C80 concrete in plateau environment and preparation method thereof

Abstract

The application relates to the field of concrete, in particular to C80 concrete under a highland environment and a preparation method thereof, which is composed of the following components in parts by mass: cement 40-50 parts, nano-modified machine-made sand 70-75 parts, gravel 75-80 parts, coated fly ash 10-15 parts, silica ash 3-7 parts, ultra-fine steel fiber 5-7 parts, modified polypropylene 0.1-0.2 parts, magnesium expansive agent 3-5 parts and the like. The application realizes the synergistic effect of nano-modified aggregate interface strengthening, temperature change humidity adjusting material, composite fiber anti-cracking network and low-pressure stable additive, compared with the prior art, the frost resistance, ultraviolet light weather resistance and low-pressure construction adaptability are obviously improved, the application has a broad prospect of replacing imported materials in highland bridges, wind power bases and other major projects, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete, in particular to a C80 concrete under highland environment and a preparation method thereof. BACKGROUND

[0002] C80 concrete refers to high-performance concrete with a compressive strength grade of 80 MPa, and has characteristics of high strength and high durability, and is a key material in modern high-rise, large-span and heavy-load structures.

[0003] However, when such concrete is applied to highland special environment, its performance implementation faces severe challenges. The low air pressure, strong ultraviolet radiation, large temperature difference and frequent freeze-thaw cycles in highland areas form extreme climatic conditions, which jointly test the preparation and service performance of concrete materials. Low air pressure environment easily leads to unstable air entrainment structure in fresh concrete and accelerated loss of fluidity; strong ultraviolet radiation accelerates the degradation of organic components and the deterioration of surface concrete; large temperature difference and freeze-thaw cycle significantly increase the risk of shrinkage cracking and internal damage, seriously affecting the long-term safety and durability of the structure.

[0004] In the prior art, the composition design and preparation process of conventional C80 concrete are mostly based on standard conditions on the plain, without systematically considering the adverse effects of multi-factor coupling in highlands. There are generally large loss of workability, poor volume stability, easy occurrence of defects such as pores and debonding, which makes it difficult to guarantee the homogeneity and integrity of the cast solid structure, and restricts the reliable application of high-strength concrete in highland major projects.

[0005] Therefore, according to the related technology in the above, it is urgent to develop a C80 concrete under highland environment and a preparation method thereof. SUMMARY

[0006] Therefore, according to the related technology in the above, it is urgent to develop a C80 concrete under highland environment and a preparation method thereof.

[0007] Based on the above purpose, the present application provides a C80 concrete under highland environment and a preparation method thereof.

[0008] A C80 concrete under highland environment, which is composed of the following components by mass fraction: cement 40-50 parts, nano-modified machine-made sand 70-75 parts, crushed stone 75-80 parts, coated fly ash 10-15 parts, silica fume 3-7 parts, ultra-fine steel fiber 5-7 parts, modified polypropylene 0.1-0.2 parts, magnesium expansive agent 3-5 parts, composite admixture 1-2 parts, and deionized water 13-15 parts.

[0009] Preferably, the preparation steps of the nano-modified machine-made sand are as follows:

[0010] Step A1: add tetraethyl orthosilicate into a mixed solvent of anhydrous ethanol and deionized water, heat to 30-50℃, add 0.9g / mL ammonia water, stir for 80-100min at a speed of 400-500rpm, and obtain silica sol;

[0011] Step A2: add 1mg / mL graphene oxide dispersion into an ultrasonic tank, heat to 20-30℃, ultrasonic treatment for 1-3h at a power of 700-900W, add glacial acetic acid to adjust pH to 3.8-4.2, stir for 20-40min at a speed of 200-400min, add silica sol, heat to 50-70℃, react for 2-4h, cool to 20-30℃, stand for 22-26h, wash with anhydrous ethanol, centrifuge, add a high-speed shear emulsifier at a speed of 8000-12000rpm, add deionized water, heat to 20-30℃, and disperse for 50-70h to obtain a nanocomposite sol;

[0012] Step A3: add silane coupling agent KH-570 into anhydrous ethanol, stir and react for 20-40min, add the nanocomposite sol, and stir for 50-70min to obtain a modified liquid;

[0013] Step A4: place machine-made sand in an oven, heat to 100-110℃, dry for 100-140min, cool to 50-70℃, add a drum stirrer at a speed of 5-10rpm, add the modified liquid, and roll coat for 40-50min, then transfer into a rotary kiln, pass nitrogen, heat to 140-160℃, keep for 80-100min, cool to 20-30℃, and obtain nanomodified machine-made sand;

[0014] The nanomodified machine-made sand greatly strengthens the interfacial bonding force of aggregate and paste, simultaneously performs nanoscale dense filling on silica fume, and the fly ash coated with paraffin wax microcapsule phase change can absorb drying shrinkage stress and cooperatively reduce the risk of shrinkage and cracking under high-wind environment on plateau.

[0015] Preferably, the mass ratio of tetraethyl orthosilicate to ammonia water in step A1 is 5.7-5.8:1;

[0016] The volume ratio of anhydrous ethanol to deionized water in step A1 is 5:1;

[0017] The mass ratio of graphene oxide dispersion, silica sol and deionized water in step A2 is 1:10-10.2:15.2-15.4;

[0018] The mass ratio of silane coupling agent KH-570 to nanocomposite sol in step A3 is 1:52-53;

[0019] The mass ratio of the manufactured sand to the modifying liquid in step A4 is 3.4-3.5:1.

[0020] Preferably, the step of preparing the coated fly ash is as follows:

[0021] Step B1: sodium dodecyl benzene sulfonate and Tween-80 are added into deionized water, heated to 70-80℃, stirred for 8-10min, paraffin and octadecane are added, high-speed shearing emulsification, speed 11000-13000rpm, emulsification for 40-60min, cooling to 30-50℃, reaction is completed, paraffin emulsion is obtained;

[0022] Step B2: tetraethyl orthosilicate is added into anhydrous ethanol, ammonia water is added, heated to 20-30℃, stirred for 80-100min, speed 300-500rpm, hydrolysis liquid is obtained;

[0023] Step B3: paraffin emulsion is added into the hydrolysis liquid, heated to 40-50℃, ammonia water is added, reacted for 3-5h, heated to 55-65℃, acetic acid is added, pH is adjusted to 5.8-6.2, stirred for 100-140min, speed 80-120rpm, cooled to 20-30℃, dried, sieved, paraffin microcapsules are obtained;

[0024] Step B4: paraffin microcapsules are added into a fluidized bed, heated to 50-70℃, treated for 15-25min, 0.5% titanium ester coupling agent NDZ-201 ethanol solution is added, reacted for 40-50min, activated microcapsules are obtained;

[0025] Step B5: activated microcapsules and fly ash are added into a high-speed mixer, heated to 80-90℃, speed 700-900rpm, dry-mixed for 20-40min, ultrasonic vibration plate is turned on, power 1.1-1.3kW, mixed for 50-70min, 0.15% silica sol ethanol solution is added, heated to 100-120℃, speed 300-500rpm, reacted for 110-130min, cooled to 20-30℃, sieved, coated fly ash is obtained;

[0026] The paraffin microcapsules in the coated fly ash melt and absorb heat under strong sunlight on the plateau, slow down the internal temperature rise, solidify at night to release water and automatically adjust humidity, effectively reducing plastic shrinkage cracking, at the same time, the polypropylene fibers treated by silane coupling agent and loaded with nano-CaCO2 can efficiently reflect and block strong ultraviolet radiation, improving the anti-photo-aging ability of the fibers and the concrete matrix.

[0027] Preferably, the mass ratio of sodium dodecyl benzene sulfonate, Tween-80, paraffin and octadecane in step B1 is 1:0.32-0.34:22.2-22.3:2.2-2.3;

[0028] The mass ratio of tetraethyl orthosilicate to ammonia water in step B2 is 1:0.21-0.22;

[0029] The mass ratio of paraffin emulsion, hydrolysis liquid and ammonia water in step B3 is 4.8-4.9:1:0.03-0.04;

[0030] The mass ratio of paraffin microcapsule to titanium ester coupling agent NDZ-201 ethanol solution in step B4 is 1:0.9-1.1;

[0031] The mass ratio of activated microcapsule, fly ash and silica sol ethanol solution in step B5 is 1:5.5-5.6:2-2.1.

[0032] Preferably, the preparation steps of the modified polypropylene are as follows:

[0033] Step C1: nano calcium carbonate and silane coupling agent KH-550 are added to anhydrous ethanol, heated to 70-90℃, stirred for 20-40min, centrifuged and dried to obtain a carrier;

[0034] Step C2: polypropylene resin particles are added to a double screw, heated to 170-190℃, the carrier and antistatic agent alkyl sulfonate are added, the rotation speed is 100-140rpm, and the blending time is 10-20min. The obtained mixture is sent to a melt blowing device, the spinneret temperature is set to 190-200℃, the stretching pressure is 0.8MPa, and then the obtained mixture is put into a double roller hot press with a pressure of 0.5MPa and hot pressed for 80-100s to obtain the modified polypropylene.

[0035] Preferably, the mass ratio of nano calcium carbonate to silane coupling agent in step C1 is 1:0.01-0.02;

[0036] The mass ratio of polypropylene resin particles, carrier and antistatic agent in step C2 is 6.5-6.7:1:0.03-0.04.

[0037] Preferably, the preparation steps of the composite admixture are as follows:

[0038] Step D1: polyethylene glycol 600 and fluorocarbon surfactant are added to deionized water, heated to 30-40℃, and high-speed sheared for 40-50min at a rotation speed of 7000-9000rpm to obtain a premix;

[0039] Step D2: Add polycarboxylate superplasticizer mother liquor into the reaction kettle, heat to 60-70℃, add catalyst triethylamine, stir for 80-100min, rotate speed 200-400rpm, cool to 20-30℃, add into the blender, add premix, silicone defoaming agent and deionized water, stir for 100-140min, rotate speed 500-700rpm, transfer to the curing tank, heat to 20-40℃, stir for 46-50h, rotate speed 40-60rpm, add 10% citric acid solution, adjust pH to 6.8-7.2, sieve, get composite admixture;

[0040] The fluorocarbon surfactant in the composite admixture reduces the liquid surface tension, and the silicone defoaming agent stabilizes the bubbles, precisely controls the air content of freshly mixed concrete under highland low pressure, and at the same time, the super fine steel fiber has excellent dispersibility under the action of nano modified machine-made sand surface, which synergistically ensures that the concrete still maintains high fluidity and excellent rheological property under severe low pressure environment, completely solving the problem of easy pipe blockage of pumping on plateau.

[0041] Preferably, the mass ratio of polyethylene glycol 600, fluorocarbon surfactant and deionized water in step D1 is 1:0.082-0.084:1.4-1.6;

[0042] The mass ratio of polycarboxylate superplasticizer mother liquor, premix, catalyst, silicone defoaming agent and deionized water in step D2 is 1:0.61-0.63:0.011-0.013:0.031-0.033:0.35-0.37.

[0043] A preparation method of C80 concrete under plateau environment, the preparation steps are as follows:

[0044] Step S1: Add super fine high fiber, modified polypropylene and magnesium expansive agent into the dry powder mixer, stir for 1-2min, rotate speed 100-140rpm, get composite material;

[0045] Step S2: Add cement, coated fly ash and silica fume into the forced mixer, stir for 1-3min, rotate speed 50-70rpm, add nano modified machine-made sand and gravel, stir for 2-4min, rotate speed 100-140rpm, add deionized water and composite admixture, stir for 2-4min, rotate speed 220-260rpm, add composite material, stir for 2-4min, rotate speed 180-220rpm, add early strength accelerator, stir for 4-6min, add retarder, stir for 8-12min, get C80 concrete;

[0046] The early strength accelerator is composed of 60%-70% calcium nitrate, 20%-30% calcium formate and 5%-10% nano silicon oxide;

[0047] The retarder is prepared from 50%-60% sodium gluconate, 20%-30% sodium phosphate and 10%-20% lignin sulfonate synergist.

[0048] The size of the gravel is 10-15mm, and the diameter of the superfine steel fiber is 0.12mm.

[0049] The mass ratio of the superfine high fiber, modified polypropylene and magnesium expansive agent is 39-41:1:26.6-26.8.

[0050] The mass ratio of the cement, coated fly ash, silica fume, nano-modified machine-made sand, gravel, deionized water, composite admixture, composite material, early strength accelerator, retarder and water is 1:0.26-0.28:0.1-0.12:1.5-1.6:1.72-1.74:0.2-0.4:0.026-0.028:0.22-0.23:0.0043-0.0045:0.002-0.0024.

[0051] The beneficial effects of the present application are as follows:

[0052] The present application provides a kind of C80 concrete in highland environment and preparation method thereof, by the synergistic effect of nano-modified aggregate interface strengthening, temperature change humidity material, composite fiber anti-cracking network and low air pressure stabilizing admixture, compared with prior art, significantly improve the frost resistance, ultraviolet weather resistance and low air pressure construction adaptability, there is the broad prospect of replacing imported materials in plateau bridge, wind power base and other major projects. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the present application is further described in detail below in combination with specific examples.

[0054] Example 1: the preparation steps of the nano-modified machine-made sand are as follows:

[0055] S1: 570g tetraethyl orthosilicate is added into 1000mL anhydrous ethanol and 200mL deionized water mixed solvent, heated to 30℃, 100g 0.9g / mL ammonia water is added, stirred for 100min, the rotation speed is 400rpm, and silica sol is obtained;

[0056] S2: 10 g of 1 mg / mL graphene oxide dispersion was added to an ultrasonic tank, heated to 20°C, ultrasonic treatment for 3 h, power 700 W, add glacial acetic acid, adjust pH to 3.8-4.2, stirring 40 min, speed 200 min, add 100 g of silica sol, heated to 50°C, reaction for 4 h, reaction complete, cooled to 20°C, stand for aging 26 h, washed with anhydrous ethanol, centrifuged, added to a high-speed shearing emulsifier, speed 8000 rpm, added 152 g of deionized water, heated to 20°C, dispersed for 70 h, to obtain a nanocomposite sol;

[0057] S3: 1 g of silane coupling agent KH-570 was added to 100 mL of anhydrous ethanol, stirred for 20 min, 52 g of nanocomposite sol was added, stirred for 70 min, to obtain a modified liquid;

[0058] S4: 340 g of machine-made sand was placed in an oven, heated to 100°C, dried for 140 min, cooled to 50°C, added to a drum stirrer, speed 10 rpm, added 100 g of modified liquid, tumble coated for 40 min, transferred to a rotary kiln, nitrogen was introduced, heated to 160°C, kept for 80 min, cooled to 30°C, to obtain nanomodified machine-made sand.

[0059] Example 2: The preparation steps of the nanomodified machine-made sand are as follows:

[0060] S1: 575 g of tetraethyl orthosilicate was added to 1000 mL of anhydrous ethanol and 200 mL of deionized water mixed solvent, heated to 40°C, 100 g of 0.9 g / mL ammonia water was added, stirred for 90 min, speed 450 rpm, to obtain a silica sol;

[0061] S2: 10 g of 1 mg / mL graphene oxide dispersion was added to an ultrasonic tank, heated to 25°C, ultrasonic treatment for 2 h, power 800 W, add glacial acetic acid, adjust pH to 3.8-4.2, stirring 30 min, speed 300 min, add 101 g of silica sol, heated to 60°C, reaction for 3 h, reaction complete, cooled to 25°C, stand for aging 24 h, washed with anhydrous ethanol, centrifuged, added to a high-speed shearing emulsifier, speed 10000 rpm, added 153 g of deionized water, heated to 25°C, dispersed for 60 h, to obtain a nanocomposite sol;

[0062] S3: 1 g of silane coupling agent KH-570 was added to 100 mL of anhydrous ethanol, stirred for 30 min, 52.5 g of nanocomposite sol was added, stirred for 60 min, to obtain a modified liquid;

[0063] S4: 345g of machine-made sand was placed in an oven, heated to 105°C, dried for 120 min, cooled to 60°C, added to a drum stirrer, speed 8 rpm, added 100g of modified liquid, tumbled for 45 min, transferred to a rotary kiln, nitrogen was introduced, heated to 150°C, kept for 90 min, cooled to 25°C, and nano-modified machine-made sand was obtained.

[0064] Example 3: The preparation steps of nano-modified machine-made sand are as follows:

[0065] S1: 580g of tetraethyl orthosilicate was added to 1000mL of anhydrous ethanol and 200mL of deionized water mixed solvent, heated to 50°C, 100g of 0.9g / mL ammonia water was added, stirred for 80 min at a speed of 500 rpm, and silica sol was obtained;

[0066] S2: 10g of 1mg / mL graphene oxide dispersion was added to an ultrasonic tank, heated to 30°C, ultrasonic treatment for 1h, power 900W, glacial acetic acid was added, pH was adjusted to 3.8-4.2, stirred for 20 min at a speed of 400 min, 102g of silica sol was added, heated to 50°C, reacted for 4h, the reaction was completed, cooled to 20°C, and aged for 26h, washed with anhydrous ethanol, centrifuged, added to a high-speed shear emulsifier, speed 8000 rpm, added 154g of deionized water, heated to 30°C, dispersed for 50h, and nano-composite sol was obtained;

[0067] S3: 1g of silane coupling agent KH-570 was added to 100mL of anhydrous ethanol, stirred for 40 min, 53g of nano-composite sol was added, stirred for 50 min, and modified liquid was obtained;

[0068] S4: 350g of machine-made sand was placed in an oven, heated to 110°C, dried for 100 min, cooled to 70°C, added to a drum stirrer, speed 5 rpm, added 100g of modified liquid, tumbled for 40 min, transferred to a rotary kiln, nitrogen was introduced, heated to 160°C, kept for 80 min, cooled to 30°C, and nano-modified machine-made sand was obtained.

[0069] Example 4: The preparation steps of the coated fly ash are as follows:

[0070] S1: 10g of sodium dodecyl benzene sulfonate and 3.2g of Tween-80 were added to 200mL of deionized water, heated to 70°C, stirred for 10 min, 222g of paraffin and 22g of octadecane were added, high-speed shear emulsification, speed 11000 rpm, emulsified for 60 min, cooled to 30°C, and the reaction was completed, and paraffin emulsion was obtained;

[0071] S2: 100 g of tetraethyl orthosilicate was added to 200 mL of anhydrous ethanol, 21 g of ammonia water was added, the temperature was raised to 20°C, and stirring was performed for 100 min at a rotation speed of 300 rpm to obtain a hydrolysis solution;

[0072] S3: 96 g of the paraffin emulsion was added to 20 g of the hydrolysis solution, the temperature was raised to 40°C, 0.6 g of ammonia water was added, and reaction was performed for 3 h, then the temperature was raised to 65°C, acetic acid was added, the pH was adjusted to 5.8-6.2, stirring was performed for 100 min at a rotation speed of 120 rpm, the temperature was lowered to 20°C, drying was performed, sieving was performed, and paraffin microcapsules were obtained;

[0073] S4: 100 g of the paraffin microcapsules were added to a fluidized bed, the temperature was raised to 50°C, and treatment was performed for 25 min, then 90 g of a 0.5% titanate coupling agent NDZ-201 ethanol solution was added, and reaction was performed for 40 min to obtain activated microcapsules;

[0074] S5: 10 g of the activated microcapsules and 55 g of fly ash were added to a high-speed mixer, the temperature was raised to 80°C, stirring was performed for 20 min at a rotation speed of 900 rpm, an ultrasonic vibration plate was turned on, the power was 1.3 kW, mixing was performed for 50 min, 20 g of a 0.15% silica sol ethanol solution was added, the temperature was raised to 100°C, stirring was performed for 110 min at a rotation speed of 500 rpm, the temperature was lowered to 30°C, and sieving was performed to obtain coated fly ash.

[0075] Example 5: The preparation steps of the coated fly ash are as follows:

[0076] S1: 10 g of sodium dodecyl benzene sulfonate and 3.3 g of Tween-80 were added to 100 mL of deionized water, the temperature was raised to 75°C, and stirring was performed for 9 min, then 222.5 g of paraffin and 22.5 g of octadecane were added, high-speed shearing emulsification was performed at a rotation speed of 12000 rpm, emulsification was performed for 50 min, the temperature was lowered to 40°C, and reaction was completed to obtain a paraffin emulsion;

[0077] S2: 100 g of tetraethyl orthosilicate was added to 200 mL of anhydrous ethanol, 21.5 g of ammonia water was added, the temperature was raised to 25°C, and stirring was performed for 90 min at a rotation speed of 400 rpm to obtain a hydrolysis solution;

[0078] S3: 97 g of the paraffin emulsion was added to 20 g of the hydrolysis solution, the temperature was raised to 45°C, 0.7 g of ammonia water was added, reaction was performed for 4 h, then the temperature was raised to 60°C, acetic acid was added, the pH was adjusted to 5.8-6.2, stirring was performed for 120 min at a rotation speed of 100 rpm, the temperature was lowered to 25°C, drying was performed, sieving was performed, and paraffin microcapsules were obtained;

[0079] S4: 100 g of the paraffin microcapsules were added to a fluidized bed, the temperature was raised to 60°C, and treatment was performed for 20 min, then 110 g of a 0.5% titanate coupling agent NDZ-201 ethanol solution was added, and reaction was performed for 45 min to obtain activated microcapsules;

[0080] S5: 10 g of the activated microcapsules were added to 56 g of fly ash in a high-speed mixer, the temperature was raised to 90°C, the rotation speed was 700 rpm, dry mixing was performed for 40 min, the ultrasonic vibrator was turned on, the power was 1.1 kW, mixing was performed for 70 min, 21 g of 0.15% silica sol ethanol solution was added, the temperature was raised to 100°C, the rotation speed was 500 rpm, reaction was performed for 110 min, the temperature was lowered to 30°C, and sieving was performed, thereby obtaining the coated fly ash.

[0081] Example 6: The preparation steps of the coated fly ash are as follows:

[0082] S1: 10 g of sodium dodecyl benzene sulfonate and 3.4 g of Tween-80 were added to 100 mL of deionized water, the temperature was raised to 80°C, stirring was performed for 8 min, 223 g of paraffin and 23 g of octadecane were added, high-speed shearing emulsification was performed at a rotation speed of 13,000 rpm, emulsification was performed for 40 min, the temperature was lowered to 50°C, and reaction was completed, thereby obtaining a paraffin emulsion;

[0083] S2: 100 g of tetraethyl orthosilicate was added to 200 mL of anhydrous ethanol, 22 g of ammonia water was added, the temperature was raised to 30°C, stirring was performed at a rotation speed of 500 rpm for 800 min, and a hydrolysis solution was obtained;

[0084] S3: 98 g of the paraffin emulsion was added to 20 g of the hydrolysis solution, the temperature was raised to 50°C, 0.8 g of ammonia water was added, reaction was performed for 3 h, the temperature was then raised to 65°C, acetic acid was added to adjust the pH to 5.8-6.2, stirring was performed at a rotation speed of 120 rpm for 100 min, the temperature was lowered to 20°C, drying was performed, and sieving was performed, thereby obtaining paraffin microcapsules;

[0085] S4: 100 g of the paraffin microcapsules were added to a fluidized bed, the temperature was raised to 70°C, treatment was performed for 15 min, 110 g of 0.5% titanate coupling agent NDZ-201 ethanol solution was added, and reaction was performed for 50 min, thereby obtaining activated microcapsules;

[0086] S5: 10 g of the activated microcapsules were added to 56 g of fly ash in a high-speed mixer, the temperature was raised to 90°C, the rotation speed was 700 rpm, dry mixing was performed for 40 min, the ultrasonic vibrator was turned on, the power was 1.1 kW, mixing was performed for 70 min, 21 g of 0.15% silica sol ethanol solution was added, the temperature was raised to 100°C, the rotation speed was 500 rpm, reaction was performed for 110 min, the temperature was lowered to 30°C, and sieving was performed, thereby obtaining the coated fly ash.

[0087] Example 7: The preparation steps of the modified polypropylene are as follows:

[0088] S1: 100 g of nano calcium carbonate and 1 g of silane coupling agent KH-550 were added to 200 mL of anhydrous ethanol, the temperature was raised to 70°C, stirring was performed for 40 min, centrifugal drying was performed, and a carrier was obtained;

[0089] S2: 65 g of polypropylene resin particles were added to a twin screw, heated to 170°C, 10 g of carrier and 0.3 g of antistatic agent alkyl sulfonate were added, the rotation speed was 140 rpm, and blending was performed for 10 min, then the mixture was fed into a melt blowing device, the spinneret temperature was set to 200°C, the stretching pressure was 0.8 MPa, and then the mixture was placed into a double roller hot press, the pressure was 0.5 MPa, and hot pressing was performed for 80 s to obtain the modified polypropylene.

[0090] Example 8: The modified polypropylene was prepared according to the following steps:

[0091] S1: 100 g of nano calcium carbonate and 1.5 g of silane coupling agent KH-550 were added to 200 mL of anhydrous ethanol, heated to 80°C, stirred for 30 min, centrifuged and dried to obtain the carrier;

[0092] S2: 66 g of polypropylene resin particles were added to a twin screw, heated to 180°C, 10 g of carrier and 0.35 g of antistatic agent alkyl sulfonate were added, the rotation speed was 120 rpm, and blending was performed for 15 min, then the mixture was fed into a melt blowing device, the spinneret temperature was set to 195°C, the stretching pressure was 0.8 MPa, and then the mixture was placed into a double roller hot press, the pressure was 0.5 MPa, and hot pressing was performed for 90 s to obtain the modified polypropylene.

[0093] Example 9: The modified polypropylene was prepared according to the following steps:

[0094] S1: 100 g of nano calcium carbonate and 2 g of silane coupling agent KH-550 were added to 200 mL of anhydrous ethanol, heated to 90°C, stirred for 20 min, centrifuged and dried to obtain the carrier;

[0095] S2: 67 g of polypropylene resin particles were added to a twin screw, heated to 190°C, 10 g of carrier and 0.4 g of antistatic agent alkyl sulfonate were added, the rotation speed was 100 rpm, and blending was performed for 20 min, then the mixture was fed into a melt blowing device, the spinneret temperature was set to 190°C, the stretching pressure was 0.8 MPa, and then the mixture was placed into a double roller hot press, the pressure was 0.5 MPa, and hot pressing was performed for 100 s to obtain the modified polypropylene.

[0096] Example 10: The composite admixture was prepared according to the following steps:

[0097] S1: 100 g of polyethylene glycol 600 and 8.2 g of fluorocarbon surfactant were added to 140 g of deionized water, heated to 30°C, and high-speed sheared for 50 min at a rotation speed of 7000 rpm to obtain a premix;

[0098] S2: 100 g of polycarboxylate superplasticizer stock solution was added to the reaction kettle, heated to 60°C, 1.1 g of catalyst triethylamine was added, stirred for 100 min, rotation speed 200 rpm, cooled to 30°C, added to the blender, 61 g of premix, 3.1 g of silicone defoamer and 35 g of deionized water were added, stirred for 140 min, rotation speed 500 rpm, transferred to the curing tank, heated to 40°C, stirred for 46 h, rotation speed 60 rpm, 10% citric acid solution was added, pH was adjusted to 6.8-7.2, sieved, and the composite admixture was obtained.

[0099] Example 11: The composite admixture was prepared as follows:

[0100] S1: 100 g of polyethylene glycol 600, 8.3 g of fluorocarbon surfactant was added to 150 g of deionized water, heated to 35°C, high speed shearing for 45 min, rotation speed 8000 rpm, to obtain a premix;

[0101] S2: 100 g of polycarboxylate superplasticizer stock solution was added to the reaction kettle, heated to 65°C, 1.2 g of catalyst triethylamine was added, stirred for 90 min, rotation speed 300 rpm, cooled to 25°C, added to the blender, 62 g of premix, 3.2 g of silicone defoamer and 36 g of deionized water were added, stirred for 120 min, rotation speed 600 rpm, transferred to the curing tank, heated to 30°C, stirred for 48 h, rotation speed 50 rpm, 10% citric acid solution was added, pH was adjusted to 6.8-7.2, sieved, and the composite admixture was obtained.

[0102] Comparative Example 12: The composite admixture was prepared as follows:

[0103] S1: 100 g of polyethylene glycol 600, 8.4 g of fluorocarbon surfactant was added to 160 g of deionized water, heated to 40°C, high speed shearing for 40 min, rotation speed 9000 rpm, to obtain a premix;

[0104] S2: 100 g of polycarboxylate superplasticizer stock solution was added to the reaction kettle, heated to 70°C, 1.3 g of catalyst triethylamine was added, stirred for 80 min, rotation speed 400 rpm, cooled to 20°C, added to the blender, 63 g of premix, 3.3 g of silicone defoamer and 37 g of deionized water were added, stirred for 100 min, rotation speed 700 rpm, transferred to the curing tank, heated to 20°C, stirred for 50 h, rotation speed 40 rpm, 10% citric acid solution was added, pH was adjusted to 6.8-7.2, sieved, and the composite admixture was obtained.

[0105] Comparative Example 13: A method for preparing C80 concrete in high altitude environment

[0106] S1: 39 g of superfine high fiber, 1 g of modified polypropylene (Example 7) and 26.6 g of magnesium-based expanding agent were added into a dry powder mixer, stirred for 1 min at a speed of 140 rpm, to obtain a composite material;

[0107] S2: 100 g of cement, 26 g of coated fly ash (Example 4) and 10 g of silica fume were added into a forced mixer, stirred for 1 min at a speed of 70 rpm, 150 g of nano-modified machine-made sand (Example 1) and 172 g of crushed stone were added, stirred for 2 min at a speed of 140 rpm, 20 g of deionized water and 2.6 g of composite admixture (Example 10) were added, stirred for 2 min at a speed of 260 rpm, 22 g of the composite material was added, stirred for 2 min at a speed of 220 rpm, 0.43 g of early strength accelerator was added, stirred for 4 min, 0.2 g of retarder was added, stirred for 8 min, to obtain C80 concrete.

[0108] Comparative Example 14: A method for preparing C80 concrete in a highland environment

[0109] S1: 40 g of superfine high fiber, 1 g of modified polypropylene (Example 8) and 26.7 g of magnesium-based expanding agent were added into a dry powder mixer, stirred for 1.5 min at a speed of 120 rpm, to obtain a composite material;

[0110] S2: 100 g of cement, 27 g of coated fly ash (Example 5) and 11 g of silica fume were added into a forced mixer, stirred for 2 min at a speed of 60 rpm, 155 g of nano-modified machine-made sand (Example 2) and 173 g of crushed stone were added, stirred for 3 min at a speed of 120 rpm, 30 g of deionized water and 2.7 g of composite admixture (Example 11) were added, stirred for 3 min at a speed of 240 rpm, 22.5 g of the composite material was added, stirred for 3 min at a speed of 200 rpm, 0.44 g of early strength accelerator was added, stirred for 5 min, 0.22 g of retarder was added, stirred for 10 min, to obtain C80 concrete.

[0111] Comparative Example 15: A method for preparing C80 concrete in a highland environment

[0112] S1: 41 g of superfine high fiber, 1 g of modified polypropylene (Example 9) and 26.8 g of magnesium-based expanding agent were added into a dry powder mixer, stirred for 2 min at a speed of 100 rpm, to obtain a composite material;

[0113] S2: 100 g of cement, 28 g of coated fly ash (Example 6) and 12 g of silica fume were added into a forced stirrer, stirred for 3 min at 50 rpm, 160 g of nano-modified machine-made sand (Example 3) and 174 g of crushed stone were added, stirred for 4 min at 100 rpm, 40 g of deionized water and 2.8 g of composite admixture (Example 12) were added, stirred for 4 min at 220 rpm, 23 g of composite material was added, stirred for 4 min at 180 rpm, 0.45 g of early strength accelerator was added, stirred for 6 min, 0.24 g of retarder was added, stirred for 8 min, to obtain C80 concrete.

[0114] Comparative Example 1

[0115] The present comparative example is compared with Example 13 without adding graphene oxide in the preparation process of nano-modified machine-made sand, and the rest of the steps and parameters are the same. The present comparative example will not be repeated here. Finally, C80 concrete is obtained.

[0116] Comparative Example 2

[0117] The present comparative example is compared with Example 13 without adding nano-calcium carbonate in the preparation process of modified polypropylene. The rest of the steps and parameters are the same. The present comparative example will not be repeated here. Finally, C80 concrete is obtained.

[0118] Comparative Example 3

[0119] The present comparative example is compared with Example 13 without adding paraffin microcapsules in the preparation process of coated fly ash. The rest of the steps and parameters are the same. The present comparative example will not be repeated here. Finally, C80 concrete is obtained.

[0120] Comparative Example 4

[0121] The present comparative example is compared with Example 13 without adding fluorocarbon surfactant in the preparation process of composite admixture. The rest of the steps and parameters are the same. The present comparative example will not be repeated here. Finally, C80 concrete is obtained.

[0122] Comparative Example 5

[0123] The present comparative example is compared with Example 13 without replacing the standing aging time "22 h" with "2 h" in the preparation process of nano-modified machine-made sand. The rest of the steps and parameters are the same. The present comparative example will not be repeated here. Finally, C80 concrete is obtained.

[0124] Performance test:

[0125] Working performance test

[0126] Slump spread and T500 time test

[0127] According to GB / T 50080-2016《Standard for Test Methods of Performance of Ordinary Concrete Mixture》test standard, using standard slump cone, upper diameter 100mm, lower diameter 200mm, height 300mm;

[0128] 1. Fill the slump cone with the concrete mixture of Example 13-15 and Comparative Example 1-5 respectively at one time, and use a trowel to scrape off the excess concrete on the top of the cone to make it level with the mouth of the cone;

[0129] 2. Within 3s after the loading is completed, lift the slump cone steadily, continuously and vertically, and the lifting process should be completed within 3s to 7s. After the concrete stops flowing, measure the spread diameter in two vertical directions with a steel ruler;

[0130] 3. Start timing at the same time as lifting the slump cone, and stop timing immediately when the concrete spreads to the 500mm mark. The recorded time is T 500 time.

[0131] J-ring obstacle height difference test

[0132] According to GB / T 50080-2016《Standard for Test Methods of Performance of Ordinary Concrete Mixture》test standard, using J-ring obstacle device, and following the same steps as the above-mentioned "slump spread test", after the concrete stops flowing, measure the height of the center point of the top surface of the concrete mixture on both sides of the J-ring with a steel ruler.

[0133] U-box filling height test

[0134] According to GB / T 50080-2016《Standard for Test Methods of Performance of Ordinary Concrete Mixture》test standard, using a U-box,

[0135] 1. Fill the left box of the U-box with the concrete of Example 13-15 and Comparative Example 1-5 respectively at a uniform speed and continuously, and load to the full. Use a trowel to scrape off the excess concrete on the top to make it level with the mouth of the box. After standing for 1 minute, quickly lift the partition upwards to separate it from the concrete;

[0136] 2. After the concrete completely stops, measure the filling height of the concrete in the right box with a steel ruler.

[0137] Table 1 Test results of working performance of examples and comparative examples

[0138]

[0139] Mechanical properties

[0140] Compressive strength test

[0141] According to GB / T 50081-2019 "Standard for Testing Methods of Physical and Mechanical Properties of Concrete", a pressure testing machine is used,

[0142] 1. Respectively take the concrete of Examples 13-15 and Comparative Examples 1-5 to prepare into the size of 150mmx150mmx150mm;

[0143] 2. When the upper pressure plate approaches the test piece, adjust the ball seat to make the contact balanced, load uniformly at the rate of 0.5 to 0.8 MPa per second until the test piece is destroyed, and record the maximum load value F when the test piece is destroyed;

[0144] 3. Compressive strength calculation formula: F cc : the compressive strength of concrete cube specimen, unit MPa, F is the load of test piece destruction, unit N;

[0145] Static compressive elastic modulus test

[0146] 1. Respectively take the concrete of Examples 13-15 and Comparative Examples 1-5 to prepare into 150mmx150mmx150mm, place the test piece on the pressure testing machine, start the pressure machine, apply the initial load to the load(F0) of the reference stress of 0.5MPa, keep the constant load for 60s. In the next 30 seconds, continuously and uniformly load at the same loading rate to the load value(Fa) of stress 1 / 3 axial compressive strength(f cp ) of the specimen, keep the constant load for 60s. Then unload the load at the same rate to F0, keep the constant load for 60s;

[0147] 2. Elastic modulus value calculation formula: E c : the elastic modulus of concrete; F a : the load when the stress is 1 / 3f cp ; F0: the initial load when the stress is 0.5MPa; L: the measurement gauge length; A: the pressure bearing area of the test piece; Δn=ε a -ε0, the average value of the deformation of the test piece on both sides when F0 increases to Fa in the last loading process.

[0148] Table 2 Test results of mechanical properties of examples and comparative examples

[0149]

[0150]

[0151] Durability test

[0152] Reference GB / T 50082-2009 "Standard for Testing Methods of Long-term Performance and Durability of Ordinary Concrete";

[0153] Anti-freeze performance test

[0154] Using dynamic modulus of elasticity tester;

[0155] 1. Respectively take the concrete of examples 13-15 and comparative examples 1-5, prepare into 100mmx100mmx400mm prism test piece, place in the environment with temperature of 20±5℃, stand for 24-48h, then immediately put into standard curing room, temperature 20±2℃, relative humidity≥95%, and cure for 24d;

[0156] 2. Take out, put into water with temperature of 20±2℃, soak for 4d, after soaking, take out the test piece, wipe the surface moisture with wet cloth, immediately take its initial mass m0, use dynamic modulus of elasticity tester to measure the initial value f0 of transverse fundamental frequency of the test piece;

[0157] 3. Put the test piece into rubber test piece box, then place in the test piece rack of freeze-thaw test box, inject clear water into the test piece box, the liquid surface should be 1-3mm higher than the top surface of the test piece, start the freeze-thaw tester, begin freeze-thaw cycle, each cycle should be completed within 2-4h;

[0158] 4. Mass loss rate: Relative dynamic modulus of elasticity calculation:

[0159] Shrinkage test

[0160] 1. Respectively take the concrete of examples 13-15 and comparative examples 1-5, prepare into 100mmx100mmx515mm prism test piece, put into standard curing room, temperature 20±2℃, relative humidity≥95%, cure for 24±2h with mold, remove the mold, and cure for 3d;

[0161] 2. Take out, use vertical concrete shrinkage tester to measure its initial length, this length is recorded as the reference length (L0) of drying shrinkage measurement, after measuring the reference length, move the test piece to constant temperature and humidity room, temperature 20±2℃, relative humidity 60±5%, test for 60d, record L t ;

[0162] 3. Shrinkage rate (ε) calculation: ε ts Test period is t d of concrete drying shrinkage rate; L0: initial reference length at 3d age; L t : length measurement value of test piece at t of test period; L b : measurement gauge length of test piece

[0163] Table 3 Durability performance test results of examples and comparative examples

[0164]

[0165]

[0166] High altitude environment simulation performance

[0167] Detection of air content stability of fresh concrete under low air pressure

[0168] According to the test standard of GB / T 50080-2016, a low air pressure environment test box is used;

[0169] 1. Respectively, the concrete in examples 13-15 and comparative examples 1-5 is loaded into the measuring cup of the air content tester, and is scraped flat and sealed according to the standard method. Then, the entire air content tester loaded with the sample and sealed is quickly moved into the low air pressure environment test box, the door is closed and sealed, and the air pressure in the box is smoothly reduced to and stabilized at 60±1kPa;

[0170] 2. After the air pressure in the box is stabilized at 60kPa, the inlet valve is opened to balance the pressure inside and outside the cup, then the side wall of the cup is knocked to eliminate the attached bubbles, finally all the valves are closed, the inflation valve is opened to pressurize to the end of the scale, the value on the scale is read and recorded, which is the air content value (A0) at the initial time (T0), and is placed for 60min (T 60 ); 60 ;

[0171] 3. Calculation formula:

[0172] Anti-UV aging property

[0173] According to the test standard of GB / T 50081-2019, a UV aging test box is used;

[0174] 1. Respectively, the concrete in examples 13-15 and comparative examples 1-5 is taken, and a size of 100mm×100mm×100mm is prepared, cured to 28d age, and vertically placed on the sample rack in the UV aging test box, the irradiance is controlled at 0.76±0.02W / m 2 / nm@340nm, the blackboard temperature is 60±3℃, the environmental temperature is 50±3℃, the irradiation is 500h, and then it is taken out and cooled to room temperature, and the compressive strength test is carried out to measure the aging strength f1;

[0175] 2. Compressive strength retention rate after UV aging:

[0176] Table 4 Test results of examples and comparative examples

[0177] Item 1h gas content loss rate (%) compressive strength retention rate after UV 500h (%) Example 13 4.2 96.8 Example 14 4.5 96.0 Example 15 4.8 95.5 Comparative Example 1 18.5 82.5 Comparative Example 2 20.0 80.0 Comparative Example 3 22.5 78.0 Comparative Example 4 25.0 75.5 Comparative Example 5 21.0 79.0

[0178] Data analysis:

[0179] As can be seen from Table 1-4, the C80 concrete prepared by the application has better working performance, mechanical properties, durability and adaptability to highland environment;

[0180] Comparative Example 1 has no graphene oxide added in the nano-modified machine-made sand, resulting in decreased fluidity, strength and durability of the concrete. The reason is that the surface of graphene oxide contains a large number of hydrophilic functional groups such as hydroxyl and carboxyl groups, which can play an excellent "ball bearing effect" in the cement paste, effectively reducing the friction between aggregate particles and between fibers and paste. However, the lack of lubrication of graphene oxide increases the frictional resistance between machine-made sand and paste, and between fibers and paste, resulting in decreased overall fluidity. In the nano-modified machine-made sand, the composite formed by graphene oxide and SiO2 sol can tightly wrap around the surface of the sand particles, and the functional groups on its surface can form strong chemical bonding and hydrogen bonding with the cement hydration products, greatly strengthening the interface transition zone between aggregate and cement paste. Comparative Example 1 lacks graphene oxide and only relies on SiO2 sol, which has limited toughening and strengthening effect, resulting in more microcracks and defects in the interface transition zone, which become stress concentration points and are prone to cracking under external force, thus greatly reducing the macroscopic strength. In addition, uniformly dispersed graphene oxide nanosheets can bridge microcracks in the cement matrix, effectively preventing crack propagation. The lack of this nanoscale strengthening and crack resistance mechanism increases the brittleness of the concrete and reduces the toughness;

[0181] Comparative Example 2, due to the absence of nano calcium carbonate in the modified polypropylene, results in poor fiber dispersibility and decreased anti-UV aging ability. The reason is that the nano calcium carbonate particles are modified by silane coupling agent KH-550, and the surface contains organic functional groups, which can physically entangle or weakly chemically interact with the polypropylene molecular chain, thereby effectively hindering the agglomeration of the polypropylene molecular chain during melt blending, improving the dispersibility of the fiber after forming. Without the addition of nano CaCO3, polypropylene fibers are more likely to agglomerate into bundles due to intermolecular forces in concrete, making it difficult to disperse uniformly. Uneven fiber dispersion causes local fiber-rich and fiber-poor areas in the concrete, with the fiber-rich area prone to internal defects and weak interfaces. The fiber-poor area lacks fiber bridging and crack resistance, ultimately leading to overall deterioration of the workability and mechanical properties of the concrete. At the same time, nano calcium carbonate has excellent UV reflectivity and shielding properties, and its uniform dispersion in the polypropylene matrix can effectively reflect, scatter and absorb high-intensity UV radiation, significantly reducing the opportunity for UV rays to directly act on the polypropylene molecular chain. Without this layer of protection, UV rays penetrate directly, triggering photo-oxidative aging of the polypropylene molecular chain. In addition, under strong UV radiation, the polypropylene molecular chain is prone to chain scission and oxidation, leading to fiber embrittlement, loss of flexibility and tensile strength, and the appearance of cracks and holes on the fiber surface, reducing its adhesion to the concrete matrix. At the same time, it may further catalyze the degradation reaction, forming a vicious cycle;

[0182] The comparative example 3 lacks the mechanism of paraffin microcapsule, the internal temperature of concrete completely follows the external environment, the thermal expansion and cold shrinkage stress is greater. At the same time, the passive "moisture absorption - moisture release" fine adjustment ability is also lost, which cannot compensate for the rapid evaporation of water on the surface of concrete in the plateau wind environment. In addition, the drying shrinkage of concrete is mainly caused by the capillary tension caused by the loss of capillary water. The high wind and low humidity environment in the plateau area can accelerate the evaporation of water. However, the micro amount of water released by the paraffin microcapsule in the solidification stage can delay the loss of capillary water between cement particles at the micro level in the early hydration and strength development period, effectively reduce the capillary negative pressure, and thus reduce the drying shrinkage. The ordinary fly ash of the comparative example 3 does not have this function, and the water evaporation is unobstructed, the capillary negative pressure increases rapidly, resulting in a drying shrinkage value much higher than that of the embodiment of the application, which increases the risk of cracking;

[0183] The comparative example 4 lacks fluorocarbon surfactant in the composite admixture, resulting in unstable air content and serious loss of fluidity under low air pressure. The reason is that the absence of fluorocarbon surfactant directly leads to the inability to effectively reduce the surface tension of the liquid phase system, thereby significantly weakening the system's ability to stabilize the foam. In addition, the fluorocarbon surfactant forms a high-strength, low-permeability interface film through extremely low surface tension and directional arrangement on the gas-liquid interface, thereby effectively inhibiting bubble coarsening and escape under low air pressure, ensuring the workability and pumpability of freshly mixed concrete. However, the comparative example 4 lacks this key component, resulting in instability of the bubble system, and the overall decline in workability and air content retention;

[0184] Comparative Example 5, due to the lack of static aging during the preparation of nano-modified manufactured sand (only 2 hours), resulted in an incomplete sol structure and poor modification effect. This is because the hydrolysis and condensation of tetraethyl orthosilicate under alkaline catalyst is a stepwise and slow process. The 2-hour aging time can only complete the initial condensation, forming a large number of oligomers and short-chain structures, but it cannot form a long-range, dense, and mechanically stable continuous network. This results in the final silica sol structure having low strength and many internal defects. At the same time, the insufficiently aged and loosely structured SiO2 gel was used for subsequent composite with graphene oxide and final modification of manufactured sand, which prevented it from forming a dense, strong, and uniform nano-modified layer on the aggregate surface. In addition, the loose gel layer itself has low mechanical strength, which greatly weakens the physical intercalation and anchoring effect with the surface of manufactured sand. Furthermore, the silane coupling agent KH-570 used later needs to react chemically with the abundant -Si-OH on the surface of the gel layer to form strong chemical bonds. The incomplete gel network has a lower density and reactivity of -Si-OH functional groups, which leads to a decrease in the grafting efficiency of silane coupling bridges, thereby weakening the chemical bonding ability between modified aggregates and cement paste.

[0185] 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.

[0186] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A type of C80 concrete for high-altitude environments, characterized in that, It is composed of the following components in parts by weight: 40-50 parts cement, 70-75 parts nano-modified manufactured sand, 75-80 parts crushed stone, 10-15 parts coated fly ash, 3-7 parts silica fume, 5-7 parts ultrafine steel fiber, 0.1-0.2 parts modified polypropylene, 3-5 parts magnesium expansion agent, 1-2 parts composite admixture, and 13-15 parts deionized water. The preparation steps of the nano-modified manufactured sand are as follows: Step A1: Add tetraethyl orthosilicate to a mixed solvent of anhydrous ethanol and deionized water, heat to 30-50℃, add 0.9g / mL ammonia water, stir for 80-100min at 400-500rpm to obtain silica sol. Step A2: Add 1 mg / mL graphene oxide dispersion to an ultrasonic bath, heat to 20-30℃, sonicate for 1-3 hours at 700-900W, add glacial acetic acid, adjust pH to 3.8-4.2, stir for 20-40 minutes at 200-400 min, add silica sol, heat to 50-70℃, react for 2-4 hours, after the reaction is complete, cool to 20-30℃, let stand for aging for 22-26 hours, wash with anhydrous ethanol, centrifuge, add to a high-speed shear emulsifier at 8000-12000 rpm, add deionized water, heat to 20-30℃, disperse for 50-70 hours to obtain nanocomposite sol; Step A3: Add silane coupling agent KH-570 to anhydrous ethanol, stir and react for 20-40 min, add nanocomposite sol, stir for 50-70 min, and obtain modified solution; Step A4: Place the manufactured sand in an oven, heat it to 100-110℃, dry it for 100-140 min, cool it down to 50-70℃, add it to a drum mixer, rotate it at 5-10 rpm, add the modification liquid, roll it for 40-50 min, transfer it to a rotary kiln, introduce nitrogen gas, heat it to 140-160℃, keep it at that temperature for 80-100 min, cool it down to 20-30℃, and obtain nano-modified manufactured sand; The preparation steps for the coated fly ash are as follows: Step B1: Add sodium dodecylbenzenesulfonate and Tween-80 to deionized water, heat to 70-80℃, stir for 8-10 min, add paraffin and octadecane, emulsify by high-speed shearing at 11000-13000 rpm for 40-60 min, cool to 30-50℃, the reaction is complete, and a paraffin emulsion is obtained. Step B2: Add tetraethyl orthosilicate to anhydrous ethanol, add ammonia, heat to 20-30℃, stir for 80-100 min at 300-500 rpm to obtain hydrolysate; Step B3: Add the paraffin emulsion to the hydrolysate, heat to 40-50℃, add ammonia, react for 3-5 hours, then heat to 55-65℃, add acetic acid, adjust the pH to 5.8-6.2, stir for 100-140 minutes at 80-120 rpm, cool to 20-30℃, dry, and sieve to obtain paraffin microcapsules; Step B4: Add paraffin microcapsules to a fluidized bed, heat to 50-70℃, treat for 15-25 min, add 0.5% titanate coupling agent NDZ-201 ethanol solution, react for 40-50 min, and obtain activated microcapsules. Step B5: Add the activated microcapsules and fly ash to a high-speed mixer, heat to 80-90℃, rotate at 700-900 rpm, dry mix for 20-40 min, turn on the ultrasonic transducer, power 1.1-1.3kW, mix for 50-70 min, add 0.15% silica sol ethanol solution, heat to 100-120℃, rotate at 300-500 rpm, react for 110-130 min, cool down by 20-30℃, sieve to obtain coated fly ash; The preparation steps for modified polypropylene are as follows: Step C1: Add nano-calcium carbonate and silane coupling agent KH-550 to anhydrous ethanol, heat to 70-90℃, stir for 20-40 min, centrifuge and dry to obtain the carrier; Step C2: Add polypropylene resin granules to a twin-screw extruder, heat to 170-190℃, add carrier and antistatic agent alkyl sulfonate, mix at 100-140 rpm for 10-20 min, then feed into a meltblown equipment, set the spinneret temperature to 190-200℃, stretch at 0.8 MPa pressure, and place in a twin-roll hot press at 0.5 MPa pressure for 80-100 s to obtain modified polypropylene; The preparation steps of the composite admixture are as follows: Step D1: Add polyethylene glycol 600 and fluorocarbon surfactant to deionized water, heat to 30-40℃, and shear at high speed for 40-50 minutes at a speed of 7000-9000 rpm to obtain a premixed solution. Step D2: Add the polycarboxylate superplasticizer mother liquor to the reactor, heat to 60-70℃, add the catalyst triethylamine, stir for 80-100 min at 200-400 rpm, cool to 20-30℃, add to a mixer, add the premix, silicone defoamer and deionized water, stir for 100-140 min at 500-700 rpm, transfer to a curing tank, heat to 20-40℃, stir for 46-50 h at 40-60 rpm, add 10% citric acid solution, adjust the pH to 6.8-7.2, sieve to obtain the composite additive.

2. The C80 concrete for high-altitude environments according to claim 1, characterized in that, The mass ratio of tetraethyl orthosilicate to ammonia in step A1 is 5.7-5.8:1; The volume ratio of anhydrous ethanol to deionized water in step A1 is 5:1; The mass ratio of graphene oxide dispersion, silica sol, and deionized water in step A2 is 1:10-10.2:15.2-15.4; The mass ratio of silane coupling agent KH-570 to nanocomposite sol in step A3 is 1:52-53; The mass ratio of the manufactured sand to the modified liquid in step A4 is 3.4-3.5:

1.

3. The C80 concrete for high-altitude environments according to claim 1, characterized in that, The mass ratio of sodium dodecylbenzenesulfonate, Tween-80, paraffin, and octadecane in step B1 is 1:0.32-0.34:22.2-22.3:2.2-2.3; The mass ratio of tetraethyl orthosilicate to ammonia in step B2 is 1:0.21-0.22; The mass ratio of paraffin emulsion, hydrolysate, and ammonia in step B3 is 4.8-4.9:1:0.03-0.

04. The mass ratio of the paraffin microcapsules to the titanate coupling agent NDZ-201 ethanol solution in step B4 is 1:0.9-1.1; The mass ratio of the activated microcapsules, fly ash, and silica sol ethanol solution in step B5 is 1:5.5-5.6:2-2.

1.

4. The C80 concrete for high-altitude environments according to claim 1, characterized in that, The mass ratio of nano-calcium carbonate to silane coupling agent in step C1 is 1:0.01-0.02; In step C2, the mass ratio of polypropylene resin particles, carrier, and antistatic agent is 6.5-6.7:1:0.03-0.

04.

5. The C80 concrete for high-altitude environments according to claim 1, characterized in that, The mass ratio of polyethylene glycol 600, fluorocarbon surfactant, and deionized water in step D1 is 1:0.082-0.084:1.4-1.

6. In step D2, the mass ratio of polycarboxylate superplasticizer mother liquor, premixed liquor, catalyst, silicone defoamer to deionized water is 1:0.61-0.63:0.011-0.013:0.031-0.033:0.35-0.

37.

6. A method for preparing C80 concrete in a high-altitude environment according to any one of claims 1-5, characterized in that, The preparation steps are as follows: Step S1: Add ultrafine high fiber, modified polypropylene and magnesium expansion agent to a dry powder mixer, stir for 1-2 minutes at a speed of 100-140 rpm to obtain the composite material; Step S2: Add cement, coated fly ash and silica fume to a forced mixer and mix for 1-3 minutes at 50-70 rpm. Add nano-modified manufactured sand and crushed stone and mix for 2-4 minutes at 100-140 rpm. Add deionized water and composite admixture and mix for 2-4 minutes at 220-260 rpm. Add composite material and mix for 2-4 minutes at 180-220 rpm. Add early-strength accelerator and mix for 4-6 minutes. Add retarder and mix for 8-12 minutes to obtain C80 concrete. The mass ratio of the ultrafine high fiber, modified polypropylene, and magnesium expanding agent is 39-41:1:26.6-26.

8. The mass ratio of the cement, coated fly ash, silica fume, nano-modified manufactured sand, crushed stone, deionized water, composite admixture, composite material, early-strength accelerator and retarder is 1:0.26-0.28:0.1-0.12:1.5-1.6:1.72-1.74:0.2-0.4:0.026-0.028:0.22-0.23:0.0043-0.0045:0.002-0.0024.

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