High-temperature resistant fire-resistant concrete and preparation method thereof

Abstract

The application relates to the technical field of concrete, and discloses a high-temperature-resistant and fire-resistant concrete and a preparation method thereof. The concrete is obtained by mixing dry materials, a hydroxyl-terminated polydimethylsiloxane pre-emulsion and an admixture aqueous solution; the admixture aqueous solution is obtained by mixing a polycarboxylic acid high-efficiency water reducing agent, a polyether modified organic silicon defoaming agent and water; the dry materials are obtained by mixing cement, fine aggregate and coarse aggregate; and the hydroxyl-terminated polydimethylsiloxane pre-emulsion is obtained by mixing a hydroxyl-terminated polydimethylsiloxane, a fatty alcohol polyoxyethylene ether and water. The application obtains good high-temperature-resistant and fire-resistant performance without sacrificing normal mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a high-temperature resistant and fire-resistant concrete and its preparation method. Background Technology

[0002] Concrete, as the most widely used structural material in modern construction engineering, is widely used in industrial and civil buildings, transportation infrastructure, super high-rise buildings and major protective projects due to its excellent load-bearing capacity, good formability and outstanding durability. It is one of the core materials to ensure the stability and safety of building structures.

[0003] Patent CN113880525B discloses a carbon nanotube concrete and its preparation method. The carbon nanotube concrete comprises the following raw materials in parts by weight: 900-1150 parts crushed stone; 650-850 parts sand; 220-260 parts marine silicate cement; 130-160 parts water; 65-90 parts fly ash; 1-3 parts polycarboxylate superplasticizer; and 0.2-1.5 parts modified carbon nanotube fibers. However, conventional concrete still has some shortcomings: the hydration products of silicate cement mainly include hydrated calcium silicate gel, calcium hydroxide, and ettringite crystalline phases. When concrete structures are exposed to high-temperature environments such as building fires, radiant heat from industrial kilns, and high-temperature conditions in underground engineering, hydrated calcium silicate gel begins to shed interlayer water and structural water, causing the gel structure to shrink and generate microcracks. Calcium hydroxide undergoes a dehydration and decomposition reaction, generating calcium oxide and water vapor. At the same time, the free water present in the capillaries and gel pores of the concrete rapidly vaporizes at high temperatures, causing a sharp expansion in volume. Due to the poor permeability of concrete itself, the rapid evaporation of internal pore water generates instantaneous steam pressure. When the steam pressure exceeds the tensile strength of the concrete, it triggers the phenomenon of concrete bursting and spalling. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature resistant and fire-resistant concrete and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A high-temperature resistant and fire-resistant concrete, wherein the concrete is obtained by mixing dry aggregates, hydroxyl-terminated polydimethylsiloxane preemulsion, and an admixture aqueous solution; the admixture aqueous solution is obtained by mixing polycarboxylate-based high-efficiency water-reducing agent, polyether-modified organosilicon defoamer, and water; the dry aggregates are obtained by mixing cement, fine aggregates, and coarse aggregates; the hydroxyl-terminated polydimethylsiloxane preemulsion is obtained by mixing hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water.

[0006] Furthermore, the cement is P.O42.5 silicate cement.

[0007] Furthermore, the fine aggregate is natural river sand with a fineness modulus of 2.4-2.8.

[0008] Furthermore, the coarse aggregate is continuously graded crushed stone with a particle size of 5-25mm.

[0009] A method for preparing high-temperature resistant and fire-resistant concrete includes the following steps: Step 1: Mix hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether and water, and stir at 8000-10000 rpm for 5-10 minutes to obtain hydroxyl-terminated polydimethylsiloxane pre-emulsion. Step 2: Add cement, fine aggregate and coarse aggregate into a forced mixer and mix at 15-25 rpm for 30-60 seconds to obtain a dry mixture. Step 3: Mix polycarboxylate-based high-efficiency water-reducing agent, polyether-modified silicone defoamer with water, and stir at 300-500 rpm for 5-10 minutes to obtain an aqueous solution of additives; Step 4: Add hydroxyl-terminated polydimethylsiloxane pre-emulsion to the mixed dry materials and stir at 25-30 rpm for 60-90 seconds. Then add the admixture aqueous solution and continue stirring at 25-30 rpm for 90-120 seconds to obtain a concrete mixture. Pour the concrete mixture into shape and cure it at 20±2℃ and relative humidity not less than 95% for 24 hours before demolding. Then continue to cure it under the same conditions for 28 days to obtain high-temperature resistant and fire-resistant concrete.

[0010] By first adding hydroxyl-terminated polydimethylsiloxane pre-emulsion and stirring, the aim is to allow the hydroxyl-terminated polydimethylsiloxane in the pre-emulsion to preferentially undergo a condensation reaction with the active hydroxyl groups on the surface of cement particles, thereby achieving preliminary hydrophobic modification of the capillary pores. The polycarboxylate superplasticizer in the subsequently added admixture aqueous solution can effectively adjust the workability of the mixture, while the polyether-modified organosilicon defoamer can eliminate the air bubbles introduced by the pre-emulsion. The synergistic effect of the three ensures the comprehensive performance of the concrete.

[0011] Furthermore, in step one, the mass ratio of terminal hydroxyl polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water is 5-15:2-4:20-30.

[0012] Furthermore, the number-average molecular weight of the hydroxyl-terminated polydimethylsiloxane mentioned in step one is 2000-5000 Daltons.

[0013] Furthermore, in step two, the mass ratio of cement, fine aggregate, and coarse aggregate is 380-420:650-700:1050-1150.

[0014] Furthermore, in step three, the mass ratio of polycarboxylate-based high-efficiency water-reducing agent, polyether-modified silicone defoamer, and water is 5-8:0.3-0.5:130-150.

[0015] Furthermore, in step four, the mass ratio of the mixed dry material, the hydroxyl-terminated polydimethylsiloxane preemulsion, and the additive aqueous solution is 2000-2200:25-45:135-160.

[0016] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: Cement undergoes a hydration reaction with water to generate hydrated calcium silicate gel and calcium hydroxide, forming an alkaline environment. The silanol groups of the hydroxyl-terminated polydimethylsiloxane molecular chain undergo a condensation reaction with the silanol groups on the surface of the hydrated calcium silicate gel and the calcium hydroxyl groups on the surface of the calcium hydroxide, forming silicon-oxygen-silicon covalent bonds. This transforms the originally hydrophilic capillary walls of concrete into hydrophobic properties, reducing the migration rate of water in the capillaries and decreasing the content of vaporizable free water under high-temperature conditions. This inhibits the accumulation of internal vapor pressure caused by the rapid vaporization of pore water, thereby reducing the risk of high-temperature cracking of concrete. When concrete is exposed to fire or high-temperature environments, the hydroxyl-terminated polydimethylsiloxane molecular chain undergoes thermal breakage, and its organic groups gradually decompose and transform into amorphous dioxide. Silica fragments, these in-situ generated silica fragments, react with calcium hydroxide, a cement hydration product, under high-temperature conditions to form calcium silicate-based high-temperature reaction products. These products are deposited and sintered on the inner walls of concrete pores and microcracks, forming a continuous or semi-continuous protective layer. This protective layer can effectively seal microcracks generated at high temperatures, prevent external heat from being transferred to the interior of the concrete, and maintain the structural integrity of the concrete under high-temperature conditions. Polycarboxylate-based high-efficiency water-reducing agents ensure good workability of the mixture and improve the dispersibility of hydroxyl-terminated polydimethylsiloxane. Polyether-modified organosilicon defoamers avoid the weakening of the concrete matrix strength caused by harmful bubbles introduced by hydroxyl-terminated polydimethylsiloxane, thus enabling the concrete to achieve good high-temperature fire resistance without sacrificing normal mechanical properties. Detailed Implementation

[0017] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0018] A high-temperature resistant and fire-resistant concrete, wherein the concrete is obtained by mixing dry aggregates, hydroxyl-terminated polydimethylsiloxane preemulsion, and an admixture aqueous solution; the admixture aqueous solution is obtained by mixing polycarboxylate-based high-efficiency water-reducing agent, polyether-modified organosilicon defoamer, and water; the dry aggregates are obtained by mixing cement, fine aggregates, and coarse aggregates; the hydroxyl-terminated polydimethylsiloxane preemulsion is obtained by mixing hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water.

[0019] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products. Example 1

[0020] Step 1: Mix hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water, and stir at 8000 rpm for 5 minutes to obtain a hydroxyl-terminated polydimethylsiloxane preemulsion; wherein the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 2000 Daltons; and the mass ratio of hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water is 5:2:20.

[0021] Step 2: Add cement, fine aggregate, and coarse aggregate into a forced mixer and mix at 15 rpm for 30 seconds to obtain a dry mixture; the cement is P.O42.5 silicate cement; the fine aggregate is natural river sand with a fineness modulus of 2.4; the coarse aggregate is continuously graded crushed stone with a particle size of 5 mm; the mass ratio of cement, fine aggregate, and coarse aggregate is 380:650:1050.

[0022] Step 3: Mix polycarboxylate superplasticizer, polyether modified silicone defoamer with water, and stir at 300 rpm for 5 minutes to obtain an aqueous solution of the additive; the mass ratio of polycarboxylate superplasticizer, polyether modified silicone defoamer to water is 5:0.3:130.

[0023] Step 4: Add hydroxyl-terminated polydimethylsiloxane preemulsion to the dry mixture and stir at 25 rpm for 60 seconds. Then add the admixture aqueous solution and continue stirring at 25 rpm for 90 seconds to obtain a concrete mixture. Pour the concrete mixture into shape and cure it at 18°C ​​and relative humidity not less than 95% for 24 hours before demolding. Then continue curing under the same conditions for 28 days to obtain high-temperature resistant and fire-resistant concrete. The mass ratio of the dry mixture, hydroxyl-terminated polydimethylsiloxane preemulsion and admixture aqueous solution is 2000:25:135. Example 2

[0024] Step 1: Mix hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water, and stir at 9000 rpm for 7 minutes to obtain a hydroxyl-terminated polydimethylsiloxane preemulsion; wherein the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 3500 Daltons; and the mass ratio of hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water is 10:3:25.

[0025] Step 2: Add cement, fine aggregate, and coarse aggregate into a forced mixer and mix at 20 rpm for 45 seconds to obtain a dry mixture; the cement is P.O42.5 silicate cement; the fine aggregate is natural river sand with a fineness modulus of 2.6; the coarse aggregate is continuously graded crushed stone with a particle size of 15 mm; the mass ratio of cement, fine aggregate, and coarse aggregate is 400:675:1100.

[0026] Step 3: Mix polycarboxylate superplasticizer, polyether modified silicone defoamer with water, and stir at 400 rpm for 7.5 minutes to obtain an aqueous solution of additives; the mass ratio of polycarboxylate superplasticizer, polyether modified silicone defoamer to water is 6.5:0.4:140.

[0027] Step four: Add hydroxyl-terminated polydimethylsiloxane preemulsion to the dry mixture and stir at 27 rpm for 75 seconds. Then add the admixture aqueous solution and continue stirring at 27 rpm for 105 seconds to obtain a concrete mixture. Pour the concrete mixture into shape and cure it at 20°C and relative humidity not less than 95% for 24 hours before demolding. Then continue curing under the same conditions for 28 days to obtain high-temperature resistant and fire-resistant concrete. The mass ratio of the dry mixture, hydroxyl-terminated polydimethylsiloxane preemulsion and admixture aqueous solution is 2100:35:147.5. Example 3

[0028] Step 1: Mix hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water, and stir at 10,000 rpm for 10 minutes to obtain a hydroxyl-terminated polydimethylsiloxane preemulsion; wherein the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 5,000 Daltons; and the mass ratio of hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water is 15:4:30.

[0029] Step 2: Add cement, fine aggregate, and coarse aggregate into a forced mixer and mix at 25 rpm for 60 seconds to obtain a dry mixture; the cement is P.O42.5 silicate cement; the fine aggregate is natural river sand with a fineness modulus of 2.8; the coarse aggregate is continuously graded crushed stone with a particle size of 25 mm; the mass ratio of cement, fine aggregate, and coarse aggregate is 420:700:1150.

[0030] Step 3: Mix polycarboxylate superplasticizer, polyether modified silicone defoamer with water, and stir at 500 rpm for 10 minutes to obtain an aqueous solution of the additive; the mass ratio of polycarboxylate superplasticizer, polyether modified silicone defoamer to water is 8:0.5:150.

[0031] Step 4: Add hydroxyl-terminated polydimethylsiloxane preemulsion to the dry mixture and stir at 30 rpm for 90 seconds. Then add the admixture aqueous solution and continue stirring at 30 rpm for 120 seconds to obtain a concrete mixture. Pour the concrete mixture into shape and cure it at 22°C and relative humidity not less than 95% for 24 hours before demolding. Then continue curing under the same conditions for 28 days to obtain high-temperature resistant and fire-resistant concrete. The mass ratio of the dry mixture, hydroxyl-terminated polydimethylsiloxane preemulsion and admixture aqueous solution is 2200:45:160.

[0032] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is the omission of the addition of terminal hydroxyl polydimethylsiloxane.

[0033] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the addition of polyether-modified silicone defoamer is omitted.

[0034] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the addition of polycarboxylate superplasticizer is omitted.

[0035] The compressive strength of concrete was tested in accordance with GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0036] The concrete was heated to 600℃ at a heating rate of 5℃ / min, held at that temperature for 2 hours, and then allowed to cool naturally before its compressive strength was tested.

[0037] Table 1 below shows the performance analysis results of the embodiments and comparative examples of the present invention.

[0038] Table 1

[0039] Experimental data from the examples and comparative examples show that this invention uses a polycarboxylate-based high-efficiency water-reducing agent as a workability regulator and a polyether-modified organosilicon defoamer as a bubble control agent. The silanol groups carried by the hydroxyl-terminated polydimethylsiloxane molecular chains undergo a condensation reaction with the silanol groups on the surface of the cement hydration product, calcium silicate gel, and the calcium hydroxide surface in the alkaline environment generated by silicate cement hydration. This transforms the originally hydrophilic capillaries into hydrophobic properties, reducing the migration rate of capillary water and the accumulation of steam pressure at high temperatures. When concrete is exposed to fire or high-temperature environments, the hydroxyl-terminated polydimethylsiloxane molecular chains undergo thermal breakage to generate amorphous silica fragments. Silica fragments react with calcium hydroxide, a cement hydration product, at high temperatures to form calcium silicate-based high-temperature reaction products. These products are deposited and sintered on the inner walls of concrete pores and microcracks, forming a continuous or semi-continuous protective layer. This protective layer can seal microcracks generated at high temperatures and prevent heat transfer to the interior of the concrete. Polycarboxylate-based high-efficiency water-reducing agents ensure good workability of the mixture, thereby improving the dispersibility of hydroxyl-terminated polydimethylsiloxane. Polyether-modified organosilicon defoamers inhibit the weakening of the concrete matrix strength caused by harmful bubbles introduced by hydroxyl-terminated polydimethylsiloxane, enabling the concrete to achieve good high-temperature fire resistance without sacrificing normal mechanical properties.

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A high-temperature resistant and fire-resistant concrete, characterized in that, The concrete is obtained by mixing dry aggregate, hydroxyl-terminated polydimethylsiloxane preemulsion, and an admixture aqueous solution; the admixture aqueous solution is obtained by mixing polycarboxylate-based high-efficiency water-reducing agent, polyether-modified organosilicon defoamer, and water; the dry aggregate is obtained by mixing cement, fine aggregate, and coarse aggregate; the hydroxyl-terminated polydimethylsiloxane preemulsion is obtained by mixing hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water.

2. The high-temperature resistant and fire-resistant concrete according to claim 1, characterized in that: The cement is P.O42.5 silicate cement.

3. The high-temperature resistant and fire-resistant concrete according to claim 1, characterized in that: The fine aggregate is natural river sand with a fineness modulus of 2.4-2.

8.

4. The high-temperature resistant and fire-resistant concrete according to claim 1, characterized in that: The coarse aggregate is continuously graded crushed stone with a particle size of 5-25mm.

5. A method for preparing high-temperature resistant and fire-resistant concrete, applied to the high-temperature resistant and fire-resistant concrete according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Mix hydroxyl-terminated polydimethylsiloxane, fatty alcohol polyoxyethylene ether and water, and stir at 8000-10000 rpm for 5-10 minutes to obtain hydroxyl-terminated polydimethylsiloxane pre-emulsion. Step 2: Add cement, fine aggregate and coarse aggregate into a forced mixer and mix at 15-25 rpm for 30-60 seconds to obtain a dry mixture. Step 3: Mix polycarboxylate-based high-efficiency water-reducing agent, polyether-modified silicone defoamer with water, and stir at 300-500 rpm for 5-10 minutes to obtain an aqueous solution of additives; Step 4: Add hydroxyl-terminated polydimethylsiloxane pre-emulsion to the mixed dry materials and stir at 25-30 rpm for 60-90 seconds. Then add the admixture aqueous solution and continue stirring at 25-30 rpm for 90-120 seconds to obtain a concrete mixture. Pour the concrete mixture into shape and cure it at 20±2℃ and relative humidity not less than 95% for 24 hours before demolding. Then continue to cure it under the same conditions for 28 days to obtain high-temperature resistant and fire-resistant concrete.

6. The method for preparing high-temperature resistant and fire-resistant concrete according to claim 5, characterized in that: In step one, the mass ratio of terminal hydroxyl polydimethylsiloxane, fatty alcohol polyoxyethylene ether, and water is 5-15:2-4:20-30.

7. The method for preparing high-temperature resistant and fire-resistant concrete according to claim 5, characterized in that: The number-average molecular weight of the hydroxyl-terminated polydimethylsiloxane mentioned in step one is 2000-5000 Daltons.

8. The method for preparing high-temperature resistant and fire-resistant concrete according to claim 5, characterized in that: In step two, the mass ratio of cement, fine aggregate, and coarse aggregate is 380-420:650-700:1050-1150.

9. The method for preparing high-temperature resistant and fire-resistant concrete according to claim 5, characterized in that: In step three, the mass ratio of polycarboxylate-based high-efficiency water-reducing agent, polyether-modified silicone defoamer, and water is 5-8:0.3-0.5:130-150.

10. The method for preparing high-temperature resistant and fire-resistant concrete according to claim 5, characterized in that: In step four, the mass ratio of the mixed dry material, the hydroxyl-terminated polydimethylsiloxane preemulsion, and the additive aqueous solution is 2000-2200:25-45:135-160.

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