A freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete, its preparation method and application

Abstract

This invention provides a freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete and its preparation method, relating to the field of recycled aggregate concrete technology. By weight, it comprises the following raw materials: 400-455 parts of roller-compacted recycled coarse aggregate; 140-160 parts of cement; 14-18 parts of silica fume; 30-38 parts of fly ash; 195-225 parts of natural aggregate; 50-65 parts of water-absorbing sepiolite fiber; 50-70 parts of water; 2-4 parts of composite fiber aggregate; 1.25-3.6 parts of composite antifreeze agent; and 1-1.5 parts of polycarboxylate high-performance water-reducing agent. This invention also provides a method for preparing the above-mentioned freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete. The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete prepared by this invention has advantages such as excellent mechanical properties and good freeze-thaw resistance. The concrete is constructed using vibratory compaction instead of traditional pouring methods, maximizing the reuse of recycled aggregate and expanding its application prospects.

Description

Technical Field

[0001] This invention belongs to the field of recycled aggregate concrete technology, specifically relating to a freeze-thaw resistant fiber recycled aggregate roller-compacted concrete and its preparation method, as well as the application of the aforementioned freeze-thaw resistant fiber recycled aggregate roller-compacted concrete. Background Technology

[0002] With the continuous increase in urbanization rate, the pace of construction industry upgrading and replacement is accelerating, resulting in a year-on-year increase in construction waste. This massive amount of construction waste has become a major challenge for economic and social development. Recycled concrete technology is one of the most common and efficient ways to utilize construction waste. However, due to the adhesion of old mortar to the surface of recycled aggregates and the presence of numerous micro-cracks inside, recycled concrete suffers from defects such as low strength. Current methods to improve these defects include aggregate reinforcement, fiber incorporation, and external restraint. However, these technologies are costly to prepare, difficult to construct, and have low performance stability, limiting their large-scale application.

[0003] Roller-compacted concrete (RCC) is an ultra-dry, hard concrete with low water consumption and near-zero slump. It is constructed using a continuous, thin-layer pouring method with vibratory compaction. Utilizing recycled aggregates in RCC preparation reduces mixing water usage and increases strength. A novel fiber-recycled aggregate RCC technology combines fiber with recycled aggregates, significantly improving the flexural strength, impact resistance, and abrasion resistance of the new material. This technology can be widely applied to new road construction, industrial surfaces, and port terminals. However, considering that these applications are often located in areas subject to cyclical temperature changes, the concrete matrix will suffer from repeated freeze-thaw cycles, leading to a significant decrease in its basic mechanical properties and severely impacting its durability.

[0004] Based on this, a freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete and its preparation method are provided. The method uses vibration compaction to replace the traditional pouring method to prepare fiber-recycled aggregate roller-compacted concrete with excellent mechanical properties and freeze-thaw resistance, which can provide a new solution for the disposal of construction waste and the utilization of recycled aggregates. Summary of the Invention

[0005] One of the objectives of this invention is to provide a freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete.

[0006] The second objective of this invention is to provide a method for preparing freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete.

[0007] The third objective of this invention is to provide an application of freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete.

[0008] One of the technical solutions adopted by this invention to achieve its objective is to provide a freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete, which, by weight, is composed of the following raw materials: 400-455 parts of roller-compacted recycled coarse aggregate; 140-160 parts of cement; 14-18 parts of silica fume; 30-38 parts of fly ash; 195-225 parts of natural aggregate; 50-65 parts of water-absorbing sepiolite fiber; 50-70 parts of water; 2-4 parts of composite fiber aggregate; 1.25-3.6 parts of composite antifreeze agent; and 1-1.5 parts of polycarboxylate high-performance water-reducing agent.

[0009] The composite antifreeze agent, by weight, is composed of the following raw materials: 0.05-0.15 parts ethylene glycol; 0.05-0.15 parts sodium thiocyanate; 0.04-0.08 parts sodium oxalate; 0.1-0.2 parts polyglycerol fatty acid ester; 0.01-0.05 parts sodium gluconate; and 1-3 parts water.

[0010] The overall concept of this invention is as follows:

[0011] The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete provided by this invention, by adding a reasonable proportion of silica fume and fly ash to the raw materials, can effectively remove the original defects such as the loose and fragile old mortar and numerous inherent cracks on the surface of the recycled coarse aggregate, thereby improving its material strength and the performance of the resulting concrete. A reasonable proportion of composite fiber aggregate can significantly improve the early crack resistance, splitting tensile strength, flexural strength, and durability of the recycled concrete. Furthermore, to improve the freeze-thaw resistance of the fiber-recycled aggregate roller-compacted concrete, this invention also provides a composite antifreeze agent, using ethylene glycol, sodium thiocyanate, and sodium oxalate as the main antifreeze components. Ethylene glycol, in combination with polyglycerol fatty acid esters, polycarboxylic acid high-performance water-reducing agents, and sodium gluconate, can improve the air bubbles introduced during concrete mixing and ensure their uniform distribution, thereby enhancing the water retention and fluidity of the concrete.

[0012] Furthermore, the water-absorbing sepiolite fiber added to the raw materials of this invention has a certain degree of adsorption, fluidity, and good durability. When incorporated into fiber-recycled aggregate concrete, it can play the following roles: First, due to the high adsorption of water-absorbing sepiolite fiber, the material has good water retention, which improves the crack resistance of concrete and the impermeability of the pavement; Second, the rheological properties of water-absorbing sepiolite fiber can improve the operability of construction, making the construction operation smoother; Third, the stability of the material properties of water-absorbing sepiolite fiber can enhance the durability of fiber-recycled aggregate concrete, making it better adaptable to various complex working environments.

[0013] Furthermore, research has found that the water-absorbing sepiolite fibers in roller-compacted concrete raw materials can synergistically work with composite antifreeze agents to slow down ice crystal precipitation and reduce concrete expansion stress during freezing, thereby improving its durability. In the concrete preparation process, it can also compensate for the original defects of recycled aggregates and improve construction operability. Preferably, the addition amount of water-absorbing sepiolite fibers in the raw materials is 6.15 wt.% - 6.67 wt.%.

[0014] Furthermore, the composite antifreeze agent provided by this invention, in addition to the main components sodium thiocyanate, sodium oxalate, and ethylene glycol, also contains polyglycerol fatty acid ester and sodium gluconate. Polyglycerol fatty acid ester is a nonionic surfactant of the polyol ester class, possessing both hydrophilic and lipophilic properties, which significantly improves dispersibility and wetting. It reduces the surface tension of water in concrete, allowing cement particles to be better dispersed in water, thereby improving the uniformity and density of fiber-recycled concrete. In addition, polyglycerol fatty acid ester can also improve the fluidity and workability of the concrete system, and synergistically works with water-absorbing sepiolite fibers to reduce bleeding and segregation during concrete pouring, resulting in a more uniform and stable texture and performance. Sodium gluconate in this invention mainly works synergistically with polycarboxylate high-performance water-reducing agent, effectively reducing the water consumption of concrete, improving fluidity, extending the initial setting time of concrete, and reducing slump loss, thereby reducing the risk of cracking during construction and improving the workability of concrete and the later strength of the matrix.

[0015] Furthermore, research has found that controlling the amount of composite antifreeze agent added to the raw materials within a reasonable range can maintain better mechanical properties and effectively reduce the mass loss rate under freeze-thaw cycle conditions. Preferably, the amount of composite antifreeze agent added to the raw materials of freeze-thaw resistant fiber recycled aggregate roller-compacted concrete is controlled at 0.21 wt.%-0.29 wt.%.

[0016] Furthermore, research has revealed that the ratio of ethylene glycol, sodium thiocyanate, and sodium oxalate, the core components of the composite antifreeze agent, determines its application effect. In this invention, under the premise that the amount of composite antifreeze agent added to the concrete raw materials remains unchanged, the most significant improvement in the freeze-thaw resistance of roller-compacted concrete is achieved when the weight ratio of ethylene glycol, sodium thiocyanate, and sodium oxalate is controlled at 5:15:6.

[0017] Furthermore, the preparation method of the composite antifreeze includes the following steps: first, sodium thiocyanate, sodium oxalate and a portion of water are mixed to obtain a mixture; then, the mixture is mixed with other raw materials of the composite antifreeze and stirred at high speed to obtain a uniform solution, which is the composite antifreeze.

[0018] Furthermore, the cement is ordinary Portland cement, and the fly ash is Grade I fly ash.

[0019] Furthermore, the natural aggregate is fine sand with an average particle size of 0.25-0.35 mm.

[0020] Furthermore, the compacted recycled coarse aggregate has a particle size of 5-20 mm and is obtained from waste building materials through crushing and screening. Preferably, the mass ratio of aggregate with a particle size of 5-10 mm to aggregate with a particle size of 10-20 mm in the compacted recycled coarse aggregate is 4:6.

[0021] Furthermore, the absorbent sepiolite fiber is a fibrous magnesium-rich clay mineral with a fiber length of 2-3 mm, a weight water absorption rate of 160%-200%, and a density of 1-1.2 g / cm³.

[0022] Furthermore, the composite fiber aggregate is composed of polypropylene fibers with a length of 25-30 mm and polyvinyl alcohol fibers mixed in a 1:1 mass ratio.

[0023] The second objective of this invention is achieved by providing a method for preparing freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete, comprising the following steps:

[0024] S1. Mix the rolled and recycled coarse aggregate with silica fume, fly ash and some water, and stir at a certain rate to obtain pretreated rolled and recycled coarse aggregate.

[0025] S2. Add natural aggregate, cement, water-absorbing sepiolite fiber and composite fiber aggregate to the pretreated rolled recycled coarse aggregate in sequence, and continue to stir to obtain the mixture.

[0026] S3. Add the remaining water, composite antifreeze agent and polycarboxylate high-performance water-reducing agent to the mixture, and continue stirring until uniformly mixed to obtain a freeze-thaw resistant fiber recycled aggregate roller-compacted concrete.

[0027] In the above preparation method, firstly, silica fume and fly ash are added to partially fill the recycled aggregate, thereby strengthening and sealing the inherent cracks in the recycled aggregate; secondly, a composite fiber filler composed of polypropylene fiber and polyvinyl alcohol fiber is added to form a network structure inside, improving the overall strength, toughness, and durability; finally, composite antifreeze, water-reducing agent, retarder, and water-absorbing sepiolite fiber are added to improve the water retention and freeze-thaw resistance of the recycled concrete, as well as to promote the repair of the recycled aggregate, reduce porosity, slow down the precipitation of ice crystals during freezing, and reduce the expansion stress of the concrete, ultimately obtaining fiber-recycled aggregate roller-compacted concrete with excellent mechanical properties and freeze-thaw resistance.

[0028] Further, in step S1, the crushed recycled coarse aggregate is made from waste building materials that have been crushed and dried and then screened. The crushed recycled coarse aggregate is divided into two grades of crushed recycled coarse aggregate: 5-10mm and 10-20mm, and the mixing ratio of the two grades of recycled coarse aggregate with different particle sizes is 4:6.

[0029] Further, in step S1, the stirring speed is 40-80 r / min, and the time is 4-6 h. Preferably, the water in step S1 accounts for 50% of the total weight of water in the raw materials. The key reason why recycled coarse aggregate and its concrete have poor performance compared to general materials is that the surface of the recycled coarse aggregate is covered with loose and fragile old mortar containing a large number of cracks, has high water absorption, and extremely poor freeze-thaw resistance. Modification and optimization treatment is necessary, but traditional treatment methods are not universally applicable and difficult to apply to practical engineering. In step S1 of this invention, using silica fume to physically strengthen the target coarse aggregate can effectively remove this original defect, improving its strength and the performance of the concrete prepared from it. Furthermore, fly ash is added during the preparation process to further improve the impermeability, durability, and freeze-thaw resistance of the recycled coarse aggregate.

[0030] Furthermore, the composite antifreeze agent used in this invention uses ethylene glycol, sodium thiocyanate, and sodium oxalate as the main antifreeze components. Ethylene glycol, in combination with polyglycerol fatty acid esters and sodium gluconate, can improve the distribution of air bubbles introduced during concrete mixing and enhance the water retention and fluidity of the concrete. The polycarboxylate high-performance water-reducing agent, a polycarboxylate-based water-reducing agent produced through esterification, can ensure the stable development of cement strength. The sodium thiocyanate in the composite antifreeze agent can compensate for the strength loss caused by the use of polycarboxylate water-reducing agent. The water-absorbing sepiolite fiber can work synergistically with the composite antifreeze agent to slow down the precipitation of ice crystals and reduce the expansion stress of concrete during freezing, thereby improving its durability. In the concrete preparation process, it can also compensate for the original defects of recycled aggregates and improve the operability of construction.

[0031] The third objective of this invention is to provide an application of the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete as described in the first objective of this invention, or the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete prepared by the preparation method described in the second objective of this invention. The application includes: constructing the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete by using a through-slot thin-layer pouring and vibratory compaction method.

[0032] The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete provided by this invention is a dry-hard, cement-lean concrete, which presents numerous difficulties and inconveniences when constructed using traditional methods. This invention utilizes a continuous thin-layer pouring and vibratory compaction method for construction, which accelerates the construction progress. The continuous thin-layer pouring enhances heat dissipation, ensures concrete density, reduces the amount of work, simplifies surface operations, and facilitates faster construction. Furthermore, the continuous thin-layer pouring and vibratory compaction method reduces cement usage and increases the amount of fly ash incorporated, thereby lowering project costs. Simultaneously, this construction method, through optimized material usage and construction processes, also reduces energy consumption and environmental pollution.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete provided by the present invention is composed of roller-compacted recycled coarse aggregate, cement, silica fume, fly ash, natural aggregate, water-absorbing sepiolite fiber, water, composite fiber aggregate, composite antifreeze agent, and polycarboxylate high-performance water-reducing agent. The addition of silica fume and fly ash can repair cracks on the surface of the recycled coarse aggregate, removing this original defect and improving the compressive strength of the concrete; the composite fiber can strengthen the adhesion between aggregates, significantly improving the crack resistance, basic mechanical properties, and durability of the matrix; the water-absorbing sepiolite fiber can improve its water retention, workability, and matrix durability; the composite antifreeze agent can greatly improve the freeze-thaw resistance of the fiber-recycled aggregate concrete while enhancing the water retention of the concrete and the mechanical properties and durability of its matrix. In the freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete of the present invention, the various materials can influence each other and work synergistically, achieving an improvement in the freeze-thaw resistance of the fiber-recycled aggregate roller-compacted concrete.

[0035] (2) In view of the insufficient resource utilization of existing construction waste, the present invention provides a freeze-thaw resistant fiber recycled aggregate roller-compacted concrete and its preparation method. The roller-compacted concrete prepared not only has excellent mechanical properties, impact resistance, wear resistance and freeze-thaw resistance, but also has the advantages of simple preparation method, low cost, low construction requirements and high efficiency. It has good application value in actual engineering, can realize large-scale and efficient utilization of construction waste, and has significant environmental effects. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart illustrating the preparation and construction method of freeze-thaw resistant fiber recycled aggregate roller-compacted concrete provided by the present invention. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0039] This invention provides a freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete, which, by weight, is composed of the following raw materials: 400-455 parts of roller-compacted recycled coarse aggregate; 140-160 parts of cement; 14-18 parts of silica fume; 30-38 parts of fly ash; 195-225 parts of natural aggregate; 50-65 parts of water-absorbing sepiolite fiber; 50-70 parts of water; 2-4 parts of composite fiber aggregate; 1.25-3.6 parts of composite antifreeze agent; and 1-1.5 parts of polycarboxylate high-performance water-reducing agent.

[0040] The composite antifreeze agent, by weight, is composed of the following raw materials: 0.05-0.15 parts ethylene glycol; 0.05-0.15 parts sodium thiocyanate; 0.04-0.08 parts sodium oxalate; 0.1-0.2 parts polyglycerol fatty acid ester; 0.01-0.05 parts sodium gluconate; and 1-3 parts water.

[0041] The flowchart illustrating the preparation and construction methods of the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete is shown below. Figure 1 As shown.

[0042] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0043] The weight proportions of each raw material in the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete of Examples 1-5 of this invention are shown in Table 1 below:

[0044] Table 1

[0045]

[0046] In the table above, the cement is ordinary Portland cement, the fly ash is grade I fly ash, the natural aggregate is fine sand with an average particle size of 0.25-0.35 mm; the particle size of the rolled recycled coarse aggregate is 5-20 mm, obtained from waste building materials through crushing and screening; the water-absorbing sepiolite fiber is a fibrous magnesium-rich clay mineral with a fiber length of 2-3 mm, a weight water absorption rate of 160%-200%, and a density of 1-1.2 g / cm³; the composite fiber aggregate is made by mixing polypropylene fibers with a length of 25-30 mm and polyvinyl alcohol fibers in a 1:1 mass ratio.

[0047] The amounts of each raw material used in the composite antifreeze prepared in Examples 1 and 6-14 are shown in Table 2 below (unit: kg).

[0048] Table 2

[0049]

[0050] Example 1

[0051] Weigh the following raw materials by weight: 400 kg of rolled recycled coarse aggregate; 140 kg of ordinary Portland cement; 14 kg of silica fume; 30 kg of industrial waste grade I fly ash; 200 kg of natural aggregate; 55 kg of water-absorbing sepiolite fiber; 50 kg of water; 2 kg of composite fiber aggregate; 2.38 kg of composite antifreeze agent (added to the raw materials at a rate of 0.27 wt.%); 1.5 kg of polycarboxylate high-performance water-reducing agent.

[0052] The composite antifreeze is prepared from the following components: 0.05 kg ethylene glycol, 0.15 kg sodium thiocyanate, 0.06 kg sodium oxalate, 0.1 kg polyglycerol fatty acid ester, 0.02 kg sodium gluconate, and 2 kg water.

[0053] The compound antifreeze is prepared through the following steps:

[0054] (1) Sodium thiocyanate, sodium oxalate and a portion of water (40% of the total amount) were mixed at 20±5℃ and stirred for 3-5 minutes to obtain mixture A;

[0055] (2) Mix mixture A with ethylene glycol, polyglycerol fatty acid ester, sodium gluconate and the remaining water (60% of the total amount) and stir at high speed until the solution is uniform to obtain a composite antifreeze.

[0056] The preparation and construction methods of the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete are as follows:

[0057] Step 1: Weigh out the following raw materials according to the weight proportions shown in Table 1: ordinary silicate cement, silica fume, industrial waste slag grade I fly ash, water, natural aggregate, rolled recycled coarse aggregate, water-absorbing sepiolite fiber, composite fiber aggregate, composite antifreeze agent, and polycarboxylate high-performance water-reducing agent.

[0058] Step 2: After crushing and drying the waste building materials, they are screened and separated into two grades of crushed recycled coarse aggregate: 5-10mm and 10-20mm. The mixing ratio of the two grades of recycled coarse aggregate with different particle sizes is 4:6.

[0059] Step 3: Place the rolled recycled coarse aggregate obtained in Step 2 into the drum of a concrete mixer and mix it with the weighed silica fume, industrial waste grade 1 fly ash and some water (50% of the total amount) at a speed of 60 r / min for 5 hours to enhance the physical properties of the recycled coarse aggregate.

[0060] Step 4: Add natural aggregate, silicate cement and composite fiber aggregate to the mixer in sequence and mix until uniform;

[0061] Step 5: Add the remaining water (50% of the total amount), composite antifreeze agent and polycarboxylate high-performance water-reducing agent to the mixer, continue mixing, and after mixing evenly, the preparation of freeze-thaw resistant fiber recycled aggregate roller-compacted concrete is complete.

[0062] Step 6: The freeze-thaw resistant fiber recycled aggregate roller-compacted concrete prepared in Step 5 is then poured in thin layers through a continuous silo and compacted by vibration.

[0063] Examples 2-5

[0064] The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete was prepared according to the weight proportions of each raw material shown in Table 1. In Examples 2-5, the mass ratio of ethylene glycol, sodium thiocyanate, sodium oxalate, polyglycerol fatty acid ester, sodium gluconate, and water in the composite antifreeze agent was 5:15:6:10:2:200 (consistent with Example 1). In Examples 2-5, the amount of composite antifreeze agent added to the concrete raw materials was 0.21 wt.%, 0.29 wt.%, 0.35 wt.%, and 0.13 wt.%, respectively.

[0065] The preparation methods of the composite antifreeze agent, the preparation methods of freeze-thaw resistant fiber recycled aggregate roller-compacted concrete, and the construction methods are all consistent with those in Example 1.

[0066] Examples 6-14

[0067] Except for the composite antifreeze agent, the dosage of other raw materials in the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete is consistent with that in Example 1. In Examples 6-14, the dosage of each raw material in the composite antifreeze agent is shown in Table 2. The preparation method of the composite antifreeze agent, the preparation method of the freeze-thaw resistant fiber recycled aggregate roller-compacted concrete, and the construction method are all consistent with those in Example 1.

[0068] Examples 15-17

[0069] The difference between Examples 15-17 and Example 1 is that the amount of water-absorbing sepiolite fiber in the roller-compacted concrete raw material of antifreeze-thaw fiber recycled aggregate prepared in Example 1 is adjusted to 50 kg, 60 kg and 65 kg respectively, while the other conditions and preparation methods are the same as in Example 1.

[0070] Example 18

[0071] The difference between this embodiment and Embodiment 1 is that in the preparation method of freeze-thaw resistant fiber recycled aggregate roller compacted concrete, the physical performance enhancement step in step 3 is omitted, and silica fume and fly ash are directly used to replace part of the cement and mixed together. The remaining conditions and preparation methods are consistent with Embodiment 1.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that the raw materials of the freeze-thaw resistant fiber recycled aggregate roller compacted concrete do not contain composite antifreeze agents, while the other conditions and preparation methods are consistent with those of Example 1.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that 55 kg of water-absorbing sepiolite fiber in the raw materials of the freeze-thaw resistant fiber recycled aggregate roller compacted concrete is replaced with an equal weight of a mixture of fly ash and silica fume (the weight ratio of the two is 1:1). All other conditions and preparation methods are the same as in Example 1.

[0076] Performance evaluation indicators and test plan

[0077] The performance of roller-compacted concrete prepared according to the various embodiments and comparative examples of the present invention was tested, including compressive strength test and freeze-thaw cycle test.

[0078] (1) Compressive strength test: Two sets of three cubes of 100mm×100mm×100mm were designed for each group. The test blocks were cured at room temperature for 28 days. After the curing period, the mechanical properties of the concrete test blocks that had not undergone and those that had undergone freeze-thaw cycle treatment were tested according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0079] (2) Freeze-thaw cycle test: Specimens were prepared according to the proportions of Examples 1-18 and Comparative Examples 1 and 2, respectively. The sample size used in this freeze-thaw test was a prism with dimensions of 100mm×100mm×400mm, with 3 specimens per group, and cured for 28 days. According to the specific requirements in the standard "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", the initial mass and initial dynamic modulus of elasticity of the samples were determined before freeze-thaw, and then the freeze-thaw test was started. In the freeze-thaw cycle test, the temperature change range of the sample center was -18±2°C to 5±2°C, each freeze-thaw cycle was 4 hours, and the sample was thawed for no less than 1 hour in each cycle.

[0080] During the experiment, the damage to the specimens was observed after every 25 freeze-thaw cycles, and the mass and dynamic modulus of elasticity were measured simultaneously. Uniaxial compressive stress and strain were collected after every 100 freeze-thaw cycles. The relative durability index of the concrete specimens was calculated based on the weight loss rate and relative dynamic modulus of elasticity to measure the freeze-thaw resistance and durability of the recycled concrete.

[0081] The test results for the relevant performance are shown in Table 3 below:

[0082] Table 3

[0083]

[0084] As can be seen from the above table,

[0085] Before undergoing freeze-thaw cycles, the 28-day compressive strength of Examples 1-18 ranged from 34.41 MPa to 43.98 MPa, exhibiting excellent mechanical properties. Meanwhile, after undergoing 250 freeze-thaw cycles, the relative dynamic elastic modulus and mass loss rate of the samples from Examples 1-18 were 72.6%-82.5% and 2.83%-3.84%, respectively, demonstrating significantly better antifreeze performance than the samples from Comparative Examples 1 and 2.

[0086] A comparison of the test results from Examples 1-5 shows that the amount of composite antifreeze agent added to the formulation system has a significant impact on frost resistance. It promotes the dissolution of various ions within the recycled aggregate concrete in the early stages, improving the fluidity and water retention of the concrete mixture. The early bonding process also lowers the freezing point of the concrete, thus achieving excellent early strength and frost resistance. Furthermore, the addition of the composite antifreeze agent promotes early structural stability while enhancing its density and homogeneity, reducing cracking and improving basic mechanical and durability properties during later use, ultimately significantly improving the frost resistance of recycled concrete. Regarding the amount of composite antifreeze agent added to the raw materials, a low addition amount leads to poor early-stage integration of components, failing to guarantee later structural performance; while an excessive addition amount not only fails to further improve the frost resistance of the concrete but also causes a decrease in compressive strength due to the excessive addition of the composite antifreeze agent components. Based on the above analysis, controlling the addition amount of composite antifreeze agent in concrete raw materials to 0.21 wt.%-0.29 wt.% results in superior frost resistance.

[0087] Furthermore, comparing the test results of Examples 1 and 6-13 reveals the following patterns in the performance of roller-compacted concrete as the main effective components of the composite antifreeze are adjusted: compressive strength decreases with increasing ethylene glycol content, reaching its highest value at 0.5 kg of ethylene glycol; concrete compressive strength initially decreases slightly and then drops sharply with increasing sodium thiocyanate content; concrete compressive strength initially increases and then decreases with increasing sodium oxalate content, reaching its optimal value at 0.6 kg of sodium oxalate. In summary, considering the actual needs of engineering projects, the best synergistic effect is achieved when the mass ratio of ethylene glycol, sodium thiocyanate, and sodium oxalate in the core components of the composite antifreeze is controlled at 5:15:6. This significantly improves the antifreeze durability of fiber-recycled aggregate roller-compacted concrete while having minimal impact on its compressive strength. Furthermore, at this ratio, the antifreeze performance of the resulting freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete is significantly enhanced. Furthermore, comparing the test results of Example 1 and Example 14, it can be seen that a decrease in the content of sodium gluconate in the composition of the composite antifreeze will also affect its compressive strength and other indicators. Therefore, the optimal mass ratio of ethylene glycol, sodium thiocyanate, sodium oxalate, and sodium gluconate is 5:15:6:0.2.

[0088] Comparing the test results of Example 1 with those of Examples 14-16, it can be seen that in the formulation system of the present invention, with the increase of the amount of water-absorbing sepiolite fiber, the compressive strength and frost resistance both show a trend of first increasing and then decreasing, reaching the optimum at 60 kg. It was also found that water-absorbing sepiolite fiber significantly improves the frost resistance of concrete; however, due to its high water absorption rate, excessive addition can lead to a certain degree of decrease in both the compressive strength and frost resistance of the concrete. Therefore, controlling the amount of water-absorbing sepiolite fiber in the raw material formulation system within the range of 6.15 wt.%-6.67 wt.% helps to further improve the mechanical properties and frost resistance of roller-compacted concrete.

[0089] Comparing the test results of Example 1 and Example 17, it can be seen that when the recycled coarse aggregate is first coated with silica fume and fly ash, its compressive strength, relative dynamic elastic modulus, and mass loss rate are all better than those of the untreated sample. This proves that this pretreatment step can effectively remove the original defects such as loose and fragile old mortar and inherent cracks on the surface of the recycled coarse aggregate, thereby improving its compressive strength and durability to a certain extent.

[0090] Comparing the test results of Example 1 and Comparative Example 1, it can be seen that the composite antifreeze added to the raw materials of Example 1 did not adversely affect the mechanical properties of the fiber-recycled aggregate roller-compacted concrete, and the compressive strength was basically consistent with that of Comparative Example 1 without the composite antifreeze. However, after 250 freeze-thaw cycles, the relative dynamic modulus of elasticity and the mass loss rate of the specimen prepared in Example 1 with the composite antifreeze were significantly better than those without the composite antifreeze.

[0091] Comparing the test results of Example 1 and Comparative Example 2, it can be seen that while replacing sepiolite fibers with silica fume and fly ash can improve compressive strength, it significantly reduces frost resistance. This indicates that in this invention, the adsorption and good water retention properties of water-absorbing sepiolite fibers can improve durability and work synergistically with composite antifreeze agents to slow down ice crystal precipitation and reduce concrete expansion stress during freezing, thereby improving durability. Furthermore, it can compensate for the original defects of recycled aggregates during concrete preparation, improving workability.

[0092] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete, characterized in that, By weight, it consists of the following raw materials: 400-455 parts of rolled recycled coarse aggregate; 140-160 parts of cement; 14-18 parts of silica fume; 30-38 parts of fly ash; 195-225 parts of natural aggregate; 50-65 parts of water-absorbing sepiolite fiber; 50-70 parts of water; 2-4 parts of composite fiber aggregate; 1.25-3.6 parts of composite antifreeze agent; and 1-1.5 parts of polycarboxylate high-performance water-reducing agent. The composite antifreeze agent, by weight, is composed of the following raw materials: 0.05-0.15 parts ethylene glycol; 0.05-0.15 parts sodium thiocyanate; 0.04-0.08 parts sodium oxalate; 0.1-0.2 parts polyglycerol fatty acid ester; 0.01-0.05 parts sodium gluconate; and 1-3 parts water; In the raw materials of the freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete, the addition amount of water-absorbing sepiolite fiber is 6.15 wt.%-6.67 wt.%; the addition amount of composite antifreeze agent is 0.21 wt.%-0.29 wt.%. The water-absorbing sepiolite fiber is a fibrous magnesium-rich clay mineral with a fiber length of 2-3 mm, a water absorption rate of 160%-200% by weight, and a density of 1-1.2 g / cm³. 3 ; In the composite antifreeze, the mass ratio of ethylene glycol, sodium thiocyanate, sodium oxalate, and sodium gluconate is 5:15:6:0.

2.

2. The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to claim 1, characterized in that, The preparation method of the composite antifreeze includes the following steps: first, sodium thiocyanate, sodium oxalate and some water are mixed to obtain a mixture; then, the mixture is mixed with other raw materials of the composite antifreeze and stirred at high speed to obtain a uniform solution, which is the composite antifreeze.

3. The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to claim 1, characterized in that, The cement is ordinary Portland cement, and the fly ash is Grade I fly ash.

4. The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to claim 1, characterized in that, The natural aggregate is fine sand with an average particle size of 0.25-0.35 mm.

5. The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to claim 1, characterized in that, The crushed recycled coarse aggregate has a particle size of 5-20mm and is obtained from waste building materials through crushing and screening.

6. The freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to claim 1, characterized in that, The composite fiber aggregate is made by mixing polypropylene fibers with a length of 25-30 mm and polyvinyl alcohol fibers in a mass ratio of 1:

1.

7. A method for preparing freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Mix the rolled and recycled coarse aggregate with silica fume, fly ash and some water, and stir at a certain rate to obtain pretreated rolled and recycled coarse aggregate. S2. Add natural aggregate, cement, water-absorbing sepiolite fiber and composite fiber aggregate to the pretreated rolled recycled coarse aggregate in sequence, and continue to stir to obtain the mixture. S3. Add the remaining water, composite antifreeze agent and polycarboxylate high-performance water-reducing agent to the mixture, and continue stirring until uniformly mixed to obtain a freeze-thaw resistant fiber recycled aggregate roller-compacted concrete.

8. The preparation method according to claim 7, characterized in that, In step S1, the stirring speed is 40-80 r / min and the time is 4-6 h.

9. The application of freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete according to any one of claims 1-6, or freeze-thaw resistant fiber-recycled aggregate roller-compacted concrete prepared by the preparation method according to claim 7 or 8, characterized in that, The freeze-thaw resistant fiber recycled aggregate roller-compacted concrete is constructed using a method of thin-layer pouring and vibratory compaction.

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