High-durability pavement concrete suitable for plateau environment and preparation method thereof

Abstract

The invention discloses high-durability pavement concrete suitable for a plateau environment and a preparation method of the high-durability pavement concrete. Each cubic meter of the concrete comprises the following raw materials: 350-380 kg / m < 3 > of cement, 610-650 kg / m < 3 > of sand, 1250-1300 kg / m < 3 > of gravel, 0.35-0.38 kg / m < 3 > of a plateau air entraining agent, 1.75-1.9 kg / m < 3 > of a water reducing agent, 0.35-0.76 kg / m < 3 > of an internal curing agent, 3.5-3.8 kg / m < 3 > of nano silicon dioxide, 0.35-0.76 kg / m < 3 > of modified mesoporous silicon dioxide and the balance of water, and the water-binder ratio is less than or equal to 0.4. The 28d strength of the concrete is greater than 40MPa, and the pore spacing factor is less than 250 microns. And compared with concrete prepared under the same condition, the durability of the pavement concrete in the plateau area is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of concrete pavement construction technology in plateau environments, specifically to a high-durability pavement concrete suitable for plateau environments and its preparation method. Background Technology

[0002] Plateau regions are characterized by high altitude, thin air, low air pressure, and large temperature differences. On the one hand, plateau regions have low average annual temperatures, large daily and annual temperature differences, and more than 300 freeze-thaw cycles per year. During the day, strong solar radiation causes the ice in concrete to melt, while at night, the temperature drops, causing the pore water in the concrete to freeze and expand. Under the strong freeze-thaw action, the performance of concrete deteriorates rapidly, and some projects have a service life of less than two years. Therefore, freeze-thaw damage is the primary problem for the durability of concrete in plateau regions.

[0003] Currently, the main method to improve the freeze-thaw resistance of concrete is through air entrainment. Since the 1940s, the United States, Europe, Japan, and other countries have conducted research on the freeze-thaw damage mechanism of hardened concrete. The widely accepted theories include Powers' early hydrostatic pressure (expansion pressure) theory and the later, more refined osmotic pressure (crystallization pressure) theory. Pore water freezing produces a 9% volume expansion. If ice crystal growth is restricted, it will compress the pipe walls, creating hydrostatic pressure and damaging the matrix. Furthermore, because the freezing points of solutions such as alkalis, chlorides, and calcium hydroxide in concrete capillaries are lower than those of pure water, local concentration gradients lead to osmotic pressure. In addition, because the interlayer water and adsorbed water of the CSH gel exist in liquid form at extremely low temperatures (-78℃), the high-energy state supercooled water migrates to the low-energy state capillaries and freezes, generating suction pressure (cryogenic pump effect). When a certain number and size of air bubbles exist in the concrete, excess water enters the air bubbles during freezing expansion, effectively preventing damage to the matrix when water freezes. Throughout the process, air bubbles act as a "pressure relief valve" and "buffer tank" for hydrostatic pressure, as well as a "storage room" for ice and solution. It is generally believed that concrete in frigid regions needs an air content of 4% to 10% and an air bubble spacing coefficient of around 200 μm to achieve good frost resistance.

[0004] On the other hand, concrete in the low-pressure environment of high altitudes suffers from problems such as weak air entrainment capacity, poor bubble stability, and large pores. For every 1000m increase in altitude, the relative atmospheric pressure decreases by 12%, with atmospheric pressure in most high-altitude areas only 30% to 50% of that in plains areas. Under these conditions, bubble stability deteriorates, bubble lifespan is shortened by about 50%, the dosage of air-entraining agents increases exponentially, air entrainment in concrete becomes difficult, and the air content is only about 50% of that at atmospheric pressure. The air content loss over time increases by about three times, significantly weakening the concrete's resistance to freeze-thaw damage. Furthermore, the concrete is prone to segregation and bleeding, increasing pumping resistance; concrete strength decreases; the bubble spacing coefficient of hardened concrete nearly doubles, the average pore size increases by 8% to 12%, the total porosity and the number of pores in the 500-1000nm range increase significantly, and the number of bubbles per unit volume decreases to only about 35% at atmospheric pressure, severely reducing the concrete's freeze-thaw resistance and other durability properties.

[0005] Currently, there is a lack of basic research both domestically and internationally on the design and preparation of air-entrained concrete in high-altitude, low-pressure environments. Given the rapid development of infrastructure construction in high-altitude areas, there is an urgent need to optimize concrete formulations and conduct research on freeze-thaw resistant concrete materials for low-pressure environments. Summary of the Invention

[0006] This invention provides a high-durability pavement concrete suitable for high-altitude environments and its preparation method, which effectively improves the durability and frost resistance of concrete under low-pressure conditions in high-altitude environments, and also has good bubble stability and high strength after hardening.

[0007] The technical solution provided by this invention is as follows: A high-durability pavement concrete suitable for high-altitude environments, wherein the raw material proportions per cubic meter of the concrete include: cement 350–380 kg / m³ 3 Sand 610~650 kg / m 3 Crushed stone 1250-1300 kg / m³ 3 High-altitude air-entraining agent: 0.35–0.38 kg / m² 3 Water-reducing agent 1.75~1.9 kg / m³ 3 Internal curing agent: 0.35–0.76 kg / m² 3 Nano-silica 3.5~3.8 kg / m 3 Modified mesoporous silica 0.35–0.76 kg / m 3 The water content and the remaining amount of water should be ≤0.4.

[0008] Furthermore, the cement is P·O 425 cement.

[0009] Furthermore, the high-altitude air-entraining agent is a triterpenoid saponin air-entraining agent.

[0010] Furthermore, the water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate of ≥25%.

[0011] Furthermore, the crushed stone is made of stone with a particle size of 5 to 31.5 mm.

[0012] Furthermore, the internal curing agent is superabsorbent resin particles with a particle size of less than 75 micrometers.

[0013] Furthermore, the nano-silica is spherical particles with a particle size of 20 nanometers.

[0014] Furthermore, the modified mesoporous silica consists of spherical hollow particles with a particle size of about 10 micrometers. The shells of the spherical hollow particles have pores with a diameter of about 20 nanometers, and each spherical hollow particle has a triterpenoid saponin gas-entraining agent molecule grafted onto its surface.

[0015] This invention also provides a method for preparing high-durability pavement concrete suitable for plateau environments, comprising the following steps: (1) Weigh each raw material according to the raw material ratio, and dry mix cement, water-reducing agent, nano silica and internal curing agent for 60s to obtain the first mixture; (2) Add sand and gravel to the first mixture and dry mix for 30 s to obtain the second mixture; (3) Add an aqueous solution containing triterpenoid saponin gas-entraining agent and modified mesoporous silica to the second mixture, stir for 240 s, and obtain a third mixture; (4) After the third mixture is cast into shape, it is covered with fiber felt and moistened with water for 7 days to obtain the high-durability pavement concrete.

[0016] Furthermore, the method for preparing the modified mesoporous silica includes the following steps: (1) Place the mesoporous silica in an oven at 200°C for 2 hours to remove surface organic impurities and activate surface hydroxyl groups; (2) Dissolve γ-aminopropyltriethoxysilane (KH560) in an ethanol / water mixed solvent at 5% of the mass ratio of mesoporous silica, and adjust the pH to 4-5 with acetic acid. The volume ratio of ethanol to water in the ethanol / water mixed solvent is 9:1. (3) Add the silica treated in step (1) to the solution prepared in step (2) and stir at 60°C for 4 to 6 hours; (4) The product obtained in step (3) is filtered, and the precipitate is washed with anhydrous ethanol to remove unreacted γ-aminopropyltriethoxysilane. After drying, epoxy-oxidized silicon dioxide is obtained. (5) Grafting triterpenoid saponins onto the surface of silica, dissolving the triterpenoid saponins in phosphate buffer at pH=7 to prepare a 1-5 wt% solution, adding epoxy-oxidized silica and condensing agent (EDC / NHS, molar ratio 1:1.2), stirring and reacting at room temperature for 12-24 hours, centrifuging to separate the product, washing with deionized water, and drying to obtain the modified mesoporous silica.

[0017] Compared with the prior art, the beneficial effects of the present invention are: The high-durability pavement concrete provided by this invention employs a triterpenoid saponin air-entraining agent that maintains excellent air-entraining capacity even in high-altitude environments, supplemented with modified silica particles to prevent bubble structure deterioration and enhance bubble stability. The modified nano-silica particles adsorb onto the bubble walls in the cement concrete, preventing gas molecules from passing through and thus preventing the dissolution of small bubbles. The addition of nano-silica promotes early cement hydration, enabling faster formation of hydration products and resulting in a dense microstructure, thereby reducing moisture loss from the concrete interior in low-humidity, dry environments. The addition of an internal curing agent replenishes the moisture lost in the early stages of newly poured concrete, providing a continuous supply of moisture to internal micro-regions to promote cement hydration and reduce micro-cracks caused by drying shrinkage. The high-durability pavement concrete prepared by this invention exhibits a 28-day strength greater than 40 MPa and a pore spacing factor less than 250 micrometers. Furthermore, compared to concrete prepared under the same conditions, this invention significantly improves the durability of pavement concrete in high-altitude areas. Attached Figure Description

[0018] Figure 1 This is a flowchart of the preparation method of high-durability pavement concrete suitable for plateau environments according to the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments.

[0020] Therefore, the detailed description of the embodiments of this application provided below with reference to the accompanying drawings is intended merely to illustrate selected embodiments of this application and is not intended to limit the scope of protection claimed by this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] It should be understood that in the description of embodiments of the present invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of the stated features.

[0022] This invention provides a high-durability pavement concrete suitable for high-altitude environments, wherein the raw material proportions per cubic meter of concrete include: cement 350–380 kg / m³ 3 Sand 610~650 kg / m 3 Crushed stone 1250-1300 kg / m³ 3 High-altitude air-entraining agent: 0.35–0.38 kg / m² 3 Water-reducing agent 1.75~1.9 kg / m³ 3 Internal curing agent: 0.35–0.76 kg / m² 3 Nano-silica 3.5~3.8 kg / m 3 Modified mesoporous silica 0.35–0.76 kg / m 3 The water content and the remaining amount of water should be ≤0.4.

[0023] In this embodiment, the cement is P·O 425 cement, the high-altitude air-entraining agent is a triterpenoid saponin air-entraining agent, the water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate ≥25%, the crushed stone particle size is 5-31.5 mm, and the internal curing agent is superabsorbent resin particles with a particle size of less than 75 micrometers. The nano-silica is spherical particles with a particle size of 20 nanometers. The modified mesoporous silica is spherical hollow particles with a particle size of 10 micrometers, with 20 nanometer pores on the shell of each spherical hollow particle, and each spherical hollow particle surface is grafted with triterpenoid saponin air-entraining agent molecules.

[0024] The high-durability pavement concrete provided in this embodiment uses a triterpenoid saponin air-entraining agent that still exhibits excellent air-entraining capabilities in high-altitude environments, supplemented with modified silica particles to prevent bubble structure deterioration and enhance bubble stability. The modified nano-silica particles adsorb onto the bubble walls in the cement concrete, preventing gas molecules from passing through and thus preventing the dissolution of small bubbles. The addition of nano-silica promotes early cement hydration, enabling faster formation of hydration products and resulting in a dense microstructure, thereby reducing moisture loss from the concrete interior in low-humidity, dry environments. The addition of an internal curing agent replenishes the moisture lost in the early stages of newly poured concrete, providing a continuous supply of moisture to internal micro-regions to promote cement hydration and reduce micro-cracks caused by drying shrinkage.

[0025] like Figure 1As shown, the method for preparing high-durability pavement concrete suitable for plateau environments provided by the present invention includes the following steps: (1) Weigh each raw material according to the raw material ratio, and dry mix cement, water-reducing agent, nano silica and internal curing agent for 60s to obtain the first mixture; (2) Add sand and gravel to the first mixture and dry mix for 30 s to obtain the second mixture; (3) Add an aqueous solution containing triterpenoid saponin gas-entraining agent and modified mesoporous silica to the second mixture, stir for 240 s, and obtain a third mixture; (4) After the third mixture is cast into shape, it is covered with fiber felt and moistened with water for 7 days to obtain the high-durability pavement concrete.

[0026] Furthermore, the method for preparing the modified mesoporous silica includes the following steps: (1) Place the mesoporous silica in an oven at 200°C for 2 hours to remove surface organic impurities and activate surface hydroxyl groups; (2) Dissolve γ-aminopropyltriethoxysilane (KH560) in an ethanol / water mixed solvent at 5% of the mass ratio of mesoporous silica, and adjust the pH to 4-5 with acetic acid. The volume ratio of ethanol to water in the ethanol / water mixed solvent is 9:1. (3) Add the silica treated in step (1) to the solution prepared in step (2) and stir at 60°C for 4 to 6 hours; (4) The product obtained in step (3) is filtered, and the precipitate is washed with anhydrous ethanol to remove unreacted γ-aminopropyltriethoxysilane. After drying, epoxy-oxidized silicon dioxide is obtained. (5) Grafting triterpenoid saponins onto the surface of silica, dissolving the triterpenoid saponins in phosphate buffer at pH=7 to prepare a 1-5 wt% solution, adding epoxy-oxidized silica and condensing agent (EDC / NHS, molar ratio 1:1.2), stirring and reacting at room temperature for 12-24 hours, centrifuging to separate the product, washing with deionized water, and drying to obtain the modified mesoporous silica.

[0027] The high-durability pavement concrete prepared by this invention exhibits a 28-day strength greater than 40 MPa and a pore spacing factor less than 250 micrometers. Furthermore, compared to concrete prepared under the same conditions, this invention significantly improves the durability of pavement concrete in high-altitude areas.

[0028] Example 1 This embodiment provides the above-mentioned high-durability pavement concrete for high-altitude environments, with the following mix proportion: cement 350kg / m³. 3 650 kg / m³ of sand 31300 kg / m³ of crushed stone 3 0.35 kg / m² of high-altitude air-entraining agent 3 Water-reducing agent 1.75kg / m 3 Internal curing agent 0.35 kg / m 3 Nano-silica 3.5 kg / m 3 Modified mesoporous silica 0.35 kg / m 3 The water-to-binder ratio is 0.4.

[0029] In this embodiment, the method for preparing high-durability pavement concrete for plateau environments is as follows: (1) Dry mix cement, water-reducing agent, nano silica and concrete internal curing agent for 60 s; (2) Add sand and gravel, and continue dry mixing for 30 seconds; (3) Add an aqueous solution containing an air-entraining agent and modified mesoporous silica, and stir for 240 s; (4) Concrete specimens were poured at the test base in Damxung County, Lhasa and placed outdoors, covered with fiber felt and moisturized with water for 7 days. The minimum outdoor temperature during the specimen curing period was greater than 10℃.

[0030] Example 2 This embodiment provides the above-mentioned high-durability pavement concrete for high-altitude environments, with the following mix proportion: cement 350kg / m³. 3 650 kg / m³ of sand 3 1300 kg / m³ of crushed stone 3 0.35 kg / m² of high-altitude air-entraining agent 3 Water-reducing agent 1.75kg / m 3 Internal curing agent 0.35 kg / m 3 Nano-silica 3.5 kg / m 3 Modified mesoporous silica 0.70 kg / m 3 The water-to-binder ratio is 0.4.

[0031] In this embodiment, the method for preparing high-durability pavement concrete for plateau environments is as follows: (1) Dry mix cement, water-reducing agent, nano silica and concrete internal curing agent for 60 s; (2) Add sand and gravel, and continue dry mixing for 30 seconds; (3) Add an aqueous solution containing an air-entraining agent and modified mesoporous silica, and stir for 240 s; (4) Concrete specimens were poured at the test base in Damxung County, Lhasa and placed outdoors, covered with fiber felt and moisturized with water for 7 days. The minimum outdoor temperature during the specimen curing period was greater than 10℃.

[0032] Example 3 This embodiment provides the above-mentioned high-durability pavement concrete for high-altitude environments, with the following mix proportion: cement 380kg / m³. 3 610 kg / m³ of sand 3 1250 kg / m³ of crushed stone 3 0.38 kg / m² of high-altitude air-entraining agent 3 Water-reducing agent 1.9 kg / m 3 Internal curing agent 0.76 kg / m 3 Nano-silica 3.8 kg / m 3 Modified mesoporous silica 0.38 kg / m 3 The water-to-binder ratio is 0.39.

[0033] In this embodiment, the method for preparing high-durability pavement concrete suitable for plateau environments is as follows: (1) Dry mix cement, water-reducing agent, nano silica and concrete internal curing agent for 60 s; (2) Add sand and crushed stone and continue dry mixing for 30 seconds; (3) Add an aqueous solution containing an air-entraining agent and modified mesoporous silica, and stir for 240 s; (4) Concrete specimens were poured at the test base in Damxung County, Lhasa and placed outdoors, covered with fiber felt and moisturized with water for 7 days. The minimum outdoor temperature during the specimen curing period was greater than 10℃.

[0034] Example 4 This embodiment provides the above-mentioned high-durability pavement concrete for high-altitude environments, with the following mix proportion: cement 380kg / m³. 3 610 kg / m³ of sand 3 1250 kg / m³ of crushed stone 3 0.38 kg / m² of high-altitude air-entraining agent 3 Water-reducing agent 1.9 kg / m 3 Internal curing agent 0.76 kg / m 3 Nano-silica 3.8 kg / m 3 Modified mesoporous silica 0.76 kg / m 3 The water-to-binder ratio is 0.39.

[0035] In this embodiment, the method for preparing high-durability pavement concrete suitable for plateau environments is as follows: (1) Dry mix cement, water-reducing agent, nano silica and concrete internal curing agent for 60 s; (2) Add sand and crushed stone and continue dry mixing for 30 seconds; (3) Add an aqueous solution containing an air-entraining agent and modified mesoporous silica, and stir for 240 s; (4) Concrete specimens were poured at the test base in Damxung County, Lhasa and placed outdoors, covered with fiber felt and moisturized with water for 7 days. The minimum outdoor temperature during the specimen curing period was greater than 10℃.

[0036] control group This embodiment provides the above-mentioned high-durability pavement concrete for high-altitude environments, with the following mix proportion: cement 365kg / m³. 3 630 kg / m³ of sand 3 1270 kg / m³ of crushed stone 3 0.7 kg / m³ of rosin-based air-entraining agent 3 Polycarboxylate superplasticizer 1.9 kg / m 3 The water-to-binder ratio is 0.4.

[0037] In this embodiment, the method for preparing high-durability pavement concrete suitable for plateau environments is as follows: (1) Dry mix cement, sand, gravel and water-reducing agent for 60 s; (2) Add an aqueous solution containing rosin air-entraining agent and stir for 240 s; (3) Concrete specimens were poured at the test base in Damxung County, Lhasa and placed outdoors, covered with fiber felt and moisturized with water for 7 days. The minimum outdoor temperature during the specimen curing period was greater than 10℃.

[0038] The mechanical and durability properties of the high-durability pavement concrete suitable for plateau environments prepared in Examples 1 and 2 were tested, and the results are shown in Table 1.

[0039] Table 1. Mechanical and durability properties of the high-durability pavement concrete prepared in the examples.

[0040] The above description is merely the preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A high-durability pavement concrete suitable for high-altitude environments, characterized in that: The raw material proportions for each cubic meter of concrete include: cement 350–380 kg / m³ 3 Sand 610~650 kg / m 3 Crushed stone 1250-1300 kg / m³ 3 High-altitude air-entraining agent: 0.35–0.38 kg / m² 3 Water-reducing agent 1.75~1.9 kg / m³ 3 Internal curing agent: 0.35–0.76 kg / m² 3 Nano-silica 3.5~3.8 kg / m 3 Modified mesoporous silica 0.35–0.76 kg / m 3 The water content and the remaining amount of water should be ≤0.

4.

2. The high-durability pavement concrete suitable for plateau environments according to claim 1, characterized in that: The cement is P·O 425 cement.

3. The high-durability pavement concrete suitable for plateau environments according to claim 1, characterized in that: The high-altitude air-entraining agent is a triterpenoid saponin air-entraining agent.

4. The high-durability pavement concrete suitable for plateau environments according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate of ≥25%.

5. The high-durability pavement concrete suitable for plateau environments according to claim 1, characterized in that: The crushed stone used is crushed stone with a particle size of 5 to 31.5 mm.

6. The high-durability pavement concrete suitable for plateau environments according to claim 1, characterized in that: The internal curing agent is superabsorbent resin particles with a particle size of less than 75 micrometers.

7. The high-durability pavement concrete suitable for plateau environments according to any one of claims 1-6, characterized in that: The nano-silica consists of spherical particles with a diameter of 20 nanometers, which promote cement hydration.

8. The high-durability pavement concrete suitable for plateau environments according to claim 7, characterized in that: The modified mesoporous silica consists of spherical hollow particles with a particle size of about 10 micrometers. The shell of each spherical hollow particle has pores of 20 nanometers, and each spherical hollow particle has a triterpenoid saponin gas-entraining agent molecule grafted onto its surface.

9. A method for preparing high-durability pavement concrete suitable for plateau environments, used to prepare the high-durability pavement concrete suitable for plateau environments as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Weigh each raw material according to the raw material ratio, and dry mix the cement, water-reducing agent, nano silica and internal curing agent for 60 s to obtain the first mixture; (2) Add sand and gravel to the first mixture and dry mix for 30 s to obtain the second mixture; (3) Add an aqueous solution containing triterpenoid saponin gas-entraining agent and modified mesoporous silica to the second mixture, stir for 240 s, and obtain a third mixture; (4) After the third mixture is cast into shape, it is covered with fiber felt and moistened with water for 7 days to obtain the high-durability pavement concrete.

10. The method for preparing high-durability pavement concrete suitable for plateau environments according to claim 9, characterized in that: The method for preparing the modified mesoporous silica includes the following steps: (1) Place the mesoporous silica in an oven at 200°C for 2 hours to remove surface organic impurities and activate surface hydroxyl groups; (2) Dissolve γ-aminopropyltriethoxysilane (KH560) in an ethanol / water mixed solvent at 5% of the mass ratio of mesoporous silica, and adjust the pH to 4-5 with acetic acid. The volume ratio of ethanol to water in the ethanol / water mixed solvent is 9:

1. (3) Add the silica treated in step (1) to the solution prepared in step (2) and stir at 60°C for 4 to 6 hours; (4) The product obtained in step (3) is filtered, and the precipitate is washed with anhydrous ethanol to remove unreacted γ-aminopropyltriethoxysilane. After drying, epoxy-oxidized silicon dioxide is obtained. (5) Grafting triterpenoid saponins onto the surface of silica, dissolving the triterpenoid saponins in phosphate buffer at pH=7 to prepare a 1-5 wt% solution, adding epoxy-oxidized silica and condensing agent (EDC / NHS, molar ratio 1:1.2), stirring and reacting at room temperature for 12-24 hours, centrifuging to separate the product, washing with deionized water, and drying to obtain the modified mesoporous silica.

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