Anti-crack shrinkage-inhibiting desert sand foam concrete and preparation method thereof

Abstract

The invention provides anti-cracking shrinkage-inhibiting desert sand foam concrete and a preparation method thereof, and belongs to the technical field of foam concrete. The anti-cracking shrinkage-inhibiting desert sand foam concrete comprises 40-70 parts of cement, 10-20 parts of desert sand, 1-3 parts of a water reducing agent, 0.5-2.5 parts of surface modified anti-cracking fibers, 1-5 parts of a thickening agent, 1-2 parts of a chlorine fixing agent, 3-10 parts of a foaming agent, 0.01-0.5 part of a foam stabilizer and 20-40 parts of water. The anti-crack shrinkage-inhibiting desert sand foam concrete has the advantages of super-strong anti-crack shrinkage-inhibiting capability, excellent slurry stability, long-acting chloride ion erosion resistance and remarkable resource and environmental benefits; through the synergistic effect of the modified fiber (enhancement), the thickening agent (stabilization) and the chlorine fixing agent (durability), multiple technical bottlenecks in a desert sand-salt water system are systematically overcome, and '1 + 1 + 1gt; and 3) a breakthrough technical effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of foamed concrete technology, and in particular to a crack-resistant and shrinkage-inhibiting desert sand foamed concrete and its preparation method. Background Technology

[0002] Foamed concrete, as an energy-saving, lightweight, and heat-insulating building material, is widely used in modern buildings. Its traditional preparation process often uses cement mortar as the matrix to balance cost and performance. However, this field faces two major challenges: (1) the aggregate resource crisis and the problem of slurry stability. Globally, high-quality river sand and lake sand resources are becoming increasingly depleted, forcing the industry to turn to mountain sand, sea sand, manufactured sand, and even desert sand with huge reserves. However, desert sand usually has small particles and poor gradation, which makes it easy to settle in highly fluid foamed concrete slurry, while causing the lighter foam to float. This serious component separation phenomenon will cause uneven internal structure and density stratification of hardened concrete, becoming an inherent cause of shrinkage cracking, which seriously restricts the application prospects of desert sand in foamed concrete. (2) the scarcity of freshwater resources and the risk of chloride corrosion. In areas such as islands, salt lakes, and Middle Eastern deserts, freshwater resources are extremely precious, and using seawater, salt lake water, or groundwater to mix concrete has become an inevitable choice. Studies have shown that while chloride ions in saline water have a limited impact on the early strength of concrete, free chloride ions that are not chemically solidified by cement hydration products will slowly migrate and leach out during service. When foamed concrete comes into contact with metal components (such as connectors and reinforcing bars), the leachated chloride ions will damage the metal passivation film, triggering electrochemical corrosion and seriously threatening the safety and long-term durability of the building structure.

[0003] Currently, existing technologies mostly focus on solving single problems, such as improving slurry stability by adding thickeners or using corrosion-resistant cement. However, there is still no mature and efficient technical solution for systematically and synergistically solving the complex technical challenge of "desert sand settlement" and "saltwater chloride erosion". Summary of the Invention

[0004] The purpose of this invention is to provide a crack-resistant and shrinkage-inhibiting desert sand foamed concrete and its preparation method to address the shortcomings of existing technologies. This invention solves the problems of poor slurry stability, air bubble floating, sand particle settling, and the resulting volume unevenness and shrinkage cracking caused by the direct use of desert sand; it also solves the risk of chloride ion leaching caused by the use of saline water, and improves the long-term durability of the material in a chloride salt environment; and it realizes the efficient and high-value utilization of these two "inferior" resources, desert sand and saline water, in building materials.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a crack-resistant and shrinkage-inhibiting desert sand foamed concrete, comprising the following components in parts by weight: 40-70 parts cement, 10-20 parts desert sand, 1-3 parts water-reducing agent, 0.5-2.5 parts surface-modified crack-resistant fiber, 1-5 parts thickener, 1-2 parts chlorine-fixing agent, 3-10 parts foaming agent, 0.01-0.5 parts foam stabilizer, and 20-40 parts water.

[0006] Preferably, the method for preparing the surface-modified crack-resistant fiber includes the following steps: 1) Hydrolyze the silane coupling agent in ethanol to obtain a hydrolysate; impregnate the chopped glass fibers in the hydrolysate and then dry them to obtain the coupled fibers; 2) The coupled fibers are impregnated in epoxy resin dilution, the solvent is removed and then cured to obtain surface-modified crack-resistant fibers.

[0007] Preferably, the silane coupling agent in step 1) is γ-glycidoxypropyltrimethoxysilane; the pH value of the ethanol is 3.8~4.2; and the drying temperature is 105~115℃.

[0008] Preferably, the epoxy resin diluent in step 2) is a mixture of bisphenol A type epoxy resin and amine curing agent.

[0009] Preferably, the curing in step 2) is a sequential process of preliminary curing and deep curing; the temperature for preliminary curing is 95~105℃ and the time is 0.8~1.2h, and the temperature for deep curing is 125~135℃ and the time is 1.5~2.5h.

[0010] Preferably, the cement comprises one or more of silicate cement, sulfoaluminate cement and phosphoaluminate cement; the desert sand is desert sand in a dry state.

[0011] Preferably, the thickener is xanthan gum and / or polyacrylamide; the chlorination agent is magnesium aluminum layered bimetallic hydroxide.

[0012] Preferably, the foaming agent is an animal protein-based foaming agent; the foam stabilizer is polyvinyl alcohol; and the water is tap water, seawater, salt lake water, or groundwater.

[0013] This invention also provides a method for preparing the aforementioned crack-resistant and shrinkage-inhibiting desert sand foamed concrete, comprising the following steps: (1) Mix cement, desert sand, chlorine-fixing agent and surface-modified crack-resistant fiber to obtain dry material; (2) Add water-reducing agent, thickener and water to dry materials to obtain cement mortar matrix; (3) Mix the foaming agent and the foam stabilizer to form foam, and mix the foam with the cement mortar matrix to obtain crack-resistant and shrinkage-inhibiting desert sand foam concrete.

[0014] Preferably, the density of the foam in step (3) is 30~50 kg / m³ and the average foam diameter is 0.5~1.0 mm; the mixing is first stirred at 120~160 rpm for 30~45 s, and then stirred at 265~305 rpm for 15~20 s.

[0015] The beneficial effects of this invention are: 1) Superior crack resistance and shrinkage suppression: The glass fiber, modified with "silane coupling + epoxy coating", has an interfacial bond strength with the cement matrix that far exceeds that of ordinary fibers. This strong interfacial bond can efficiently bridge microcracks, effectively transfer and disperse shrinkage stress, fundamentally inhibit the generation of early plastic shrinkage and late drying cracks, and significantly improve the toughness and crack resistance of the material.

[0016] 2) Excellent slurry stability: The introduction of thickener precisely controls the rheological parameters of fresh slurry, which greatly improves plastic viscosity while ensuring the fluidity of construction, effectively "locking in" foam and desert sand, and completely solving the stubborn problems of air bubble floating and sand particle settling, thus ensuring the uniformity and consistency of the internal structure of the hardened concrete.

[0017] 3) Long-lasting resistance to chloride ion corrosion: Magnesium-aluminum layered bimetallic hydroxides (LDHs) act as "chloride ion traps". Through their unique interlayer anion exchange capacity, they physically adsorb and chemically fix harmful free chloride ions in the slurry into their layered structure, which greatly reduces the migration rate and leaching amount of chloride ions, providing a reliable guarantee for long-term safe use in saline water environments.

[0018] 4) Significant resource and environmental benefits: This invention successfully transforms abundant but difficult-to-utilize desert sand and saline water into high-performance building materials. It not only solves the resource dilemma in specific regions but also avoids the excessive consumption of natural sand and freshwater resources. It is in line with the national strategy of green building materials and sustainable development, and has huge economic and social benefits.

[0019] 5) Systemic innovation with synergistic effects: This invention is not a simple superposition of single technologies, but rather a systematic breakthrough in overcoming multiple technical bottlenecks in the desert sand-saline water system through the synergistic effect of "modified fiber (reinforcement) - thickener (stabilization) - chlorine fixation agent (durability)", achieving a breakthrough technical effect of "1+1+1>3". Detailed Implementation

[0020] This invention provides a crack-resistant and shrinkage-inhibiting desert sand foamed concrete, comprising the following components in parts by weight: 40-70 parts cement, 10-20 parts desert sand, 1-3 parts water-reducing agent, 0.5-2.5 parts surface-modified crack-resistant fiber, 1-5 parts thickener, 1-2 parts chlorine-fixing agent, 3-10 parts foaming agent, 0.01-0.5 parts foam stabilizer, and 20-40 parts water.

[0021] The desert sand foamed concrete of the present invention comprises the following components in parts by weight: 40-70 parts of cement, preferably 45-65 parts, more preferably 55 parts; 10-20 parts of desert sand, preferably 12-18 parts, more preferably 15-16 parts; 1-3 parts of water-reducing agent, preferably 1.5-2.5 parts, more preferably 2 parts; 0.5-2.5 parts of surface-modified crack-resistant fiber, preferably 1-2 parts, more preferably 1.5 parts; 1-5 parts of thickener, preferably 2-4 parts, more preferably 3 parts; 1-2 parts of chlorine-fixing agent, preferably 1.2-1.8 parts, more preferably 1.5-1.6 parts; 3-10 parts of foaming agent, preferably 4-8 parts, more preferably 5-6 parts; 0.01-0.5 parts of foam stabilizer, preferably 0.1-0.4 parts, more preferably 0.2-0.3 parts; and 20-40 parts of water, preferably 25-35 parts, more preferably 30 parts.

[0022] In this invention, the method for preparing the surface-modified crack-resistant fiber preferably includes the following steps: 1) Hydrolyze the silane coupling agent in ethanol to obtain a hydrolysate; impregnate the chopped glass fibers in the hydrolysate and then dry them to obtain the coupled fibers; 2) The coupled fibers are impregnated in epoxy resin dilution, the solvent is removed and then cured to obtain surface-modified crack-resistant fibers.

[0023] In this invention, the silane coupling agent in step 1) is preferably γ-glycidoxypropyltrimethoxysilane (GPTMS); the pH value of the ethanol is preferably 3.8~4.2, more preferably 3.9~4.1, and even more preferably 4.0; the drying temperature is preferably 105~115℃, more preferably 107~112℃, and even more preferably 110℃.

[0024] In this invention, the ethanol is an aqueous solution of anhydrous ethanol, and after drying, a silane coupling layer containing epoxy groups is grafted onto the surface of the chopped glass fiber.

[0025] In this invention, the epoxy resin diluent in step 2) is preferably a mixture of bisphenol A type epoxy resin and amine curing agent; the bisphenol A type epoxy resin is preferably E44 epoxy resin, and the amine curing agent is preferably an amine adduct curing agent or a polyamide curing agent; the volume ratio of bisphenol A type epoxy resin to amine curing agent is preferably 1~2:1~2; more preferably 1:1.

[0026] In this invention, the curing in step 2) is a sequential process of preliminary curing and deep curing; the temperature for preliminary curing is preferably 95~105℃, more preferably 97~102℃, more preferably 100℃, and the time is preferably 0.8~1.2h, more preferably 1h; the temperature for deep curing is preferably 125~135℃, more preferably 127~132℃, more preferably 130℃, and the time is preferably 1.5~2.5h, more preferably 2h.

[0027] In this invention, after initial curing and deep curing, a dense epoxy resin coating is formed on the fiber surface.

[0028] In this invention, the cement preferably comprises one or more of silicate cement, sulfoaluminate cement and phosphoaluminate cement; the desert sand is preferably desert sand in a dry state.

[0029] In this invention, the thickener is preferably xanthan gum and / or polyacrylamide; the chlorination agent is preferably magnesium aluminum layered bimetallic hydroxides (MgAl-LDHs), more preferably MgAl-C LDHs.

[0030] In this invention, the thickener functions to regulate the rheological properties of the slurry and inhibit component separation; the layered structure of the magnesium-aluminum layered bimetallic hydroxide can efficiently solidify free chloride ions through ion exchange effect.

[0031] In this invention, the foaming agent is preferably an animal protein-based foaming agent; the foam stabilizer is preferably polyvinyl alcohol; and the water is preferably tap water, seawater, salt lake water, or groundwater.

[0032] In this invention, seawater, salt lake water or groundwater is a saline environment, and the chloride ion mass concentration in the saline environment is preferably 0.5-5% (based on the mass of NaCl), more preferably 1-4% (based on the mass of NaCl), and even more preferably 2-3% (based on the mass of NaCl).

[0033] The surface of the crack-resistant and shrinkage-inhibiting desert sand foam concrete of the present invention is a composite modified glass fiber with both Si-O-Si chemical bonds and epoxy functional groups, which significantly improves the interfacial bonding force between the fiber and the cement matrix.

[0034] This invention also provides a method for preparing the aforementioned crack-resistant and shrinkage-inhibiting desert sand foamed concrete, comprising the following steps: (1) Mix cement, desert sand, chlorine-fixing agent and surface-modified crack-resistant fiber to obtain dry material; (2) Add water-reducing agent, thickener and water to dry materials to obtain cement mortar matrix; (3) Mix the foaming agent and the foam stabilizer to form foam, and mix the foam with the cement mortar matrix to obtain crack-resistant and shrinkage-inhibiting desert sand foam concrete.

[0035] In this invention, the mixing time in step (1) is preferably 1~2 min, more preferably 1.5 min, and slow stirring is carried out during the mixing process; in step (2), it is preferred that the water-reducing agent, thickener and water are mixed evenly and then slowly added to the dry material. After the addition is completed, the mixture is quickly stirred for 1~2 min to obtain the cement mortar matrix.

[0036] In this invention, the density of the foam in step (3) is preferably 30~50 kg / m³. 3 Further preferred is 35~45 kg / m 3 More preferably 40 kg / m 3 The average bubble diameter is preferably 0.5~1.0 mm, more preferably 0.7~0.9 mm; the mixing is preferably slow stirring for 30~45 s, followed by fast stirring for 15~20 s, more preferably slow stirring for 35~40 s, followed by fast stirring for 16~19 s, and more preferably slow stirring for 37 s, followed by fast stirring for 17~18 s.

[0037] In this invention, the slow stirring rate is preferably 120~160 rpm, more preferably 130~150 rpm, and even more preferably 140 rpm, and the fast stirring rate is preferably 265~305 rpm, more preferably 275~295 rpm, and even more preferably 285 rpm.

[0038] The foam and cement mortar matrix of the present invention are mixed and then poured, molded and cured sequentially.

[0039] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] In this embodiment, the desert sand is naturally dried desert sand with a mud content of <1.5%; the chlorination agent is MgAl-C. LDHs; foam stabilizer is polyvinyl alcohol with a molecular weight of 250,000; polyacrylamide has a molecular weight of 6 million and is an anionic polyacrylamide; foaming agent is animal hair foaming agent; water reducing agent is low-foaming polycarboxylate water reducing agent; chopped glass fiber has a length of 12 mm and a diameter of 9~13 μm; The slow stirring speed is 140 rpm, and the fast stirring speed is 285 rpm.

[0041] Example 1

[0042] The preparation method of surface-modified crack-resistant fibers is as follows: γ-glycidyl etheroxypropyltrimethoxysilane is hydrolyzed in ethanol with a pH of 4.0 until the solution is clear and transparent to obtain a hydrolysate. Short glass fibers are added to the hydrolysate and stirred slowly until the fiber bundles are fully dispersed. Then, the fibers are dried at 110°C to obtain coupling-treated fibers. The coupling-treated fibers are impregnated in an epoxy resin dilution (a mixture of E44 epoxy resin and polyamide 650 curing agent with a volume ratio of 1:1) and stirred slowly until the fibers are fully and uniformly coated by the resin dilution. After the solvent is evaporated, the fibers are cured. First, the fibers are cured at 110°C for 1 hour, and then cured at 130°C for 2 hours to obtain surface-modified crack-resistant fibers.

[0043] Crack-resistant and shrinkage-inhibiting desert sand foamed concrete is prepared from the following components in parts by weight: 48 parts cement (PO 42.5 cement), 16 parts desert sand, 2 parts water-reducing agent, 0.5 parts surface-modified crack-resistant fiber, 1 part thickener (xanthan gum), 2 parts chlorine-fixing agent, 6 parts foaming agent, 0.01 parts foam stabilizer, and simulated seawater (Cl). - 30 portions (3% by mass).

[0044] Cement, desert sand, chlorine-fixing agent, and surface-modified crack-resistant fibers were poured into a mixing pot and slowly stirred for 1.5 minutes to obtain a uniform dry material. Simulated seawater, water-reducing agent, and thickener were mixed evenly and then slowly stirred and added to the mixing pot. After the addition was complete, the material was quickly stirred for 1.5 minutes to obtain a uniform cement mortar matrix. Foaming agent and foam stabilizer were used to make stable foam with a density of 40 kg / m³ and an average foam diameter of 0.5~1.0 mm. The foam was added to the cement mortar matrix and slowly stirred for 40 seconds, then quickly stirred for 18 seconds. After stirring, the mixture was poured into a steel mold, covered with a polyethylene film, and demolded after 24 hours. It was then cured in a standard curing room (20±2℃) for 28 days to obtain crack-resistant and shrinkage-inhibiting desert sand foam concrete.

[0045] The performance test results of the crack-resistant and shrinkage-inhibiting desert sand foamed concrete cured for 28 days in Example 1 are shown in Table 1.

[0046] Table 1 Performance test results of crack-resistant and shrinkage-inhibiting desert sand foamed concrete

[0047] The dry density of the crack-resistant and shrinkage-inhibiting desert sand foamed concrete in Example 1 indicates that the foamed concrete achieves excellent lightweighting, which is beneficial for reducing structural loads, and has good thermal insulation performance; the compressive strength meets the strength requirements of foamed concrete as a thermal insulation filler material, satisfying most engineering application scenarios; the thermal conductivity indicates that the foamed concrete has good thermal insulation capabilities, contributing to building energy conservation; the chloride ion leaching amount indicates that the solidifying agent (MgAl-C) LDHs have a significant effect, effectively solidifying chloride ions in saline water and fundamentally improving long-term durability in chloride salt environments.

[0048] Example 2

[0049] The crack-resistant and shrinkage-inhibiting desert sand foamed concrete of this embodiment is prepared from the following components in parts by weight: 55 parts cement (PO 42.5 cement), 12 parts desert sand, 2.5 parts water-reducing agent, 1.5 parts surface-modified crack-resistant fiber, 3 parts thickener (xanthan gum), 1.5 parts chloride-fixing agent, 7 parts foaming agent, 0.2 parts foam stabilizer, and groundwater (Cl... - 25 portions (4% by mass).

[0050] The preparation method of the surface-modified crack-resistant fiber and the preparation process of the crack-resistant and shrinkage-inhibiting desert sand foam concrete in this embodiment are the same as those in Example 1.

[0051] Example 3

[0052] The crack-resistant and shrinkage-inhibiting desert sand foamed concrete of this embodiment is prepared from the following components in parts by weight: 45 parts cement (PO 42.5 cement), 18 parts desert sand, 1.5 parts water-reducing agent, 2 parts surface-modified crack-resistant fiber, 4 parts thickener (polyacrylamide), 1 part chlorine-fixing agent, 4 parts foaming agent, 0.05 parts foam stabilizer, and salt lake water (Cl). - 35 portions (2% by mass).

[0053] The preparation method of the surface-modified crack-resistant fiber and the preparation process of the crack-resistant and shrinkage-inhibiting desert sand foam concrete in this embodiment are the same as those in Example 1.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A crack-resistant shrinkage-reducing desert sand foam concrete, characterized in that, The cement 40~70 parts, desert sand 10~20 parts, water reducing agent 1~3 parts, surface modified anti-cracking fiber 0.5~2.5 parts, thickening agent 1~5 parts, chlorine fixation agent 1~2 parts, foaming agent 3~10 parts, foam stabilizer 0.01~0.5 parts, water 20~40 parts. The preparation method of the surface modified anti-cracking fiber comprises the following steps:

2. Anti-cracking shrinkage reducing desert sand foam concrete according to claim 1, characterized in that, 1) hydrolyzing silane coupling agent in ethanol to obtain a hydrolysis solution; dipping chopped glass fiber in the hydrolysis solution and drying to obtain coupling-treated fiber; 2) dipping the coupling-treated fiber in an epoxy resin diluent, removing the solvent and curing to obtain the surface modified anti-cracking fiber. In step 1), the silane coupling agent is γ-glycidoxypropyltrimethoxysilane; the pH value of ethanol is 3.8~4.2; and the drying temperature is 105~115℃.

3. The anti-cracking shrinkage reducing desert sand foam concrete according to claim 2, characterized in that, In step 2), the epoxy resin diluent is a mixture of bisphenol A type epoxy resin and amine curing agent.

4. Anti-cracking shrinkage reducing desert sand foam concrete according to claim 2 or 3, characterized in that, In step 2), the curing is sequentially carried out by primary curing and deep curing; the temperature for primary curing is 95~105℃, and the time is 0.8~1.2h; the temperature for deep curing is 125~135℃, and the time is 1.5~2.5h.

5. The anti-cracking shrinkage reducing desert sand foam concrete according to claim 4, characterized in that, The cement comprises one or more of Portland cement, sulphoaluminate cement and phosphoaluminate cement; and the desert sand is in a dry state.

6. Anti-cracking shrinkage reducing desert sand foam concrete according to claim 1 or 5, characterized in that, The thickening agent is xanthan gum and / or polyacrylamide; and the chlorine fixation agent is magnesium-aluminum layered double hydroxide.

7. The anti-cracking shrinkage reducing desert sand foam concrete according to claim 6, characterized in that, The foaming agent is animal protein foaming agent; the foam stabilizer is polyvinyl alcohol; and the water is tap water, seawater, salt lake water or underground brackish water.

8. The anti-cracking shrinkage reducing desert sand foam concrete according to claim 7, characterized in that, The method comprises the following steps:

9. A process for the preparation of anti-cracking shrinkage desert sand foam concrete according to any one of claims 1 to 8, characterized in that, (1) mixing cement, desert sand, chlorine fixation agent and surface modified anti-cracking fiber to obtain dry materials; (2) adding water reducing agent, thickening agent and water to the dry materials to obtain a cement mortar matrix; (3) mixing foaming agent and foam stabilizer to form foam, and mixing the foam and the cement mortar matrix to obtain anti-cracking and shrinkage-reducing desert sand foam concrete. In step (3), the density of the foam is 30~50kg / m³, and the average bubble diameter is 0.5~1.0mm; and the mixing is first stirring at 120~160rpm for 30~45s, and then stirring at 265~305rpm for 15~20s.

10. The method of claim 9, wherein, ​

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