High-ductility concrete based on composite modified rubber powder and preparation method thereof

Abstract

The application discloses high-ductility concrete based on composite modified rubber powder and a preparation method thereof, and production raw material formula includes the following component in the mass fraction ratio: cementing material 910-1050 parts, river sand 370-400 parts, composite modified filler 400-430 parts, fiber 13-20 parts, water reducing agent 5-6 parts, thickening agent 0.8-1.0 parts, and defoaming agent 2-6 parts; the composite modified filler is composed of calcined clay, oyster shell powder and composite modified waste rubber powder in the mass ratio of 0.8:0.1-0.15:0.05-0.1. The application has the following advantages: 1) experiments show that the application can significantly improve the mechanical properties of concrete, and the obtained high-ductility concrete has high compressive strength (>=67MPa), high flexural toughness (>=790kJ / m³), high tensile strength (>=5.6MPa) and high elongation rate (>=7.7%); and 2) the application realizes the resource utilization of waste rubber powder, oyster shell and other solid wastes, and conforms to the development direction of green building materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a fiber reinforced cement-based composite material, especially a concrete with high strength, high toughness and high ductility and a preparation method thereof. BACKGROUND

[0002] As the most important building material in modern times, concrete has inherent shortcomings such as brittleness, easy cracking and low tensile strength, which limit its application in complex stress or harsh environment.

[0003] Engineered Cementitious Composite (ECC) is a cement-based composite material based on the principle of micro-mechanical design, which is reinforced by short fibers and exhibits significant strain hardening characteristics and multi-crack behavior. Compared with ordinary concrete, ECC has extremely high tensile toughness (the ultimate tensile strain is usually more than 3%), can effectively control the crack width, and significantly improves the durability and seismic performance of the structure.

[0004] However, to achieve high ductility, traditional ECC usually relies on high cement content and special high-performance fibers (such as polyvinyl alcohol PVA fibers), resulting in high material cost. At the same time, high cement content also brings the problem of carbon emissions that cannot be ignored. On the other hand, using industrial or domestic solid waste (such as waste rubber powder) as filler or admixture in concrete is an important way to realize resource recycling and reduce environmental load. However, untreated rubber powder has weak interfacial adhesion with the cement matrix, which can seriously weaken the mechanical strength of the concrete; and the incorporation of a single solid waste often cannot balance the strength, toughness and workability of the concrete.

[0005] In the prior art, although some studies have tried to modify the rubber powder alone (such as alkali treatment, silane coupling agent treatment) or use it in combination with mineral admixtures (such as fly ash, silica fume), there are still problems such as limited modification effect, incomplete performance improvement, or lack of synergistic effect between different components. In particular, how to build a multi-component composite filler system so that the active mineral components produce a synergistic effect, thereby simultaneously and significantly improving the compressive, tensile, bending and deformation capacity of the concrete at low cost and low environmental impact, is still a technical problem to be solved in the field. SUMMARY

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-ductility concrete based on composite modified rubber powder and its preparation method. This technical solution, through specific raw material ratios and preparation processes, particularly by innovatively employing a composite modified filler system composed of calcined clay, oyster shell powder, and composite modified waste rubber powder in a specific proportion, and through synergistic effects with modified fibers and other components, achieves a unified high ductility, high strength, and high toughness in the concrete. Simultaneously, it efficiently utilizes solid waste, resulting in significant economic and environmental benefits.

[0007] This invention provides a method for preparing high-ductility concrete based on composite modified rubber powder, the core feature of which lies in the formulation and proportion of the raw materials. The formulation includes: 910-1050 parts of cementitious material, 370-400 parts of river sand, 400-430 parts of composite modified filler, 13-20 parts of fiber, 5-6 parts of water-reducing agent, 0.8-1.0 parts of thickener, and 2-6 parts of defoamer. The composite modified filler is composed of calcined clay, oyster shell powder, and composite modified waste rubber powder in a mass ratio of 0.8:0.1-0.15:0.05-0.1.

[0008] The waste rubber powder mentioned in this invention refers to 400~600μm rubber powder made from waste tires and / or sealing strips through mechanical crushing. The main rubber components of the waste tires are styrene-butadiene rubber, polybutadiene rubber and natural rubber, and the main component of the sealing strip rubber is vulcanized ethylene propylene rubber.

[0009] Preferably, the preparation of the composite modified waste rubber powder is the result of multi-stage composite modification, which includes water soaking, alkali treatment, acid treatment, silane coupling agent treatment and surface coating treatment in sequence. To enable those skilled in the art to better implement this invention, we have further refined the parameters of each step: water soaking (20-28h) can remove some water-soluble impurities; alkali treatment (8-12% NaOH, 25-35min) is mainly used to remove grease, plasticizers and other organic matter from the rubber surface, and slightly erode the surface to increase roughness; acid treatment (30-40% H2SO4, 20-28h) can further etch the surface and introduce oxygen-containing polar functional groups (such as -COOH, -OH), greatly improving surface energy; silane coupling agent treatment (0.8-1.2% solution, first at room temperature and then heated) can graft siloxane groups onto the activated rubber surface to achieve chemical "bridging" with the inorganic cement matrix; the final silica fume coating (mixed with rubber powder at a mass ratio of 1:0.1-0.3 for 20-40min) is based on chemical modification, and further enhances the mechanical interlocking and chemical bonding with cement hydration products by physically encapsulating highly active nano-silica fume particles. This series of treatments, from cleaning, activation, coupling to enhanced coating, systematically solves the core problem of weak rubber-cement interfacial adhesion.

[0010] Preferably, the waste rubber powder is composed of waste tire rubber in the total amount of styrene butadiene rubber and polybutadiene rubber and waste sealant strip in the amount of vulcanized ethylene-propylene rubber according to a mass ratio of 1:0.1-0.6. Experiments show that the two are compounded in this ratio, and treated by the aforementioned compounding modification process, a modified product with better comprehensive performance can be obtained.

[0011] Preferably, the cementitious material is composed of ordinary Portland cement, gypsum and fly ash according to a mass ratio of 4.5-5:0.5:1.5-2. This system utilizes cement to provide early strength, gypsum to regulate setting and to stimulate fly ash activity, and fly ash to play the role of pozzolanic effect and morphological effect (microbead lubrication), which helps to improve the workability and late strength. The fiber is a modified ultra-high molecular weight polyethylene (UHMWPE) fiber, with a single fiber diameter of 15-25 μm, a length of 12-18 mm, an elongation at break of ≤4.0%, a breaking strength of ≥30 cN / dtex, and an initial modulus of ≥1100 cN / dtex. These performance parameters ensure that the fiber has the characteristics of high strength and high modulus, and is the basis for bearing load and bridging cracks. The nano-cellulose solution modification and water bath heating treatment of the fiber aims to improve the interfacial adhesion between the fiber and the cement-based material.

[0012] The modified ultra-high molecular weight polyethylene fiber in the present application can be prepared according to the following specific preparation method: first, ultrasonically disperse nano-cellulose in water to form a uniform dispersion liquid of 1.5-2.5 mg / ml; then immerse the UHMWPE fiber and stir and heat in a water bath at 75-85°C for 3-5 h; and finally clean and dry. In this process, the nano-cellulose is attached to the surface of the fiber by physical adsorption and possible hydrogen bonding, forming a hydrophilic nano-coating rich in hydroxyl groups. This coating significantly improves the wettability and dispersibility of the hydrophobic UHMWPE fiber in the cement paste, and more importantly, the active groups on the surface of the fiber can form stronger chemical bonds with the cement hydration products (such as C-S-H gel), thereby greatly enhancing the adhesion strength of the fiber-matrix interface and enabling the bridging and toughening effect of the fiber to be fully exerted.

[0013] As those skilled in the art can easily understand, the present application can be prepared according to the commonly used concrete preparation method in the art, and in order to enable those skilled in the art to better implement the present application, we provide a preferred preparation method as follows:

[0014] S1. Weigh each raw material according to the raw material formula;

[0015] S2. Put the cementitious material, river sand and composite modified filler into a mixer, dry mix at a speed of 80-120 r / min for 1-2 min, and mix uniformly to obtain dry mixture;

[0016] S3, adding water reducing agent, thickening agent, defoaming agent and 50% to 70% of total water to the dry mixture, stirring at a speed of 120 to 180 r / min for 2 to 3 min to obtain a premixed slurry;

[0017] S4, uniformly scattering the modified ultra-high molecular weight polyethylene fiber into the premixed slurry, slowly stirring at a speed of 60 to 100 r / min for 1 to 2 min to uniformly disperse the fiber;

[0018] S5, adding the remaining mixing water, stirring at a speed of 180 to 250 r / min for 3 to 5 min to obtain a uniform concrete mixture;

[0019] S6, injecting the concrete mixture into a mold, vibrating and compacting, covering a curing film, demolding after curing at a temperature of 20±2℃ and a relative humidity of ≥95% for at least 24 h, and continuing to cure under the same conditions to the specified age to obtain the high ductility concrete; wherein the mass ratio of total water to cementitious material is 0.23 to 0.25:1.

[0020] The water-binder ratio is the key to achieving a high-strength, high-density matrix, but this puts extremely high requirements on the workability of the mixture and the dispersion of the fiber. The present application effectively ensures that a uniformly dispersed fiber, a mixture with suitable fluidity can be obtained under extremely low water-binder ratio by forming a premixed slurry first, then adding fiber, adding water in stages, and using a high-efficiency water reducing agent and thickening agent in coordination. Those skilled in the art can understand that the water used should meet the "Standard for Water for Concrete" (JGJ 63-2006).

[0021] Preferably, the calcined clay is preferably kaolinite clay calcined at 750 to 850℃ for 60 to 120 min, with a particle size of 1 to 100μm and a median particle size of 20 to 30μm. This calcination condition can remove the structural hydroxyl groups in kaolin to form metakaolin with high pozzolanic activity. The particle size of the oyster shell powder is 1 to 100μm, and the median particle size is 10 to 15μm. The oyster shell powder with such fineness (main component is CaCO3) not only fills the pores as micro-aggregate, but also provides heterogeneous nucleation sites for the hydration products, optimizing the morphology and distribution of C-S-H gel, thereby refining the pore structure.

[0022] Preferably, the river sand is graded by 40-70 mesh, 70-140 mesh, 140-200 mesh in a mass ratio of 1.1-1.5:1:0.4. The grading design is conducive to forming a close packing and reducing the porosity of the mortar system. The thickening agent is hydroxypropyl methyl cellulose ether (HPMC) for improving the cohesiveness of the paste, preventing particle settlement and fiber floating. The defoaming agent is a polyether modified silicone defoaming agent, which can effectively eliminate the air bubbles introduced during stirring and improve the density of the hardened body. The water reducing agent is a polycarboxylic acid based high performance water reducing agent with a water reducing rate of 35% or more, which is the core additive for realizing low water-binder ratio and ensuring fluidity.

[0023] The application also provides a high ductility concrete product based on composite modified rubber powder, which is prepared by the method for preparing the high ductility concrete product based on composite modified rubber powder.

[0024] The application has the following advantages:

[0025] 1) Comprehensive excellent mechanical properties: the product has high strength (compressive strength ≥67 MPa) and ultra-high ductility (elongation rate ≥7.7%), high toughness (equivalent bending toughness ≥790 kJ / m³), which breaks through the bottleneck that traditional materials are difficult to have both strength and toughness.

[0026] 2) Green and environmental protection and resource utilization: a large amount of solid waste such as waste rubber, discarded oyster shells and fly ash is consumed, the consumption of natural sand and gravel and the amount of cement are reduced, and the environmental benefits are significant.

[0027] 3) Strong process feasibility: all modification and preparation processes are carried out under conventional conditions without special equipment, which is convenient for industrial production and popularization. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The tensile failure pattern of the high ductility concrete sample prepared in Example One can be seen to have a good multi-crack cracking phenomenon during the tensile process.

[0029] Figure 2 The tensile stress-strain curve of the tensile performance test of the high ductility concrete sample prepared in Example One can be seen to have obvious strain hardening capacity and excellent tensile rate and tensile strength.

[0030] Figure 3 The bending failure pattern of the high ductility concrete sample prepared in Example One can be seen to have a large bending toughness capacity.

[0031] Figure 4 The load-deflection curve of the bending performance test of the high ductility concrete sample prepared in Example One can be seen to have excellent bending toughness and bending strength. DETAILED DESCRIPTION

[0032] The application is further illustrated below with reference to examples.

[0033] Example 1

[0034] The present example provides a preparation method of high ductility concrete based on composite modified rubber powder.

[0035] 1. Raw material preparation:

[0036] Binder: 1000 parts by mass in total, which is a mixture of P·O 42.5R ordinary portland cement, dihydrate gypsum, and Class II fly ash in a mass ratio of 4.7:0.5:1.8.

[0037] River sand: 385 parts by mass, which is graded by 40-70 mesh, 70-140 mesh, and 140-200 mesh river sand in a mass ratio of 1.3:1:0.4.

[0038] Composite modified filler: 415 parts by mass, which consists of:

[0039] Calcined clay: kaolin calcined at 800℃ for 90min and ground to a median particle size D50=25μm.

[0040] Oyster shell powder: waste oyster shells are washed, dried, ground, and sieved to a median particle size D50=12μm.

[0041] Composite modified waste rubber powder: the preparation method is as follows:

[0042] (1) Mix 400-600μm of waste tire rubber (total amount of butadiene styrene rubber and polybutadiene rubber) and waste sealant strip (total amount of vulcanized ethylene-propylene rubber) in a mass ratio of 1:0.3, soak in tap water for 24h, stir, filter, and dry in an oven at 60℃.

[0043] (2) Soak the dried rubber powder in a 10% (w / w) NaOH solution at room temperature for 30min with slight stirring. After taking out, wash repeatedly with deionized water until the filtrate pH≈7.0, and dry again.

[0044] (3) Soak the rubber powder obtained in step (2) in a 35% (w / w) H2SO4 solution at room temperature for 24h. After taking out, wash with a large amount of deionized water until neutral (pH≈7.0) and dry.

[0045] (4) Configuration 1% (w / w) of KH-550 silane coupling agent ethanol aqueous solution (ethanol: water = 9:1). The rubber powder obtained in step (3) is immersed in the solution, and mechanically stirred at room temperature for 20 min. Then the system is heated to 80℃, and continues to stir for 30 min. After natural cooling, filtration, and air drying.

[0046] (5) The rubber powder obtained in step (4) is mixed with silica (SiO2≥92%) at a mass ratio of 10:1, and placed in a high-speed mixer to stir at 500 r / min for 30 min, so that the silica uniformly coats the surface of the rubber powder, obtaining a composite modified waste rubber powder.

[0047] The calcined clay, oyster shell powder, and composite modified waste rubber powder are weighed and pre-mixed at a mass ratio of 0.8:0.12:0.08.

[0048] Fiber: 16 parts by mass of modified ultra-high molecular weight polyethylene fiber. The modification method is as follows:

[0049] (1) Nanocellulose (diameter 5-20 nm) is ultrasonically dispersed in deionized water to prepare a uniform dispersion with a concentration of 2.0 mg / ml.

[0050] (2) UHMWPE fibers with a breaking strength of 32 cN / dtex, an initial modulus of 1150 cN / dtex, a length of 15 mm, and a diameter of 19 μm are immersed in the above dispersion.

[0051] (3) The system is placed in a constant temperature water bath at 80℃, and continuously mechanically stirred for 4 hours.

[0052] (4) The fibers are removed, washed with deionized water to remove the residual nanocellulose on the surface, and dried in an oven at 60℃ to a constant weight.

[0053] Admixture: Polycarboxylic acid-based high-performance water reducing agent (solid content 40%, water reducing rate 40%) 5.5 parts; hydroxypropyl methylcellulose ether (viscosity 40000 mPa·s) 0.9 parts; polyether modified silicone defoamer 4.0 parts.

[0054] Water: The total water amount is 0.24 times the mass of the cementitious material, i.e. 240 parts.

[0055] 2. Preparation process:

[0056] S1: Accurately weigh each raw material according to the above formulation.

[0057] S2: The cementitious material, river sand, and pre-mixed composite modified filler are put into a planetary cement mortar mixer, and dry mixed at a speed of 100 r / min for 1.5 minutes to obtain a uniform dry mixture.

[0058] S3: Add water-reducing agent, thickening agent, defoaming agent and 60% of the total water (144 parts of water) to the dry mixture. Increase the stirring speed of the mixer to 150 r / min and stir for 2.5 minutes to obtain a well-flowing pre-mixed slurry without dry powder clumps.

[0059] S4: Suspend the stirring, and evenly and slowly sprinkle the modified ultra-high molecular weight polyethylene fibers onto the surface of the slurry. Restart the mixer at a lower speed of 80 r / min and stir for 1.5 minutes to ensure uniform dispersion of the fibers without clumping.

[0060] S5: Add the remaining 40% of the mixing water (96 parts of water), increase the stirring speed of the mixer to 220 r / min, and stir for 4 minutes until a uniformly colored, well-distributed fiber concrete mixture with appropriate fluidity is obtained.

[0061] S6: Pour the mixture into 100mm cubic test molds, 40mm x 40mm x 160mm prism test molds, and special dumbbell-shaped tensile test molds that have been coated with a release agent, and vibrate them on a vibrating table to compact them. Smooth the surface and cover it with plastic film to prevent water evaporation. After 24 hours in a standard curing room (temperature 20±1℃, relative humidity ≥95%), remove the test molds. Continue to cure the test pieces in the same standard curing room until the 28-day age, and then obtain the high-ductility concrete samples.

[0062] Example Two:

[0063] The difference between this example and Example One is the adjustment of the composition ratio of the composite modified filler and the proportion of each component in the cementitious material, aiming to demonstrate different implementations within the scope of the claims.

[0064] Raw material preparation adjustment section:

[0065] Cementitious material: total amount 950 parts by mass, composed of P·O 42.5R cement, gypsum, and fly ash in a mass ratio of 4.5:0.5:2.0.

[0066] Composite modified filler: 405 parts by mass. The mass ratio of calcined clay, oyster shell powder, and composite modified waste rubber powder is adjusted to 0.8:0.1:0.1.

[0067] Modified ultra-high molecular weight polyethylene fiber: dosage adjusted to 14 parts by mass.

[0068] Admixtures: polycarboxylic acid water reducer 5.0 parts, hydroxypropyl methylcellulose ether 0.8 parts, and defoaming agent 3.0 parts.

[0069] Water: total water amount is 0.23 times the mass of the cementitious material (218.5 parts).

[0070] The preparation process is completely same as example one.

[0071] Example three:

[0072] The difference between this example and example one is that the composition of the composite modified filler and the grading of the river sand are further adjusted.

[0073] Raw material preparation adjustment part:

[0074] Cementitious material: total amount 1050 mass parts, composed of P·O 42.5R cement, gypsum, fly ash in a mass ratio of 5.0:0.5:1.5.

[0075] River sand: 395 mass parts, graded by 40-70 mesh, 70-140 mesh, 140-200 mesh river sand in a mass ratio of 1.5:1:0.4.

[0076] Composite modified filler: 425 mass parts. Among them, the mass ratio of calcined clay, oyster shell powder, composite modified waste rubber powder is adjusted to 0.8:0.15:0.05.

[0077] Modified ultra-high molecular weight polyethylene fiber: the dosage is adjusted to 18 mass parts.

[0078] Admixtures: polycarboxylic acid water reducer 6.0 parts, hydroxypropyl methylcellulose ether 1.0 part, defoaming agent 5.0 parts.

[0079] Water: the total water amount is 0.25 times the mass of cementitious material (262.5 parts).

[0080] The preparation process is completely same as example one.

[0081] Example four:

[0082] This comparative example is a control experiment of example one, which is implemented according to the same steps and conditions as example one, and all raw materials are the same batch as example one, and the only difference is that when preparing the composite modified waste rubber powder, the waste seal strip rubber powder is not used, only the waste tire rubber powder is used. That is, the waste rubber powder is 100% waste tire rubber powder, and the composite modification process steps are completely same as example one.

[0083] All other raw material ratios, specifications, preparation steps and curing conditions are consistent with example one.

[0084] Example five:

[0085] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that when preparing the composite modified waste rubber powder, the waste tire rubber powder is not used, only the waste seal strip rubber powder is used. That is, the waste rubber powder is 100% waste seal strip rubber powder, and the composite modification process steps are exactly the same as Example 1.

[0086] All other raw material ratios, specifications, preparation steps, and curing conditions remain the same as Example 1.

[0087] Comparative Example 1:

[0088] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that the composite modified filler does not contain composite modified waste rubber powder. That is, the composite modified filler is only composed of calcined clay and oyster shell powder, the mass ratio of which is kept at 0.8:0.12, and the total mass of the composite modified filler is still 415 parts.

[0089] Comparative Example 2:

[0090] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that the composite modified filler does not contain calcined clay. That is, the composite modified filler is only composed of oyster shell powder and composite modified waste rubber powder, the mass ratio of which is kept at 0.12:0.08, and the total mass of the composite modified filler is still 415 parts.

[0091] Comparative Example 3:

[0092] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that the composite modified filler does not contain oyster shell powder. That is, the composite modified filler is only composed of calcined clay and composite modified waste rubber powder, the mass ratio of which is kept at 0.8:0.08, and the total mass of the composite modified filler is still 415 parts.

[0093] Comparative Example 4:

[0094] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that the original waste rubber powder without any modification (homologous to the rubber powder used in Example 1) is used instead of the composite modified waste rubber powder. The composition ratio of the composite modified filler (calcined clay:oyster shell powder:original waste rubber powder = 0.8:0.12:0.08) and the total amount remain unchanged.

[0095] Comparative Example 5:

[0096] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that the original ultra-high molecular weight polyethylene fiber without nano-cellulose modification (same specification as the fiber used in Example 1) is used instead of modified ultra-high molecular weight polyethylene fiber, and the fiber dosage remains unchanged.

[0097] Comparative Example 6:

[0098] The comparative example is a control experiment of Example 1, which is implemented according to the same steps and conditions as Example 1, and all raw materials are the same batch as Example 1, the only difference is that the water-binder ratio is increased from 0.24 to 0.28, that is, the total water amount is adjusted to 0.28 times the mass of cementitious materials (280 parts of water).

[0099] Mechanical property detection comparison experiment:

[0100] Detection method:

[0101] (1) Cube compressive strength: Referring to the "Standard for Testing Methods of Physical and Mechanical Properties of Concrete" GB / T 50081-2019, the compressive strength of 100mm cube specimens at 28d age is tested.

[0102] (2) Equivalent bending toughness and equivalent bending strength: Referring to Appendix A of "Technical Specification for High Toughness Concrete Reinforced Masonry Structures" T / CECS 997-2022, four-point bending test is performed on 40mm×40mm×160mm prism specimens to calculate bending toughness index and equivalent bending strength.

[0103] (3) Ultimate tensile strength and ultimate elongation: Referring to "Test Method for Mechanical Properties of High Ductility Fiber Reinforced Cementitious Composites" JC / T 2491-2018, dumbbell-shaped specimens are subjected to direct tensile test to obtain stress-strain curve, and ultimate tensile strength and corresponding ultimate elongation are calculated.

[0104] The detection results are shown in Table 1.

[0105] Table 1: Mechanical property test results of concrete obtained from Examples and Comparative Examples

[0106] Serial number Cubic compressive strength / MPa Equivalent bend flexibility / (kJ / m 3 ])]] Equivalent bending strength / MPa Ultimate tensile strength / MPa Ultimate elongation / % Example one 72.2 901.2 13.9 5.9 8.9 Example two 69.6 843.5 13.8 5.7 7.7 Example three 67.5 792.3 13.2 5.6 7.8 Example four (single waste tire rubber powder) 65.8 832.5 13.2 5.4 7.5 Example five (single waste sealant strip rubber powder) 64.2 801.3 12.9 5.2 7.3 Comparative example one (without modified rubber powder) 61.3 698.5 12.1 4.9 5.8 Comparative example two (without calcined clay) 58.7 655.3 11.5 4.8 6.2 Comparative example three (without oyster shell powder) 63.1 721.8 12.4 5.1 6.5 Comparative example four (rubber powder not modified) 50.8 580.1 11.0 4.5 6.3 Comparative example five (unmodified polyethylene fiber) 69.5 715.3 12.0 5.1 7.0 Comparative example six (water binder ratio 0.28 : 1) 57.3 630.5 10.9 4.8 5.6

[0107] From the comparison of the detection results in Table 1, it can be seen that:

[0108] 1. Synergistic effect of the composite modified filler components: under the condition of the same total amount of the composite modified filler, the performance of Example One (all three components) is overall and significantly better than that of Comparative Example One (without modified rubber powder), Comparative Example Two (without calcined clay), and Comparative Example Three (without oyster shell powder), which confirms the necessity of the synergy of the components.

[0109] In comparison with Comparative Example One (missing modified rubber powder): the compressive strength (61.3 MPa) and flexural toughness (698.5 kJ / m³) of Comparative Example One are both significantly reduced. The reason could be that although the calcined clay and oyster shell powder can improve the matrix density and strength, the lack of the elastic deformation ability and optimized interface transition zone provided by the composite modified waste rubber powder makes the material unable to achieve high ductility (elongation only 5.8%) and high energy dissipation (low toughness), and its performance is closer to that of ordinary high-strength mortar rather than ECC.

[0110] In comparison with Comparative Example Two (missing calcined clay): the performance of Comparative Example Two is one of the lowest in each item, especially the compressive strength (58.7 MPa) is significantly low. The reason could be that the pozzolanic reaction of calcined clay is crucial for the generation of additional C-S-H gel, the improvement of the matrix bulk strength and density. Its absence leads to a loose matrix structure, not only the strength decreases, but also its ability to constrain rubber particles and transfer stress is weakened, which further affects the toughness development.

[0111] In comparison with Comparative Example Three (missing oyster shell powder): the compressive strength (63.1 MPa) of Comparative Example Three is acceptable, but the flexural toughness (721.8 kJ / m³) and elongation (6.5%) are limited. The reason could be that the oyster shell powder mainly plays the micro-aggregate filling effect (optimizing particle size distribution, reducing harmful pores) and nucleation effect (promoting the ordered growth of hydration products), which are more focused on further densification and strengthening the interface region of the matrix and fibers, calcined clay, rubber. Its absence does not lead to a significant decrease in strength, but increases the brittleness of the matrix, which limits the material's ability to dissipate energy by generating multiple cracks during loading.

[0112] Conclusion: calcined clay, oyster shell powder and composite modified waste rubber powder form a synergistic system with complementary functions. Calcined clay and oyster shell powder work together to build a cement stone matrix with high strength and high density; while the composite modified waste rubber powder forms a strong and tough interface with this strengthened matrix, effectively initiating, bridging and stabilizing a large number of micro-cracks during loading. The three components show obvious synergistic effect in improving the mechanical properties of concrete.

[0113] 2. Synergistic effect of rubber powder source combination: The data of Comparative Example 1 (tire rubber powder combined with sealing strip rubber powder), Example 4 (tire rubber powder only) and Example 5 (sealing strip rubber powder only) can be clearly seen that under the same composite modification process and exactly the same concrete ratio, after using the two sources of waste rubber powder in a specific proportion, all the mechanical performance indicators of the high ductility concrete obtained are better than using any one of the rubber powder alone.

[0114] Compressive strength: Example 1 (72.2 MPa) is about 9.7% and 12.5% higher than Example 4 (65.8 MPa) and Example 5 (64.2 MPa) respectively.

[0115] Equivalent flexural toughness: Example 1 (901.2 kJ / m³) is about 8.3% and 12.5% higher than Example 4 (832.5 kJ / m³) and Example 5 (801.3 kJ / m³) respectively.

[0116] Ultimate tensile strength and elongation also show the same trend.

[0117] This shows that the tire rubber powder based on styrene butadiene rubber and the sealing strip rubber powder based on ethylene propylene rubber produce a positive synergistic effect in the concrete system after being modified by the present application. The inventors believe that this may be because the molecular chain structure, polarity and filler contained (such as carbon black in tire rubber powder) of the two rubbers are different, resulting in differences in surface chemical state and micro-morphology after the same modification process. This differentiated interface property may form a more optimal stress transfer and energy dissipation mechanism when interacting with the cement matrix, thereby achieving the effect of "1+1>2".

[0118] 3. Modification process and necessity of key parameters:

[0119] Necessity of rubber powder modification (Example 1 vs. Comparative Example 4): The compressive strength of Comparative Example 4 using unmodified waste rubber powder (50.8 MPa) dropped sharply, about 29.3% lower than Example 1. This directly proves that untreated rubber powder has very poor interface adhesion with the cement matrix, becoming a weak point in the structure, seriously weakening the overall strength of the composite material. The multi-stage composite modification process of the present application (alkali washing to remove oil, acid etching to activate, silane coupling, and silica coating) systematically solves this problem, and through physical and chemical methods, an active interface layer that can firmly combine with the cement hydration products is constructed on the surface of the rubber powder, which is the key to achieving "no strength reduction with rubber" or even "strength enhancement with rubber".

[0120] Necessity of fiber modification (Example 1 vs. Comparative Example 5): Comparative Example 5 using unmodified UHMWPE fiber has a flexural toughness (715.3 kJ / m³) and ultimate tensile strength (5.05 MPa) that are 20.1% and 14.6% lower than Example 1, respectively. UHMWPE fiber has a smooth surface and is chemically inert, with weak adhesion to cementitious matrix. The nanocellulose solution water bath modification method described in the present invention introduces a hydrophilic nanocoating rich in hydroxyl groups on the fiber surface. This significantly improves the wettability of the fiber and enables it to form stronger physical adsorption and chemical bonding with C-S-H gel, thereby greatly improving the efficiency of the fiber in bridging cracks, transmitting stress, and dissipating energy, which is the core guarantee of high toughness.

[0121] Necessity of low water-binder ratio (Example 1 vs. Comparative Example 6): Increasing the water-binder ratio of Comparative Example 6 to 0.28 results in a sharp deterioration in all its properties, especially compressive strength (57.3 MPa) and elongation (5.6%). Water-binder ratio is the most sensitive factor affecting the porosity and density of cementitious materials. The present invention strictly controls the water-binder ratio to be between 0.23 and 0.25, which is the lowest limit for obtaining workable mixtures under the premise of using high-efficiency water-reducing agents and thickening agents. This low water-binder ratio ensures the ultra-high density of the hardened matrix, providing an almost defect-free matrix platform for the synergistic effect of the aforementioned components. Once the water-binder ratio increases, the porosity increases, the strength of the matrix itself decreases, and the interface region becomes weaker, making it impossible to achieve synergistic effect.

[0122] In summary, the present invention solves the industry problems of difficult simultaneous improvement of strength and toughness of high ductility concrete and performance degradation caused by solid waste utilization through the following three-in-one technical innovations: (1) synergistic effect of specific composite modified filler components (calcined clay / oyster shell powder / composite modified rubber powder), (2) optimized combination of waste rubber powder sources (tire rubber / seal strip rubber), and (3) key modification process and preparation parameters (modification of rubber powder and fiber, low water-binder ratio). The present invention achieves the unification of performance breakthrough and green preparation.

Claims

1. A method for producing a high-ductility concrete based on a composite modified rubber powder, characterized in that, The production raw material formula comprises the following components in the mass ratio: cementing material 910-1050 parts, river sand 370-400 parts, composite modified filler 400-430 parts, fiber 13-20 parts, water reducing agent 5-6 parts, thickening agent 0.8-1.0 parts, and defoaming agent 2-6 parts; the composite modified filler is composed of calcined clay, oyster shell powder and composite modified waste rubber powder in the mass ratio of 0.8:0.1-0.15:0.05-0.1; the cementing material is composed of ordinary Portland cement, gypsum and fly ash in the mass ratio of 4.5-5:0.5:1.5-2; the composite modified waste rubber powder is prepared by sequentially treating waste rubber powder with water immersion, alkali treatment, acid treatment, silane coupling agent treatment and surface coating treatment, and the specific method is as follows: (1) waste rubber powder with a particle size of 400-600 μm is soaked in water for 20-28 h, washed, filtered and air dried; (2) the waste rubber powder treated in step (1) is soaked in a 8%-12% NaOH solution for 25-35 min, washed with water until the pH is 6.9-7.1, and air dried; (3) the waste rubber powder treated in step (2) is soaked in a 30%-40% H2SO4 solution for 20-28 h, washed with water until the pH is 6.9-7.1, and air dried; (4) the waste rubber powder treated in step (3) is immersed in a 0.8%-1.2% silane coupling agent solution, stirred at 20-30 ℃ for 15-25 min, then heated to 75-85 ℃ and continuously stirred for 25-35 min, cooled and air dried; (5) the waste rubber powder treated in step (4) is mixed with silica ash by mechanical stirring at a mass ratio of 1:0.1-0.3 for 20-40 min to complete the surface coating, and the composite modified waste rubber powder is obtained; The waste rubber powder is composed of waste tire rubber, which accounts for 1:0.1-0.6 of the total amount of styrene-butadiene rubber and polybutadiene rubber, and waste sealant strip, which accounts for 1:0.1-0.6 of the total amount of vulcanized ethylene-propylene rubber.

2. The method for preparing a high-ductility concrete based on composite modified rubber powder according to claim 1, characterized in that: The fiber is a modified ultra-high molecular weight polyethylene fiber; the modified ultra-high molecular weight polyethylene fiber is prepared by modifying ultra-high molecular weight polyethylene fiber with a nanocellulose solution and heating in a water bath; the single-fiber diameter of the ultra-high molecular weight polyethylene fiber is 15-25 μm, the length is 12-18 mm, the elongation at break is ≤4.0%, the breaking strength is ≥30 cN / dtex, and the initial modulus is ≥1100 cN / dtex.

3. The method for preparing a high ductility concrete based on composite modified rubber powder according to claim 2, characterized in that: The modified ultra-high molecular weight polyethylene fiber is prepared by the following method: (1) nanocellulose is dispersed in water to prepare a dispersion liquid with a concentration of 1.5-2.5 mg / ml, and ultrasonic treatment is performed for 10-30 min; (2) the ultra-high molecular weight polyethylene fiber is immersed in the nanocellulose dispersion liquid and stirred and heated in a 75-85 ℃ water bath for 3-5 h; (3) the fiber is taken out, washed with deionized water, dried, and the modified ultra-high molecular weight polyethylene fiber is obtained.

4. The method of claim 2, wherein the high ductility concrete based on the composite modified rubber powder is prepared by mixing the composite modified rubber powder, the cement, the fine aggregate, the coarse aggregate, the water, and the additive. The method comprises the following steps: S1, each raw material is weighed according to the production raw material formula; S2, the cementitious material, river sand and composite modified filler into the mixer, at a speed of 80-120 r / min dry mixing 1-2 min, mixed evenly to get dry mix; S3, to the dry mix adding water reducing agent, thickening agent, defoaming agent and the total water 50%-70%, at a speed of 120-180 r / min stirring 2-3 min, get premix slurry; S4, to the premix slurry evenly into the modified ultra high molecular weight polyethylene fiber, at a speed of 60-100 r / min slow stirring 1-2 min, make fiber dispersion uniform; S5, add the remaining mixing water, at a speed of 180-250 r / min stirring 3-5 min, get uniform concrete mixture; S6, the concrete mixture into the mold, vibrating compaction, cover curing film, under the condition of temperature 20±2℃, relative humidity ≥95% curing at least 24 h after demolding, continue to be cured under the same conditions to the specified age, get the high ductility concrete; wherein, the total water and cementitious material mass ratio is 0.23-0.25:

1.

5. The method of claim 1, wherein the method is characterized by: The calcined clay is kaolinite clay calcined at 750-850℃ for 60-120 min, then crushed and sieved, with a particle size of 1-100 μm and a median particle size of 20-30 μm; the oyster shell powder has a particle size of 1-100 μm and a median particle size of 10-15 μm.

6. The method of claim 1, wherein the method is characterized by: The river sand is graded from 40-70 mesh river sand, 70-140 mesh river sand and 140-200 mesh river sand at a mass ratio of 1.1-1.5:1:0.4; the thickening agent is hydroxypropyl methyl cellulose ether; the defoaming agent is polyether modified silicone defoaming agent; and the water reducing agent is polycarboxylic acid water reducing agent with a water reducing rate of ≥35%.

7. A high ductility concrete based on composite modified rubber powder, characterized in that, Prepared by the method of any one of claims 1-6.

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