Anti-crack mass concrete and preparation method thereof

Abstract

The invention relates to the technical field of building materials, in particular to anti-crack mass concrete and a preparation method thereof, and the concrete is prepared from a gelling system, composite aggregate, a gradient functional additive and water according to a specific ratio. The preparation method is achieved through premixing, gradient stirring and gradient temperature control curing, the three-stage expansion effect of the compound expanding agent is utilized to be matched with the concrete shrinkage process, the hydration heat inhibitor is combined for reducing the temperature peak, basalt fiber is used for reinforcing, and the cracking risk is quantitatively evaluated, so that the 28-day restrained expansion rate of the concrete reaches 0.012% or above, the cracking risk coefficient is smaller than or equal to 0.7, and the concrete has the good crack resistance. The hydration heat peak value is reduced to 48 DEG C or below, and the cement is suitable for engineering of ultra-long structures, large-volume side walls and the like, has no harmful cracks within one year or above, has crack resistance and mechanical properties, and is wide in application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, and in particular to an anti-cracking mass concrete and a preparation method thereof. BACKGROUND

[0002] A large amount of heat released in the hydration process of mass concrete can cause a sharp rise in internal temperature, while the surface heat dissipation is faster to form a significant temperature difference, resulting in temperature stress and cracking. At the same time, the volume shrinkage in the hardening process of concrete further aggravates the risk of cracking under the constraint condition. In the prior art, the anti-cracking measures mainly focus on single material modification or process optimization: Chinese patent 2019106841554 discloses an anti-freezing and anti-cracking concrete, which reduces the hydration heat by adding vitrified microbeads, rubber powder and other lightweight aggregates, but does not solve the problem of early temperature stress concentration; The preparation method of a kind of anti-permeation and anti-cracking mass concrete of Zhongjian Shangtuo adopts modified blast furnace slag powder and expanded perlite to work together, but the action period of its expansion agent is not matched with the shrinkage process of concrete; Chinese patent CN201711096949.6 uses nanomaterials to reduce the shrinkage rate, but does not involve temperature stress regulation; and the hydration heat regulation type calcium-magnesium composite expansion agent can compensate for the shrinkage, but lacks the synergistic design of the fiber reinforced system.

[0003] The main defects of the prior art include: (1) the expansion component is not synchronized with the shrinkage process, and the early expansion is insufficient or the late expansion is excessive; (2) a single temperature control measure is difficult to adapt to the complex temperature field distribution of mass concrete; (3) the fiber and the matrix interface bonding force is insufficient, and cannot effectively transfer stress.

[0004] Therefore, according to the related technology in the above, it is urgent to develop an anti-cracking mass concrete and a preparation method thereof. SUMMARY

[0005] Therefore, according to the related technology in the above, it is urgent to develop an anti-cracking mass concrete and a preparation method thereof.

[0006] Based on the above purpose, the present application provides an anti-cracking mass concrete and a preparation method thereof.

[0007] An anti-cracking mass concrete, comprising the following mass parts of raw materials: a cementitious system 400-500 parts, a composite aggregate 1600-1800 parts, a gradient functional additive 60-80 parts and water 140-160 parts; The cementitious system includes ordinary portland cement, S105 mineral powder and fly ash; The composite aggregate includes gravel and river sand; The gradient functional additives include an expansive agent, a hydration heat inhibitor, a fiber, a water reducing agent, a plasticizing agent, and a moisture control component.

[0008] Preferably, the mass ratio of ordinary Portland cement, S105 mineral powder, and fly ash in the cementitious system is 300-350:80-120:80-100.

[0009] The cementitious system is used to provide the basic strength and structural framework of the concrete, the hydration heat peak is reduced (by 0%-25% compared with a pure cement system) through the addition of mineral powder and fly ash, and the interface structure is optimized through the micro aggregate effect of the mineral admixture. Action: The active components of S105 powder can react with the cement hydration products to generate additional-S-H glue, thereby improving the late strength; the glass bead form of fly ash improves the fluidity of the concrete and reduces the water consumption per unit.

[0010] Preferably, the mass ratio of gravel and river sand in the composite aggregate is 1000-1100:600-700. The gravel is continuously graded gravel with a particle size of 5-25 nm, the mass ratio of gravel with a particle size of 5-10 mm to gravel with a particle size of 10-25 mm is 400:600, and the river sand is machine-made sand with a fineness modulus of 2.6-2.8, the stone powder content of the machine-made sand is 5.0%-5.5%, and the MB value is ≤0.35.

[0011] The composite aggregate realizes a skeleton dense structure through the 4:6 grading design of 5-10 mm and 10-25 mm gravel, and the stone powder (5.0%-5.5%) of the machine-made sand fills the micro pores. Action: Reduce the amount of cementitious material under the condition that the aggregate void ratio is reduced to 22%; the machine-made sand with an MB value of ≤0.35 avoids the risk of alkali-aggregate reaction and improves the volume stability.

[0012] Preferably, the mass ratio of the expansive agent, the hydration heat inhibitor, the fiber, the water reducing agent, the superplasticizer, and the moisture control component in the gradient functional additive is 25-30:4-6:10-15:8-10:5-8:3-5.

[0013] Preferably, the expansive agent is a calcium oxide-calcium sulphoaluminate type II expansive agent and a nano calcium carbonate modified calcium-magnesium composite expansive agent compounded at a mass ratio of 1:1, the hydration heat inhibitor is a liquid preparation containing phosphate ester compounds, the fiber is basalt fiber, the water reducing agent is a polycarboxylic acid water reducing agent with a water reducing rate of 31.5%, the superplasticizer is a slump retaining type superplasticizer, and the moisture control component is a porous carbon moisture control component.

[0014] Preferably, the nano calcium carbonate modified calcium-magnesium composite expansion agent is prepared from the following raw materials in mass percentage: low-activity magnesium oxide 35%-40%, ion-doped modified calcium oxide-calcium aluminate clinker 45%-50%, nano calcium carbonate 5%-8%, and starch derivative hydration heat regulating component 2%-3%. The nano calcium carbonate has an average particle size of 50-100 nm.

[0015] Preferably, the basalt fiber has a length of 12-18 mm and a diameter of 13-20 μm, and the content accounts for 2.5%-3.5% of the total amount of the cementitious system. The interface transition zone with the concrete matrix is modified by a silane coupling agent.

[0016] The calcium oxide-calcium aluminate expansion agent in the expansion agent provides early expansion (3-7 d) to compensate for temperature shrinkage, and the nano calcium carbonate modified calcium-magnesium composite expansion agent realizes sustained expansion in the middle and late stages (14-28 d) to offset dry shrinkage. Effect: 1:1 compounding makes the expansion rate at 28 d reach 0.012%, solving the defects of "excessive early expansion and insufficient late expansion" of single expansion agent.

[0017] The hydration heat inhibitor is adsorbed on the surface of the cement particles to delay the hydration of tricalcium silicate and reduce the 3d hydration heat by more than 22%. Effect: The hydration heat peak is reduced from 55℃ to below 48℃, reducing early cracking caused by temperature stress.

[0018] The basalt fiber forms a three-dimensional spatial network to transfer stress through the interface transition zone (modified by a silane coupling agent) and inhibit the expansion of microcracks. Effect: The splitting tensile strength of the concrete is increased by 5%-20%, and the stress intensity factor at the crack tip is reduced by 0%.

[0019] The polycarboxylic acid water reducer and the polycarboxylic acid water reducer in the slump retaining type superplasticizer have a high water-reducing rate of 31.5%, reducing the water consumption, and the slump retaining agent maintains the workability for 20 min. Effect: The water-binder ratio is reduced to 0.38-0.40, reducing the porosity; avoiding construction defects caused by loss of slump during pouring.

[0020] The porous carbon humidity control component adjusts the internal humidity of the concrete by adsorbing and releasing water through the microporous structure. Effect: The relative humidity during curing is maintained at more than 90%, promoting the full reaction of the expansion agent and the cement hydration.

[0021] A preparation method of anti-cracking mass concrete, comprising the following steps: Step S1. Preparation of expanding agent: low-activity magnesium oxide, modified calcium oxide-calcium sulfoaluminate clinker, nano calcium carbonate are put into a ball mill in proportion, 10%-15% of water is added, ball milling is carried out at a speed of 300 r / min for 30-40 min, then a starch derivative is added and ball milling is continued for 10 min, to obtain a nano calcium carbonate modified calcium-magnesium composite expanding agent, the calcium oxide-calcium sulfoaluminate type II expanding agent is mixed with the nano calcium carbonate modified calcium-magnesium composite expanding agent at a mass ratio of 1:1, to obtain the expanding agent; Step S2. Premixing: the components of the cementitious system and the composite aggregate are put into a mixer, dry mixing is carried out for 2-3 min until uniform, to form a mixed base material; Step S3. Gradient mixing: 70% of water is mixed with polycarboxylic acid water reducer and then added to the mixed base material, stirring is carried out at a speed of 500 r / min for 2 min, basalt fibers, slump retention type superplasticizer and the remaining 30% of water are added, stirring is carried out at a speed of 800 r / min for 3-4 min, finally the expanding agent and the porous carbon moisture control component are added, stirring is carried out at a speed of 600 r / min for 2 min, to obtain a concrete mixture; Step S4. Gradient temperature control curing: a steel formwork is used, continuous layering is carried out, the layering height is ≤600 mm, the next layer is poured before the previous layer is initially cured, a temperature sensor is pre-embedded for monitoring 0-12 h after pouring, the surface temperature is maintained at 33-37℃, the core temperature does not exceed 60℃; 12-30 d after pouring, a spraying device is used for moisture curing, the environmental humidity is ≥90%, the temperature is reduced in steps in the first 72 h, the temperature is reduced by ≤5℃ every 12 h, to ensure that the internal and external temperature difference is ≤25℃.

[0022] Preferably, the cracking performance is evaluated by a cracking risk coefficient k in step S4, , wherein is the tensile stress at t, is the splitting tensile strength at t, and k ≤ 0.7 is controlled.

[0023] Preferably, the formula for calculating the tensile stress is , wherein is the linear expansion coefficient, is the elastic modulus at t, is the temperature rise temperature difference, is the shrinkage equivalent temperature difference, is the constraint coefficient, is the relaxation coefficient, is the Poisson's ratio.

[0024] The beneficial effects of the present application are: The present application provides an anti-cracking mass concrete and a preparation method thereof, the present application has the following effects through the synergistic design of the material system and the innovative optimization of the preparation process: Significantly improve the anti-cracking performance, solve the problem of multi-stage shrinkage: using calcium oxide calcium aluminate type expansive agent and nano calcium carbonate modified calcium magnesium composite expansive agent 1:1 compound, form "early micro expansion-mid stable-late continuous compensation" three-stage expansion effect, precise match the whole cycle of concrete temperature shrinkage, autogenous shrinkage and drying shrinkage. Cooperate with basalt fiber three-dimensional reinforced network (interface modified by silane coupling agent), can effectively inhibit the micro crack initiation and expansion, make the 28 days limited expansion rate increase to more than 0.012%, the cracking risk coefficient k is stably controlled at 0.7, the anti-cracking efficiency is improved by 40% compared with the traditional single expansive agent scheme; Effectively reduce the hydration heat hazard, control temperature stress: the hydration heat inhibitor containing phosphate compound can reduce the hydration heat of cement by more than 22%, combined with the "dilution effect" of S105 powder and fly ash, the peak value of concrete hydration heat is reduced from 55 DEG C to less than 48 DEG C; Cooperate with gradient temperature control curing (internal and external temperature difference ≤25 DEG C), the temperature stress is reduced by 50%, completely solve the problem of through crack caused by large temperature difference of mass concrete; Optimize material interface and structure density, improve comprehensive performance: the composite aggregate is designed by 4:6 of 5-10mm and 10-25mm gravel, combined with the fine modulus 2.6-2.8 mechanism sand (stone powder content 5.0%-5.5%), form skeleton dense structure, the void ratio is reduced to 22%; Polycarboxylic acid water reducing agent (water reducing rate 31.5%) reduces the water-cement ratio to 0.38-0.40, cooperates with the humidity adjusting effect of porous carbon humidity control component, makes the 28 compressive strength of concrete increase by 15%-20%, at the same time improves the impermeability and durability; Strong process adaptability, ensure the reliability of engineering application: gradient mixing process (control the speed and feeding sequence in stages) avoids the basalt fiber balling, the dispersion uniformity is improved by 30%; Layered pouring (height ≤600mm) and 30 days of spray curing (humidity ≥90%) ensure that the material performance fully plays, especially suitable for complex engineering scenes such as super long structure, mass wall, etc., verified by practice for more than one year without harmful cracks, the waterproofness and structural safety are significantly improved; Quantitative evaluation guides design, realizes controllable anti-cracking performance: through the cracking risk coefficient k of concrete, the scientific nature of anti-cracking design is ensured from the theoretical level, the blindness of traditional experience type design is avoided, and clear guidance is provided for concrete anti-cracking scheme optimization in different engineering environments. Wherein t is the tensile stress at t, t is the splitting tensile strength at t, from the theoretical level, the scientific nature of anti-cracking design is ensured, the blindness of traditional experience type design is avoided, and clear guidance is provided for concrete anti-cracking scheme optimization in different engineering environments.

[0025] In summary, through the systematic innovation of "material coordination-process optimization-theory quantization", the anti-cracking performance of mass concrete is broken through, which has advanced technology and engineering practicability, and is suitable for large projects with high durability requirements in the fields of building, water conservancy, transportation, etc. DETAILED DESCRIPTION

[0026] 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 specific examples.

[0027] Example 1 A preparation method of anti-cracking mass concrete, comprising the following steps: S1. Preparing an expansive agent: low-activity magnesium oxide, modified calcium oxide-calcium sulfoaluminate clinker, and nano calcium carbonate are put into a ball mill in proportion, 10% of the total mass of water is added, and ball milling is carried out at a speed of 300 r / min for 30 min, then starch derivatives are added and ball milling is continued for 10 min, to obtain a nano calcium carbonate modified calcium-magnesium composite expansive agent, wherein the proportion of low-activity magnesium oxide in the nano calcium carbonate modified calcium-magnesium composite expansive agent is 35%, the proportion of modified calcium oxide-calcium sulfoaluminate clinker is 45%, the proportion of nano calcium carbonate is 5%, and the proportion of starch derivatives is 2%, wherein the starch derivatives can be dextrin derivatives, hydroxypropyl distarch phosphate, and acetylated distarch phosphate, etc., then the calcium oxide-calcium sulfoaluminate type II expansive agent is mixed with the nano calcium carbonate modified calcium-magnesium composite expansive agent with an average particle size of 50-100 nm at a mass ratio of 1:1, to obtain the expansive agent; S2. Mixing ordinary portland cement, S105 mineral powder, and fly ash at a mass ratio of 300:80:80 to obtain a cementitious system; S3. Mixing crushed stone with a particle size of 5-10 mm and crushed stone with a particle size of 10-25 mm at a mass ratio of 400:600 to obtain continuous graded crushed stone with a particle size of 5-25 nm; S4. Mixing the continuous graded crushed stone with a particle size of 5-25 mm and river sand at a mass ratio of 1000:600 to obtain composite aggregate, wherein the river sand is machine-made sand with a fineness modulus of 2.6-2.8, a stone powder content of 5.0%, and MB≤0.35; S5. Putting 400 parts of the cementitious system and 1600 parts of the composite aggregate into a mixer, dry mixing for 2 min until uniform to form a mixed base material, then gradient mixing is carried out: 70% of water is mixed with 8 parts of polycarboxylic acid water reducer and added to the mixed base material, stirring at a speed of 500 r / min for 2 min, then 10 parts of basalt fiber, 5 parts of slump retention type superplasticizer, and the remaining 30% of water are added, wherein the total amount of water is 140 parts, stirring at a speed of 800 r / min for 3 min, finally 25 parts of the expansive agent, 4 parts of the hydration heat inhibitor, and 3 parts of the porous carbon moisture control component are added, stirring at a speed of 600 r / min for 2 min, to obtain a concrete mixture; S6. Gradient temperature control maintenance: steel formwork is adopted, continuous layer pouring is adopted, the layer height is less than or equal to 600 mm, the next layer pouring is completed before the initial setting of the previous layer, the temperature sensor is pre-buried for monitoring 0-12 h after pouring, the surface temperature is maintained at 33-37 DEG C, the core temperature is not more than 60 DEG C; 12-30 d after pouring, the spraying device is used for moisture curing, the environmental humidity is greater than or equal to 90%, the step-by-step cooling is carried out in the first 72 h, the temperature is reduced by less than or equal to 5 DEG C every 12 h, the internal and external temperature difference is less than or equal to 25 DEG C, the cracking performance is evaluated by the cracking risk coefficient k, wherein is the tensile stress at t, is the splitting tensile strength at t, the control k is less than or equal to 0.7, the calculation formula of the tensile stress is wherein is the linear expansion coefficient, is the elastic modulus at t, is the temperature difference, is the shrinkage equivalent temperature difference, is the constraint coefficient, is the relaxation coefficient, is the Poisson's ratio.

[0028] Example 2: A preparation method of anti-cracking mass concrete, comprising the following steps: S1. Preparation of expansion agent: low-activity magnesium oxide, modified calcium oxide-calcium sulfoaluminate clinker, nano calcium carbonate are put into a ball mill according to a proportion, 15% of the total mass of water is added, ball milling is carried out at a speed of 300 r / min for 40 min, then starch derivatives are added and ball milling is continued for 10 min, to obtain nano calcium carbonate modified calcium-magnesium composite expansion agent, the proportion of low-activity magnesium oxide in the nano calcium carbonate modified calcium-magnesium composite expansion agent is 40%, the modified calcium oxide-calcium sulfoaluminate clinker is ion-doped modified calcium oxide-calcium sulfoaluminate clinker, wherein the proportion of the modified calcium oxide-calcium sulfoaluminate clinker is 50%, the proportion of nano calcium carbonate is 8%, and the proportion of starch derivatives is 3%, wherein the starch derivatives can be dextrin derivatives, hydroxypropyl distarch phosphate and acetylated distarch phosphate, etc., the calcium oxide-calcium sulfoaluminate type II expansion agent is mixed with the nano calcium carbonate modified calcium-magnesium composite expansion agent with an average particle size of 50-100 nm at a mass ratio of 1:1 to obtain the expansion agent; S2. The ordinary portland cement, S105 mineral powder and fly ash are mixed at a mass ratio of 350:120:100 to obtain a cementing system; S3. The broken stone with a particle size of 5-10 mm is mixed with the broken stone with a particle size of 10-25 mm at a mass ratio of 400:600 to obtain continuous graded broken stone with a particle size of 5-25 nm; S4. Mix the continuous gradation macadam with a particle size of 5-25 mm and river sand in a mass ratio of 1100:700 to obtain a composite aggregate, wherein the river sand is machine-made sand with a fineness modulus of 2.6-2.8, a stone powder content of 5.5%, and MB≤0.35; S5. Put 500 parts of the cementitious system and 1800 parts of the composite aggregate into a mixer, dry mix for 3 min until uniform, to form a mixed base material, and then perform gradient mixing: first mix 70% of the water with 10 parts of polycarboxylic acid superplasticizer and add it to the mixed base material, stir at a speed of 500 r / min for 2 min, then add 15 parts of basalt fiber, 8 parts of slump retention superplasticizer, and the remaining 30% of the water, wherein the total amount of water is 160 parts, stir at a speed of 800 r / min for 4 min, and finally add 30 parts of the expanding agent, 6 parts of the hydration heat inhibitor, and 5 parts of the porous carbon moisture control component, stir at a speed of 600 r / min for 2 min, to obtain a concrete mixture; S6. Gradient temperature control curing: use a steel formwork to continuously layer pouring, the layer height is ≤600 mm, the next layer pouring is completed before the previous layer initial setting, and the pre-embedded temperature sensor is monitored at 0-12 h after pouring, the surface temperature is maintained at 33-37℃, and the core temperature is not more than 60℃; after pouring, 12-30 d, use a spraying device for moisture curing, the environmental humidity is ≥90%, the temperature is reduced by steps in the first 72 h, the temperature is reduced by ≤5℃ every 12 h, the internal and external temperature difference is ensured to be ≤25℃, and the cracking performance is evaluated by the cracking risk coefficient k, wherein is the tensile stress at t, is the splitting tensile strength at t, the control k≤0.7, the calculation formula of the tensile stress is wherein is the linear expansion coefficient, is the elastic modulus at t, is the temperature rise temperature difference, is the shrinkage equivalent temperature difference, is the constraint coefficient, is the relaxation coefficient, is the Poisson's ratio.

[0029] Comparative Example 1: Without adding a hydration heat inhibitor: Design idea: under the condition of keeping other ingredients and preparation process the same as Example 1, only remove the hydration heat inhibitor, to explore the influence of the hydration heat inhibitor on the performance of the concrete.

[0030] Ingredient adjustment: the amounts of the cementitious system, the composite aggregate, the expanding agent, the fiber, the water reducing agent, the superplasticizer, the moisture control component, and the water are consistent with Example 1, but no liquid preparation containing a phosphate ester compound (hydration heat inhibitor) is added.

[0031] Comparative Example 2: Without adding expansion agent: Design idea: Remove all expansion agent components, observe the performance changes of concrete without expansion compensation, and focus on the role of expansion agent on the crack resistance and shrinkage deformation of concrete.

[0032] Component adjustment: Cancel calcium oxide-calcium aluminate type II expansion agent and nano calcium carbonate modified calcium and magnesium composite expansion agent, other components are the same as example 1.

[0033] Comparative example 3: Without using gradient mixing process: Design idea: Change the mixing process in the preparation method, use the traditional one-time mixing method, compare the improvement effect of the gradient mixing process on the performance of concrete, especially the influence on the uniformity of fiber dispersion and additive dissolution.

[0034] Process adjustment: All raw materials are added to the mixer at one time, and stirred at a speed of 500 r / min for 5-6 min, instead of the original gradient mixing process.

[0035] Comparative example 4: Without gradient temperature control curing: Design idea: Use conventional curing methods, do not perform layered pouring and gradient temperature control, and analyze the importance of gradient temperature control curing on the crack resistance, strength development and internal structure of concrete.

[0036] Curing adjustment: Use one-time pouring, natural curing after pouring, do not monitor and control the temperature, and do not take spraying and moisture curing measures.

[0037] The products prepared in examples 1-2 and comparative examples 1-4 are tested for the following properties: Hydration heat peak test: According to GB / T 1028-2015 “Technical Specification for Temperature Measurement and Control of Mass Concrete”, embedded temperature sensors are used to monitor the temperature change of concrete within 7 days after pouring, and the highest temperature value is recorded as the hydration heat peak.

[0038] Limited expansion rate test: According to GB / T 3439-2017 “Concrete Expanding Agent”, 100mm×100mm×400mm limited specimens are prepared, and the limited expansion rates at 3d, 7d and 28d are tested under standard curing conditions (temperature 20±2℃, relative humidity ≥90%).

[0039] Cracking risk coefficient (k) calculation: According to JTS / T 202-1-2022 “Technical Specification for Temperature Cracking Control of Mass Concrete in Water Transport Engineering”, the formula is used to calculate the cracking risk coefficient (k), where is the tensile stress at t: the formula for calculating the tensile stress is , where coefficient of linear expansion, elastic modulus at t, temperature rise temperature difference, shrinkage equivalent temperature difference, constraint coefficient, relaxation coefficient, Poisson's ratio; splitting tensile strength at t, tested according to GB / T 50081-2019 "Standard Test Methods for Physical and Mechanical Properties of Concrete".

[0040] 28d compressive strength test: according to GB / T 50081-2019, 150mm×150mm×150mm cubic test pieces were prepared, and the compressive strength was tested by a pressure testing machine after standard curing for 28 days.

[0041] Drying shrinkage test: according to GB / T 50082-2009 "Standard Test Methods for Long-Term Performance and Durability of Ordinary Concrete", 100mm×100mm×515mm prismatic test pieces were prepared, and the 28d drying shrinkage was tested under the environment of temperature 20±2℃ and relative humidity 60±5%.

[0042] Splitting tensile strength test: according to GB / T 50081-2019, 150mm×150mm×150mm cubic test pieces were used to test the 28d splitting tensile strength.

[0043] The performance test data are shown in Tables 1-3 below: Table 1

[0044]

[0045] Table 2

[0046] Table 3

[0047] Data analysis: 1. Hydration heat control effect: the hydration heat peak value (47-48℃) of Examples 1-2 is significantly lower than that of Comparative Example 1 (56℃) and Comparative Example 4 (58℃), indicating that the synergistic effect of hydration heat inhibitor and gradient temperature control curing can effectively reduce the temperature peak, with a reduction of 15%-20%. Although Comparative Example 2 does not add an expansive agent, the hydration heat peak value (49℃) is close to that of the examples, indicating that the expansive agent has little effect on hydration heat, which is consistent with the conclusion in the patent that "the influence of expansive agent on temperature peak change can be ignored".

[0048] 2. Expansion compensation performance: The comparative example 2 has a limited expansion rate of 0 due to the absence of expansion agent, and the 28d dry shrinkage rate (0.058%) is 81% higher than that of example 1, and 5 through cracks occur, proving that the compounded expansion agent is the core means to compensate for shrinkage. The 28d limited expansion rate (0.012-0.013%) of examples 1-2 is higher than that of comparative examples 3-4, indicating that the gradient mixing process can ensure uniform dispersion of the expansion agent and improve the expansion efficiency.

[0049] 3. Anti-cracking risk assessment: The 28d cracking risk coefficient (0.63-0.65) of examples 1-2 is ≤0.7, meeting the "basically no cracking" standard; while comparative example 1 (0.88), comparative example 2 (1.12), and comparative example 4 (0.95) all exceed the safety threshold, verifying the synergistic anti-cracking effect of hydration heat inhibitor + expansion agent + temperature control curing. Comparative example 3 has uneven fiber dispersion due to the absence of gradient mixing, resulting in a splitting tensile strength (3.2MPa) that is 16% lower than that of example 1, causing the k value (0.75) to slightly exceed the safe range, indicating that process optimization is crucial to improving anti-cracking performance.

[0050] 4. Influence on mechanical properties: The 28d compressive strength (48.5-50.2MPa) of examples 1-2 is higher than that of all comparative examples, indicating that the patented technology improves anti-cracking performance without sacrificing mechanical properties, and even slightly improves due to increased material density. The compressive strength (40.5MPa) of comparative example 4 is the lowest due to improper curing, proving that gradient temperature control curing is the key to ensuring strength development.

[0051] 5. Long-term engineering effect: One-year tracking shows that examples 1-2 have no cracks, while comparative example 2 (5) and comparative example 4 (4) have through cracks, directly verifying the long-term anti-cracking reliability of the patented technology in ultra-long structures and complex environments.

[0052] Conclusion: Material synergy: The combination of hydration heat inhibitor (peak reduction) and compounded expansion agent (shrinkage compensation) is the core of cracking control, and the combination of the two can reduce the cracking risk coefficient by more than 40%.

[0053] 1. Process optimization value: Gradient mixing (fiber dispersion) and gradient temperature control curing (temperature difference control) can further reduce the cracking risk by 10-15% without affecting the mechanical properties.

[0054] 2. Systematic solution: The patent realizes a breakthrough in the anti-cracking performance of mass concrete through systematic innovation of "material design-process optimization-risk quantification", especially suitable for ultra-long structure projects such as subway side walls.

[0055] 3. The function of the gradient stirring process is to control the stirring speed (500-800 r / min) and the feeding sequence in stages to ensure uniform dispersion of fibers and sufficient dissolution of additives. Effect: Avoids basalt fiber clumping, and improves the uniformity of fiber distribution in the matrix by 30%.

[0056] The function of the layered pouring and gradient temperature control curing is to reduce the pouring thickness to less than 600 mm to reduce the difficulty of heat dissipation caused by excessive pouring thickness, and to control the temperature difference by controlling the temperature (surface 33-37°C, core ≤60°C) for 0-12h and stepwise temperature reduction (≤5°C every 12h). Effect: The temperature difference between inside and outside is ≤25°C, and the temperature stress is reduced by 50%; 30d spray curing ensures complete expansion agent reaction.

[0057] The function of the cracking risk quantitative evaluation (k value control) is to quantify the cracking risk by the formula , where is the tensile stress at t, is the splitting tensile strength at t, and k ≤ 0.7. Effect: Ensures the safety of concrete anti-cracking from a theoretical level, and avoids the blindness of empirical design.

[0058] The spatiotemporal matching of hydration heat inhibition and expansion compensation, where the hydration heat inhibitor reduces the early (3-7d) temperature peak and reduces the temperature stress; at the same time, calcium oxide-sulphoaluminate type II expansion agent generates micro-expansion (0.008%-0.010%), offsetting the temperature shrinkage, both of which cooperatively reduce the early cracking risk coefficient k to below 0.6. In the middle and later stages (14-28d), nano calcium carbonate modified calcium-magnesium composite expansion agent continues to expand, and works together with the porous carbon humidity control component to compensate for the dry shrinkage, at this time the hydration heat inhibitor has completed its mission and does not affect the later strength development.

[0059] Multi-scale synergy of fiber reinforcement and interface optimization: basalt fibers are modified by silane coupling agent, and the interface transition zone thickness between the fibers and the cementitious system is reduced from 50-100μm to 20-30μm, and the interface bonding strength is increased by 25%; at the same time, the dense gradation of composite aggregate reduces the interface defects, and both of them together strengthen the stress transfer efficiency of "fiber-matrix".

[0060] After the water-cement ratio is reduced by polycarboxylate superplasticizer, the cement stone density is improved, the bridging effect of the fibers is more effectively played, and the anti-cracking performance shows a superposition effect of 1+1>2.

[0061] Workability synergy of water-reducing, slump-preserving, and humidity-controlling: the high water-reducing property of polycarboxylate superplasticizer and the retarding property of slump-preserving superplasticizer cooperate to reduce the water consumption and maintain the workability; porous carbon releases water after hardening to make up for the loss of humidity in dry environment, and the three form a whole-cycle workability guarantee of "slump-preserving in construction stage-humidity control in hardening stage".

[0062] Synergy of gradient stirring and fiber dispersion: first stir the water-reducing agent and water to make the slurry fluidized, then add basalt fiber and increase the stirring speed to 800 r / min to disperse the fiber by fluid shear force; finally, add the expanding agent, hydration heat inhibitor and porous carbon to avoid the destruction of the crystal structure of the expanding agent by high-speed stirring. This process improves the uniformity of fiber distribution by 30%, ensuring the reinforcement effect.

[0063] Synergy of layered pouring and temperature control curing: layered pouring (≤600 mm) shortens the heat dissipation path, and real-time monitoring by pre-embedded temperature sensors makes gradient temperature control curing more accurate (temperature difference control accuracy ±2℃); the strong constraint characteristics of steel formwork and the compensation effect of the expanding agent form a "constraint-expansion" balance, further reducing the risk of shrinkage cracking.

[0064] Quantitative evaluation and feedback synergy of material adjustment: when the cracking risk coefficient k calculation value is close to 0.7, dynamic adjustment can be made by increasing the expanding agent content (by 0.5%-1.0%) or reducing the hydration heat inhibitor content (by 0.2%), forming a closed-loop synergy of "theoretical calculation-material optimization-actual verification".

[0065] Through the multi-dimensional synergy of "heat reduction-compensation-reinforcement-temperature control-quantification", the following overall effects are achieved: The hydration heat peak value is reduced by 30%, and the 28d drying shrinkage rate is reduced by 45%; the cracking risk coefficient is stably controlled at 0.65±0.05, and there is no penetrating crack in 1 year of engineering application; compared with a single technical solution (such as only adding expanding agent), the anti-cracking efficiency is improved by 60%, and the comprehensive cost is reduced by 15%.

[0066] This synergy breaks through the limitations of traditional anti-cracking technology "single link optimization", forming a systematic solution from material design to construction control, especially suitable for harsh engineering scenarios such as super-long mass walls.

[0067] Those skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to suggest that the scope of the present application is limited to these examples; under the idea of the present application, 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 changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail.

[0068] The present application is intended to cover all such alternatives, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omission, modification, equivalent replacement, improvement, etc. made in the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A crack-resistant mass concrete, characterized in that: The method comprises the following raw materials in parts by weight: 400-500 parts of a gelling system, 1600-1800 parts of a composite aggregate, 60-80 parts of a gradient functional additive and 140-160 parts of water; The cementitious system includes ordinary Portland cement, S105 slag and fly ash; The composite aggregate includes crushed stone and river sand; The gradient functional additives include an expander, a hydration heat inhibitor, fibers, a water reducer, a plasticizer, and a moisture control component; The expansion agent is a calcium oxide-calcium sulfoaluminate type II expansion agent and a nano-calcium carbonate modified calcium magnesium composite expansion agent mixed in a mass ratio of 1:1, and the hydration heat inhibitor is a liquid preparation containing a phosphate compound.

2. The crack-resistant mass concrete according to claim 1, characterized in that: The mass ratio of ordinary Portland cement, S105 slag and fly ash in the cementitious system is 300-350:80-120:80-100.

3. The crack-resistant mass concrete according to claim 1, characterized in that: The mass ratio of crushed stone to river sand in the composite aggregate is 1000-1100:600-700; The gravel is continuously graded gravel with a particle size of 5-25 nm, the mass ratio of gravel with a particle size of 5-10 mm to gravel with a particle size of 10-25 mm in the gravel is 400:600, the river sand is machine-made sand with a fineness modulus of 2.6-2.8, the stone powder content of the machine-made sand is 5.0%-5.5%, and the MB value is ≤0.

35.

4. The crack-resistant mass concrete according to claim 1, characterized in that: The mass ratio of the expansion agent, hydration heat inhibitor, fiber, water reducer, superplasticizer and moisture control component in the gradient functional additive is 25-30:4-6:10-15:8-10:5-8:3-5.

5. The crack-resistant mass concrete according to claim 4, characterized in that: The fiber is basalt fiber, the water reducer is a polycarboxylic acid water reducer, the water reduction rate of the polycarboxylic acid water reducer is 31.5%, the superplasticizer is a slump-retaining superplasticizer, and the moisture control component is a porous carbon moisture control component.

6. The crack-resistant mass concrete according to claim 5, characterized in that: The nano-calcium carbonate-modified calcium-magnesium composite expansion agent is prepared from the following raw materials in percentage by mass: 35%-40% low-activity magnesium oxide, 45%-50% ion-doped modified calcium oxide-calcium sulfoaluminate clinker, 5%-8% nano-calcium carbonate, and 2%-3% starch derivative hydration heat control component. It is prepared through a wet ball milling process, wherein the average particle size of the nano-calcium carbonate is 50-100 nm.

7. The crack-resistant mass concrete according to claim 5, characterized in that: The basalt fiber has a length of 12-18 mm and a diameter of 13-20 μm, and its content accounts for 2.5%-3.5% of the total amount of the cementitious system. The interface transition zone with the concrete matrix is ​​modified by a silane coupling agent.

8. A method for preparing crack-resistant mass concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step S1. Preparing an expansion agent: low-activity magnesium oxide, modified calcium oxide-calcium sulfoaluminate clinker, and nano-calcium carbonate are placed in a ball mill in proportion, 10%-15% of water is added to the total mass, and ball milling is carried out at a speed of 300 r / min for 30-40 minutes. Then, a starch derivative is added and ball milling is continued for 10 minutes to obtain a nano-calcium carbonate-modified calcium-magnesium composite expansion agent. The calcium oxide-calcium sulfoaluminate type II expansion agent and the nano-calcium carbonate-modified calcium-magnesium composite expansion agent are mixed in a mass ratio of 1:1 to obtain an expansion agent; Step S2. Premixing: Put the cementitious system components and composite aggregate into a mixer and dry mix for 2-3 minutes until uniform to form a mixed base material; Step S3. Gradient stirring: First, 70% of the water and the polycarboxylate water-reducing agent were mixed, and then the mixed base material was added and stirred at 500 r / min for 2 minutes. Then, the basalt fiber, the collapse-retaining superplasticizer, and the remaining 30% of the water were added and stirred at 800 r / min for 3-4 minutes. Finally, the expansion agent, the hydration heat inhibitor, and the porous carbon moisture control component were added and stirred at 600 r / min for 2 minutes to obtain a concrete mixture; Step S4. Gradient temperature control curing: Use steel formwork and continuously cast in layers with a layer height of ≤600mm. The next layer should be cast before the previous layer begins to set. Pre-embed temperature sensors are used for monitoring 0-12 hours after casting to maintain a surface temperature of 33-37°C and a core temperature not exceeding 60°C. 12-30 days after casting, use a spray device for moisturizing curing with an ambient humidity of ≥90%. Cool the material in a stepwise manner for the first 72 hours, with a cooling rate of ≤5°C every 12 hours, to ensure that the temperature difference between the inside and outside is ≤25°C.

9. The method for preparing crack-resistant mass concrete according to claim 8, characterized in that: In step S4, the cracking performance is evaluated by the cracking risk coefficient k. ,in is the tensile stress at time t, is the splitting tensile strength at time t, controlling k≤0.

7.

10. The method for preparing crack-resistant mass concrete according to claim 8, characterized in that: The calculation formula of the tensile stress is: ,in is the linear expansion coefficient, is the elastic modulus at time t, is the temperature rise and temperature difference, is the contraction equivalent temperature difference, is the constraint coefficient, is the relaxation coefficient, is Poisson's ratio.

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