Machine-made sand UHPC capable of being used for producing prefabricated concrete formwork and preparation method of machine-made sand UHPC

Abstract

The invention discloses machine-made sand UHPC capable of being used for producing a precast concrete formwork and a preparation method of the machine-made sand UHPC, and belongs to the technical field of construction engineering material preparation. Comprising the following raw materials in parts by weight: 650 to 850 parts of cement, 70 to 120 parts of slag powder, 30 to 60 parts of silica fume, 80 to 140 parts of microbeads, 1100 to 1400 parts of machine-made sand, 30 to 50 parts of steel fibers, 15 to 20 parts of a water reducing agent, 0.8 to 1.5 parts of sodium gluconate, 0.3 to 0.6 part of a defoaming agent and 165 to 200 parts of mixing water. The machine-made sand is used for replacing traditional natural sand / carborundum, the cost is reduced, and raw materials are easy to obtain; the workability and the mechanical property of the machine-made sand are improved through cooperation of the water reducing agent, the microbeads and the defoaming agent, and the workability is prolonged through sodium gluconate; the compactness and durability of the concrete are improved through the slag powder and the micro-silicon powder, the overall proportion is scientific, and prefabricated concrete formworks can be efficiently produced in batches.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building engineering material preparation, and particularly relates to machine-made sand UHPC for producing prefabricated concrete formworks and a preparation method thereof. BACKGROUND

[0002] UHPC (ultra-high performance concrete) is a high-toughness cement-based composite material with ultra-high mechanical properties and ultra-high impermeability, which is made of cement, mineral admixtures, aggregates, fibers, admixtures and water. Due to the composition and performance characteristics of UHPC, the size and self-weight of the component can be greatly reduced, and UHPC has the characteristics of ultra-high strength, high toughness and excellent workability, etc. Therefore, concrete thin components (30-50mm thick) can be produced as formworks for construction, which can achieve the effect of formwork removal. Traditional preparation of UHPC mainly relies on the use of natural sand and quartz sand, which is high in cost and limited in resources, and large-scale mining of river sand will cause serious environmental problems. Machine-made sand is widely used in construction, but machine-made sand has the problems of large fluctuation in stone powder content and many particle corners, which can easily lead to poor flowability, high viscosity, high air content and difficult construction of UHPC.

[0003] Application No. 202311717761.4 discloses the use of quartz sand as aggregate to prepare ultra-high performance concrete, which has high flowability, low viscosity, small shrinkage and excellent mechanical properties; Application No. 202211669878.5 discloses the use of corundum sand and machine-made sand as aggregate to prepare UHPC, which is economical, environmentally friendly, superior in performance and low in price; Application No. 202011145825.4 discloses the use of river sand, quartz sand and other aggregates to prepare ultra-high performance concrete. Although the use of one or more of quartz sand, corundum sand and river sand in the above-mentioned disclosures improves the performance of UHPC, the raw materials used are not easy to obtain, and the cost is high in large-scale production. SUMMARY

[0004] One of the purposes of the present application is to provide machine-made sand UHPC for producing prefabricated concrete formworks, which not only solves the problems of poor flowability, high viscosity, high air content and difficult construction of concrete when machine-made sand is used to prepare UHPC, but also solves the problems of difficult acquisition of raw materials, high price, complex production process and complicated preparation method in UHPC production, and meets the requirements of large-scale production.

[0005] The second purpose of the present application is to provide a preparation method of machine-made sand UHPC for producing prefabricated concrete formworks, which is used to prepare the machine-made sand UHPC.

[0006] The purposes of the present application can be achieved by the following technical solutions: A machine-made sand UHPC that can be used to produce prefabricated concrete formworks, comprising the following raw materials by weight: cement 650-850 parts, slag powder 70-120 parts, microsilica powder 30-60 parts, microbeads 80-140 parts, machine-made sand 1100-1400 parts, steel fiber 30-50 parts, water reducing agent 15-20 parts, sodium gluconate 0.8-1.5 parts, defoaming agent 0.3-0.6 parts, and mixing water 165-200 parts.

[0007] Further, the cement is one or a combination of Portland cement and ordinary Portland cement with a strength grade of 52.5 MPa.

[0008] Further, the slag powder is S105 grade slag.

[0009] Further, the microsilica powder has a silicon dioxide content of not less than 95.0% and a specific surface area of not less than 25000 m 2 / kg.

[0010] Further, the microbeads are micron-level high-fineness microbeads with a particle size of 0.1-0.5 um, a 7d activity index of ≥90%, a 28d activity index of ≥110%, and a 56d activity index of ≥120%.

[0011] Further, the machine-made sand is crushed from basalt or quartzite, has a fineness modulus of 2.5-3.2, a stone powder content of not more than 2.0%, and other indicators meet the requirements of Class I sand.

[0012] Further, the steel fiber has a length of 13-20 mm, a diameter of 0.18-0.22 mm, and a tensile strength of not less than 2500 MPa.

[0013] Further, the water reducing agent is a polycarboxylic acid high-performance water reducing agent with a water-reducing rate of not less than 30%.

[0014] Further, the sodium gluconate is a white crystalline powder of industrial grade with a content of 98.0% and above.

[0015] Further, the defoaming agent is a polyether-based defoaming agent with a pH value of 6.0-8.0 and a viscosity of 500-2000 mPa.s.

[0016] Further, the mixing water is tap water that meets the relevant provisions of JGJ63 "Water Standards for Concrete".

[0017] A preparation method of a machine-made sand UHPC that can be used to produce prefabricated concrete formworks, comprising the following steps: The cement, slag powder, microsilica powder, microbead, machine-made sand, sodium gluconate are added into a stirrer, after stirring for 1-3 minutes, the steel fiber is slowly and evenly scattered into the stirrer, and stirring is continuously carried out to ensure that the steel fiber is uniformly mixed with the concrete, then the polycarboxylate superplasticizer, defoaming agent and mixing water are added into the stirrer and stirred uniformly to obtain the UHPC.

[0018] The beneficial effects of the present application are: (1) The machine-made sand is used as the aggregate in the present application, compared with the natural sand and the diamond sand relied by the traditional UHPC, the raw material source is more extensive, and the acquisition cost is lower, which realizes the efficient recycling of mineral resources, and provides aggregate supply guarantee for mass production of prefabricated concrete formwork; meanwhile, aiming at the technical pain points of poor fluidity, high viscosity and excessive air content of UHPC caused by the many edges and corners of machine-made sand particles and the fluctuation of stone powder content, the water reducing agent (polycarboxylate superplasticizer) in the system can reduce the interparticle attraction through adsorption and dispersion, and significantly improve the fluidity of the fresh mixture; the micron-sized high-fineness microbead fills the gap between the machine-made sand and the cementitious material, optimizes the particle size distribution to reduce the viscosity of the system, and cooperates with the defoaming agent (polyether defoaming agent) to accurately control the air content, and the three form a synergistic effect to effectively improve the construction operability.

[0019] (2) In the cementitious system, the slag powder and the microsilica powder are used to play the high-activity pozzolanic effect, which can react with the calcium hydroxide generated by the hydration of cement to generate more hydrated calcium silicate gel, which not only improves the compactness and mechanical properties of the hardened body, but also replaces part of the cement dosage, reduces the industrial solid waste discharge and reduces the production cost. Mixing water is used as a mixing medium for each solid component of the grouting material; sodium gluconate is used as a retarder to reduce the cement hydration heat and hydration rate, so that the fresh UHPC maintains good workability for a long time and prolongs the construction application period.

[0020] (3) The weight ratio of each raw material in the present application is scientifically matched, the cementitious material (cement, slag powder, microsilica powder, microbead), aggregate (machine-made sand), reinforcing phase (steel fiber) and admixture (water reducing agent, sodium gluconate, defoaming agent) and mixing water are matched, which ensures the good workability, mechanical properties and construction properties of the machine-made sand UHPC; each component is complementary in principle and synergistic in effect, which solves the problems of high raw material cost and complex production process of traditional UHPC, and finally forms the machine-made sand UHPC which has the advantages of easy acquisition of raw materials, low cost, excellent workability, convenient construction, etc., and fully meets the technical and economic needs of mass production of prefabricated concrete formwork. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below.

[0022] The embodiment of the present application provides a machine-made sand UHPC which can be used for producing prefabricated concrete formwork, and includes the following raw materials by weight: cement 650-850 parts, slag powder 70-120 parts, microsilica powder 30-60 parts, microbeads 80-140 parts, machine-made sand 1100-1400 parts, steel fiber 30-50 parts, water reducing agent 15-20 parts, sodium gluconate 0.8-1.5 parts, defoaming agent 0.3-0.6 parts and mixing water 165-200 parts.

[0023] The cementitious system (cement, slag powder, microsilica powder, microbeads) cooperatively provides sufficient strength and compactness, the slag powder and microsilica powder can also reduce the cement dosage to reduce costs, and the microbeads can reduce viscosity and improve toughness; the machine-made sand and steel fiber are respectively used as low-cost aggregate and crack-resistant reinforcing phase to ensure the load bearing and crack resistance of the formwork; the water reducing agent, sodium gluconate and defoaming agent are used in a suitable amount to improve fluidity, prolong working time and reduce air content, thereby solving the construction problems; and the amount of mixing water is matched with each component to ensure hydration stability.

[0024] Preferably, the weight ratio of cement, slag powder, microsilica powder, microbeads, machine-made sand, steel fiber, water reducing agent, sodium gluconate, defoaming agent and mixing water is 700:100:40:90:1300:35:16:0.9:0.4:175. Further optimization of the performance balance makes the machine-made sand UHPC more suitable for the batch production requirements of the formwork in terms of cost, workability and mechanical properties.

[0025] In some embodiments, the cement is one or more combinations of Portland cement and ordinary Portland cement with a strength grade of 52.5 MPa, which can provide sufficient basic cementitious strength for the machine-made sand UHPC of the present application, and meet the core requirements of the prefabricated concrete formwork for load bearing performance.

[0026] In some embodiments, the slag powder is S105 grade slag, which has high activity and can cooperatively react with cement hydration products, thereby reducing the cement dosage to reduce costs and improving the compactness and durability of the hardened UHPC body.

[0027] In some embodiments, the microsilica powder has a silicon dioxide content of not less than 95.0% and a specific surface area of not less than 25000 m² / kg, and high purity and large specific surface area make it have strong pozzolanic activity, which can fully participate in the hydration reaction to generate more cementitious products and significantly enhance the mechanical properties of the UHPC.

[0028] In some embodiments, the microbeads are micron-level high-fineness microbeads with a particle size of 0.1-0.5 um, a 7d activity index of ≥90%, a 28d activity index of ≥110% and a 56d activity index of ≥120%. The ultra-fine particle size can fill the internal voids of the system to reduce the viscosity, and the high activity can ensure the continuous development of the early and late strength of the UHPC, and balance the workability and mechanical properties.

[0029] In some embodiments, the manufactured sand is broken from basalt or quartzite, the fineness modulus is 2.5-3.2, the stone powder content is not more than 2.0%, and other indicators meet the requirements of I-class sand. The hard raw material and reasonable gradation ensure the strength of the aggregate, and the low stone powder content can avoid its adverse effect on the fluidity of UHPC, providing a stable aggregate basis for the production of the formwork.

[0030] In some embodiments, the steel fiber has a length of 13-20 mm and a diameter of 0.18-0.22 mm, and a tensile strength of not less than 2500 MPa. The steel fiber with such size and strength can form a uniform reinforcing network inside the UHPC, effectively improving the crack resistance and toughness of the material, and avoiding cracking of the prefabricated formwork during use or transportation.

[0031] In some embodiments, the water reducing agent is a polycarboxylic acid high-performance water reducing agent, and the water reducing rate is not less than 30%. The high water reducing rate can significantly improve the fluidity of fresh UHPC at low water-binder ratio, solve the problem of high viscosity caused by manufactured sand, and improve the strength of the hardened body.

[0032] In some embodiments, the sodium gluconate is a white crystalline powder, industrial grade, with a content of 98.0% and above. The high purity allows it to precisely delay the cement hydration speed and prolong the workability retention time of UHPC, adapting to the construction rhythm of prefabricated formwork production.

[0033] In some embodiments, the defoaming agent is a polyether defoaming agent, with a pH value of 6.0-8.0 and a viscosity of 500-2000 mPa.s. The performance parameters make it have good dispersibility and stable defoaming stability in the UHPC system, which can effectively reduce the air content of the system and avoid the influence of air bubbles on the density and strength of the formwork.

[0034] In some embodiments, the mixing water is tap water, and all indicators meet the relevant provisions of JGJ63 "Water Standard for Concrete". The water quality meeting the standard can avoid the interference of impurities with the cement hydration reaction, ensuring the stability and consistency of the performance of UHPC.

[0035] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments.

[0036] Example 1

[0037] This embodiment provides a manufactured sand UHPC that can be used to produce prefabricated concrete formwork, which is prepared by the following steps: A machine-made sand UHPC which can be used for producing concrete formwork comprises the following raw materials by weight: cement 700 parts, slag powder 100 parts, microsilica powder 40 parts, microbead 90 parts, machine-made sand 1300 parts, steel fiber 35 parts, water reducing agent 16 parts, sodium gluconate 0.9 parts, defoaming agent 0.4 parts, mixing water 175 parts. The cement is Portland cement with a strength grade of 52.5 MPa. The slag powder is S105 grade slag. The microsilica powder has a silicon dioxide content of 98.2% and a specific surface area of 26500 m 2 / kg. The microbead is micron-level high-fineness microbead with a particle size of 0.1-0.5 um, a 7d activity index of 92%, a 28d activity index of 115%, and a 56d activity index of 126%. The machine-made sand is broken from basalt, has a fineness modulus of 2.9, a stone powder content of 1.1%, and other indicators meeting the requirements of I-class sand. The steel fiber has a length of 15 mm, a diameter of 0.2 mm, and a tensile strength of 2770 MPa. The water reducing agent is a polycarboxylic acid high-performance water reducing agent with a water-reducing rate of 32%. The sodium gluconate is a white crystalline powder, an industrial grade, and has a content of 98.5%. The defoaming agent is a polyether defoaming agent with a pH value of 6.5 and a viscosity of 1500 mPa.s. The mixing water is tap water, and all indicators meet the relevant provisions of JGJ63 "Water Standard for Concrete". The cement, slag powder, microsilica powder, microbead, machine-made sand, and sodium gluconate are added into a stirrer, stirred for 2 min, and then the steel fiber is slowly and evenly scattered into the stirrer while continuing to stir to ensure that the steel fiber is uniformly mixed with the concrete. Then, the polycarboxylic acid water reducing agent, defoaming agent, and mixing water are added into the stirrer and stirred uniformly to obtain the UHPC. The freshly mixed UHPC is transported to the site for pouring by using a tank car or a hopper.

[0038] Example 2

[0039] A machine-made sand UHPC which can be used for producing concrete formwork comprises the following raw materials by weight: cement 780 parts, slag powder 80 parts, microsilica powder 50 parts, microbead 100 parts, machine-made sand 1200 parts, steel fiber 40 parts, water reducing agent 17 parts, sodium gluconate 1.0 parts, defoaming agent 0.4 parts, and mixing water 190 parts.

[0040] The cement is ordinary Portland cement with a strength grade of 52.5 MPa.

[0041] The slag powder is S105 grade slag.

[0042] The microsilica powder contains 99.1% of silicon dioxide, and the specific surface area is 28000 m 2 / kg.

[0043] The microbead is micron grade high fineness microbead, the particle size is 0.1-0.5um, the 7d activity index is 94%, the 28d activity index is 116%, and the 56d activity index is 125%.

[0044] The machine-made sand is broken from basalt, the fineness modulus is 3.0, the stone powder content is 0.9%, and other indexes need to meet the requirements of I type sand.

[0045] The steel fiber has a length of 18mm and a diameter of 0.2mm, and the tensile strength is 2810MPa.

[0046] The water reducing agent is polycarboxylic acid high performance water reducing agent, and the water reducing rate is 34%.

[0047] The sodium gluconate is white crystalline powder, industrial grade, and the content is 98.9%.

[0048] The defoaming agent is polyether defoaming agent, the pH value is 7.0, and the viscosity is 1650mPa.s.

[0049] The mixing water is tap water, and all indexes meet the relevant provisions of JGJ63 "water standard for concrete".

[0050] The cement, slag powder, microsilica powder, microbead, machine-made sand and sodium gluconate are added into the stirrer, stirred for 2.5min, then the steel fiber is slowly and uniformly scattered into the stirrer, and the stirring is continued to ensure that the steel fiber is uniformly mixed with the concrete, then the polycarboxylic acid water reducing agent, defoaming agent and mixing water are added into the stirrer and stirred uniformly to obtain the UHPC, and the freshly mixed UHPC is transported to the site by tank car or hopper for pouring.

[0051] The remaining raw materials and preparation process are the same as those of example 1.

[0052] Example 3

[0053] A machine-made sand UHPC for producing concrete formwork, comprising the following raw materials in parts by weight: cement 670 parts, slag powder 110 parts, microsilica powder 55 parts, microbead 105 parts, machine-made sand 1280 parts, steel fiber 45 parts, water reducing agent 15 parts, sodium gluconate 1.2 parts, defoaming agent 0.5 parts, and mixing water 178 parts. The cement is Portland cement with a strength grade of 52.5MPa; The slag powder is S105 grade slag; The microsilica powder contains 98.7% of silicon dioxide, and has a specific surface area of 27800 m 2 / kg. The microbead is a micron-level high-fineness microbead, has a particle size of 0.1-0.5 um, a 7d activity index of 96%, a 28d activity index of 118%, and a 56d activity index of 129%; The machine-made sand is crushed from basalt, has a fineness modulus of 2.7, a stone powder content of 1.4%, and other indexes meeting the requirements of I-class sand; The steel fiber has a length of 15 mm, a diameter of 0.2 mm, and a tensile strength of 2860 MPa; The water reducing agent is a polycarboxylic acid high-performance water reducing agent, and has a water-reducing rate of 38%; The sodium gluconate is a white crystalline powder, is an industrial grade, and has a content of 98.4%; The defoaming agent is a polyether defoaming agent, has a pH value of 7.0, and a viscosity of 1650 mPa.s; The mixing water is tap water, and all indexes meet the relevant provisions of JGJ63 “Water Standard for Concrete”; The cement, the slag powder, the microsilica powder, the microbead, the machine-made sand, and the sodium gluconate are added into a stirrer, stirred for 2 minutes, and then the steel fiber is slowly and uniformly scattered into the stirrer, while stirring is continuously performed to ensure that the steel fiber is uniformly mixed with the concrete, and then the polycarboxylic acid water reducing agent, the defoaming agent, and the mixing water are added into the stirrer and stirred uniformly to obtain the UHPC, and the freshly mixed UHPC is transported to a site for pouring by using a tank car or a hopper.

[0054] The remaining raw materials and the preparation process are the same as those in Example 1.

[0055] Example 4

[0056] Compared with Example 1, the difference lies in that the raw material formula is as follows in terms of weight parts: cement 750 parts, slag powder 90 parts, microsilica powder 45 parts, microbead 110 parts, machine-made sand 1150 parts, steel fiber 32 parts, water reducing agent 18 parts, sodium gluconate 1.1 parts, defoaming agent 0.35 parts, and mixing water 180 parts.

[0057] The machine-made sand is crushed from quartzite, has a fineness modulus of 2.5, a stone powder content of 1.3%, and meets the requirements of I-class sand; The steel fiber has a length of 13 mm, a diameter of 0.18 mm, and a tensile strength of 2600 MPa; The water reducing agent is a polycarboxylic acid high-performance water reducing agent, and has a water-reducing rate of 30%.

[0058] The remaining raw materials and the preparation process are the same as those in Example 1.

[0059] Example 5

[0060] The embodiment is different from example 1 in that the raw material formula is as follows: cement 820 parts, slag powder 75 parts, microsilica powder 55 parts, microbead 130 parts, machine-made sand 1350 parts, steel fiber 48 parts, water reducing agent 19 parts, sodium gluconate 1.4 parts, defoaming agent 0.55 parts, and mixing water 195 parts by weight; The machine-made sand is basalt broken, with fineness modulus 3.2 and stone powder content 0.8%, meeting the requirement of I type sand; The steel fiber has length 20 mm (upper limit) and diameter 0.22 mm, with tensile strength 2900 MPa; The water reducing agent is polycarboxylic acid high-performance water reducing agent, with water reducing rate 36%.

[0061] The remaining raw materials and preparation process are the same as those of example 1.

[0062] Example 6

[0063] The embodiment is different from example 1 in that the raw material formula is as follows: cement 650 parts, slag powder 120 parts, microsilica powder 60 parts, microbead 80 parts, machine-made sand 1400 parts, steel fiber 50 parts, water reducing agent 15 parts, sodium gluconate 0.8 parts, defoaming agent 0.6 parts, and mixing water 165 parts by weight; Machine-made sand: quartzite broken, with fineness modulus 2.8 and stone powder content 1.7%, meeting the requirement of I type sand; Microsilica powder: silicon dioxide content 95.5%, specific surface area 25500 m 2 / kg; Defoaming agent: polyether type, PH 7.5, viscosity 2000 mPa.s.

[0064] The remaining raw materials and preparation process are the same as those of example 1.

[0065] Comparative example 1

[0066] The comparative example is different from example 1 in that 1300 parts of machine-made sand are replaced by "natural river sand 800 parts and corundum sand 300 parts"; The remaining raw materials and preparation process are the same as those of example 1.

[0067] Comparative example 2

[0068] The comparative example is different from example 1 in that "microbead 90 parts" is deleted; The remaining raw materials and preparation process are the same as those of example 1.

[0069] Comparative example 3

[0070] The comparative example is different from example 1 in that "defoaming agent 0.4 parts" is deleted; The remaining raw materials and preparation process are the same as those of Example 1.

[0071] Comparative Example 4

[0072] The present comparative example is compared with Example 1, the difference is that the “S95 grade slag powder” is used to replace the “S105 grade slag powder”; the remaining raw materials and preparation process are the same as those of Example 1.

[0073] Comparative Example 5

[0074] The present comparative example is compared with Example 1, the difference is that the “0.9 parts of sodium gluconate” is deleted; The remaining raw materials and preparation process are the same as those of Example 1.

[0075] Performance test

[0076] The performance tests of Examples 1-6 and Comparative Examples 1-5 are carried out, and the test standards are as follows: 1. Extension (initial / 1h): According to GB / T50080-2016 “Standard Test Methods for Performance of Ordinary Concrete Mixture”, the fluidity and workability retention ability of the prepared UHPC are tested; 2. Compressive strength (3d / 28d), flexural strength (3d / 28d): According to GB / T50081-2019 “Standard Test Methods for Physical and Mechanical Properties of Concrete”, the mechanical properties of hardened body are tested to reflect the formwork bearing capacity; The results are shown in Table 1: Table 1

[0077] As can be seen from Table 1, the initial extension of the examples is all ≥650mm, and the 1h extension is ≥620mm, which meets the requirements of “high fluidity and long workability” for precast formwork pouring; the 28d compressive strength is ≥124MPa, and the flexural strength is ≥18.9MPa, which far exceeds the requirements of precast concrete formwork on mechanical properties, proving that the workability and mechanical properties of the machine-made sand UHPC of the present application are coordinated and meet the standards, and can be adapted to mass production.

[0078] Comparative Example 1 uses "natural sand and corundum" to replace machine-made sand, although the mechanical properties are close to Example 1, but the raw material cost is high: the unit price of natural river sand is about 180 yuan / ton, corundum is about 800 yuan / ton, and basalt machine-made sand is only 80 yuan / ton. The aggregate cost of Comparative Example 1 is 3.2 times that of Example 1; and it is strongly dependent on resources. Comparative Example 2 lacks microbeads, and the expansion degree and compressive strength are reduced. This is because micron-sized microbeads can fill the small gaps between machine-made sand and cementitious materials, optimize the particle size distribution, and reduce the internal friction of the system. Comparative Example 3 lacks defoaming agent, and the 28d compressive strength decreases from 129MPa to 112MPa, and the flexural strength decreases from 19.7MPa to 16.8MPa. Machine-made sand particles are mostly angular, and air is easily entrained during mixing. Polyether defoaming agent can quickly break bubbles, reduce the air content of the system, and avoid strength defects caused by air bubbles.

[0079] Comparative Example 4 uses S95 slag powder to replace S105 grade, and the 28d compressive strength decreases from 129MPa to 118MPa (decrease of 8.5%). This is because S105 grade slag powder has higher activity (28d activity index ≥95%), which can synergistically react with microsilica (SiO2≥95%) to generate more hydrated calcium silicate gel, improving the density of the hardened body. Comparative Example 5 lacks sodium gluconate, and the 1h expansion degree decreases from 685mm to 500mm. This is because industrial-grade sodium gluconate can slow down the hydration rate of cement, reduce the hydration heat, and make the freshly mixed UHPC still have good fluidity within 1h. However, in Comparative Example 5, the mortar becomes thick and loses fluidity due to rapid hydration.

[0080] The above disclosure is only a few specific embodiments of the present application, but the embodiments of the present application are not limited to this. Any changes that can be thought of by those skilled in the art should fall within the scope of the present application.

Claims

1. A machine-made sand UHPC that can be used to produce precast concrete forms, characterized in that, The raw materials include cement 650-850 parts, slag powder 70-120 parts, microsilica powder 30-60 parts, microbead 80-140 parts, machine-made sand 1100-1400 parts, steel fiber 30-50 parts, water reducing agent 15-20 parts, sodium gluconate 0.8-1.5 parts, defoaming agent 0.3-0.6 parts, and mixing water 165-200 parts.

2. A machine-made sand UHPC that can be used to produce precast concrete formworks according to claim 1, characterized in that, The cement is one or a combination of Portland cement and ordinary Portland cement with a strength grade of 52.5 MPa; and the slag powder is S105 grade slag.

3. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The microsilica silicon dioxide content is not less than 95.0%, the specific surface area is not less than 25000 m 2 / kg.

4. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The microbead is micron-level high-fineness microbead with a particle size of 0.1-0.5 um, a 7d activity index of ≥90%, a 28d activity index of ≥110%, and a 56d activity index of ≥120%.

5. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The machine-made sand is broken from basalt or quartzite, has a fineness modulus of 2.5-3.2, a stone powder content of not more than 2.0%, and other indexes meeting the requirements of I-class sand.

6. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The steel fiber has a length of 13-20 mm, a diameter of 0.18-0.22 mm, and a tensile strength of not less than 2500 MPa.

7. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The water reducing agent is polycarboxylic high-performance water reducing agent with a water-reducing rate of not less than 30%; and the sodium gluconate is white crystalline powder with an industrial grade and a content of 98.0% and above.

8. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The defoaming agent is polyether defoaming agent with a pH value of 6.0-8.0 and a viscosity of 500-2000 mPa.s.

9. The machine-made sand UHPC for producing precast concrete form according to claim 1, wherein, The mixing water is tap water meeting the relevant requirements of JGJ63 "Water Standard for Concrete".

10. A method of manufacture, characterized by, A method for preparing machine-made sand UHPC for producing prefabricated concrete formworks, as claimed in any one of claims 1-9, comprises the following steps: Cement, slag powder, microsilica powder, microbead, machine-made sand, and sodium gluconate are added into a mixer, and after stirring for 1-3 min, steel fiber is slowly and evenly scattered into the mixer while continuing to stir to ensure uniform mixing of the steel fiber and the concrete; and then polycarboxylic water reducing agent, defoaming agent, and mixing water are added into the mixer and stirred uniformly to obtain the UHPC.

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