High-strength heat-resistant concrete and its production process

Abstract

This invention relates to the field of building materials technology, specifically to a high-strength heat-resistant concrete and its production process. The concrete uses steel slag, silicate cement, microsilica, and double-grafted modified nano-silica as main raw materials. The innovative process includes in-situ wet carbonation of steel slag with carbonated water, interface optimization of modified nano-silica, and multi-stage composite curing. These measures significantly improve the concrete's mechanical strength, high-temperature resistance, and freeze-thaw durability, achieving a compressive strength of 108 MPa after 28 days. This method effectively utilizes steel slag resources, achieving a balance between high strength and heat resistance, and possesses both green, low-carbon, and engineering application value.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a high-strength heat-resistant concrete and its production process. Background Technology

[0002] With the increasing demand for high-performance concrete in modern engineering construction, especially in special applications such as high-temperature industrial environments, nuclear power plant reactor shielding, and steel metallurgical furnace linings, traditional concrete often struggles to meet the dual requirements of high strength and heat resistance. Existing high-strength concrete mainly improves strength by reducing the water-cement ratio and adding active admixtures such as silica fume, but it is prone to problems such as a sharp drop in strength and poor thermal stability under high-temperature environments.

[0003] The degradation mechanism of traditional concrete under high temperature mainly includes: decomposition and dehydration of hydration products, thermal expansion mismatch between aggregates and cementitious materials, and propagation of microcracks in the interfacial transition zone. Especially in temperature environments above 400℃, hydration products such as calcium hydroxide begin to decompose, leading to a significant reduction in matrix strength; at a high temperature of 800℃, the CSH gel structure is completely destroyed, and the load-bearing capacity of the concrete is almost lost.

[0004] In recent years, steel slag, as a byproduct of the iron and steel industry, has attracted widespread attention due to its rich content of active components such as dicalcium silicate and tricalcium silicate. However, steel slag has a high content of free calcium oxide and magnesium oxide, which easily leads to volume instability; at the same time, it is difficult to activate the cementitious activity of steel slag, limiting its direct application effectiveness. Existing technologies mainly use mechanical grinding and chemical activation methods to treat steel slag, but these generally suffer from high energy consumption and unsatisfactory results.

[0005] Nano-silica, as a highly active admixture, possesses an extremely large specific surface area and pozzolanic activity, which can significantly improve the mechanical properties and durability of concrete. However, unmodified nano-silica is prone to agglomeration in alkaline environments, making uniform dispersion difficult; simultaneously, its interfacial bonding with the cement matrix is ​​relatively weak, making it susceptible to interfacial failure at high temperatures. Current surface modification technologies mainly employ single modifiers such as silane coupling agents, resulting in limited modification effects and failing to simultaneously meet the dual requirements of dispersibility and interfacial adhesion.

[0006] In terms of curing processes, traditional standard curing or steam curing can only achieve basic strength development and is unlikely to achieve excellent high-temperature performance. Although carbonation curing can improve the density of concrete, simple carbonation treatment often leads to excessive surface hardening and insufficient internal densification. Existing composite curing processes mostly adopt simple sequential treatments and lack systematic synergistic optimization design.

[0007] Furthermore, existing research on high-strength, heat-resistant concrete largely focuses on improving single technical approaches, such as optimizing the composition of cementitious materials or adjusting curing regimes. It lacks a systematic integration of technologies from multiple dimensions, including raw material pretreatment, interface modification, and composite curing. This limitation results in concrete that often excels in a single performance indicator, but its overall performance fails to meet the stringent requirements of practical engineering projects, particularly in the coordinated development of high strength and heat resistance.

[0008] Therefore, how to achieve efficient utilization of steel slag resources through innovative technological approaches and develop high-strength concrete with both excellent mechanical and heat resistance properties has become a key technical problem that urgently needs to be solved. Summary of the Invention

[0009] In view of this, the purpose of this invention is to propose a high-strength heat-resistant concrete and its production process, so as to achieve the synergistic effect of efficient activation of steel slag and interface optimization, and to prepare concrete with both high strength and excellent heat resistance.

[0010] To achieve the above objectives, the present invention provides a production process for high-strength heat-resistant concrete, comprising the following steps:

[0011] (1) Mix steel slag and carbonated water and ball mill for 100-140 min, filter and dry to obtain pretreated steel slag fine powder;

[0012] (2) Mix silicate cement, pretreated steel slag fine powder, micro silica powder, and double-grafted modified nano silica. Stir at low speed for 100-140s and let stand for 8-12min. Then add manufactured sand and continuously graded crushed stone. Continue stirring at low speed for 80-100s. Then add carbonated water and polycarboxylate superplasticizer. Stir at medium speed for 100-140s and then at high speed for 50-70s to obtain concrete mix.

[0013] (3) The concrete mix is ​​put into the mold, compacted on the vibrating table, and left to stand for 50-70 minutes before the first steam curing is carried out to obtain the first steam-cured concrete.

[0014] (4) The first steam-cured concrete was subjected to room temperature carbonation treatment in a carbon dioxide environment to obtain carbonized concrete.

[0015] (5) The carbonized concrete is steam cured a second time, then demolded, and then cured in a standard curing room. After curing, high-strength heat-resistant concrete is obtained.

[0016] Preferably, the steel slag in step (1) is a product of BSSF drum process, with an average particle size of less than 5 mm, a free CaO content of less than 6%, and a free MgO content of less than 3%.

[0017] Preferably, the weight ratio of steel slag to carbonated water in step (1) is 350-450:85-115.

[0018] Preferably, in step (1), the ball-to-material ratio of the ball mill is 1.0-1.4:1, and the mill speed is 15-21 rpm.

[0019] Preferably, the drying in step (1) is performed at 100-110°C for 10-14 hours.

[0020] Furthermore, in step (2), the double-grafted modified nano-silica is obtained by grafting nano-silica with silanized polyethylene glycol carboxyl end groups and silanized polyethylene glycol amino end groups under an alkaline environment.

[0021] The average particle size of the nano-silica is 25-35 nm.

[0022] The silanized polyethylene glycol carboxyl terminus is a functionalized polyethylene glycol derivative with triethoxysilane and carboxyl terminus, with a weight average molecular weight of 2000, and is derived from Silane-PEG-COOH of Nanocs Corporation.

[0023] The silanized polyethylene glycol amino-terminal group is a functionalized polyethylene glycol derivative with triethoxysilane and amino-terminal groups, with a weight-average molecular weight of 20,000, and is derived from Nanocs' Silane-PEG-NH2.

[0024] The weight ratio of the nano-silica, the silanized polyethylene glycol carboxyl end group, and the silanized polyethylene glycol amino end group is 600-1000:6-10:3-5.

[0025] Preferably, in step (2), the weight ratio of silicate cement, pretreated steel slag fine powder, micro silica powder, double-grafted modified nano silica, manufactured sand, continuously graded crushed stone, carbonated water and polycarboxylate superplasticizer is 360-480:260-380:45-75:6-10:730-870:650-750:160-200:6.5-9.5.

[0026] Preferably, the grade of silicate cement in step (2) is P.II52.5R.

[0027] Preferably, the type of microsilica powder used in step (2) is Microsilica 920.

[0028] Preferably, the fineness modulus of the manufactured sand in step (2) is 2.4-2.8, and the mud content is less than 3%.

[0029] Preferably, in step (2), the particle size of the continuously graded crushed stone is 5-20 mm, and the crushing index is 8%-9%.

[0030] Preferably, in steps (1) and (2), the carbonated water is prepared by dissolving carbon dioxide in deionized water and has a pH of 4.2-4.8.

[0031] Preferably, the polycarboxylate superplasticizer used in step (2) is Sika ViscoCrete-20HE.

[0032] Preferably, in step (2), the stirring linear velocity of low-speed stirring is 1.8-2.2 m / s, the stirring linear velocity of medium-speed stirring is 2.2-2.8 m / s, and the stirring linear velocity of high-speed stirring is 2.8-3.2 m / s.

[0033] Preferably, the vibration frequency of the compaction molding in step (3) is 45-55Hz, the amplitude is 0.4-0.6mm, and the vibration time is 18-22s.

[0034] Preferably, the first steam curing in step (3) is as follows: during the heating stage, the temperature is increased to 50-70℃ at a rate of 12-18℃ / h; during the constant temperature curing stage, the temperature is maintained at 50-70℃ and relative humidity of 90%-98% for 160-200 minutes; and during the cooling stage, the temperature is reduced to 25℃ at a rate of 8-12℃ / h.

[0035] Preferably, the partial pressure of carbon dioxide in the carbon dioxide environment in step (4) is 0.07-0.13 MPa, and the carbonization time is 50-70 min.

[0036] Preferably, the second steam curing in step (5) is as follows: during the heating stage, the temperature is increased to 70-90℃ at a rate of 10-14℃ / h; during the constant temperature curing stage, the temperature is maintained at 70-90℃ and relative humidity of 90%-98% for 100-140 minutes; and during the cooling stage, the temperature is reduced to 25℃ at a rate of 6-10℃ / h.

[0037] Preferably, the temperature of the standard curing room in step (5) is 20°C and the relative humidity is 95%.

[0038] Preferably, in step (5), the specimen is turned over every 24 hours during the standard curing period to ensure uniform curing.

[0039] Furthermore, the present invention provides a high-strength heat-resistant concrete, which is obtained by the above-mentioned production process of high-strength heat-resistant concrete.

[0040] This invention achieves an effective balance between high strength and heat resistance through innovative technical approaches such as in-situ wet carbonization pretreatment of ultrafine steel slag powder with carbonated water, interface optimization of dual-grafted modified nano-silica, and synergistic multi-stage composite curing process. It exhibits the following significant beneficial effects:

[0041] In-situ wet carbonation with carbonated water: This method uses carbonated water containing dissolved carbon dioxide as the grinding medium, simultaneously carrying out in-situ carbonation during the ultrafine refining of steel slag. This allows free calcium oxide and magnesium oxide to react with carbonate ions during the grinding stage to form stable carbonate micronuclei. This in-situ treatment method avoids the problem of a dense surface layer hindering internal reactions in traditional dry carbonation, achieving uniform carbonation of steel slag particles from the surface to the interior. It effectively eliminates the potential for volume instability and provides abundant and uniformly distributed nucleation sites for subsequent hydration reactions, significantly improving early strength development and the density of the interface transition zone.

[0042] Interface enhancement through dual grafting modification of nano-silica: Dual grafting modification with carboxyl-terminated polyethylene glycol (PEG) of molecular weight 2000 and amino-terminated PEG of molecular weight 20000 fully utilizes the chemical properties of different end groups and the spatial effects of different molecular weights. The carboxyl end groups form stable coordination bonds with calcium ions through complexation, providing strong chemical anchoring; the amino end groups enhance the interaction with the silicate phase through electron donor action, improving interfacial adhesion. The two PEGs with different molecular weights form a multi-layered spatial network structure, ensuring good dispersion stability at room temperature, and effectively suppressing the generation and propagation of interfacial microcracks at high temperatures by dissipating heat stress through the cooperative movement of molecular chain segments.

[0043] Synergistic effects of multi-stage composite curing process: An innovative alternating process of steam curing, dry carbonation, and re-steam curing is employed to achieve a multi-layered densification mechanism involving nucleation, solidification, filling, and rearrangement. The first steam curing promotes rapid hydration reactions and the formation of initial strength; dry carbonation further activates the steel slag and fills micropores; the second steam curing reconstructs the arrangement of hydration products at higher temperatures, optimizing pore size distribution. This cyclical treatment avoids the limitations of single curing methods, optimizing the internal structure of concrete at different scales and significantly improving the density and uniformity of the matrix.

[0044] Resource Utilization and Environmental Benefits: This invention effectively utilizes steel slag, an industrial byproduct, and achieves high-value utilization of waste through technological innovation, aligning with the concepts of green development and circular economy. Simultaneously, optimized maintenance processes reduce energy consumption and environmental impact, resulting in significant economic and social benefits.

[0045] The high-strength heat-resistant concrete prepared by this invention achieves significant improvements in mechanical properties, high-temperature stability, and durability. The pore structure of the concrete matrix is ​​comprehensively optimized, defects in the interfacial transition zone are greatly reduced, and the crystallinity and orientation of the hydration products are significantly improved. Under high-temperature conditions, the bridging effect of modified nano-silica and the stability of steel slag carbonization products jointly maintain the structural integrity, effectively inhibiting the accumulation of thermal damage and achieving a significant improvement in strength retention. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0047] Figure 1 The X-ray diffraction patterns of the concrete mix, carbon dioxide treated concrete, first steam cured concrete, and high-strength heat-resistant concrete in Embodiment 2 of the present invention are shown.

[0048] Figure 2 The infrared spectra of nano-silica and double-grafted modified nano-silica in Example 2 of this invention are shown. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0050] Example 1

[0051] (1) Take 6000g of nano silica (average particle size 25nm), 4500g of anhydrous ethanol, 1500g of deionized water, 60g of ammonia (concentration 20wt%), 60g of silanized polyethylene glycol carboxyl end group (Nanos Silane-PEG-COOH, weight average molecular weight 2000), and 30g of silanized polyethylene glycol amino end group (Nanos Silane-PEG-NH2, weight average molecular weight 20000) and add them sequentially to a three-necked flask with mechanical stirring. Stir the reaction at 50℃ for 4h. After the reaction is completed, wash with deionized water until neutral and dry in an oven at 70℃ for 4h to obtain double-grafted modified nano silica.

[0052] (2) Take 250 kg of deionized water and put it into a pressure-resistant stainless steel container. Pass carbon dioxide gas through the container at a flow rate of 150 mL / min. Continue to pass the gas through the container at room temperature and pressure. Detect the pH value with a pH meter every 10 min during the gas passage until the pH value stabilizes in the range of 4.2-4.4 and the change in the pH value is ≤0.05 for 3 consecutive measurements. Stop passing the gas passage to obtain carbonated water.

[0053] (3) Take 350 kg of steel slag (the product of BSSF roller process of China Baowu Steel Group, with an average particle size of 3.5 mm, free CaO content of 5.2%, and free MgO content of 2.1%), add 85 kg of carbonated water into a ball mill, with a ball-to-material ratio of 1.0:1, a mill speed of 15 rpm, wet grinding for 100 min, filter and dehydrate, and dry in an oven at 100℃ for 10 h to obtain pretreated steel slag fine powder;

[0054] (4) Add 360 kg of silicate cement (China Resources Cement Runfeng brand P.II52.5R), 260 kg of pretreated steel slag fine powder, and 45 kg of microsilica powder (Elken Company Microsilica). 920), 6 kg of double-grafted modified nano-silica were mixed at low speed for 100 s (mixing linear velocity 1.8 m / s) in a forced mixer, and then allowed to stand for 8 min. Then 730 kg of manufactured sand (conch aggregate, fineness modulus 2.6, mud content 2.4%) and 650 kg of continuously graded crushed stone (conch aggregate 5-20 mm, crushing index 8.5%) were added, and the mixture was mixed at low speed for 80 s (mixing linear velocity 1.8 m / s). Then 160 kg of carbonated water and 6.5 kg of polycarboxylate superplasticizer (SikaViscoCrete-20HE) were added. The mixture was first mixed at medium speed for 100 s (mixing linear velocity 2.2 m / s), and then mixed at high speed for 50 s (mixing linear velocity 2.8 m / s) to obtain the concrete mix.

[0055] (5) The concrete mix was loaded into the mold and compacted on the vibrating table (vibration frequency 45Hz, amplitude 0.4mm, vibration time 18s). The surface of the mold was covered with plastic film to prevent water loss. After standing for 50 minutes to complete the initial setting, the mold was sent to the steam curing chamber. The curing regime was as follows: the temperature was increased to 50℃ at a rate of 12℃ / h during the heating stage, the constant temperature curing stage was maintained at 50℃ and 90% relative humidity for 160 minutes, and the temperature was reduced to 25℃ at a rate of 8℃ / h during the cooling stage. The concrete was then taken out of the curing chamber to obtain the first steam-cured concrete.

[0056] (6) Place the first steam-cured concrete into the carbonation chamber, introduce carbon dioxide gas to stabilize the partial pressure of carbon dioxide in the chamber at 0.08±0.01MPa, and carbonate for 50 minutes at room temperature to obtain carbonated concrete.

[0057] (7) The carbonized concrete was placed in the steam curing chamber again. The curing regime was as follows: during the heating stage, the temperature was increased to 70℃ at a rate of 10℃ / h; during the constant temperature curing stage, the temperature was maintained at 70℃ and 90% relative humidity for 100 minutes; during the cooling stage, the temperature was reduced to 25℃ at a rate of 6℃ / h. After demolding, the specimen was placed in a standard curing chamber with a temperature of 20℃ and 95% relative humidity for continued curing. During the curing period, the specimen was turned over once every 24 hours to ensure uniform curing. After curing, high-strength heat-resistant concrete was obtained.

[0058] Example 2

[0059] (1) Take 8000g of nano silica (average particle size 30nm), 6000g of anhydrous ethanol, 2000g of deionized water, 80g of ammonia (concentration 25wt%), 80g of silanized polyethylene glycol carboxyl end group (Nanos Silane-PEG-COOH, weight average molecular weight 2000), and 40g of silanized polyethylene glycol amino end group (Nanos Silane-PEG-NH2, weight average molecular weight 20000) and add them sequentially to a three-necked flask with mechanical stirring. Stir and react at 60℃ for 6h. After the reaction is completed, wash with deionized water until neutral and dry in an oven at 80℃ for 6h to obtain double-grafted modified nano silica.

[0060] (2) Take 300 kg of deionized water and put it into a pressure-resistant stainless steel container. Pass carbon dioxide gas through the container at a flow rate of 200 mL / min. Continue to pass the gas through the container at room temperature and pressure. Detect the pH value with a pH meter every 10 min during the gas passage until the pH value stabilizes in the range of 4.4-4.6 and the change in the pH value is ≤0.05 for 3 consecutive measurements. Stop passing the gas passage to obtain carbonated water.

[0061] (3) Take 400 kg of steel slag (the product of BSSF roller process of China Baowu Steel Group, with an average particle size of 3.5 mm, free CaO content of 5.2%, and free MgO content of 2.1%), add 100 kg of carbonated water into a ball mill, with a ball-to-material ratio of 1.2:1, a mill speed of 18 rpm, wet grinding for 120 min, filter and dehydrate, and dry in an oven at 105℃ for 12 h to obtain pretreated steel slag fine powder;

[0062] (4) Add 420 kg of silicate cement (China Resources Cement Runfeng brand P.II52.5R), 320 kg of pretreated steel slag fine powder, and 60 kg of microsilica powder (Elken Company Microsilica). 8 kg of double-grafted modified nano-silica was mixed at low speed for 120 s (mixing linear velocity 2.0 m / s) in a forced mixer, and then allowed to stand for 10 min. Then, 800 kg of manufactured sand (conch aggregate, fineness modulus 2.6, mud content 2.4%) and 700 kg of continuously graded crushed stone (conch aggregate 5-20 mm, crushing index 8.5%) were added, and the mixture was mixed at low speed for 90 s (mixing linear velocity 2.0 m / s). Then, 180 kg of carbonated water and 8 kg of polycarboxylate superplasticizer (SikaViscoCrete-20HE) were added. The mixture was first mixed at medium speed for 120 s (mixing linear velocity 2.5 m / s), and then mixed at high speed for 60 s (mixing linear velocity 3.0 m / s) to obtain the concrete mix.

[0063] (5) The concrete mix is ​​loaded into the mold and compacted on the vibrating table (vibration frequency 50Hz, amplitude 0.5mm, vibration time 20s). The surface of the mold is covered with plastic film to prevent water loss. After standing for 60 minutes to complete the initial setting, the mold and the mold are sent to the steam curing chamber. The curing regime is as follows: the temperature rises to 60℃ at a rate of 15℃ / h during the heating stage, the constant temperature curing stage is maintained at 60℃ and 95% relative humidity for 180 minutes, and the temperature drops to 25℃ at a rate of 10℃ / h during the cooling stage. The concrete is then taken out of the curing chamber to obtain the first steam-cured concrete.

[0064] (6) Place the first steam-cured concrete into the carbonation chamber, introduce carbon dioxide gas to stabilize the partial pressure of carbon dioxide in the chamber at 0.10±0.01MPa, and carbonate for 60 minutes at room temperature to obtain carbonized concrete.

[0065] (7) The carbonized concrete was placed in the steam curing chamber again. The curing regime was as follows: during the heating stage, the temperature was increased to 80℃ at a rate of 12℃ / h; during the constant temperature curing stage, the temperature was maintained at 80℃ and 95% relative humidity for 120 minutes; during the cooling stage, the temperature was reduced to 25℃ at a rate of 8℃ / h. After demolding, the specimen was placed in a standard curing chamber with a temperature of 20℃ and 95% relative humidity for continued curing. During the curing period, the specimen was turned over once every 24 hours to ensure uniform curing. After curing, high-strength heat-resistant concrete was obtained.

[0066] Example 3

[0067] (1) Take 10,000 g of nano silica (average particle size 35 nm), 7,500 g of anhydrous ethanol, 2,500 g of deionized water, 100 g of ammonia (concentration 30 wt%), 100 g of silanized polyethylene glycol carboxyl end group (Nanos Silane-PEG-COOH, weight average molecular weight 2,000), and 50 g of silanized polyethylene glycol amino end group (Nanos Silane-PEG-NH2, weight average molecular weight 20,000) and add them sequentially to a three-necked flask with mechanical stirring. Stir and react at 70 °C for 8 h. After the reaction is complete, wash with deionized water until neutral and dry in an oven at 90 °C for 8 h to obtain double-grafted modified nano silica.

[0068] (2) Take 350 kg of deionized water and put it into a pressure-resistant stainless steel container. Pass carbon dioxide gas through the container at a flow rate of 250 mL / min. Continue to pass the gas through the container at room temperature and pressure. Detect the pH value with a pH meter every 10 min during the gas passage until the pH value stabilizes in the range of 4.6-4.8 and the change in the three consecutive measurements is ≤0.05. Stop passing the gas passage to obtain carbonated water.

[0069] (3) Take 450 kg of steel slag (the product of BSSF roller process of China Baowu Steel Group, with an average particle size of 3.5 mm, free CaO content of 5.2%, and free MgO content of 2.1%), add 115 kg of carbonated water into a ball mill, with a ball-to-material ratio of 1.4:1, a mill speed of 21 rpm, wet grinding for 140 min, filter and dehydrate, and dry in an oven at 110℃ for 14 h to obtain pretreated steel slag fine powder;

[0070] (4) Add 480 kg of silicate cement (China Resources Cement Runfeng brand P.II52.5R), 380 kg of pretreated steel slag fine powder, and 75 kg of microsilica powder (Elken Company Microsilica). 920), 10 kg of double-grafted modified nano-silica were mixed at low speed for 140 s (mixing linear velocity 2.2 m / s) in a forced mixer, and then allowed to stand for 12 min. Then 870 kg of manufactured sand (conch aggregate, fineness modulus 2.6, mud content 2.4%) and 750 kg of continuously graded crushed stone (conch aggregate 5-20 mm, crushing index 8.5%) were added, and the mixture was mixed at low speed for 100 s (mixing linear velocity 2.2 m / s). Then 200 kg of carbonated water and 9.5 kg of polycarboxylate superplasticizer (SikaViscoCrete-20HE) were added. The mixture was first mixed at medium speed for 140 s (mixing linear velocity 2.8 m / s), and then mixed at high speed for 70 s (mixing linear velocity 3.2 m / s) to obtain the concrete mix.

[0071] (5) The concrete mix was loaded into the mold and compacted on the vibrating table (vibration frequency 55Hz, amplitude 0.6mm, vibration time 22s). The surface of the mold was covered with plastic film to prevent water loss. After standing for 70 minutes to complete the initial setting, the mold was sent to the steam curing chamber. The curing regime was as follows: the temperature was increased to 70℃ at a rate of 18℃ / h during the heating stage, the constant temperature curing stage was maintained at 70℃ and 98% relative humidity for 200 minutes, and the temperature was reduced to 25℃ at a rate of 12℃ / h during the cooling stage. The concrete was then taken out of the curing chamber to obtain the first steam-cured concrete.

[0072] (6) Place the first steam-cured concrete into the carbonation chamber, introduce carbon dioxide gas to stabilize the partial pressure of carbon dioxide in the chamber at 0.12±0.01MPa, and carbonate for 70 minutes at room temperature to obtain carbonated concrete.

[0073] (7) The carbonized concrete was placed in the steam curing chamber again. The curing regime was as follows: during the heating stage, the temperature was increased to 90℃ at a rate of 14℃ / h; during the constant temperature curing stage, the temperature was maintained at 90℃ and 98% relative humidity for 140 minutes; during the cooling stage, the temperature was reduced to 25℃ at a rate of 10℃ / h. After demolding, the specimen was placed in a standard curing chamber with a temperature of 20℃ and 95% relative humidity for continued curing. During the curing period, the specimen was turned over once every 24 hours to ensure uniform curing. After curing, high-strength heat-resistant concrete was obtained.

[0074] Comparative Example 1:

[0075] The difference between Comparative Example 1 and Example 2 is that the wet grinding media for the ultrafine steel slag powder was changed from carbonated water to deionized water, while the other conditions were the same as in Example 2.

[0076] Comparative Example 2:

[0077] The difference between Comparative Example 2 and Example 2 is that the dry carbonization-steam curing process is cancelled, and instead only one steam curing is performed (the temperature, relative humidity and holding time are the same as the first steam curing stage in Example 2), while the other conditions are the same as in Example 2.

[0078] Comparative Example 3:

[0079] The difference between Comparative Example 3 and Example 2 is that: instead of using double-grafted modified nano-silica, unmodified nano-silica was used, while the other conditions were the same as in Example 2;

[0080] Comparative Example 4:

[0081] The difference between Comparative Example 4 and Example 2 is that only carboxyl-terminated polyethylene glycol (weight average molecular weight 2000) was used to perform single graft modification on nano-silica, and the grafting of amino-terminated polyethylene glycol (weight average molecular weight 20000) was cancelled. The other conditions were the same as in Example 2.

[0082] Comparative Example 5:

[0083] The difference between Comparative Example 5 and Example 2 is that only amino-terminated polyethylene glycol (weight average molecular weight 20000) was used to perform single graft modification on nano-silica, and the grafting of carboxyl-terminated polyethylene glycol (weight average molecular weight 2000) was cancelled. The other conditions were the same as in Example 2.

[0084] Comparative Example 6:

[0085] The difference between Comparative Example 6 and Example 2 is that the constant temperature during the first steam curing stage was adjusted from 60°C to 80°C, while the heating and cooling rates remained unchanged, and the other conditions were the same as in Example 2.

[0086] Performance testing:

[0087] X-ray diffraction analysis: Tests were performed using an X-ray diffractometer with a scanning range of 5°–70° (2θ). The results are as follows: Figure 1 As shown.

[0088] Infrared spectroscopy analysis: Tests were performed using a Fourier transform infrared spectrometer, with a scanning range of 4000-400 cm⁻¹. -1 Wavenumber, results as follows Figure 2 As shown.

[0089] Cube compressive strength test: The test was conducted according to GB / T 50081-2019. The specimen size was 100mm×100mm×100mm, with 3 specimens per group. The specimens were loaded on a universal testing machine at a loading speed of 0.8MPa / s. The compressive strength at 28d and 56d was tested respectively. The results are shown in Table 1.

[0090] Splitting tensile strength test: The test was conducted according to GB / T 50081-2019. The specimens were φ100mm×200mm cylindrical specimens aged 28 days, with 3 specimens per group. The splitting method was used on a universal testing machine with a loading rate of 0.05MPa / s until the specimen failed. The splitting tensile strength was calculated according to the formula fts=2P / (πdt), where P is the failure load, d is the specimen diameter, and t is the specimen thickness. The results are shown in Table 1.

[0091] High-temperature compressive strength retention rate test: The heat resistance performance was tested according to GB / T 50082-2009. 100mm×100mm×100mm cubic specimens aged 28 days were placed in high-temperature environments of 200℃, 400℃, and 800℃ for 2 hours each, and then allowed to cool naturally at room temperature for 24 hours before compressive strength testing. The high-temperature compressive strength retention rate was calculated using the formula ηt=(fcu,t / fcu,20)×100%, where fcu,t is the compressive strength after high-temperature treatment, and fcu,20 is the compressive strength at room temperature. The results are shown in Table 1.

[0092] Freeze-thaw resistance test: The test was conducted according to the rapid freezing method in GB / T 50082-2009 standard. The specimen size was 100mm×100mm×400mm beam specimens, with 6 specimens per group. Three specimens were used for the freeze-thaw test, and three served as reference specimens. The freeze-thaw test was conducted in a concrete rapid freezing test machine. The freeze-thaw cycle regime was: freezing temperature -18±2℃, thawing temperature 8±2℃, and each cycle time 2-4 hours. The transverse fundamental frequency and mass loss of the specimen were measured after every 25 freeze-thaw cycles. The relative dynamic modulus of elasticity and mass loss rate were calculated. The number of freeze-thaw cycles required for the relative dynamic modulus of elasticity to drop to 60% or the mass loss rate to reach 5% was used as the evaluation index for freeze-thaw resistance. The results are shown in Table 1.

[0093] Table 1 Performance Test Results

[0094]

[0095] Data Analysis:

[0096] As can be seen from the data in Examples 1-3, the high-strength heat-resistant concrete prepared by this invention exhibits excellent performance in terms of room temperature mechanical properties, strength retention after heating, and freeze-thaw durability. This is presumably due to the following factors: First, the fine steel slag powder treated with in-situ carbonation using a carbonated water wet method forms abundant carbonate nucleation sites and a dense surface layer during the grinding stage, providing a uniform and stable nucleation environment for subsequent hydration reactions, thereby suppressing early capillary pores and interface defects. Second, the reciprocating sequence of steam curing, dry carbonation, and re-steam curing continuously reconstructs the pore size distribution during the nucleation-solidification-filling-rearrangement process, making it difficult for microcracks to penetrate and reducing the structural degradation sensitivity in the mid-temperature region. Third, the dual-grafted modified nano-silica with differentiated molecular weight and end-group design forms an adjustable bridge in the interface transition region, which has both complexation stability and steric hindrance dispersion effects, further refining the morphology of hydration products and improving the migration paths of ions and water. The combination of these three factors enables the material to exhibit a steady-state plateau in the mid-temperature range and maintain a relatively favorable residual load-bearing capacity and dynamic elastic modulus even after extreme temperatures.

[0097] Data from Example 2 and Comparative Example 1 show that replacing carbonated water with deionized water makes it difficult to continuously generate stable carbonate micronuclei at the wear interface. The passivation and volume stabilization process of the active phase in the steel slag is insufficient, and interconnected pores are more easily formed in the interface transition zone. This explains the simultaneous decrease in mechanical strength at room temperature and strength in the intermediate temperature range, as well as the increasing freeze-thaw sensitivity.

[0098] As can be seen from the data of Example 2 and Comparative Example 2, the system only undergoes single-stage steam curing, which makes it difficult to complete the multi-stage microstructure optimization of nucleation-filling-rearrangement. The orientation and pore size distribution of hydration products tend to be unimodal, the microcrack passivation is insufficient, and the damage accumulation under temperature disturbance and freeze-thaw action is faster, which is reflected in the decreased coordination of multiple indicators.

[0099] Data from Example 2 and Comparative Example 3 show that after removing the grafting design with dual-terminal groups and molecular weight ladder, the dispersion stability and interfacial chemical anchoring ability of nano-silica in strongly alkaline and saline environments decrease, the bridging and confinement effects weaken, and the pore wall density and intergranular connectivity are insufficient. This change can lead to a general deterioration in load-bearing capacity at room temperature and intermediate temperature ranges, but short-term rebound may occur at individual intermediate temperature points due to dehydration shrinkage and local recrystallization.

[0100] As can be seen from the data of Example 2 and Comparative Example 4, single carboxyl end-group grafting mainly provides complexation and hydrogen bonding, but lacks sufficient stretching and shear synergy for interfacial bridging, and has a low molecular weight window, making it difficult to maintain long-range constraints under temperature perturbation; this is manifested in the lower integrity of the interfacial transition region in thermal and humid cycling compared to the double-grafted system, resulting in a stepwise decline in temperature rise retention and freeze-thaw durability.

[0101] As can be seen from the data of Example 2 and Comparative Example 5, single amino-terminated polyethylene glycol has strong coordination and electron donor capabilities, and its dispersibility is relatively better than that of the case with only carboxyl-terminated groups. However, it lacks a soft and hard dual-scale bridging network with the carboxyl-terminated groups, and its temperature response consistency and interfacial energy dissipation capability are insufficient. Therefore, in many aspects, it is between unmodified and double-grafted polyethylene glycol.

[0102] As can be seen from the data of Example 2 and Comparative Example 6, raising the temperature of the first steam curing to a higher range can easily cause rapid precipitation of early hydration products and insufficient crystal rearrangement, increase the peak value of internal stress and pore pressure, and compress the densification space in the subsequent dry carbonization and resteaming stages. The overall result is a synergistic decrease in room temperature mechanics, medium temperature holding and freeze-thaw criticality.

[0103] from Figure 1 It can be seen that after dry carbonization, the calcite 29.4° main peak and its high-angle accompanying peaks in the sample of Example 2 were significantly enhanced, while the calcium hydroxide 18.0° / 34.1° peaks were significantly attenuated. After steam-standard curing, the C–S–H amorphous peaks in the 27–34° range were further broadened and maintained a high calcite peak intensity, while the residual clinker diffraction peaks continued to weaken. The overall spectrum changed from clinker-dominated to carbonate-filled and amorphous gel-densified-dominated.

[0104] from Figure 2 It can be seen that, compared with unmodified nano-silica, the double-grafted modified sample at 1100 cm⁻¹... -1 The nearby main band is significantly enhanced and slightly displaced (1105cm). -1 And it is 1145cm -1 (acromion), with 2930 / 2855cm appearing simultaneously. -1 CH2 stretchable, 1725cm -1 -COOH carbonyl group and 1560cm -1 The characteristic absorption features, such as the bending of -NH2, indicate that PEG-COOH and PEG-NH2 have been successfully introduced and have a bonding / additional effect with the silicon-oxygen framework, while the unmodified sample shows absorption values ​​of 1090, 800, and 460 cm⁻¹. -1 The vibrations of the silicon-oxygen framework are dominant and only exhibit a wide band of surface hydroxyl / adsorbed water.

[0105] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A production process of high-strength heat-resistant concrete, characterized by, Includes the following steps: (1) Mix steel slag and carbonated water and ball mill for 100-140 min, filter and dry to obtain pretreated steel slag fine powder; (2) Mix silicate cement, pretreated steel slag fine powder, micro silica powder, and double-grafted modified nano silica. Stir at low speed for 100-140s and let stand for 8-12min. Then add manufactured sand and continuously graded crushed stone. Continue stirring at low speed for 80-100s. Then add carbonated water and polycarboxylate superplasticizer. Stir at medium speed for 100-140s and then at high speed for 50-70s to obtain concrete mix. (3) The concrete mix is ​​put into the mold, compacted on the vibrating table, and left to stand for 50-70 minutes before the first steam curing is carried out to obtain the first steam-cured concrete. (4) The first steam-cured concrete was subjected to room temperature carbonation treatment in a carbon dioxide environment to obtain carbonized concrete. (5) The carbonized concrete is steam cured a second time, then demolded, and then cured in a standard curing room. After curing, high-strength heat-resistant concrete is obtained. In step (2), the double-grafted modified nano-silica is obtained by grafting nano-silica with silanized polyethylene glycol carboxyl end groups and silanized polyethylene glycol amino end groups in an alkaline environment. The silanized polyethylene glycol carboxyl terminus is a functionalized polyethylene glycol derivative with a triethoxysilane and a carboxyl terminus, and has a weight-average molecular weight of 2000. The silanized polyethylene glycol amino terminus is a functionalized polyethylene glycol derivative with a triethoxysilane and an amino terminus, and has a weight-average molecular weight of 20000. The weight ratio of the nano-silica, the silanized polyethylene glycol carboxyl end group, and the silanized polyethylene glycol amino end group is 600-1000:6-10:3-5; In steps (1) and (2), the carbonated water is prepared by dissolving carbon dioxide in deionized water, and the pH is 4.2-4.

8.

2. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, In step (1), the steel slag is a product of BSSF drum process, with an average particle size of less than 5 mm, a free CaO content of less than 6%, and a free MgO content of less than 3%.

3. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, In step (1), the weight ratio of steel slag to carbonated water is 350-450:85-115.

4. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, In step (1), the ball-to-material ratio of the ball mill is 1.0-1.4:1, and the mill speed is 15-21 rpm.

5. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, In step (2), the weight ratio of silicate cement, pretreated steel slag fine powder, micro silica powder, double-grafted modified nano silica, manufactured sand, continuously graded crushed stone, carbonated water and polycarboxylate superplasticizer is 360-480:260-380:45-75:6-10:730-870:650-750:160-200:6.5-9.

5.

6. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, In step (2), the stirring linear velocity of low-speed stirring is 1.8-2.2 m / s, the stirring linear velocity of medium-speed stirring is 2.2-2.8 m / s, and the stirring linear velocity of high-speed stirring is 2.8-3.2 m / s.

7. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, The first steam curing in step (3) is as follows: during the heating stage, the temperature is increased to 50-70℃ at a rate of 12-18℃ / h; during the constant temperature curing stage, the temperature is maintained at 50-70℃ and relative humidity of 90%-98% for 160-200 minutes; and during the cooling stage, the temperature is reduced to 25℃ at a rate of 8-12℃ / h.

8. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, In step (4), the partial pressure of carbon dioxide in the carbon dioxide environment is 0.07-0.13 MPa, and the carbonization time is 50-70 min.

9. The production process of high-strength heat-resistant concrete according to claim 1, characterized in that, The second steam curing in step (5) is as follows: during the heating stage, the temperature is increased to 70-90℃ at a rate of 10-14℃ / h; during the constant temperature curing stage, the temperature is maintained at 70-90℃ and relative humidity of 90%-98% for 100-140 minutes; and during the cooling stage, the temperature is reduced to 25℃ at a rate of 6-10℃ / h.

10. A high-strength heat-resistant concrete, characterized in that, It is obtained by the production process of high-strength heat-resistant concrete according to any one of claims 1-9.

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