Desert sand polyvinyl alcohol fiber cement-based composite material and preparation method thereof

Abstract

The invention relates to the technical field of concrete, in particular to a desert sand polyvinyl alcohol fiber cement-based composite material and a preparation method thereof. The desert sand polyvinyl alcohol fiber cement-based composite material is prepared from the following raw materials in parts by mass: 50 to 100 parts of cement, 20 to 40 parts of desert sand, 40 to 60 parts of fly ash, 1 to 3 parts of gamma-aminopropyltriethoxysilane, 5 to 15 parts of activated fiber, 5 to 15 parts of polyvinyl alcohol fiber, 1.5 to 3 parts of water reducing agent, 0.5 to 2 parts of thickening agent and 40 to 60 parts of water. The use amount of cement can be reduced, waste is reused, desert sand resources are reasonably developed, the waste is reused, and meanwhile the preparation method is simple and suitable for large-scale application and popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, in particular to a desert sand polyvinyl alcohol fiber cement-based composite material and a preparation method thereof. Background Art

[0002] Concrete has long been a widely used and in-demand building material in industrial structures and civil construction projects. Sand, a key component of concrete, is currently primarily sourced from natural river sand and manufactured sand. Most sand and gravel companies operate on a small scale, with outdated production and processing technology and management, resulting in low equipment and mechanical efficiency. This results in various performance indicators of medium-grade sand failing to meet regulatory requirements. Consequently, serious challenges exist in terms of production quantity, quality, gradation requirements, economic benefits, and environmental protection. Furthermore, the use of sand in construction projects is complex, directly impacting the quality of construction.

[0003] In recent years, the ultra-high performance of polyvinyl alcohol (PVA) fiber-cement composites has attracted the attention of numerous experts and scholars both domestically and internationally. PVA fiber-cement composites typically use cement, or cement plus fillers, or small-particle fine aggregate as a base, with PVA fibers as the reinforcement. Compared to carbon and steel fibers, PVA fibers offer lower density, higher adhesion, better dispersibility, and easier mixing. Compared to other synthetic fibers, PVA fibers exhibit greater hydrophilicity, a higher elastic modulus, and a larger specific surface area. They are also highly compatible with cement and offer a significant reinforcement effect. Furthermore, PVA fiber-cement composites exhibit high-temperature resistance, wear resistance, fatigue resistance, and are environmentally friendly.

[0004] Therefore, it has excellent research prospects to use PVA fiber cement-based composites to replace traditional concrete, and to use desert sand to replace silica sand or river sand in PVA fiber cement-based composites, to improve the compressive and tensile strength of desert sand PVA fiber cement-based composites, and to enhance the tensile strain properties of desert sand PVA fiber cement-based composites. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a desert sand polyvinyl alcohol fiber cement-based composite material and a preparation method thereof.

[0006] A desert sand polyvinyl alcohol fiber cement-based composite material comprises the following raw materials in parts by mass: 50-100 parts of cement, 20-40 parts of desert sand, 40-60 parts of fly ash, 1-3 parts of gamma-aminopropyltriethoxysilane, 5-15 parts of activated fiber, 5-15 parts of polyvinyl alcohol fiber, 1.5-3 parts of a water reducer, 0.5-2 parts of a thickener, and 40-60 parts of water.

[0007] Preferably, the cement is Portland cement and / or fast-hardening sulphoaluminate cement.

[0008] Preferably, the cement is composed of Portland cement and rapid hardening sulphoaluminate cement in a mass ratio of 10:1-2.

[0009] Preferably, the water reducer is a polycarboxylic acid high performance water reducer.

[0010] Preferably, the thickener is hydroxypropyl methylcellulose and / or polyacrylamide.

[0011] Preferably, the activated fiber is prepared by the following steps: adding basalt fiber to a mixed acid solution, ultrasonically treating at 50-60°C for 2-4 hours, centrifuging, washing, and vacuum drying; adding to a Tris solution, adjusting the pH value of the system to 8-9, adding dopamine hydrochloride, stirring at 50-60°C for 1-2 hours, centrifuging, washing, and vacuum drying.

[0012] More preferably, the mass ratio of basalt fiber to dopamine hydrochloride is 5-15:1-2.

[0013] More preferably, in the mixed acid solution, the concentration of phosphoric acid is 2-4 mol / L, and the concentration of sodium nitrate is 1-2 mol / L.

[0014] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Mix cement, desert sand and fly ash for 10-20 minutes to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to an ethanol aqueous solution, adjust the pH value of the system to 8-9, stir for 1-2 hours, add activated fiber thereto, reflux at 60-80° C. under nitrogen protection and stir for 1-2 hours, filter, wash, and vacuum dry, add premix a and stir for 5-10 minutes to obtain premix b; S3. Add polyvinyl alcohol fiber, water reducer, thickener and water to premix b and stir for 1-5 minutes.

[0015] Beneficial effects: The present invention utilizes low-cost desert sand mixed with polyvinyl alcohol fiber, fully utilizes desert sand resources and high-content fly ash, and cooperates with the effect of activated fiber to ensure that the concrete has sufficient compressive strength while giving it higher tensile strength and excellent strain capacity.

[0016] The present invention covers basalt fibers with a polydopamine layer as a load layer, optimizes the interface of the polydopamine layer, ensures high dispersion uniformity between the product and the premix a, and comprehensively improves the mechanical properties of the product; polyvinyl alcohol fibers have the problem of poor long chain fluidity, and directly blending with basalt fibers will lead to deterioration of mechanical strength. The present invention activates and grafts the basalt fibers, further controlling the mass ratio with the polyvinyl alcohol fibers, so that the cement-based composite material has both high mechanical strength and excellent inhibition of crack expansion in the mortar.

[0017] The invention can reduce cement usage and reuse waste, thereby rationally developing desert sand resources and reusing waste materials. The preparation method is simple and suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a comparison chart of the compressive strength of samples prepared using the cement-based composite materials obtained in Example 5 and Comparative Examples 1-2.

[0019] Figure 2 1 is a comparison chart of the tensile strength of samples prepared using the cement-based composite materials obtained in Example 5 and Comparative Examples 1-2.

[0020] Figure 3 1 and 2 are comparative diagrams of tensile strain of samples respectively prepared using the cement-based composite materials obtained in Example 5 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0021] The present invention will be further explained below with reference to specific embodiments.

[0022] The cement used below is sourced from a local cement manufacturer in Ordos. The desert sand used below is mined from the Kubuqi Desert in Ordos, with a mud content of ≤2.05% and a particle size of 100-400μm. The polyvinyl alcohol fiber used below is purchased from Inner Mongolia Shuangmou Environmental Protection Materials Co., Ltd., with a length of 6mm and a diameter of 30μm. The basalt fiber used below is sourced from Inner Mongolia Damou New Materials Co., Ltd., with a length of 6mm.

[0023] Example 1: A desert sand polyvinyl alcohol fiber cement-based composite material, whose raw materials include: 500g of PO 42.5 ordinary Portland cement, 200g of desert sand, 400g of Class I fly ash, 10g of γ-aminopropyltriethoxysilane, 50g of activated fiber, 50g of polyvinyl alcohol fiber, 15g of polycarboxylic acid high-performance water reducer, 5g of polyacrylamide, and 400g of water.

[0024] The activated fiber was prepared by the following steps: 50 g of basalt fiber was added to 300 g of mixed acid solution (wherein the concentration of phosphoric acid was 2 mol / L and the concentration of sodium nitrate was 1 mol / L), ultrasonically treated at a temperature of 50°C for 2 h and an ultrasonic frequency of 40 kHz, centrifuged, washed once with deionized water, vacuum dried, added to 300 g of Tris solution, adjusted the pH value of the system to 8-9, added 10 g of dopamine hydrochloride, stirred at a temperature of 50°C for 1 h, centrifuged, washed, and vacuum dried.

[0025] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add PO 42.5 ordinary Portland cement, desert sand, and Class I fly ash into a mixer and stir at a speed of 200 r / min for 10 min to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to 300 g of 40% ethanol solution by mass, adjust the pH value of the system to 8-9 with 1 mol / L sodium hydroxide solution, stir for 1 hour, add activated fiber, reflux and stir at 60°C under nitrogen protection for 1 hour, filter, wash, and vacuum dry, add premix a and stir for 5 minutes at a stirring speed of 100 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, polyacrylamide and water to premix b and stir for 1 minute.

[0026] Example 2: A desert sand polyvinyl alcohol fiber cement-based composite material, whose raw materials include: 1000g of R.SAC 42.5 fast-hardening sulphoaluminate cement, 400g of desert sand, 600g of Class I fly ash, 30g of γ-aminopropyltriethoxysilane, 150g of activated fiber, 150g of polyvinyl alcohol fiber, 30g of polycarboxylic acid high-performance water reducer, 20g of polyacrylamide, and 600g of water.

[0027] The activated fiber was prepared by the following steps: 150 g of basalt fiber was added to 600 g of mixed acid solution (wherein the concentration of phosphoric acid was 4 mol / L and the concentration of sodium nitrate was 2 mol / L), ultrasonically treated at 60°C for 4 h and an ultrasonic frequency of 60 kHz, centrifuged, washed once with deionized water, vacuum dried, added to 600 g of Tris solution, adjusted the pH value of the system to 8-9, added 20 g of dopamine hydrochloride, stirred at 60°C for 2 h, centrifuged, washed, and vacuum dried.

[0028] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add R.SAC 42.5 fast-hardening sulphoaluminate cement, desert sand, and Class I fly ash into a mixer and stir at 300 r / min for 20 min to obtain premix a. S2. Add γ-aminopropyltriethoxysilane to 500 g of 60% ethanol solution, adjust the pH value of the system to 8-9 with 2 mol / L sodium hydroxide solution, stir for 2 h, add activated fiber, reflux and stir at 80°C under nitrogen for 2 h, filter, wash, and vacuum dry, add premix a and stir for 10 min at a stirring speed of 500 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, polyacrylamide and water to premix b and stir for 5 minutes.

[0029] Example 3: A desert sand polyvinyl alcohol fiber cement-based composite material, the raw materials of which include: 700g cement, 350g desert sand, 450g Class I fly ash, 25g γ-aminopropyltriethoxysilane, 80g activated fiber, 120g polyvinyl alcohol fiber, 20g polycarboxylate high-performance water reducer, 16g hydroxypropyl methylcellulose, and 450g water. The cement is composed of PO 42.5 ordinary Portland cement and R.SAC 42.5 rapid-hardening sulfoaluminate cement in a mass ratio of 10:2.

[0030] The activated fiber was prepared by the following steps: 80 g of basalt fiber was added to 500 g of mixed acid solution (wherein the concentration of phosphoric acid was 2.5 mol / L and the concentration of sodium nitrate was 1.7 mol / L), ultrasonically treated at a temperature of 52°C for 3.5 h and an ultrasonic frequency of 45 kHz, centrifuged, washed twice with deionized water, vacuum dried, added to 500 g of Tris solution, adjusted the pH value of the system to 8-9, added 12 g of dopamine hydrochloride, stirred at a temperature of 58°C for 80 min, centrifuged, washed, and vacuum dried.

[0031] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add cement, desert sand, and Class I fly ash into a mixer and stir at a speed of 360 r / min for 12 min to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to 450 g of 45% by mass ethanol solution, adjust the pH value of the system to 8-9 with 1.8 mol / L sodium hydroxide solution, stir for 80 min, add activated fiber, reflux and stir at 75°C under nitrogen for 80 min, filter, wash, and vacuum dry, add premix a and stir for 9 min at a stirring speed of 200 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, hydroxypropyl methylcellulose and water to premix b and stir for 4 minutes.

[0032] Example 4: A desert sand polyvinyl alcohol fiber cement-based composite material, comprising: 900g cement, 250g desert sand, 550g Class I fly ash, 15g γ-aminopropyltriethoxysilane, 120g activated fiber, 80g polyvinyl alcohol fiber, 24g polycarboxylate high-performance water reducer, 10g hydroxypropyl methylcellulose, and 550g water. The cement is composed of PO 42.5 ordinary Portland cement and R.SAC 42.5 rapid-hardening sulfoaluminate cement in a mass ratio of 10:1.

[0033] The activated fiber was prepared by the following steps: 120 g of basalt fiber was added to 400 g of mixed acid solution (wherein the concentration of phosphoric acid was 3.5 mol / L and the concentration of sodium nitrate was 1.3 mol / L), ultrasonically treated at a temperature of 58°C for 2.5 h and an ultrasonic frequency of 55 kHz, centrifuged, washed twice with deionized water, vacuum dried, added to 400 g of Tris solution, adjusted the pH value of the system to 8-9, added 18 g of dopamine hydrochloride, stirred at a temperature of 52°C for 100 min, centrifuged, washed, and vacuum dried.

[0034] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add cement, desert sand, and Class I fly ash into a mixer and stir at a speed of 240 r / min for 18 min to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to 350 g of 55% ethanol solution, adjust the pH value of the system to 8-9 with 1.2 mol / L sodium hydroxide solution, stir for 100 min, add activated fiber, reflux and stir at 65°C under nitrogen for 100 min, filter, wash, and vacuum dry, add premix a and stir for 7 min at a stirring speed of 400 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, hydroxypropyl methylcellulose and water to premix b and stir for 2 minutes.

[0035] Example 5: A desert sand polyvinyl alcohol fiber cement-based composite material, comprising: 800g cement, 300g desert sand, 500g Class I fly ash, 20g γ-aminopropyltriethoxysilane, 100g activated fiber, 100g polyvinyl alcohol fiber, 22g polycarboxylate high-performance water reducer, 15g hydroxypropyl methylcellulose, and 500g water. The cement is composed of PO 42.5 ordinary Portland cement and R.SAC 42.5 rapid-hardening sulfoaluminate cement in a mass ratio of 10:1.5.

[0036] The activated fiber was prepared by the following steps: 100 g of basalt fiber was added to 450 g of mixed acid solution (wherein the concentration of phosphoric acid was 3 mol / L and the concentration of sodium nitrate was 1.5 mol / L), ultrasonically treated at a temperature of 55°C for 3 h and an ultrasonic frequency of 50 kHz, centrifuged, washed twice with deionized water, vacuum dried, added to 450 g of Tris solution, adjusted the pH value of the system to 8-9, added 15 g of dopamine hydrochloride, stirred at a temperature of 55°C for 90 min, centrifuged, washed, and vacuum dried.

[0037] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add cement, desert sand, and Class I fly ash into a mixer and stir at a speed of 300 r / min for 15 min to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to 400 g of 50% by mass ethanol solution, adjust the pH value of the system to 8-9 with 1.5 mol / L sodium hydroxide solution, stir for 90 min, add activated fiber, reflux and stir at 70°C under nitrogen for 90 min, filter, wash, and vacuum dry, add premix a and stir for 8 min at a stirring speed of 300 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, hydroxypropyl methylcellulose and water to premix b and stir for 3 minutes.

[0038] Comparative Example 1: A desert sand polyvinyl alcohol fiber cement-based composite material, the raw materials of which include: 800g cement, 300g desert sand, 500g Class I fly ash, 20g γ-aminopropyltriethoxysilane, 100g activated fiber, 100g polyvinyl alcohol fiber, 22g polycarboxylate high-performance water reducer, 15g hydroxypropyl methylcellulose, and 500g water. The cement is composed of PO 42.5 ordinary Portland cement and R.SAC 42.5 rapid-hardening sulfoaluminate cement in a mass ratio of 10:1.5.

[0039] The activated fiber was prepared by the following steps: 100 g of basalt fiber was added to 450 g of mixed acid solution (wherein the concentration of phosphoric acid was 3 mol / L and the concentration of sodium nitrate was 1.5 mol / L), ultrasonically treated at a temperature of 55°C for 3 h and an ultrasonic frequency of 50 kHz, centrifuged, washed twice with deionized water, and vacuum dried.

[0040] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add cement, desert sand, and Class I fly ash into a mixer and stir at a speed of 300 r / min for 15 min to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to 400 g of 50% by mass ethanol solution, adjust the pH value of the system to 8-9 with 1.5 mol / L sodium hydroxide solution, stir for 90 min, add activated fiber, reflux and stir at 70°C under nitrogen for 90 min, filter, wash, and vacuum dry, add premix a and stir for 8 min at a stirring speed of 300 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, hydroxypropyl methylcellulose and water to premix b and stir for 3 minutes.

[0041] Comparative Example 2: A desert sand polyvinyl alcohol fiber cement-based composite material, the raw materials of which include: 800g cement, 300g desert sand, 500g Class I fly ash, 20g γ-aminopropyltriethoxysilane, 100g activated fiber, 100g polyvinyl alcohol fiber, 22g polycarboxylate high-performance water reducer, 15g hydroxypropyl methylcellulose, and 500g water. The cement is composed of PO 42.5 ordinary Portland cement and R.SAC 42.5 rapid-hardening sulfoaluminate cement in a mass ratio of 10:1.5.

[0042] The activated fiber was prepared by the following steps: 100 g of basalt fiber was added to 450 g of mixed acid solution (wherein the concentration of phosphoric acid was 3 mol / L and the concentration of sodium nitrate was 1.5 mol / L), ultrasonically treated at a temperature of 55°C for 3 h and an ultrasonic frequency of 50 kHz, centrifuged, washed twice with deionized water, vacuum dried, added to 450 g of Tris solution, adjusted the pH value of the system to 8-9, added 15 g of dopamine hydrochloride, stirred at a temperature of 55°C for 90 min, centrifuged, washed, and vacuum dried.

[0043] The method for preparing the above-mentioned desert sand polyvinyl alcohol fiber cement-based composite material comprises the following steps: S1. Add cement, desert sand, and Class I fly ash into a mixer and stir at a speed of 300 r / min for 15 min to obtain premix a; S2. Evenly mix γ-aminopropyltriethoxysilane and activated fiber, add premix a and stir for 8 minutes at a stirring speed of 300 r / min to obtain premix b; S3. Add polyvinyl alcohol fiber, polycarboxylic acid high-performance water reducer, hydroxypropyl methylcellulose and water to premix b and stir for 3 minutes.

[0044] The cement-based composite materials obtained in Example 5 and Comparative Examples 1-2 were poured into a mold (40 mm × 40 mm × 160 mm), demolded, and placed in a curing chamber (temperature 20 ± 2°C, humidity ≥ 95%) for 7-28 days. Performance tests were conducted on each set of concrete specimens in accordance with T / CECS 864-2021, "Test Methods for Ultra-High Performance Concrete."

[0045] like Figures 1 to 3 As shown, the compressive strength, tensile strength and tensile strain of the sample prepared by using the cement-based composite material obtained in Example 5 are the highest, which are better than those of Comparative Examples 1-2 (P < 0.05).

[0046] The reasons for the above results are as follows: the present invention covers the basalt fiber with a polydopamine layer as a load layer, optimizes the interface of the polydopamine layer, makes the dispersion uniformity between the product and the premix a high, and comprehensively improves the mechanical properties of the product; the polyvinyl alcohol fiber has the problem of poor long chain fluidity, and directly blending it with the basalt fiber will lead to deterioration of mechanical strength. The present invention activates and grafts the basalt fiber, further controlling the mass ratio with the polyvinyl alcohol fiber, so that the cement-based composite material has both high mechanical strength and excellent inhibitory effect on the expansion of mortar cracks. At the same time, the present invention uses low-cost desert sand mixed with polyvinyl alcohol fiber, fully utilizing desert sand resources and high fly ash content, combined with the effect of activated fibers, to ensure that the concrete has sufficient compressive strength, so that it has high tensile strength and excellent strain capacity.

[0047] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A desert sand polyvinyl alcohol fiber cement-based composite material, characterized in that: The raw materials include, by mass, 50-100 parts of cement, 20-40 parts of desert sand, 40-60 parts of fly ash, 1-3 parts of gamma-aminopropyltriethoxysilane, 5-15 parts of activated fiber, 5-15 parts of polyvinyl alcohol fiber, 1.5-3 parts of water reducer, 0.5-2 parts of thickener and 40-60 parts of water.

2. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 1, characterized in that: The cement is silicate cement and / or fast-hardening sulphoaluminate cement.

3. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 1, characterized in that: The cement is composed of silicate cement and fast-hardening sulphoaluminate cement in a mass ratio of 10:1-2.

4. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 1, characterized in that: The water reducer is a polycarboxylic acid high performance water reducer.

5. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 1, characterized in that: The thickener is hydroxypropyl methylcellulose and / or polyacrylamide.

6. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 1, characterized in that: The activated fiber is prepared by the following steps: adding basalt fiber to a mixed acid solution, ultrasonically treating at 50-60°C for 2-4 hours, centrifuging, washing, and vacuum drying; adding basalt fiber to a Tris solution, adjusting the pH value of the system to 8-9, adding dopamine hydrochloride, stirring at 50-60°C for 1-2 hours, centrifuging, washing, and vacuum drying.

7. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 7, characterized in that: The mass ratio of basalt fiber to dopamine hydrochloride is 5-15:1-2.

8. The desert sand polyvinyl alcohol fiber cement-based composite material according to claim 7, characterized in that: In the mixed acid solution, the concentration of phosphoric acid is 2-4 mol / L, and the concentration of sodium nitrate is 1-2 mol / L.

9. A method for preparing the desert sand polyvinyl alcohol fiber cement-based composite material according to any one of claims 1 to 9, characterized in that: The steps include: S1. Mix cement, desert sand and fly ash for 10-20 minutes to obtain premix a; S2. Add γ-aminopropyltriethoxysilane to an ethanol aqueous solution, adjust the pH value of the system to 8-9, stir for 1-2 hours, add activated fiber thereto, reflux at 60-80° C. under nitrogen protection and stir for 1-2 hours, filter, wash, and vacuum dry, add premix a and stir for 5-10 minutes to obtain premix b; S3. Add polyvinyl alcohol fiber, water reducer, thickener and water to premix b and stir for 1-5 minutes.

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