Machine-made sand anti-freezing concrete and preparation method thereof

Abstract

The invention relates to the technical field of concrete, in particular to machine-made sand anti-freezing concrete and a preparation method thereof.The machine-made sand anti-freezing concrete is prepared from, by weight, 650-750 parts of machine-made sand, 1100-1200 parts of coarse aggregate, 55-65 parts of silica fume, 45-60 parts of metakaolin, 85-100 parts of slag powder, 210-250 parts of cement and 4-10 parts of a water reducing agent and water. The use amount of water meets the requirement that the water-binder ratio is 0.30-0.38. The slag powder activator has the advantages that the slag powder activator is prepared according to a specific proportion, the activity of the slag powder in a low-temperature environment is improved, the hydration reaction is accelerated, more hydration products are generated, the aperture is refined, the porosity is reduced, especially harmful macropores are reduced, and the frost resistance of the machine-made sand concrete is effectively enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete, in particular to a machine-made sand anti-freezing concrete and a preparation method thereof. BACKGROUND

[0002] Natural sand has been widely used as fine aggregate in various projects for decades, but its large-scale mining has caused serious environmental damage. With the strict restriction of natural resource mining by the state, natural sand is increasingly scarce and its price is soaring, prompting the industry to turn its attention to machine-made sand. After years of development, machine-made sand has been proven to be able to replace natural sand, but its own defects are still prominent: high stone powder content, strong water absorption, easy to make concrete workability poor; if additional water is added to improve workability, segregation will occur. Poor gradation weakens the internal secondary skeleton strength of concrete; under the action of freeze-thaw cycle, machine-made sand particles are easy to peel off, reducing the durability of concrete, and continuously deteriorating in long-term service in cold regions.

[0003] The patent for application with patent publication number CN109455992A, publication date of 2019.03.12, and patent name of "a machine-made sand concrete and a preparation method thereof" proposes to obtain good workability, cohesiveness and strength by controlling the conventional proportioning of machine-made sand, crushed stone, cement, mineral admixture and water reducing agent, but its core improvement point is focused on the construction pumping performance and economy, and only simple screening is made on the aggregate gradation, no quantitative design is given on the stone powder content, fineness modulus and mineral admixture synergy mechanism, and no system optimization of frost resistance and durability is involved. The Tepo theory gradation, mineral admixture-activator synergy or interface densification measures are not introduced for the use requirements in cold regions, so there are still technical problems such as difficulty in releasing pore pressure, rapid expansion of secondary cracks and insufficient durability life under freeze-thaw cycle, and the present application is proposed to solve this problem.

[0004] However, subsequent studies have shown that if the particle shape and stone powder content of machine-made sand are not properly controlled, the concrete is easy to appear surface peeling and strength decay in salt freezing or water freezing cycle, especially when the stone powder content or MB value deviates from 7% to 10%, the anti-freezing performance decreases significantly. SUMMARY

[0005] Based on this, the machine-made sand anti-freezing concrete and the preparation method thereof are proposed, the machine-made sand with excellent gradation is prepared by the Tepo theory with n of 0.45 based on the close packing theory, which can obtain an aggregate skeleton with good continuity, high packing density and low porosity, can reduce the cement content and reduce the large pores that can be invaded by water and cause frost heaving damage.

[0006] To achieve the above purpose, the technical scheme created by the present application is as follows: a machine-made sand anti-freezing concrete is prepared from the following raw materials by weight: 650-750 parts of machine-made sand, 1100-1200 parts of coarse aggregate, 55-65 parts of silica fume, 45-60 parts of metakaolin, 85-100 parts of slag powder, 210-250 parts of cement, 4-10 parts of water reducing agent and water, the amount of water meets the water-binder ratio of 0.30-0.38; wherein the stone powder content in the machine-made sand is 8%-15%, the particle size range of the machine-made sand is 0.075 mm-4.75 mm, and the cumulative percentage of each particle size of the machine-made sand is calculated according to the Tybo formula: ; Pi represents the cumulative percentage of the machine-made sand with particle size d, D represents the maximum particle size of the machine-made sand, and n represents the Tybo formula coefficient.

[0007] Further, n=0.40-0.45.

[0008] Further, the machine-made sand includes six particle size intervals, which are 0.075 mm-0.15 mm, 0.15 mm-0.30 mm, 0.30 mm-0.60 mm, 0.60 mm-1.18 mm, 1.18 mm-2.36 mm and 2.36 mm-4.75 mm; and the fineness modulus of the machine-made sand is 2.6-3.5.

[0009] Further, the coarse aggregate is 5 mm-20 mm continuous gradation of gravel.

[0010] Further, the mass ratio of the silica fume, the metakaolin and the slag powder is 1.0-1.3:0.8-1.1:1.4-1.8.

[0011] Further, the slag powder is added with an activator, and the activator includes Na2SO4 with a concentration of 0.8% and triethanolamine with a concentration of 0.03%.

[0012] A preparation method of machine-made sand anti-frozen concrete, for preparing the machine-made sand anti-frozen concrete, comprising the following steps: S1: mechanically vibrating the machine-made sand at a preset frequency, removing the particles with particle size greater than 4.75 mm, and then performing secondary screening to control the stone powder content of the machine-made sand within a preset range.

[0013] S2: first, taking the Tybo formula coefficient n=0.45, calculating the cumulative percentage of each particle size interval of the machine-made sand according to the Tybo formula; then, determining the amount of each particle size interval of the machine-made sand according to the calculation result, so as to obtain the close-packed packing ratio of the machine-made sand.

[0014] S3: putting the machine-made sand with the close-packed packing ratio obtained in step S2, gravel, silica fume, metakaolin, slag powder, cement, water and water reducing agent into a mixer and stirring until uniform.

[0015] Further, step S2 comprises: S21: taking the coefficient n=0.45 of the Tybo formula, calculating the cumulative percentage of sieve residue of the manufactured sand in each particle size interval according to the Tybo formula, and the calculation formula is: ; Wherein, Pi represents the cumulative percentage of sieve residue of the manufactured sand with particle size d, and D represents the maximum particle size of the manufactured sand.

[0016] S22: The manufactured sand is physically sieved according to six particle size intervals, the theoretical mass ratio of the manufactured sand in each particle size interval is obtained according to the calculation result of S21, and the manufactured sand is mixed according to the proportion, and finally the manufactured sand with optimized gradation is obtained, and the fineness modulus is 2.6-3.5; The six particle size intervals of the manufactured sand are: 0.075mm-0.15mm, 0.15mm-0.30mm, 0.30mm-0.60mm, 0.60mm-1.18mm, 1.18mm-2.36mm and 2.36mm-4.75mm; S23: The manufactured sand of step S22 is mixed with other raw materials according to the following ratio: coarse aggregate 1100-1200 parts, manufactured sand 650-750 parts, cement 210-250 parts, silica fume 55-65 parts, metakaolin 45-60 parts, slag powder 85-100 parts, and water reducing agent 4-10 parts.

[0017] Further, step S3 comprises: S31: A slag powder activator is prepared with a concentration of 0.8% Na2SO4 and a concentration of 0.03% triethanolamine, and is synchronously put into a mixer with mineral admixtures composed of silica fume, metakaolin and slag powder, and is stirred for a first preset time to obtain mineral admixtures containing the activator.

[0018] S32: The manufactured sand is added and stirred with the mineral admixtures containing the activator for a second preset time, so that the activator uniformly wraps the slag powder, and the silica fume and metakaolin fill the voids of the manufactured sand.

[0019] S33: Cement, water and water reducing agent are added and stirred for a third preset time to form a uniform slurry.

[0020] S34: Coarse aggregate is added and stirred for a fourth preset time to obtain homogeneous manufactured sand frost-resistant concrete.

[0021] Further, when a single manufactured sand cannot meet the Tybo gradation requirement, two different gradations of manufactured sand are mixed according to the following formula: ; a+b=1; Wherein, Cumulative percent of sieve residue of two different manufactured sands; n a , n b Tebor coefficient of two different graded manufactured sands, respectively; a and b represent the proportion of two different graded manufactured sands, respectively.

[0022] The present invention can achieve the following beneficial effects: 1) Replacing river sand with manufactured sand reduces dependence on river sand, reduces overexploitation of river sand, reduces environmental pollution, realizes sustainable use of resources, and has good ecological and economic benefits.

[0023] 2) The concrete of the present invention shows good frost resistance in long-term freeze-thaw, which improves the durability of manufactured sand concrete in cold conditions and reduces maintenance costs caused by frost damage.

[0024] 3) The specific proportion of slag powder activator is configured to improve the activity of slag powder in low temperature environment and accelerate the hydration reaction, produce more hydration products, refine the pore size, reduce the porosity, especially the harmful macropores, and effectively enhance the frost resistance of manufactured sand concrete.

[0025] 4) The manufactured sand is screened by applying a fixed frequency of mechanical vibration to remove large-sized manufactured sand, ensuring that the maximum particle size of the manufactured sand meets the requirements, avoiding the influence of coarse particles on the continuity of the grading, and controlling the stone powder content of the manufactured sand in the range of 8% to 15% through secondary screening. Reducing the stone powder content directly improves the workability of the concrete and reduces the weak points of freeze-thaw cycles, thereby directly reducing the risk of freeze-thaw damage. The manufactured sand of different particle sizes obtained by screening provides raw materials for on-demand adjustment and optimization of grading, and is also a prerequisite for applying the Tebor theory.

[0026] 5) The manufactured sand and mineral admixtures are thoroughly mixed before adding water, and the fine mineral admixture particles are uniformly dispersed and wrapped on the surface of the manufactured sand particles in a dry state, avoiding the formation of large particle groups that are difficult to disperse when water is added later. Avoiding internal macropores and uneven areas caused by clumping of admixtures and insufficient hydration, thereby improving overall durability. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application and their description are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings: Fig. 1 is a flowchart of the manufactured sand frost-resistant concrete provided according to the embodiments of the present invention; Fig. 2 is a curve graph of the number of freeze-thaw cycles and the mass loss rate of the manufactured sand frost-resistant concrete according to the embodiments of the present invention; Fig. 3 is a graph of freeze-thaw cycle times and relative dynamic elastic modulus of the machine-made sand frost-resistant concrete according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not constitute a limitation on the present application.

[0029] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0030] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0031] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0032] The present application will be described in detail below with reference to the embodiments.

[0033] As shown in Figs. 1 to 3 The machine-made sand frost-resistant concrete provided by the embodiment of the present application is made of raw materials containing the following weight parts: 650 parts to 750 parts of machine-made sand, 1100 parts to 1200 parts of coarse aggregate, 55 parts to 65 parts of silica fume, 45 parts to 60 parts of metakaolin, 85 parts to 100 parts of slag powder, 210 parts to 250 parts of cement, 4 parts to 10 parts of water reducing agent and water, the amount of water meets the water-binder ratio of 0.30 to 0.38. Among them, the stone powder content in the machine-made sand is 8% to 15%, the particle size range of the machine-made sand is 0.075mm to 4.75mm, and the cumulative percentage of each particle size of the machine-made sand is calculated according to the Tybo formula: ; Among them, Pi represents the Tybo formula, which represents the percentage of machine-made sand with particle size d passing through here, D represents the maximum particle size of the machine-made sand, and n represents the Tybo formula coefficient, n = 0.45.

[0034] In this embodiment, 1 part is 1 The water reducing agent is a polycarboxylic acid water reducing agent.

[0035] It should be noted that the silica fume, metakaolin and slag powder constitute the mineral admixture. The amount of water in the mix proportion is determined according to the water-binder ratio. The water-binder ratio refers to the mass ratio of water to cementitious materials (the sum of cement and mineral admixtures).

[0036] Further, the machine-made sand includes six particle size intervals, which are 0.075mm to 0.15mm, 0.15mm to 0.30mm, 0.30mm to 0.60mm, 0.60mm to 1.18mm, 1.18mm to 2.36mm and 2.36mm to 4.75mm, and the fineness modulus of the machine-made sand is 2.6 to 3.5.

[0037] Further, the coarse aggregate is 5mm to 20mm continuous gradation of gravel.

[0038] Further, the mass ratio of silica fume, metakaolin and slag powder is 1.0 to 1.3:0.8 to 1.1:1.4 to 1.8.

[0039] Further, the slag powder is added with an activator, and the activator includes Na2SO4 with a concentration of 0.8% and triethanolamine with a concentration of 0.03%. The dosage of Na2SO4 is 2% to 5% of the mass of the slag powder. The dosage of triethanolamine is 0.02% to 0.05% of the total mass of silica fume, metakaolin, slag powder and cement.

[0040] The slag powder activator is configured in a specific proportion to improve the activity of the slag powder in a low temperature environment and accelerate the hydration reaction, generate more hydration products, refine the pore size, reduce the porosity, especially the harmful large pores, and effectively enhance the frost resistance of machine-made sand concrete.

[0041] A preparation method of a machine-made sand anti-freezing concrete comprises the following steps: S1: mechanically vibrating the machine-made sand at a preset frequency (25 Hz), removing the particles with a particle size greater than 4.75 mm, and then performing secondary screening through a 200-400 mesh screen to control the stone powder content of the machine-made sand in a range of 8%-15%.

[0042] The machine-made sand is screened by applying mechanical vibration at a fixed frequency to remove the particles with a particle size greater than 4.75 mm, so as to ensure that the maximum particle size meets the requirements, thereby avoiding the influence of coarse particles on the gradation continuity. Then, secondary screening is performed through a 200-400 mesh screen to control the stone powder content in a range of 8%-15%. The process directly improves the workability of the concrete by reducing the stone powder content, and reduces the risk of freeze-thaw damage by reducing the weak points of freeze-thaw cycles. In addition, the machine-made sand of different particle sizes obtained by screening provides raw materials for on-demand adjustment and optimization of the gradation, and is also a prerequisite for applying the Terzaghi theory.

[0043] S2: First, the coefficient n of the Terzaghi formula is taken as 0.45, and the cumulative percentage of the machine-made sand in each particle size interval is calculated according to the Terzaghi formula; then, the amount of the machine-made sand in each particle size interval is determined according to the calculation result, and finally the compacted packing ratio of the machine-made sand is obtained Specifically, the coefficient n of the Terzaghi formula is taken as 0.45, and the proportion of each particle size sand is determined with n being 0.3, 0.35, 0.4, 0.45, 0.5 (the Terzaghi theory considers that a better density is obtained within this range), and the remaining factors are kept the same. It is found that when n is 0.45, the mass loss and elastic modulus of the concrete after freeze-thaw are relatively optimal, so n is taken as 0.45. The cumulative percentage of the machine-made sand in each particle size interval is calculated according to the Terzaghi formula, and the calculation formula is: ; Wherein, Pi represents the Terzaghi formula, which here represents the passing percentage of the machine-made sand with a particle size of d, and D represents the maximum particle size of the machine-made sand.

[0044] It should be noted that the coefficient n of the Terzaghi formula is 0.45 when the machine-made sand is prepared according to the above formula. In view of the fact that the fine aggregate of the machine-made sand is prone to peeling after freeze-thaw and affects the anti-freezing performance, the value of n can be increased. This adjustment aims to optimize the gradation of the machine-made sand, so that it forms a more compact bonding structure with the mineral admixture (composed of silica fume, metakaolin and slag powder), thereby enhancing the anti-peeling ability. It should be noted that the value of n is not strictly limited in the present application, and it can be adjusted adaptively according to the target anti-freezing grade.

[0045] The machine-made sand with excellent gradation prepared with n=0.45 has the characteristics of good continuity, high bulk density and low void ratio. This can reduce the cement content and reduce the large pores that are prone to water intrusion and cause frost heaving damage.

[0046] S22: The manufactured sand is physically classified in six particle size intervals, and the theoretical mass ratio of the manufactured sand in each particle size interval is obtained according to the calculation result of S21, and the manufactured sand with optimized gradation is finally obtained by mixing in the proportion.

[0047] The six particle size intervals of the manufactured sand are 0.075mm-0.15mm, 0.15mm-0.30mm, 0.30mm-0.60mm, 0.60mm-1.18mm, 1.18mm-2.36mm and 2.36mm-4.75mm.

[0048] Table 1: Screened gradation table of manufactured sand (after optimization according to Tybo theory)

[0049] The cumulative screen residue percentage in Table 1 is obtained by Tybo formula. The classified screen residue percentage is obtained by subtracting the cumulative screen residue percentage of the adjacent two particle size intervals. The mass ratio (i.e. percentage) of the manufactured sand in each particle size interval is determined by the classified screen residue percentage.

[0050] The freeze-thaw cycle test shows (see Tables 2 and 3) that when the maximum particle size of the optimized manufactured sand is 4.75mm and n=0.45, the secondary skeleton porosity formed by the coarse aggregate and the mineral admixture (silica fume, metakaolin and slag powder) is the lowest, and the frost resistance grade can reach F300 or above.

[0051] Maximum particle size limit: 4.75mm ensures that the manufactured sand and the coarse aggregate form a continuous gradation, avoiding particle size faults. By substituting n=0.45 into the cumulative screen residue percentage formula and taking d as 2.36, 1.18, 0.6, 0.3, 0.15 and 0.075 in turn, the cumulative screen residue percentage is obtained, and then the classified screen residue percentage of each particle size interval, i.e. the proportion of the manufactured sand in each particle size interval, is obtained according to the cumulative screen residue percentage, and the manufactured sand with optimized gradation is finally obtained by mixing in the proportion. The fineness modulus of the manufactured sand is 2.6-3.5. The value of n can be appropriately increased to improve the frost resistance of the manufactured sand concrete Table 2: Mass loss rate (%) in freeze-thaw cycle

[0052] Table 3: Relative dynamic elastic modulus (%) in freeze-thaw cycle

[0053] As can be seen from the above experimental examples, the manufactured sand concrete prepared by the present invention has good anti-freeze performance (measured by mass loss rate and relative dynamic modulus of elasticity). In particular, it was not damaged after 300 freeze-thaw cycles, and there is still a relatively long freeze-thaw margin before damage.

[0054] If it is difficult to formulate a gradation of manufactured sand that conforms to the Teibo theory based on a single type of manufactured sand, then two types of manufactured sand can be combined in a two-way coupling manner to form a good gradation of manufactured sand.

[0055] Two types of manufactured sand with different gradations are mixed according to the following formula: ; a+b=1; in, This represents the cumulative percentage of residue on the sieve for two different types of manufactured sand; n a n b These are the Thabo coefficients for two different gradations of manufactured sand; a and b represent the proportions of the two different gradations of manufactured sand, respectively. Adjust the gradation ratios of each interval according to the above steps to obtain well-graded manufactured sand and enhance the freeze-thaw resistance of manufactured sand concrete.

[0056] First, determine the mixing of two types of manufactured sand with different gradations. The target gradation value was then calculated, and the gradation values ​​of the two types of manufactured sand in each particle size range were calculated separately. Pi The value represents the particle size distribution of the two types of manufactured sand within each particle size range. Pi Substitute the values ​​respectively In the formula, the values ​​of a and b for each particle size range of the two types of manufactured sand can be obtained based on a + b = 1. Finally, the weighted average of the a and b values ​​for all particle size ranges is taken as the final a and b values.

[0057] It should be noted that the two types of manufactured sand used can refer to two types of manufactured sand with different particle size ranges, or two types of manufactured sand with different particle sizes.

[0058] S23: Mix the manufactured sand from step S22 with other raw materials in the following proportions: 1100-1200 parts coarse aggregate, 650-750 parts manufactured sand, 210-250 parts cement, 55-65 parts silica fume, 45-60 parts metakaolin, 85-100 parts slag powder, and 4-10 parts water-reducing agent.

[0059] To improve the freeze-thaw resistance of concrete, high-performance manufactured sand concrete was prepared by controlling the proportion of metakaolin, silica fume and slag powder, utilizing their synergistic effect, and combining the Thabo theory to improve the gradation of manufactured sand.

[0060] The three mineral admixtures are all high-activity pozzolanic materials, and their combined use can generate more C-S-H gel, effectively refine the pore structure and improve the interface transition zone (ITZ) structure, making it more compact. In addition, due to the different particle size distributions of the three, a step filling effect can be formed in the slurry, which not only optimizes the hydration process, but also avoids the negative effects that may be caused by excessive use of a single admixture.

[0061] At the same time, the mechanism sand tight packing grading realized by the theory of Taylor provides a stable macroscopic skeleton foundation for the micro-filling and strengthening effect of mineral admixtures in the slurry and ITZ.

[0062] Finally, a full range of multi-level cooperation is achieved from the optimization of aggregate grading on a macro scale to the enhancement of pore and ITZ structure on a micro scale, which significantly optimizes the pore structure of concrete, thereby making it have strong freeze-thaw resistance.

[0063] S3: Put the tightly packed and graded mechanism sand obtained in step S2, gravel, silica fume, metakaolin, slag powder, cement, water and water reducing agent into a mixer and stir until uniform.

[0064] Specifically, S31: Prepare a slag powder activator with a concentration of 0.8% Na2SO4 and a concentration of 0.03% triethanolamine, and simultaneously put the mineral admixture composed of silica fume, metakaolin and slag powder into the mixer, and stir for 10-15s (first preset time) to obtain a mineral admixture containing an activator.

[0065] The mechanism sand and the mineral admixture are thoroughly mixed before adding water. In a dry state, the fine mineral admixture particles are uniformly dispersed and wrapped around the surface of the mechanism sand particles, avoiding the formation of large particle groups that are difficult to disperse when water is added later. This avoids the formation of large internal pores and uneven areas caused by the agglomeration of admixtures and insufficient hydration, thereby improving the overall durability.

[0066] S32: Add the mechanism sand and stir the mineral admixture containing the activator for 15-20s (second preset time) to uniformly coat the slag powder with the activator, while the silica fume and metakaolin fill the gaps in the mechanism sand; S33: Add cement, water and water reducing agent and stir for 20-30s (third preset time) to form a uniform slurry; S34: Add coarse aggregate and stir for 3min (fourth preset time) to obtain a homogeneous mechanism sand freeze-resistant concrete.

[0067] It should be noted that the stirring time of steps S31 to S34 can be adjusted according to the actual stirring efficiency to ensure uniform stirring.

[0068] The performance of the concrete prepared by the method is verified through several specific examples.

[0069] Example One: C50 machine-made sand anti-freezing concrete for highway bridge deck 1150 of 5mm-20mm continuous graded gravel 700 of machine-made sand (the stone powder content is 10%, and the fineness modulus is 2.9), 230 of cement 60 of silica fume 50 of metakaolin 90 of slag powder When preparing the activator, 0.8% of Na2SO4 and 0.03% of TEA (triethanolamine) are added according to the mass of the slag powder. The dosage of the polycarboxylic acid water reducing agent is 8 , and the water-binder ratio is 0.34. After the machine-made sand is sieved by a 25Hz vibration sieve, the coefficient n=0.45 of the Tybo formula is taken, and the machine-made sand is divided into six particle size intervals. The deviation between the measured value and the target value of the cumulative percentage of each sieve size is not more than 3%.

[0070] The concrete is obtained by stirring according to steps S31-S34, and the concrete is poured into a mold for 24 hours, and then cured for 28 days in an environment of 20°C and a relative humidity of 95%.

[0071] According to GB / T50082-2009, the mass loss is 2.1% after 300 freeze-thaw cycles at-18°C +4°C, the relative dynamic elastic modulus retention rate is 96.2%, and the compressive strength is 57.4MPa, which meets the use requirements.

[0072] Example Two: C40 machine-made sand anti-freezing concrete (double sand coupling) for airport runway in cold regions When the single machine-made sand cannot meet the grading of n=0.45, a second machine-made sand (fineness modulus 2.4) is introduced, the coupling coefficients of the two are a=0.65 and b=0.35, the proportion of each particle size interval is recalculated according to the formula of mixing two different graded machine-made sands, the comprehensive fineness modulus is adjusted to 2.8, and the stone powder content is 12%. The remaining materials are: 1120 of gravel 220 of cement 55 of silica fume 55 of metakaolin 95 of slag powder 7 of water reducing agent , and the water-binder ratio is 0.36.

[0073] The concrete is obtained by stirring according to steps S31-S34, and the concrete is poured into a mold for 24 hours, and then cured for 28 days in an environment of 20°C and a relative humidity of 95%. After 200 freeze-thaw cycles at +5°C, the mass loss was 1.8%, and the dynamic elastic modulus retention rate was 95.7%. The 90-day flexural strength of the core sample was 6.8 MPa, and there was no cracking or peeling on the runway surface, which verified the improvement effect of the double-sand coupling grading method on the frost resistance.

[0074] Example Three: C30 Machine-made Sand Frost-resistant Concrete for Hydraulic Structures in Extremely Cold Regions For an environment of -40°C, the coefficient n of the Taylor formula is 0.42, more voids are left to facilitate mineral admixture filling, and the interface density is improved. The mix proportion is: broken stone 1100 , machine-made sand 680 , cement 210 , silica fume 65 , metakaolin 60 , slag powder 88 , water reducing agent 6 , and water-binder ratio 0.38.

[0075] It should be noted that the coefficient n of the Taylor formula has been adjusted downward in this embodiment according to the target frost resistance grade in extremely cold regions.

[0076] 100mm×100mm×400mm concrete specimens were prepared, and after 300 freeze-thaw cycles at -40°C +5°C, the mass loss was 2.6%, and the dynamic elastic modulus retention rate was 95.1%; at the same time, the water seepage height was reduced by 25% compared with ordinary machine-made sand concrete, which proved the adaptability of the n value adjustable strategy to extremely cold environments.

[0077] Example Four: C60 High-strength Frost-resistant Concrete for Municipal Precast Segments Broken stone 1180 , machine-made sand 720 (the stone powder content is 9%, and the fineness modulus is 3.1), 52.5R cement (early strength portland cement) 250 , silica fume 62 , metakaolin 48 , slag powder 100 , water reducing agent 10 , and water-binder ratio 0.30. To meet the high fluidity and early strength, the dry mixing time of silica fume and metakaolin was additionally extended to 30s during the mixing stage.

[0078] After 12h steam curing of the segment, the 1-day compressive strength was 32.5MPa, and the 28-day compressive strength was 73.6MPa. According to JC / T941-2005, 50 freeze-thaw cycles in 25% salt solution resulted in a mass loss of 0.4% and a dynamic elastic modulus retention rate of 98%. This high-strength example verified the synergistic effect of mineral admixture proportioning design on the frost resistance-salt frost resistance of high-grade concrete.

[0079] Example five: Mechanism sand grading process verification According to the Taylor formula, the mechanism sand is divided into six grades and the target ratio is reconstituted, the process adopts online laser particle size analysis correction, and the particle size error of each grade is less than or equal to 1%. The fineness modulus of the mechanism sand is 2.75, and the grading curve is well matched with the theoretical curve.

[0080] The mechanism sand is replaced by the original natural sand in the precast beam field, and under the condition that other mix proportions are not changed, after 28 days of maintenance, the compressive strength of the concrete is increased from 46.2MPa to 49.8MPa. After-18℃ +4℃ freeze-thaw 300 times, the mass loss is reduced from 4.5% to 2.7%, which fully illustrates the universality and replicability of the grading method for improving frost resistance and durability.

[0081] The application replaces river sand with mechanism sand, reduces the dependence on river sand, reduces the overexploitation of river sand, reduces environmental pollution, realizes sustainable use of resources, and has good ecological and economic benefits.

[0082] The application shows good frost resistance in long-term freeze-thaw, improves the durability of mechanism sand concrete in cold conditions, and reduces the maintenance cost caused by frost damage.

[0083] The application reoptimizes the synergistic ratio of mineral admixtures and modifiers (activators) in mechanism sand concrete, and finely controls the grading and pore structure of mechanism sand under the guidance of Taylor theory, which significantly improves the frost resistance and overall durability of concrete in-40℃ long-term low temperature cycle. Compared with traditional natural sand concrete, the freeze-thaw spalling is reduced by more than 30%, and the life cycle of bridge, road and other cold region concrete components is expected to be extended by at least five years, thereby reducing the maintenance frequency and comprehensive maintenance cost.

[0084] The application provides a reliable path for the large-scale application of mechanism sand in high-standard projects such as heavy traffic, cold regions and water conservancy, and has significant engineering promotion and commercial value.

[0085] More importantly, the application successfully breaks through the long-standing technical prejudice in the industry that "mechanism sand concrete has inherent frost resistance": after multiple freeze-thaw cycles, the dynamic elastic modulus attenuation is less than 5% compared with natural sand concrete, which fully proves that mechanism sand can completely replace natural sand for high durability concrete in cold regions; This not only alleviates the dilemma of the increasingly exhausted high-quality natural sand resources, but also opens up a new incremental market for the green sand and stone industry chain.

[0086] The above detailed description does not limit the scope of the application. Various modifications, combinations, sub-combinations and alternatives can be made to the detailed description. Any modification, equivalent replacement and improvement etc. made within the spirit and principle of the application shall be included in the scope of the application.

Claims

1. A frost-resistant concrete of machine-made sand, characterized in that, The mechanism sand anti-frozen concrete is made of raw materials including the following weight parts: 650-750 parts of mechanism sand, 1100-1200 parts of coarse aggregate, 55-65 parts of silica fume, 45-60 parts of metakaolin, 85-100 parts of slag powder, 210-250 parts of cement, 4-10 parts of water reducing agent and water, and the water amount satisfies the water-binder ratio of 0.30-0.38; The stone powder content in the mechanism sand is 8-15%, the particle size range of the mechanism sand is 0.075-4.75 mm, and the cumulative percentage of each particle size of the mechanism sand is calculated according to the Tybo formula as follows: ； Pi represents the cumulative percentage of the mechanism sand with the particle size d, D represents the maximum particle size of the mechanism sand, and n represents the Tybo formula coefficient.

2. The frost-resistant concrete of manufactured sand according to claim 1, characterized in that, n=0.40～0.45。 3. The frost-resistant concrete of manufactured sand according to claim 1, characterized in that, The mechanism sand includes six particle size intervals, i.e., 0.075-0.15 mm, 0.15-0.3 mm, 0.30-0.60 mm, 0.60-1.18 mm, 1.18-2.36 mm and 2.3-4.75 mm, and the fineness modulus of the mechanism sand is 2.6-3.

5.

4. The frost-resistant concrete of manufactured sand according to claim 1, characterized in that, The coarse aggregate is 5-20 mm continuous graded gravel.

5. The frost-resistant concrete of manufactured sand according to claim 1, characterized in that, The mass ratio of the silica fume, the metakaolin and the slag powder is 1-1.3:0.8-1.1:1.4-1.

8.

6. The frost-resistant concrete of manufactured sand according to claim 1, characterized in that, The slag powder is added with an activator, and the activator includes Na2SO4 with a concentration of 0.8% and triethanolamine with a concentration of 0.03%.

7. A method for producing a frost-resistant concrete of machine-made sand, for producing the frost-resistant concrete of machine-made sand according to any one of claims 1 to 6, characterized in that, The method includes the following steps: S1: mechanically vibrating the mechanism sand at a preset frequency, removing the particles with a particle size greater than 4.75 mm, and then performing secondary screening to control the stone powder content of the mechanism sand within a preset range; S2: first, taking the Tybo formula coefficient n=0.45, calculating the cumulative percentage of each particle size interval of the mechanism sand according to the Tybo formula; then, determining the amount of each particle size interval of the mechanism sand according to the calculation result, so as to obtain the close-packed packing ratio of the mechanism sand; S3: putting the mechanism sand with the close-packed packing ratio obtained in step S2, the gravel, the silica fume, the metakaolin, the slag powder, the cement, the water and the water reducing agent into a mixer and stirring until uniform.

8. The method of producing frost-resistant concrete from manufactured sand according to claim 7, characterized in that, Step S2 includes: S21: taking the Tybo formula coefficient n=0.45, calculating the cumulative percentage of each particle size interval of the mechanism sand according to the Tybo formula, and the calculation formula is as follows: ； wherein Pi represents the cumulative percentage of the mechanism sand with the particle size d, and D represents the maximum particle size of the mechanism sand; S22: physically screening the mechanism sand according to the six particle size intervals, obtaining the theoretical mass ratio of each particle size interval of the mechanism sand according to the calculation result of S21, and mixing according to the ratio, so as to finally obtain the mechanism sand with optimized gradation, and the fineness modulus of the mechanism sand is 2.6-3.5; The six particle size intervals of the mechanism sand are as follows: 0.075-0.15 mm, 0.15-0.30 mm, 0.30-0.60 mm, 0.60-1.18 mm, 1.18-2.36 mm and 2.36-4.75 mm. S23: The manufactured sand of step S22 is mixed with other raw materials in the following proportions: coarse aggregate 1100-1200 parts, manufactured sand 650-750 parts, cement 210-250 parts, silica fume 55-65 parts, metakaolin 45-60 parts, slag powder 85-100 parts, and water reducing agent 4-10 parts.

9. The method of producing frost-resistant concrete from manufactured sand according to claim 7, characterized in that, Step S3 comprises: S31: A slag powder activator is prepared with a concentration of 0.8% Na2SO4 and a concentration of 0.03% triethanolamine, and is simultaneously put into a mixer with mineral admixtures composed of silica fume, metakaolin and slag powder, and is stirred for a first preset time to obtain mineral admixtures containing the activator; S32: The manufactured sand is added and stirred with the mineral admixtures containing the activator for a second preset time, so that the activator uniformly coats the slag powder, and the silica fume and metakaolin fill the voids of the manufactured sand; S33: Cement, water and water reducing agent are added and stirred for a third preset time to form a uniform slurry; S34: Coarse aggregate is added and stirred for a fourth preset time to obtain homogeneous manufactured sand frost-resistant concrete.

10. The method of producing frost-resistant concrete from manufactured sand according to claim 7, characterized in that, When a single manufactured sand cannot meet the requirements of the Tebo grading, two different gradings of manufactured sand are mixed according to the following formula: ； a+b=1; wherein, represents the cumulative percentage of sieve residue of two different manufactured sands; n a , n b are the Taylor coefficients of two different manufactured sands, respectively; a and b represent the proportions of two different manufactured sands, respectively.

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