Freeze-thaw resistant modified foam concrete and preparation method thereof

Abstract

The invention provides freeze-thaw resistant modified foam concrete and a preparation method thereof. The foam concrete comprises the following raw materials in parts by weight: 30-50 parts of cement, 40-60 parts of modified steel slag, 1-1.5 parts of a nano-composite foam stabilizer, 3-5 parts of a foaming agent, 25-35 parts of fine aggregate, 3-5 parts of an activator, 1-2 parts of an early strength agent, 0.3-0.5 parts of a water reducer, and 80-300 parts of water. The modified steel slag is prepared by adding steel slag, tetramethylguanidinopropyltrimethoxysilane, and water in a mass ratio of 100:5-7.5:40-50 to a wet grinder, performing wet grinding, and drying. The nano-composite foam stabilizer is prepared by compounding coupling agent-modified nano-silica, hydroxypropyl methylcellulose ether, and an alcoholamine ester cationic surfactant in a mass ratio of 3-5:1:3-5. With the synergistic cooperation of the modified ground steel slag and the nano-composite foam stabilizer, foam concrete with excellent mechanical properties and durability is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of foam concrete, and particularly relates to freeze-thaw resistant modified foam concrete and a preparation method thereof. Background Art

[0002] Foamed concrete is a lightweight, porous concrete containing numerous closed pores, created by physically or chemically introducing air bubbles into a cementitious paste. This material, after solidification, creates a highly enclosed pore structure. Due to its numerous closed pores, foamed concrete offers superior properties such as lightweight, thermal insulation, sound insulation, and fire resistance. This significantly reduces building energy consumption and has become a research hotspot in civil engineering.

[0003] Currently, researchers have conducted extensive research on the raw material composition, maintenance systems, and engineering applications of foamed concrete, yielding numerous beneficial results. Regarding raw material composition, steel slag, an industrial solid waste discharged from the steelmaking industry, has similar active ingredients to Portland cement. Using steel slag as an admixture in foamed concrete not only absorbs the slag but also partially replaces the cement. Furthermore, the micro-expansion of steel slag can be utilized to compensate for the large drying shrinkage of foamed concrete, ultimately achieving the goals of energy conservation and emission reduction, transforming waste into valuable resources, and protecting the environment.

[0004] For example, patent CN103771797B discloses a foamed concrete block prepared by mixing steel slag and mineral slag, and a preparation method thereof. The concrete block is prepared by mixing a slurry and a foaming agent solution, and then forming, demolding, and curing. The slurry comprises, by weight, 20-50 parts of steel slag, 20-40 parts of mineral slag, 40-150 parts of cement, 10-70 parts of water, 0-10 parts of an early strength agent, 0-5 parts of a coagulant, 0-2 parts of a fiber, and 0-6 parts of a water reducer. The foaming agent solution is prepared by mixing and foaming a foaming agent and water in a mass ratio of 1:20-1:60. The volume of foam generated by foaming the foaming agent solution is 30-100 times the volume of the slurry. Patent CN103011723B discloses a high-volume steel slag foam concrete block and a preparation method thereof. The concrete block is prepared by mixing a slurry with a foaming agent solution, forming, demolding, and curing. The slurry comprises, by weight, 50-150 parts of cement, 20-60 parts of steel slag, 10-60 parts of water, 0-8 parts of an early strength agent, 0-3 parts of a coagulant, 0-1.5 parts of fiber, 0-5 parts of a water reducer, and 0-5 parts of an activator.

[0005] The above describes the technology used to incorporate ground steel slag as an admixture in foamed concrete, achieving both solid waste disposal and resource recycling. Because steel slag has low activity, it is often ground to increase its activity. The surface of the ground steel slag powder carries static electricity. During the foamed concrete preparation process, this statically charged steel slag powder tends to aggregate and adsorb around the foam, affecting the uniformity of the mixing of the steel slag powder and cement around the foam and forming stress around the pore walls. Although this stress does not significantly impact foamed concrete, which has low mechanical property requirements, during freeze-thaw cycles, when water in the pores freezes and expands, the expansion force of the ice and the stress around the pore walls combine, causing local stress to exceed the tensile strength of the concrete, leading to cracks in the concrete. Furthermore, once cracks appear, they rapidly expand during subsequent freeze-thaw cycles, further reducing the concrete's freeze-thaw resistance.

[0006] Therefore, it is necessary to further improve the foam concrete with ground steel slag as an admixture to improve the durability of foam concrete. Summary of the Invention

[0007] To solve the problem of poor freeze-thaw resistance of foamed concrete, the present invention adds tetramethylguanidinopropyltrimethoxysilane to the wet-grinded raw material of steel slag to prepare modified ground steel slag, and introduces a nano-composite foam stabilizer composed of modified nano-silica, hydroxypropyl methylcellulose ether, and a cationic surfactant (triethanolamine monooleate) into the foamed concrete raw material. With the synergistic cooperation of the modified ground steel slag and the nano-composite foam stabilizer, foamed concrete with excellent mechanical properties and durability is obtained.

[0008] In order to achieve the above objectives, the following technical solutions are adopted:

[0009] A freeze-thaw resistant modified foam concrete comprises the following raw materials in parts by weight: 30-50 parts of cement, 40-60 parts of modified steel slag, 1-1.5 parts of a nano-composite foam stabilizer, 3-5 parts of a foaming agent, 25-35 parts of fine aggregate, 3-5 parts of an activator, 1-2 parts of an early strength agent, 0.3-0.5 parts of a water reducer, and 80-300 parts of water. The modified steel slag is prepared by adding steel slag, tetramethylguanidinopropyltrimethoxysilane, and water in a mass ratio of 100:5-7.5:40-50 to a wet grinder, performing wet grinding, and drying. The nano-composite foam stabilizer is prepared by compounding coupling agent-modified nano-silica, hydroxypropyl methylcellulose ether, and an alcoholamine ester cationic surfactant in a mass ratio of 3-5:1:3-5.

[0010] The alcoholamine ester cationic surfactant is selected from one or a combination of two or more of triethanolamine monooleate, triisopropanolamine oleate, and triethanolamine monostearate.

[0011] The coupling agent modified nano-silica is prepared by a method comprising the following steps: dispersing nano-silica in a modified liquid to form a mixed liquid, heating the mixed liquid to a reflux state for reaction, and filtering, washing, and drying the mixed liquid after the reaction is completed to obtain the coupling agent modified nano-silica.

[0012] The modified liquid is a solution containing 5-10 wt% of a silane coupling agent, and the solvent is an organic solvent. The silane coupling agent is selected from one or a combination of aminosilane coupling agents and hydroxysilane coupling agents, preferably an aminosilane coupling agent. The aminosilane coupling agent is selected from one or a combination of two or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane. The organic solvent is selected from one or a combination of two or more of benzene and toluene. The silane coupling agent is 5-10 wt% of the nano-silica. The average particle size of the nano-silica is 20-50 nm. The mass fraction of the nano-silica in the mixed solution is 40-60 wt%. The washing step is 1-3 washes with ethanol. The drying step is drying at 80-100°C to constant weight.

[0013] The viscosity of the hydroxypropyl methylcellulose ether is 80,000-100,000 Pa·s.

[0014] The wet grinding process uses ceramic balls with a mass ratio of 1.1-1.2 mm: 0.7-0.8 mm: 0.5-0.6 mm = 1-3: 2-4: 1-3. The wet grinding process lasts for 0.5-1 h at a rotation speed of 200-500 r / min. The drying process is performed at 60-100° C. to a constant weight.

[0015] The median particle size of the modified steel slag is 1-5 μm.

[0016] The basicity of the steel slag is 1.4-2.4, and the steel slag is selected from one or a combination of two or more of converter steel slag, open-hearth steel slag, and electric furnace steel slag.

[0017] During the wet grinding process, adding an appropriate amount of tetramethylguanidinopropyltrimethoxysilane can form a conductive channel on the surface of the modified ground steel slag, eliminate static electricity, prevent excessive steel slag powder from gathering and adsorbing around the foam, reduce stress concentration, and have a positive effect on improving durability.

[0018] However, the inventors found that modifying ground steel slag with tetramethylguanidinopropyltrimethoxysilane not only did not improve durability, but also reduced the mechanical properties of foamed concrete. Only after adding an appropriate amount of a nano-composite foam stabilizer composed of modified nano-silica, hydroxypropyl methylcellulose ether, and cationic surfactant in a mass ratio of 3-5:1:3-5, was foamed concrete with excellent mechanical properties and durability produced. It is speculated that the use of tetramethylguanidinopropyltrimethoxysilane is equivalent to grafting a long-chain structure containing guanidine groups on the surface of steel slag. Compared with the case where it is not used, the phenomenon of its aggregation and adsorption around the foam and the degree of stress concentration have been improved to a certain extent, and the problem of excessive aggregation and adsorption will not occur; but it does not rule out the possibility that the modified ground steel slag is adsorbed with the foam. Once it is adsorbed with the foam, it will be integrated into the foam liquid film and become a part of the liquid film; since the particle size of the modified ground steel slag is still relatively large, it has rigidity and low surface energy. This characteristic has a negative impact on the elastic strength of the foam liquid film, so that when the liquid film is subjected to external force, the buffering and deformation ability of the liquid film is weakened, the stability of the foam is reduced, and the connected pores of the foam concrete are increased, the mechanical properties are reduced, and the durability improvement effect is poor.

[0019] This nanocomposite foam stabilizer, formulated from modified nanosilica, hydroxypropyl methylcellulose ether, and cationic surfactants in specific proportions, effectively protects foam from three dimensions: steric hindrance, physical barrier, and charge barrier. Hydroxypropyl methylcellulose ether forms a tough, high-strength film around the foam, creating steric hindrance; modified nanosilica, with its tiny particles, creates a physical barrier; and cationic surfactants, with their inherent charge, create a charge barrier. The synergistic effect of these three ingredients ensures foam stability.

[0020] The cement is silicate cement with a strength grade of 42.5-52.5.

[0021] The activator is selected from one or a combination of two or more of calcium hydroxide, sodium hydroxide and sodium carbonate.

[0022] The early strength agent is selected from one or a combination of two or more of sodium formate, sodium acetate and triethanolamine.

[0023] The water reducing agent has a water reducing rate of 18-25%, and is selected from one or a combination of two or more of polycarboxylic acid water reducing agents and naphthalene water reducing agents.

[0024] The foaming agent is a physical foaming agent, which is selected from one or a combination of two or more of rosin resins, synthetic surfactants, and proteins.

[0025] Furthermore, the foaming agent is a synthetic surfactant.

[0026] Furthermore, the foaming agent is sodium dodecylbenzenesulfonate.

[0027] The fine aggregate is quartz sand with a fineness modulus of 2.2-2.4.

[0028] The present invention also provides a method for preparing modified foam concrete, comprising the following steps:

[0029] 1) adding a foaming agent and a nano-composite foam stabilizer into water for dilution, and then adding the dilution into the foaming agent for foaming to obtain foam;

[0030] 2) uniformly mixing cement, modified ground steel slag, fine aggregate, activator, early strength agent, water reducing agent and water to obtain a mixture;

[0031] 3) Add foam to the mixture and stir to obtain modified foam concrete.

[0032] In step 1), the mass ratio of the foaming agent to water is 1:30-50.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The invention prepares modified ground steel slag by adding tetramethylguanidinopropyltrimethoxysilane to the wet-grinded raw material of steel slag, and introduces a nano-composite foam stabilizer prepared by compounding modified nano-silica, hydroxypropyl methylcellulose ether and triethanolamine monooleate, a cationic surfactant, into the foamed concrete raw material. With the synergistic cooperation of the modified ground steel slag and the nano-composite foam stabilizer, foamed concrete with excellent mechanical properties and durability is obtained. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0036] Electric furnace slag was purchased from Hebei Wenfeng Industrial Group Co., Ltd. with a basicity of 2.0.

[0037] Nano-silica with an average particle size of 20 nm was purchased from Beijing Solebow Technology Co., Ltd. with the product number NM000840.

[0038] SSF-1000 series naphthalene-based high-efficiency water-reducing agent with a water-reduction rate of 21.8% was purchased from Hubei Shanshufeng Building Materials Technology Co., Ltd.

[0039] Hydroxypropyl methylcellulose ether with a viscosity of 100,000 Pa·s was purchased from Shanghai Kelaman Reagent Co., Ltd.

[0040] Example 1

[0041] S1) preparing modified ground steel slag: adding steel slag, tetramethylguanidinopropyltrimethoxysilane, and water in a mass ratio of 100:7.5:50 to a wet grinder, wet grinding at 500 r / min for 1 h using ceramic balls in a mass ratio of 1.2 mm:0.8 mm:0.6 mm = 2:3:1, and drying at 60° C. to constant weight to obtain modified ground steel slag with a median particle size of 3.6 μm;

[0042] S2) Preparation of modified nano-silica: 500 g of nano-silica NM000840 was dispersed in 1000 g of a modification solution prepared by mixing 3-aminopropyltrimethoxysilane and benzene in a mass ratio of 5:95, stirred to form a stable suspension, and heated to reflux for reaction for 24 h. After the reaction, the mixture was filtered, washed three times with ethanol, and dried at 100° C. to constant weight to obtain modified nano-silica.

[0043] S3) preparing modified foam concrete:

[0044] S31) 500g sodium dodecylbenzene sulfonate, 150g of modified nano silicon dioxide, hydroxypropyl methylcellulose ether, and triethanolamine monooleate agent are added to 15kg water in a mass ratio for compounding a nano composite foam stabilizer of 5:1:3 and diluted, and then the dilution is added to a foaming agent and foamed to obtain foam;

[0045] S32) 3000g cement, 6000g modified ground steel slag, 2500g fineness modulus are 2.2 quartz sand, 500g sodium hydroxide, 200g sodium formate, 50gSSF-1000 series naphthalene-based high-efficiency water-reducing agent, 4500g water are mixed to obtain mixture;

[0046] S33) Adding the foam from step S31) to the mixture from step S32) and stirring to obtain modified foamed concrete.

[0047] Example 2

[0048] The rest is the same as Example 1, except that in step S31), the amount of the nano-composite foam stabilizer is 100 g.

[0049] Example 3

[0050] The rest is the same as Example 1, except that in step S31), the mass ratio of modified nano-silica, hydroxypropyl methylcellulose ether, and triethanolamine monooleate is 5:1:5.

[0051] Example 4

[0052] The rest is the same as Example 1, except that in step S31), the mass ratio of modified nano-silica, hydroxypropyl methylcellulose ether, and triethanolamine monooleate is 3:1:3.

[0053] Example 5

[0054] The rest is the same as Example 1, except that in step S31), the mass ratio of modified nano-silica, hydroxypropyl methylcellulose ether, and triethanolamine monooleate is 3:1:5.

[0055] Example 6

[0056] The rest is the same as Example 1, except that in step S2), 3-aminopropyltrimethoxysilane is replaced by hydroxymethyltriethoxysilane of equal mass.

[0057] Example 7

[0058] S1) preparing modified ground steel slag: adding steel slag, tetramethylguanidinopropyltrimethoxysilane, and water in a mass ratio of 100:7.5:50 to a wet grinder, wet grinding at 500 r / min for 1 h using ceramic balls in a mass ratio of 1.2 mm:0.8 mm:0.6 mm = 2:3:1, and drying at 60° C. to constant weight to obtain modified ground steel slag with a median particle size of 3.6 μm;

[0059] S2) Preparation of modified nano-silica: 500 g of nano-silica NM000840 was dispersed in 1000 g of a modification solution prepared by mixing 3-aminopropyltriethoxysilane and benzene in a mass ratio of 5:95, stirred to form a stable suspension, and heated to reflux for reaction for 24 h. After the reaction, the mixture was filtered, washed three times with ethanol, and dried at 100° C. to constant weight to obtain modified nano-silica.

[0060] S3) preparing modified foam concrete:

[0061] S31) 500g sodium dodecylbenzene sulfonate, 100g of modified nano silicon dioxide, hydroxypropyl methylcellulose ether, and triethanolamine monooleate agent are added to 15kg water in a mass ratio for a composite nano-composite foam stabilizer of 5:1:5 and diluted, and then the dilution is added to a foaming agent and foamed to obtain foam;

[0062] S32) 5000g cement, 4000g modified ground steel slag, 2500g fineness modulus are 2.4 quartz sand, 300g sodium hydroxide, 200g sodium formate, 50gSSF-1000 series naphthalene-based high-efficiency water-reducing agent, 4500g water are mixed to obtain mixture;

[0063] S33) Adding the foam from step S31) to the mixture from step S32) and stirring to obtain modified foamed concrete.

[0064] Example 8

[0065] The rest is the same as Example 1, except that, in step S1), steel slag, tetramethylguanidinopropyltrimethoxysilane and water are added to the wet grinder in a mass ratio of 100:5:50.

[0066] Comparative Example 1

[0067] The rest is the same as Example 1, except that in step S31), the nanocomposite foam stabilizer is replaced by a conventional foam stabilizer hydroxypropyl methylcellulose ether of equal mass.

[0068] Comparative Example 2

[0069] The rest is the same as Example 1, except that in step S1), the wet grinding medium is entirely water and does not contain a quaternary ammonium silane coupling agent.

[0070] Comparative Example 3

[0071] The rest is the same as Example 1, except that in step S1), the wet grinding medium is entirely water and does not contain a quaternary ammonium silane coupling agent; in step S31), no nanocomposite foam stabilizer is added.

[0072] Comparative Example 4

[0073] The rest is the same as Example 1, except that in step S31), the cationic surfactant - octadecylamine acetate is used instead of the cationic surfactant - triethanolamine monooleate with an equal mass.

[0074] The foamed concrete prepared in the above examples and comparative examples was cured under standard conditions and then subjected to the following performance tests:

[0075] Compressive strength: The test was conducted with reference to the standard JG / T 266-2011 foam concrete. The testing equipment was NYL-2000 pressure testing machine, and the 28d compressive strength test was carried out.

[0076] Freeze-thaw cycle: refer to the slow freezing method in the standard GB / T 50082-2009 Test method for long-term performance and durability of ordinary concrete, and cycle 50 times. One cycle includes: dropping from 25℃ to -25℃ for 4 hours, maintaining the temperature at -25℃ for 4 hours, raising from -25℃ to 25℃ for 2 hours, and maintaining the temperature at 25℃ for 2 hours. Then re-measure the compressive strength and calculate the 28-day compressive strength loss rate.

[0077] Pore structure analysis: Specimens measuring 100 mm × 100 mm × 100 mm were prepared and cut in half. A DJCK-2 crack width gauge (Jinmai Instruments) was used to photograph the interface with an interface size of 11 mm × 9 mm. The pores were marked using Image ProPlus image processing software. The pore structure was analyzed using Namo Measurer image processing software, and the average roundness value was recorded.

[0078] Uniformity: Prepare a cylindrical specimen with a diameter of 5 cm and a height of 1 m. Remove a small cylinder 3 cm high from the bottom and top of the specimen and calculate its density. According to the following formula, the greater the top density / bottom density value of the sample, the worse the uniformity.

[0079] R=ρ 底 / ρ 顶

[0080] Table 1 Performance test results

[0081]

[0082] It can be seen from Example 1 and Comparative Examples 1-3 in Table 1 that the nanocomposite foam stabilizer has the effect of reducing pore size and significantly synergistically modifying the ground steel slag to improve uniformity and pore roundness, further increasing the strength of the foam concrete and improving durability.

[0083] It can be seen from Examples 1 and 3-5 that changing the mass ratio of modified nano-silica, hydroxypropyl methylcellulose ether, and triethanolamine monooleate will produce a significant change in the average roundness value. Only when the mass ratio of the three is 5:1:3, the average roundness value is closest to 1, indicating that the nano-composite foam stabilizer has a significant synergistic isolation effect. When the modified ground steel slag is close to the foam, the nano-composite foam stabilizer can prevent the modified ground steel slag from direct contact with the foam to the greatest extent, thereby improving the stability of the foam.

[0084] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A freeze-thaw resistant modified foam concrete, characterized in that: The raw materials include the following parts by weight: 30-50 parts of cement, 40-60 parts of modified steel slag, 1-1.5 parts of nano-composite foam stabilizer, 3-5 parts of foaming agent, 25-35 parts of fine aggregate, 3-5 parts of activator, 1-2 parts of early strength agent, 0.3-0.5 parts of water reducer, and 80-300 parts of water; the modified steel slag is prepared by adding steel slag, tetramethylguanidinopropyltrimethoxysilane, and water in a mass ratio of 100:5-7.5:40-50 to a wet grinder for wet grinding. The nano-composite foam stabilizer is prepared by mixing coupling agent-modified nano-silica, hydroxypropyl methylcellulose ether, and alcohol amine ester cationic surfactant in a mass ratio of 3-5:1:3-5. The coupling agent-modified nano-silica is prepared by a method comprising the following steps: dispersing nano-silica in a modified liquid to form a mixed liquid, heating the mixture to a reflux state for reaction, and after the reaction is completed, filtering, washing, and drying to obtain the coupling agent-modified nano-silica.

2. The freeze-thaw resistant modified foam concrete according to claim 1, characterized in that: The alcoholamine ester cationic surfactant is selected from one or a combination of two or more of triethanolamine monooleate, triisopropanolamine oleate, and triethanolamine monostearate.

3. The freeze-thaw resistant modified foam concrete according to claim 1, characterized in that: The average particle size of the nano-silicon dioxide is 20-50 nm.

4. The freeze-thaw resistant modified foam concrete according to claim 1, characterized in that: The coupling agent is selected from one or a combination of aminosilane coupling agents and hydroxysilane coupling agents.

5. The freeze-thaw resistant modified foam concrete according to claim 4, characterized in that: The coupling agent is an aminosilane coupling agent; the aminosilane coupling agent is selected from one or a combination of two or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane.

6. The freeze-thaw resistant modified foam concrete according to claim 1, characterized in that: The viscosity of the hydroxypropyl methylcellulose ether is 80,000-100,000 Pa·s; the basicity of the steel slag is 1.4-2.4, and the slag is selected from one or a combination of two or more of converter slag, open-hearth slag, and electric furnace slag.

7. The freeze-thaw resistant modified foam concrete according to claim 1, characterized in that: The grinding bodies used in the wet grinding are ceramic balls with a mass ratio of 1.1-1.2mm:0.7-0.8mm:0.5-0.6mm=1-3:2-4:1-3; the wet grinding time is 0.5-1h, and the rotation speed is 200-500r / min; the median particle size of the modified steel slag is 1-5μm.

8. The freeze-thaw resistant modified foam concrete according to claim 1, characterized in that: The foaming agent is a physical foaming agent, which is selected from one or a combination of two or more of rosin resins, synthetic surfactants, and proteins.

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