High-temperature-resistant anti-cracking concrete and its application in tunnel lining

Abstract

The present application relates to the technical field of concrete, in particular to a high-temperature-resistant and anti-bursting concrete and its application in tunnel lining. The concrete is prepared from Portland cement, dry powder silica fume, blast furnace slag powder, machine-made sand, crushed stone, mixing water, polycarboxylate superplasticizer and sand-carrying fiber dispersion. The sand-carrying fiber dispersion is formed by pre-dispersion of machine-made sand and temperature-controlled pore releasing fiber. The temperature-controlled pore releasing fiber is obtained by modifying core-shell fiber with silicon calcium hydrophilic modifier and then with polyethylene wax powder modifier. The core layer is composed of low molecular weight polyethylene wax and linear low density polyethylene, and the shell layer is composed of maleic anhydride grafted polypropylene and maleic anhydride grafted polypropylene wax. The present application also applies the concrete to the function layer of the fire-facing side of the secondary lining of the tunnel, and continuously forms the wet joint with the conventional anti-permeable concrete of the same strength grade on the backfire side. The present application can reduce the bursting depth of the concrete and improve the anti-permeability and anti-chloride ion permeability after single-side fire.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a high-temperature resistant and explosion-proof concrete and its application in tunnel lining. Background Technology

[0002] Tunnel fires are characterized by rapid temperature rise, long duration, and high peak temperatures, posing a serious threat to the safety of the concrete lining structure. Existing tunnel linings mostly use ordinary high-performance concrete, which has a low water-cement ratio and high density. When exposed to fire, the free and bound water inside rapidly vaporizes, causing a sharp increase in pore vapor pressure, making the concrete highly susceptible to spalling and cracking. Especially within the first 30 minutes of a fire, the surface concrete on the fire-facing side often collapses over a large area because it cannot release pore pressure in time, leaving the reinforcing steel directly exposed to the high-temperature environment and significantly weakening the structure's load-bearing capacity.

[0003] To mitigate bursting issues, ordinary polypropylene fibers are often incorporated into engineering projects, utilizing their high-temperature melting to form venting channels. However, ordinary polypropylene fibers have only a single melting temperature range, making it difficult to dynamically match the development of pore pressure within the concrete during the rapid temperature rise in a tunnel fire. Often, even after the pore pressure peaks, an effective venting network cannot be established, resulting in limited burst-proof performance. Furthermore, the strong hydrophobicity of ordinary polypropylene fibers makes them prone to agglomeration in low water-cement ratio slurries, affecting concrete flowability and causing uneven fiber distribution, further weakening the reliability of their burst-proof effect. In addition, existing burst-proof technologies often fail to consider the temperature gradient distribution characteristics of tunnel linings under fire, lacking targeted design for burst-proof functional layers. This results in the material's performance not being fully utilized, and the post-fire lining's impermeability and durability still significantly decrease. Summary of the Invention

[0004] In view of this, the purpose of this invention is to propose a high-temperature resistant and explosion-proof concrete and its application in tunnel lining, so as to solve the problems of existing low water-cement ratio tunnel lining concrete with ordinary polypropylene fiber, which has a single melting temperature zone that does not match the pore pressure development and is prone to agglomeration due to surface hydrophobicity, resulting in large explosion depth after fire and insufficient resistance to impermeability and chloride ion penetration after fire.

[0005] To achieve the above objectives, the present invention provides a high-temperature resistant and explosion-proof concrete, which is prepared by weight from the following raw materials: 430-490 parts silicate cement, 45-65 parts dry silica fume, 65-95 parts blast furnace slag powder, 635-702 parts manufactured sand, 940-1020 parts continuous 5-20mm limestone crushed stone, 145-158 parts mixing water, 4.8-7.2 parts polycarboxylate superplasticizer, and sand-loaded fiber dispersion. The sand-loaded fiber dispersion is obtained by pre-dispersing 18-25 parts of manufactured sand and 1.2-2 parts of temperature-controlled release porous fiber; The temperature-controlled release pore fiber is a fiber obtained by sequentially modifying the core shell fiber with silica-calcium hydrophilic modification and polyethylene wax micro powder modification, including the core shell fiber, the silica-calcium hydrophilic modification layer on the surface of the core shell fiber, and the waxy hydrophobic release pores located outside the silica-calcium hydrophilic modification layer. The core layer of the core-shell fiber is composed of low molecular weight polyethylene wax and linear low density polyethylene, and the shell layer is composed of maleic anhydride grafted polypropylene and maleic anhydride grafted polypropylene wax. The mass ratio of the core layer to the shell layer is 60:40 to 68:32. The silica-calcium hydrophilic modified layer is formed by hydrophilic fumed silica and calcium hydroxide, and the waxy hydrophobic release pores are formed by polyethylene wax micropowder.

[0006] Preferably, based on the weight parts of the raw materials used to prepare the core and shell fibers, the core layer is prepared from 5200-5600 parts of low molecular weight polyethylene wax and 800-1200 parts of linear low-density polyethylene, and the shell layer is prepared from 2700-3100 parts of maleic anhydride-grafted polypropylene and 500-900 parts of maleic anhydride-grafted polypropylene wax.

[0007] Preferably, based on 10,000 parts of the core shell fiber, the silicon-calcium hydrophilic modified layer is prepared from 100-150 parts of hydrophilic fumed silica and 16-25 parts of calcium hydroxide; based on 10,000 parts of the silicon-calcium hydrophilic modified core shell fiber, the waxy hydrophobic release pores are prepared from 150-220 parts of polyethylene wax micropowder.

[0008] Preferably, the average diameter of the core shell fiber is 32-42 μm, and the cut length of the core shell fiber is 6-12 mm.

[0009] Preferably, the silicate cement is P·O52.5 ordinary silicate cement; the blast furnace slag powder is S95 grade blast furnace slag powder; the manufactured sand is manufactured medium sand with a fineness modulus of 2.3-2.8; the limestone crushed stone is limestone crushed stone with a continuous particle size of 5-20mm; the polycarboxylate superplasticizer is powdered polycarboxylate superplasticizer; and the specific surface area of ​​the hydrophilic fumed silica is 150-250m². 2 / g.

[0010] Preferably, the low molecular weight polyethylene wax has a viscosity of 50-80 mPa·s at 140°C; the maleic anhydride-grafted polypropylene has a melting point of 160-170°C; and the maleic anhydride-grafted polypropylene wax has a viscosity of 1000-1300 mPa·s at 170°C.

[0011] Preferably, the specific steps of the silica-calcium hydrophilic modification are as follows: the core shell fiber is added to a drum mixer, hydrophilic fumed silica is dispersed in a mixture of anhydrous ethanol and deionized water and then sprayed into the drum mixer, calcium hydroxide is dispersed in deionized water and then sprayed into the drum mixer, and after drying, silica-calcium modified core shell fiber is obtained.

[0012] Preferably, the polyethylene wax micro powder modification involves adding the silicon-calcium modified core shell fiber and the polyethylene wax micro powder to a heated drum mixer for tumbling and mixing, followed by cooling and sieving to remove agglomerates, thereby obtaining temperature-controlled release porous fiber. The temperature of the heated drum mixer is 105-115℃, the rotation speed is 40-50 rpm, and the tumbling time is 12-18 min. After tumbling and mixing, heating is stopped, and air at 23-28℃ is introduced for cooling for 18-25 min. After cooling, agglomerates are removed using a 20 mm aperture sieve.

[0013] This invention also provides a method for preparing high-temperature resistant and explosion-proof concrete, comprising the following steps: (1) Preparation of the temperature-controlled release pore fiber; (2) Dry-mix 18-25 parts of manufactured sand and 1.2-2 parts of the temperature-controlled release pore fiber to obtain a sand-loaded fiber dispersion; (3) Mix 430-490 parts of silicate cement, 45-65 parts of dry silica fume, 65-95 parts of blast furnace slag powder, 635-702 parts of manufactured sand and 940-1020 parts of continuous 5-20mm limestone crushed stone to obtain a cementitious skeleton dry mix. (4) Mix 101-110 parts of mixing water and 3.36-5.04 parts of polycarboxylate superplasticizer to obtain the first water-reducing agent aqueous solution, and mix 44-48 parts of mixing water and 1.44-2.16 parts of polycarboxylate superplasticizer to obtain the second water-reducing agent aqueous solution; (5) Add the first part of the water-reducing agent aqueous solution to the cementitious skeleton dry mix and stir, then add all of the sand-loaded fiber dispersion and the second part of the water-reducing agent aqueous solution and continue stirring to obtain the high-temperature resistant and explosion-proof concrete.

[0014] This invention also provides an application of high-temperature resistant and explosion-proof concrete for the functional layer of the fire-facing side of a tunnel secondary lining. The high-temperature resistant and explosion-proof concrete is poured onto the fire-facing side of the tunnel secondary lining, forming a functional layer extending 40-80mm inward from the fire-facing side. Within 30 minutes of the completion of the functional layer pouring, conventional impermeable concrete of the same strength grade is poured onto the unfired side. The conventional impermeable concrete of the same strength grade on the unfired side is continuously and wet-bonded with the functional layer. The thickness of the functional layer is controlled using 40-80mm positioning pads. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

[0015] The beneficial effects of this invention are: (1) This invention utilizes a radial melting point gradient design of the core and shell fibers. The core layer consists of low molecular weight polyethylene wax and linear low-density polyethylene forming a low-temperature melting unit (126-128℃), while the shell layer consists of maleic anhydride-grafted polypropylene forming a high-temperature melting unit (162-165℃). This achieves phased pore release during fire exposure: in the low-temperature stage, preliminary venting channels are preferentially formed to alleviate initial pore pressure; in the high-temperature stage, the channels are expanded to improve venting efficiency, precisely matching the temperature rise curve and pore pressure development law of tunnel fires. Data shows that in Example 3, the maximum burst depth after 120 minutes of fire exposure was only 3.4 mm, which is 89.9% lower than that of Comparative Example 2 (ordinary polypropylene fiber).

[0016] (2) The pore release process of the present invention includes three stages: In the first stage, the outer layer of polyethylene wax powder softens or melts at about 110-116°C, forming local relinquishment sites at the fiber-slurry interface; in the second stage, the low molecular weight polyethylene wax and linear low-density polyethylene in the core layer soften or melt at 126-128°C, forming initial venting channels through the fiber ends, the core-shell interface, and the relinquishment sites of the outer wax layer; in the third stage, the maleic anhydride-grafted polypropylene and maleic anhydride-grafted polypropylene wax in the shell layer further soften or melt at 162-165°C, expanding and connecting the venting channels. The above-mentioned staged pore release process can gradually release pore vapor pressure during the temperature rise of a tunnel fire, reducing the risk of surface cracking on the fire-facing surface.

[0017] (3) The silica-calcium hydrophilic modification layer forms anchoring points on the fiber surface through hydrophilic fumed silica and calcium hydroxide, which significantly improves the dispersibility of the fiber in low water-to-binder ratio slurry. The slump of Example 1 reached 210 mm in 30 minutes, which is 20% higher than that of Comparative Example 3 (without silica-calcium modification). The outer layer of polyethylene wax micropowder hydrophobic release pores form waxy hydrophobic release pores after melting under fire, avoiding secondary pore pressure caused by water retention at high temperature. The synergy of the two makes the compressive strength retention rate of Example 3 reach 77.6% after being exposed to fire, which is 59.3% higher than that of Comparative Example 2.

[0018] (4) The pre-dispersion process using sand carriers isolates fibers and prevents agglomeration during mixing; the 40-80mm functional layer on the fire-facing side precisely covers the peak pore pressure area, and combined with conventional wet-bonding of concrete on the unfired side, maximizes the anti-burst performance. In Comparative Example 7 (functional layer located on the unfired side), the maximum burst depth increased to 42.1mm after being exposed to fire, confirming the key role of the fire-facing side positioning. Detailed Implementation

[0019] 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.

[0020] The sources and types of raw materials used are as follows: Silicate cement is Anhui Conch Cement Co., Ltd.'s Conch brand P·O52.5 ordinary Silicate cement; dry silica fume is Elkem's ELKEMMICROSILICA940U dry silica fume; blast furnace slag powder is Shanghai Baosteel New Building Materials Technology Co., Ltd.'s S95 grade blast furnace slag powder; manufactured sand is Anhui Conch Cement Co., Ltd.'s manufactured medium sand, with a fineness modulus controlled at 2.3-2.8; crushed stone is Anhui Conch Cement Co., Ltd.'s limestone crushed stone, with a continuous particle size of 5-20mm; polycarboxylate superplasticizer is Jiangsu Subote New Material Co., Ltd.'s PCA-300P powdered polycarboxylate superplasticizer; low molecular weight polyethylene wax is Clariant's Licocene PE4201 granules, with a dropping point of 128℃, a viscosity of 62 mPa·s at 140℃, and a density of 0.97 g / cm³ at 23℃. 3 The linear low-density polyethylene used was DFDA-7042 linear low-density polyethylene from Sinopec Zhenhai Refining & Chemical Branch; the maleic anhydride-grafted polypropylene used was Fine-Blend CMG9801 from Jiayirong Polymer Shanghai Co., Ltd., with a melting point of 167℃ and a melt flow rate of 58.5 g / 10 min; the maleic anhydride-grafted polypropylene wax used was Licocene PPMA 7452 granules from Clariant, with a softening point of 158℃, an acid value of 42.5 mg KOH / g, and a viscosity of 1150 mPa·s at 170℃; the hydrophilic fumed silica used was AEROSIL 200 from Evonik, with a specific surface area of ​​198.5 m² / g; the calcium hydroxide used was analytical grade calcium hydroxide from Sinopharm Chemical Reagent Co., Ltd.; the anhydrous ethanol used was analytical grade anhydrous ethanol from Sinopharm Chemical Reagent Co., Ltd.; the polyethylene wax micro powder used was PEW-0276 from Nanjing Tianshi New Material Technology Co., Ltd.; and the ordinary polypropylene fiber used was Runqiangsi-I polypropylene fiber from Jiangsu Subote New Material Co., Ltd.

[0021] Example 1: Step 1: Add 5400g of low molecular weight polyethylene wax and 1000g of linear low-density polyethylene to the core layer barrel of a two-component melt spinning machine, and add 2900g of maleic anhydride-grafted polypropylene and 700g of maleic anhydride-grafted polypropylene wax to the shell layer barrel; set the core layer barrel temperature to 140℃, 150℃ and 155℃ respectively, set the shell layer barrel temperature to 185℃, 195℃ and 200℃ respectively, set the spinneret temperature to 190℃, and control the mass flow rate ratio of the core layer to the shell layer to be 64:36; after spinning, use 25℃ air cooling, control the draw ratio to 3 times, and control the cut length to 9mm to obtain core and shell fibers with an average diameter of 36.5μm; Step 2: Add 10,000g of the core-shell fiber obtained in Step 1 to a drum mixer and tumble at 30℃ and 35rpm for 10min; disperse 120g of hydrophilic fumed silica in a mixture of 1800g of anhydrous ethanol and 200g of deionized water, disperse at 1000rpm for 20min using a high-speed disperser, and then spray it into the drum mixer for 15min, followed by tumbling for another 20min; then disperse 20g of calcium hydroxide in 300g of deionized water, stir at 500rpm for 10min, and then spray it into the drum mixer for 10min, followed by tumbling for another 20min; finally, dry in hot air at 60℃ for 120min to obtain the silicon-calcium modified core-shell fiber; Step 3: Add 10,000g of the silicon-calcium modified core shell fiber obtained in Step 2 and 180g of polyethylene wax micro powder to a heated drum mixer, and mix at 110℃ and 45rpm for 15min. Then stop heating and cool with 25℃ air for 20min. After cooling, use a 20mm sieve to remove agglomerates to obtain temperature-controlled release porous fiber. Step 4: Take 20kg of manufactured sand and 1600g of temperature-controlled release pore fiber obtained in Step 3 and add them to a forced concrete mixer. Dry mix at 20rpm for 60s to obtain sand-loaded fiber dispersion. Step 5: Add 460kg of silicate cement, 55kg of dry silica fume, 80kg of S95 grade blast furnace slag powder, 680kg of manufactured sand and 980kg of continuous 5-20mm limestone crushed stone to a forced concrete mixer and dry mix at 25rpm for 90s to obtain a cementitious skeleton dry mix. Step 6: Mix 105kg of mixing water and 4200g of polycarboxylate superplasticizer, and stir at 500rpm for 3min to obtain the first water-reducing agent aqueous solution; mix 45kg of mixing water and 1800g of polycarboxylate superplasticizer, and stir at 500rpm for 3min to obtain the second water-reducing agent aqueous solution; add the first water-reducing agent aqueous solution to the dry mix of cementitious skeleton obtained in Step 5, and stir at 30rpm for 120s; then uniformly add all the sand-loaded fiber dispersion obtained in Step 4 within 90s, and simultaneously add the second water-reducing agent aqueous solution, and continue stirring at 35rpm for 180s to obtain high-temperature resistant and explosion-proof concrete; Step 7: Use the high-temperature resistant and explosion-proof concrete obtained in Step 6 for the 0-60mm functional layer on the fire-facing side of the tunnel secondary lining. The thickness of the functional layer is controlled by 60mm positioning pads. Within 30 minutes after the functional layer is poured, pour conventional impermeable concrete of the same strength grade on the unfired side. The unfired side concrete and the fire-facing functional layer are continuously formed by wet bonding. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

[0022] Example 2: Step 1: Add 5200g of low molecular weight polyethylene wax and 800g of linear low-density polyethylene to the core layer barrel of a two-component melt spinning machine, and add 3100g of maleic anhydride-grafted polypropylene and 900g of maleic anhydride-grafted polypropylene wax to the shell layer barrel; set the core layer barrel temperature to 138℃, 148℃ and 153℃ respectively, set the shell layer barrel temperature to 183℃, 193℃ and 198℃ respectively, set the spinneret temperature to 188℃, and control the mass flow ratio of the core layer to the shell layer to be 60:40; after spinning, use 23℃ air cooling, control the draw ratio to 2.5 times, and control the cut length to 6mm to obtain core and shell fibers with an average diameter of 42.0μm; Step 2: Add 10,000g of the core-shell fiber obtained in Step 1 to a drum mixer and tumble at 28℃ and 30rpm for 8 minutes; disperse 100g of hydrophilic fumed silica in a mixture of 1700g of anhydrous ethanol and 180g of deionized water, disperse at 900rpm for 18 minutes using a high-speed disperser, and then spray it into the drum mixer for 12 minutes, continuing to tumble for 15 minutes after spraying; then disperse 16g of calcium hydroxide in 260g of deionized water, stir at 450rpm for 8 minutes, and then spray it into the drum mixer for 8 minutes, continuing to tumble for 15 minutes after spraying; finally, dry in hot air at 55℃ for 100 minutes to obtain silicon-calcium modified core-shell fiber; Step 3: Add 10,000g of the silicon-calcium modified core shell fiber obtained in Step 2 and 150g of polyethylene wax micro powder to a heated drum mixer, and mix at 105℃ and 40rpm for 12min. Then stop heating and introduce 23℃ air to cool for 18min. After cooling, use a 20mm sieve to remove agglomerates to obtain temperature-controlled release porous fiber. Step 4: Take 18kg of manufactured sand and 1200g of temperature-controlled release pore fiber obtained in Step 3 and add them to a forced concrete mixer. Dry mix at 20rpm for 60s to obtain sand-loaded fiber dispersion. Step 5: Add 430kg of silicate cement, 45kg of dry silica fume, 65kg of S95 grade blast furnace slag powder, 702kg of manufactured sand and 1020kg of continuous 5-20mm limestone crushed stone to a forced concrete mixer and dry mix at 25rpm for 90s to obtain a cementitious skeleton dry mix. Step 6: Mix 101kg of mixing water and 3360g of polycarboxylate superplasticizer, and stir at 500rpm for 3min to obtain the first water-reducing agent aqueous solution; mix 44kg of mixing water and 1440g of polycarboxylate superplasticizer, and stir at 500rpm for 3min to obtain the second water-reducing agent aqueous solution; add the first water-reducing agent aqueous solution to the dry mix of cementitious skeleton obtained in Step 5, and stir at 30rpm for 120s; then uniformly add all the sand-loaded fiber dispersion obtained in Step 4 within 90s, and simultaneously add the second water-reducing agent aqueous solution, and continue stirring at 35rpm for 180s to obtain high-temperature resistant and explosion-proof concrete; Step 7: Use the high-temperature resistant and explosion-proof concrete obtained in Step 6 for the 0-40mm functional layer on the fire-facing side of the tunnel secondary lining. The thickness of the functional layer is controlled by 40mm positioning pads. Within 30 minutes after the functional layer is poured, pour conventional impermeable concrete of the same strength grade on the unfired side. The unfired side concrete and the fire-facing functional layer are continuously formed by wet bonding. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

[0023] Example 3: Step 1: Add 5600g of low molecular weight polyethylene wax and 1200g of linear low-density polyethylene to the core layer barrel of a two-component melt spinning machine, and add 2700g of maleic anhydride-grafted polypropylene and 500g of maleic anhydride-grafted polypropylene wax to the shell layer barrel. The core layer barrel temperature is set to 145℃, 155℃ and 160℃ respectively, the shell layer barrel temperature is set to 188℃, 198℃ and 203℃ respectively, the spinneret temperature is set to 193℃, and the mass flow ratio of the core layer to the shell layer is controlled at 68:32. After spinning, the fibers are cooled with air at 28℃, the draw ratio is controlled at 3.5 times, and the cut length is controlled at 12mm to obtain core and shell fibers with an average diameter of 32.0μm. Step 2: Add 10,000g of the core-shell fiber obtained in Step 1 to a drum mixer and tumble at 35℃ and 40rpm for 12min; disperse 150g of hydrophilic fumed silica in a mixture of 2000g of anhydrous ethanol and 250g of deionized water, disperse at 1200rpm for 25min using a high-speed disperser, and then spray it into the drum mixer for 18min, followed by tumbling for another 25min; then disperse 25g of calcium hydroxide in 350g of deionized water, stir at 550rpm for 12min, and then spray it into the drum mixer for 12min, followed by tumbling for another 25min; finally, dry in hot air at 65℃ for 140min to obtain the silicon-calcium modified core-shell fiber; Step 3: Add 10,000g of the silicon-calcium modified core shell fiber obtained in Step 2 and 220g of polyethylene wax micro powder to a heated drum mixer, and mix at 115℃ and 50rpm for 18min. Then stop heating and cool with 28℃ air for 25min. After cooling, use a 20mm sieve to remove agglomerates to obtain temperature-controlled release porous fiber. Step 4: Take 25kg of manufactured sand and 2000g of temperature-controlled release pore fiber obtained in Step 3 and add them to a forced concrete mixer. Dry mix at 20rpm for 60s to obtain sand-loaded fiber dispersion. Step 5: Add 490kg of silicate cement, 65kg of dry silica fume, 95kg of S95 grade blast furnace slag powder, 635kg of manufactured sand and 940kg of continuous 5-20mm limestone crushed stone to a forced concrete mixer and dry mix at 25rpm for 90s to obtain a cementitious skeleton dry mix. Step 6: Mix 110kg of mixing water and 5040g of polycarboxylate superplasticizer, and stir at 500rpm for 3min to obtain the first water-reducing agent aqueous solution; mix 48kg of mixing water and 2160g of polycarboxylate superplasticizer, and stir at 500rpm for 3min to obtain the second water-reducing agent aqueous solution; add the first water-reducing agent aqueous solution to the dry mix of cementitious skeleton obtained in Step 5, and stir at 30rpm for 120s; then uniformly add all the sand-loaded fiber dispersion obtained in Step 4 within 90s, and simultaneously add the second water-reducing agent aqueous solution, and continue stirring at 35rpm for 180s to obtain high-temperature resistant and explosion-proof concrete; Step 7: Use the high-temperature resistant and explosion-proof concrete obtained in Step 6 for the 0-80mm functional layer on the fire-facing side of the tunnel secondary lining. The thickness of the functional layer is controlled by 80mm positioning pads. Within 30 minutes after the functional layer is poured, pour conventional impermeable concrete of the same strength grade on the unfired side. The unfired side concrete and the fire-facing functional layer are continuously formed by wet bonding. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

[0024] Example 4: Step 1: Add 5300g of low molecular weight polyethylene wax and 900g of linear low-density polyethylene to the core layer barrel of a two-component melt spinning machine, and add 3000g of maleic anhydride-grafted polypropylene and 800g of maleic anhydride-grafted polypropylene wax to the shell layer barrel; set the core layer barrel temperature to 139℃, 149℃ and 154℃ respectively, set the shell layer barrel temperature to 184℃, 194℃ and 199℃ respectively, set the spinneret temperature to 189℃, and control the mass flow ratio of the core layer to the shell layer to be 62:38; after spinning, use 24℃ air cooling, control the draw ratio to 2.8 times, and control the cut length to 8mm to obtain core and shell fibers with an average diameter of 39.5μm; Step 2: Add 10,000g of the core-shell fiber obtained in Step 1 to a drum mixer and tumble at 30℃ and 32rpm for 9min; disperse 110g of hydrophilic fumed silica in a mixture of 1750g of anhydrous ethanol and 190g of deionized water, disperse at 950rpm for 19min using a high-speed disperser, and then spray it into the drum mixer for 14min, followed by tumbling for 18min; then disperse 18g of calcium hydroxide in 280g of deionized water, stir at 480rpm for 9min, and then spray it into the drum mixer for 9min, followed by tumbling for 18min; finally, dry in hot air at 58℃ for 110min to obtain the silicon-calcium modified core-shell fiber; Step 3: Add 10,000g of the silicon-calcium modified core shell fiber obtained in Step 2 and 200g of polyethylene wax micro powder to a heated drum mixer, and mix at 108℃ and 42rpm for 14min. Then stop heating and introduce 24℃ air to cool for 19min. After cooling, use a 20mm sieve to remove agglomerates to obtain temperature-controlled release porous fiber. Step 4: Take 19kg of manufactured sand and 1400g of temperature-controlled release pore fiber obtained in Step 3 and add them to a forced concrete mixer. Dry mix at 20rpm for 60s to obtain sand-loaded fiber dispersion. Step 5: Add 450kg of silicate cement, 50kg of dry silica fume, 75kg of S95 grade blast furnace slag powder, 671kg of manufactured sand and 1000kg of continuous 5-20mm limestone crushed stone to a forced concrete mixer and dry mix at 25rpm for 90s to obtain a cementitious skeleton dry mix. Step 6: Mix 103 kg of mixing water and 3780 g of polycarboxylate superplasticizer, and stir at 500 rpm for 3 min to obtain the first water-reducing agent aqueous solution; mix 45 kg of mixing water and 1620 g of polycarboxylate superplasticizer, and stir at 500 rpm for 3 min to obtain the second water-reducing agent aqueous solution; add the first water-reducing agent aqueous solution to the dry mix of cementitious skeleton obtained in Step 5, and stir at 30 rpm for 120 s; then uniformly add all the sand-loaded fiber dispersion obtained in Step 4 within 90 s, and simultaneously add the second water-reducing agent aqueous solution, and continue stirring at 35 rpm for 180 s to obtain high-temperature resistant and explosion-proof concrete; Step 7: Use the high-temperature resistant and explosion-proof concrete obtained in Step 6 for the 0-50mm functional layer on the fire-facing side of the tunnel secondary lining. The thickness of the functional layer is controlled by 50mm positioning pads. Within 30 minutes after the functional layer is poured, pour conventional impermeable concrete of the same strength grade on the unfired side. The unfired side concrete and the fire-facing functional layer are continuously formed by wet bonding. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

[0025] Example 5: Step 1: Add 5500g of low molecular weight polyethylene wax and 1100g of linear low-density polyethylene to the core layer barrel of a two-component melt spinning machine, and add 2800g of maleic anhydride-grafted polypropylene and 600g of maleic anhydride-grafted polypropylene wax to the shell layer barrel; set the core layer barrel temperature to 142℃, 152℃ and 157℃ respectively, set the shell layer barrel temperature to 187℃, 197℃ and 202℃ respectively, set the spinneret temperature to 192℃, and control the mass flow ratio of the core layer to the shell layer to be 66:34; after spinning, use 26℃ air cooling, control the draw ratio to 3.2 times, and control the cut length to 10mm to obtain core and shell fibers with an average diameter of 34.5μm; Step 2: Add 10,000g of the core-shell fiber obtained in Step 1 to a drum mixer and tumble at 33℃ and 38rpm for 11min; disperse 140g of hydrophilic fumed silica in a mixture of 1950g of anhydrous ethanol and 230g of deionized water, disperse at 1100rpm for 22min using a high-speed disperser, and then spray it into the drum mixer for 16min, continuing tumbling for 22min after spraying; then disperse 22g of calcium hydroxide in 330g of deionized water, stir at 520rpm for 11min, and then spray it into the drum mixer for 11min, continuing tumbling for 22min after spraying; finally, dry in hot air at 62℃ for 130min to obtain silicon-calcium modified core-shell fiber; Step 3: Add 10,000g of the silicon-calcium modified core shell fiber obtained in Step 2 and 165g of polyethylene wax micro powder to a heated drum mixer, and mix at 112℃ and 48rpm for 16min. Then stop heating and cool with 26℃ air for 22min. After cooling, use a 20mm sieve to remove agglomerates to obtain temperature-controlled release porous fiber. Step 4: Take 22kg of manufactured sand and 1800g of temperature-controlled release pore fiber obtained in Step 3 and add them to a forced concrete mixer. Dry mix at 20rpm for 60s to obtain sand-loaded fiber dispersion. Step 5: Add 480kg of silicate cement, 60kg of dry silica fume, 88kg of S95 grade blast furnace slag powder, 653kg of manufactured sand and 960kg of continuous 5-20mm limestone crushed stone to a forced concrete mixer and dry mix at 25rpm for 90s to obtain a cementitious skeleton dry mix. Step 6: Mix 107 kg of mixing water and 4620 g of polycarboxylate superplasticizer, and stir at 500 rpm for 3 min to obtain the first water-reducing agent aqueous solution; mix 45 kg of mixing water and 1980 g of polycarboxylate superplasticizer, and stir at 500 rpm for 3 min to obtain the second water-reducing agent aqueous solution; add the first water-reducing agent aqueous solution to the dry mix of cementitious skeleton obtained in Step 5, and stir at 30 rpm for 120 s; then uniformly add all the sand-loaded fiber dispersion obtained in Step 4 within 90 s, and simultaneously add the second water-reducing agent aqueous solution, and continue stirring at 35 rpm for 180 s to obtain high-temperature resistant and explosion-proof concrete; Step 7: Use the high-temperature resistant and explosion-proof concrete obtained in Step 6 for the 0-70mm functional layer on the fire-facing side of the tunnel secondary lining. The thickness of the functional layer is controlled by 70mm positioning pads. Within 30 minutes after the functional layer is poured, pour conventional impermeable concrete of the same strength grade on the unfired side. The unfired side concrete and the fire-facing functional layer are continuously formed by wet bonding. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

[0026] Comparative Example 1: The difference from Example 1 is that: in step 1, the core layer and shell layer material are not fed in layers. 5400g of low molecular weight polyethylene wax, 1000g of linear low density polyethylene, 2900g of maleic anhydride-grafted polypropylene and 700g of maleic anhydride-grafted polypropylene wax are mixed and melt-spun in the same material to obtain homogeneous fibers with an average diameter of 36.5μm and a length of 9mm; the other conditions are the same as in Example 1.

[0027] Comparative Example 2: The difference from Example 1 is that in step 4, 1600g of temperature-controlled release pore fiber obtained in step 3 is replaced with 1600g of ordinary polypropylene fiber, and steps 1 to 3 are omitted; the other conditions are the same as in Example 1.

[0028] Comparative Example 3: The difference from Example 1 is that: in step 2, 120g of hydrophilic fumed silica and 20g of calcium hydroxide are not added; in step 4, the total mass of the fiber used for mixing is still controlled at 1600g, and the insufficient part is made up with the core shell fiber obtained in step 1; the other conditions are the same as in Example 1.

[0029] Comparative Example 4: The difference from Example 1 is that: 180g of polyethylene wax powder is not added in step 3, and the total mass of fibers used for mixing in step 4 is still controlled at 1600g, with the insufficient part made up by the silicon-calcium modified core shell fiber obtained in step 2; the other conditions are the same as in Example 1.

[0030] Comparative Example 5: The difference from Example 1 is that the order of surface construction in steps 2 and 3 is reversed. Specifically, 10,000g of the core shell fiber obtained in step 1 and 180g of polyethylene wax micro powder are first rolled and mixed at 110°C and 45rpm for 15min and then cooled. Then, the hydrophilic fumed silica dispersion and calcium hydroxide dispersion are sprayed in according to the dosage and conditions of step 2 in Example 1. The other conditions are the same as in Example 1.

[0031] Comparative Example 6: The difference from Example 1 is that: in step 4, no sand-loaded fiber dispersion is prepared; 20 kg of manufactured sand is added to step 5, totaling 700 kg with the original 680 kg of manufactured sand; 1600 g of temperature-controlled release porous fiber is added simultaneously at once when the second water-reducing agent aqueous solution is added in step 6; the other conditions are the same as in Example 1.

[0032] Comparative Example 7: The difference from Example 1 is that in step 7, the functional layer is changed from the fire-facing 0-60mm to the unfire-facing 0-60mm, and the fire-facing 0-60mm is filled with conventional impermeable concrete of the same strength grade as the unfire-facing side; the other conditions are the same as in Example 1.

[0033] Comparative Example 8: The difference from Example 1 is that the mass flow ratio of the core layer and the shell layer in step 1 is changed from 64:36 to 75:25, and the control of ejection, cooling, stretching, cutting and subsequent steps is the same as in Example 1; the other conditions are the same as in Example 1.

[0034] Performance testing: Sample Preparation: Test samples included Examples 1-5 and Comparative Examples 1-8. Concrete mixtures were prepared for each sample according to the corresponding example or comparative example. Nine 150mm×150mm×150mm cubic specimens were formed for each sample, used for testing 28-day compressive strength and compressive strength retention rate after single-sided fire exposure; three 300mm×300mm×100mm plate specimens were formed for testing burst depth after single-sided fire exposure, water penetration resistance height of the functional layer core sample, and chloride ion flux of the functional layer core sample.

[0035] Temperature-controlled release pore fiber melting temperature test: Fiber samples from Examples 1-5 and Comparative Examples 1-8 before entering concrete were taken and subjected to differential scanning calorimetry (DSC) testing according to GB / T19466.3-2004 "Differential Scanning Calorimetry (DSC) for Plastics - Part 3: Determination of Melting and Crystallization Temperatures and Enthalpy". For each sample, 5.0 mg of the middle section of the fiber was cut and placed in an aluminum crucible. The nitrogen flow rate was controlled at 50 mL / min, and the temperature was increased from 25°C to 220°C at a rate of 10°C / min. The first melting peak temperature and the second melting peak temperature were recorded.

[0036] Slump retention performance test of the mixture: Fresh concrete from Examples 1-5 and Comparative Examples 1-8 was tested for slump over time according to GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". For each sample, 20L of mixture was taken within 5 minutes after mixing in step 6 to test the initial slump. The remaining mixture from the same batch was then placed in a covered plastic container and allowed to stand at 20℃ for 30 minutes before the slump was tested again. The slump at 30 minutes was recorded.

[0037] 28-day compressive strength test. 150mm × 150mm × 150mm cubic specimens from Examples 1-5 and Comparative Examples 1-8 were used for compressive strength testing according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". Three specimens were tested for each sample. After removing the specimens from the curing environment and wiping off any standing water, they were placed in the center of the pressure plate of the compression testing machine and continuously loaded at a loading rate of 0.8 MPa / s until failure. The 28-day compressive strength was recorded.

[0038] Standard Heating and Fire Exposure Depth Test: 300mm×300mm×100mm plate specimens from Examples 1-5 and Comparative Examples 1-8 were subjected to single-sided fire exposure tests under the standard heating conditions specified in GB / T9978.1-2008 "Fire Resistance Test Methods for Building Components Part 1: General Requirements". The fire-facing side of the specimen faced the furnace, while the unfired side and all four sides were sealed with 25mm thick ceramic fiberboard. The furnace temperature was increased according to T=20+345log10(8t+1), where T is the furnace temperature in °C and t is the heating time in min. Heating was stopped after 120 minutes of continuous exposure, and the specimens were allowed to cool naturally to below 40°C with the furnace door closed. After removing the specimens, loose spalling material was removed. Spalling depths were measured at each point on the fire-facing side using a 20mm×20mm grid, and the maximum explosion depth was recorded.

[0039] Test for retention rate of compressive strength after single-sided fire exposure: Take a 150mm×150mm×150mm cubic specimen, take one surface as the fire-exposed surface, and cover the other five surfaces with 25mm thick ceramic fiber board. According to the standard heating curve of GB / T9978.1-2008, expose one side to fire for 120 minutes. After naturally cooling to below 40℃, place it at 20℃ and 60% relative humidity for 24 hours, and then conduct a compressive strength test. The retention rate of compressive strength after single-sided fire exposure is calculated by the ratio of the compressive strength after single-sided fire exposure to the compressive strength after 28 days without fire exposure of the same age.

[0040] Water penetration resistance test after single-sided fire exposure: Take a plate specimen after standard heating and single-sided fire exposure, drill a cylindrical core sample with a diameter of 100 mm and a height of 100 mm from the center of the fire-facing side, and record the actual bursting depth and loose layer thickness; seal the side of the core sample with epoxy resin, and take the fire-facing direction as the water-facing direction, and conduct water penetration resistance test according to the current effective test methods for long-term performance and durability of concrete.

[0041] Chloride ion flux test after single-sided fire exposure: Take a plate specimen after standard temperature rise and single-sided fire exposure, drill a 100mm diameter core sample from the functional layer area, and cut it into 50mm thick circular pieces; when there is a loose layer on the fire-facing surface, remove the loose layer first and record the removal thickness. The flux test sample is taken from the functional layer area 10-60mm away from the actual fire-facing surface. Three specimens are tested in each group, and the results are expressed as mean ± standard deviation.

[0042] Table 1 Performance Test Results

[0043] As shown in Table 1, when ordinary polypropylene fiber was used in Comparative Example 2, the fiber only showed a single melting peak around 165.0℃, and the maximum bursting depth after being exposed to fire reached 33.8 mm. The compressive strength retention rate after being exposed to fire was only 48.7%, indicating that a single melting temperature zone is difficult to establish a stable steam venting channel in the early stage of fire exposure in low water-cement ratio, high-density lining concrete. Although Comparative Example 1 had two melting peaks similar to those in Example 1, its fiber had a homogeneous structure, and the maximum bursting depth after being exposed to fire was still 20.6 mm. This indicates that simply having similar melting components is not enough to obtain a good anti-burst effect, and the core-shell structure plays an important role in the staged release of pores.

[0044] After removing the silica and calcium in Comparative Example 3, the slump at 30 minutes decreased from 210 mm in Example 1 to 175 mm, and the compressive strength at 28 days decreased to 72.8 MPa. The electrical flux after firing increased to 1248°C, indicating that the silica-calcium hydrophilic modification layer formed by the hydrophilic fumed silica and calcium hydroxide is beneficial for improving the wetting and dispersion of fibers in low water-to-binder ratio slurry. After removing the waxy hydrophobic release pores in Comparative Example 4, the workability and compressive strength at room temperature remained good, but the maximum bursting depth after firing increased to 16.4 mm, indicating that the waxy hydrophobic release pores... The main contributions are local relocation and steam exhaust efficiency in the early stage of fire exposure; after changing the order of hydrophilic and hydrophobic construction in Comparative Example 5 and canceling the pre-dispersion of sand in Comparative Example 6, the slump, compressive strength retention rate and durability after fire exposure all decreased, indicating that the sequential construction of the surface and the pre-dispersion of sand have a synergistic effect on the uniform distribution of fibers; after moving the functional layer to the unfired side in Comparative Example 7, although the room temperature compressive strength is close to that of Example 1, the maximum burst depth after fire exposure increased to 42.1 mm, indicating that the position of the functional layer should match the peak pressure area of ​​the fire-facing surface.

[0045] Examples 1-5 all exhibited lower fire-induced cracking depth and higher compressive strength retention rate after fire. Among them, Example 3, due to the use of a higher core layer ratio, higher fiber content, higher silicon-calcium loading, and an 80mm fire-facing functional layer thickness, reduced the maximum cracking depth after fire to 3.4mm, increased the compressive strength retention rate to 77.6%, and reduced the water penetration height and electrical flux to 10.8mm and 412C, respectively. Example 5 was the second best, indicating that a higher level of hydrophilic dispersion and fire-facing positioning have a good matching effect.

[0046] In summary, this invention combines core-shell fiber, silicon-calcium modification, waxy hydrophobic release pores, sand-carrying pre-dispersion, and a functional layer on the fire-facing surface. This combination enables low-temperature initial release pores, high-temperature continuous release pores, room-temperature dispersion, and fire-facing surface positioning to work together. As a result, while maintaining a room-temperature compressive strength of 70.9-88.6 MPa, the maximum bursting depth after fire is controlled within the range of 3.4-17.2 mm. This demonstrates more stable bursting resistance and post-fire durability than ordinary polypropylene fiber systems.

[0047] 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, 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 high-temperature resistant and explosion-proof concrete, characterized in that, The following raw materials are used to prepare the product by weight: 430-490 parts silicate cement, 45-65 parts dry silica fume, 65-95 parts blast furnace slag powder, 635-702 parts manufactured sand, 940-1020 parts continuous 5-20mm limestone crushed stone, 145-158 parts mixing water, 4.8-7.2 parts polycarboxylate superplasticizer, and sand-loaded fiber dispersion. The sand-loaded fiber dispersion is obtained by pre-dispersing 18-25 parts of manufactured sand and 1.2-2 parts of temperature-controlled release porous fiber; The temperature-controlled release pore fiber is a fiber obtained by sequentially modifying the core shell fiber with silica-calcium hydrophilic modification and polyethylene wax micro powder modification, including the core shell fiber, the silica-calcium hydrophilic modification layer on the surface of the core shell fiber, and the waxy hydrophobic release pores located outside the silica-calcium hydrophilic modification layer. The core layer of the core-shell fiber is composed of low molecular weight polyethylene wax and linear low density polyethylene, and the shell layer is composed of maleic anhydride grafted polypropylene and maleic anhydride grafted polypropylene wax. The mass ratio of the core layer to the shell layer is 60:40 to 68:

32. The silica-calcium hydrophilic modified layer is formed by hydrophilic fumed silica and calcium hydroxide, and the waxy hydrophobic release pores are formed by polyethylene wax micropowder.

2. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, Based on the weight parts of the raw materials used to prepare the core and shell fibers, the core layer is prepared from 5200-5600 parts of low molecular weight polyethylene wax and 800-1200 parts of linear low-density polyethylene, and the shell layer is prepared from 2700-3100 parts of maleic anhydride-grafted polypropylene and 500-900 parts of maleic anhydride-grafted polypropylene wax.

3. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, Based on 10,000 parts of the core shell fiber, the silicon-calcium hydrophilic modified layer is prepared from 100-150 parts of hydrophilic fumed silica and 16-25 parts of calcium hydroxide; based on 10,000 parts of the silicon-calcium hydrophilic modified core shell fiber, the waxy hydrophobic release pores are prepared from 150-220 parts of polyethylene wax micropowder.

4. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, The core shell fiber has an average diameter of 32-42 μm and a cut length of 6-12 mm.

5. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, The portland cement is P·O52.5 ordinary portland cement; the blast furnace slag powder is S95 grade blast furnace slag powder; the machine-made sand is machine-made medium sand with fineness modulus of 2.3-2.8; the limestone crushed stone is limestone crushed stone with continuous particle size of 5-20 mm; the polycarboxylic acid water reducing agent is powdery polycarboxylic acid water reducing agent; the specific surface area of the hydrophilic fumed silica is 150-250 m 2 / g.

6. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, The low molecular weight polyethylene wax has a viscosity of 50-80 mPa·s at 140°C; the maleic anhydride-grafted polypropylene has a melting point of 160-170°C; and the maleic anhydride-grafted polypropylene wax has a viscosity of 1000-1300 mPa·s at 170°C.

7. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, The specific steps of the silicon-calcium hydrophilic modification are as follows: the core shell fiber is added to a drum mixer, hydrophilic fumed silica is dispersed in a mixture of anhydrous ethanol and deionized water and then sprayed into the drum mixer, calcium hydroxide is dispersed in deionized water and then sprayed into the drum mixer, and after drying, silicon-calcium modified core shell fiber is obtained.

8. The high-temperature resistant and explosion-proof concrete according to claim 1, characterized in that, The modification of polyethylene wax micropowder involves adding the silicon-calcium modified core shell fiber and polyethylene wax micropowder to a heated drum mixer for tumbling and mixing. After cooling, agglomerates are sieved out to obtain temperature-controlled release porous fiber. The temperature of the heated drum mixer is 105-115℃, the rotation speed is 40-50rpm, and the tumbling time is 12-18min. After tumbling and mixing, heating is stopped, and air at 23-28℃ is introduced for cooling for 18-25min. After cooling, agglomerates are sieved out using a 20mm aperture screen.

9. A method for preparing high-temperature resistant and explosion-proof concrete according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Preparation of the temperature-controlled release pore fiber; (2) Dry-mix 18-25 parts of manufactured sand and 1.2-2 parts of the temperature-controlled release pore fiber to obtain a sand-loaded fiber dispersion; (3) Mix 430-490 parts of silicate cement, 45-65 parts of dry silica fume, 65-95 parts of blast furnace slag powder, 635-702 parts of manufactured sand and 940-1020 parts of continuous 5-20mm limestone crushed stone to obtain a cementitious skeleton dry mix. (4) Mix 101-110 parts of mixing water and 3.36-5.04 parts of polycarboxylate superplasticizer to obtain the first water-reducing agent aqueous solution, and mix 44-48 parts of mixing water and 1.44-2.16 parts of polycarboxylate superplasticizer to obtain the second water-reducing agent aqueous solution; (5) Add the first part of the water-reducing agent aqueous solution to the cementitious skeleton dry mix and stir, then add all of the sand-loaded fiber dispersion and the second part of the water-reducing agent aqueous solution and continue stirring to obtain the high-temperature resistant and explosion-proof concrete.

10. An application of the high-temperature resistant and explosion-proof concrete according to any one of claims 1-8, characterized in that, Used for the functional layer on the fire-facing side of the secondary lining of tunnels; the high-temperature resistant and explosion-proof concrete is poured onto the fire-facing side of the secondary lining of the tunnel, forming a functional layer extending 40-80mm inward from the fire-facing side. Within 30 minutes after the functional layer is poured, conventional impermeable concrete of the same strength grade is poured on the unfired side. The conventional impermeable concrete of the same strength grade on the unfired side is continuously formed by wet bonding with the functional layer. The thickness of the functional layer is controlled by 40-80mm positioning pads. The overall curing regime is 7 days of curing at 20℃ and 95% relative humidity, followed by conventional moist curing for 28 days.

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