, and curing period not less than 28 days.

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