A high crack-resistant cement-based composite material and its preparation method

Abstract

This invention belongs to the field of building materials technology and discloses a high-crack-resistant cement-based composite material and its preparation method. The material is composed of silicate cement, activated fly ash, modified titanium gypsum, composite expansion agent, regulating agent, aggregate, and water. During preparation, the raw materials undergo pretreatment, dry mixing, wet mixing, and vibration molding, followed by 3 days of carbonization curing, and then standard wet curing for 28 days. This invention fundamentally solves the imbalance problem in the strength-crack resistance-durability triangle of existing cement-based materials by systematically integrating three core technologies: solid waste activation, two-stage expansion compensation, and synergistic carbonization-wet curing. It overcomes the technical bottlenecks of insufficient timeliness of single expansion sources and low-activity utilization of industrial solid waste, providing a new generation of cement-based composite materials with high performance, high durability, and high environmental friendliness, along with an industrially feasible preparation method.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and relates to a high crack-resistant cement-based composite material and its preparation method. Background Technology

[0002] In modern infrastructure construction, cement-based composite materials serve as the core load-bearing and protective system for critical components such as road base layers, bridge pavement layers, and underground structures. Their volume stability and crack resistance directly affect the durability and service life of engineering structures. Especially in long-service scenarios such as high-grade highways, large-scale water conservancy facilities, and urban underground utility tunnels, the early shrinkage deformation induced by the release of heat of hydration, water evaporation, and environmental temperature changes can easily lead to the initiation and expansion of microcracks. This provides a channel for the intrusion of corrosive media, accelerating steel corrosion and structural deterioration.

[0003] To suppress such early cracking, conventional crack-resistant methods such as reducing cement content, optimizing aggregate gradation, or adding fibers are commonly used in engineering practice. However, while excessive reduction of cementitious materials can alleviate shrinkage, it significantly weakens the load-bearing capacity of the base layer; and relying solely on physical crack-prevention measures cannot regulate the shrinkage-expansion dynamics at the level of chemical-physical coupling mechanism, resulting in limited and uncontrollable crack-resistant effects.

[0004] Introducing expansion components to improve crack resistance has become a common approach. Currently, most mainstream expansion agents are designed based on a single active mineral phase, such as calcium sulfoaluminate or dolomite expansion sources. Their mechanism of action relies on the formation of specific hydration products (such as ettringite or magnesium hydroxide) to produce moderate expansion. However, the initial expansion rate of such a single-source expansion system is too fast, which can easily lead to a loose structure. In the later stages, due to the depletion of reactants or changes in environmental conditions, the expansion effect rapidly decays, which in turn creates a new stress imbalance inside the material and induces secondary cracking.

[0005] Among existing expansion technologies, titanium gypsum, although rich in calcium sulfate and possessing potential expansion contribution, has high impurity content and unstable crystal form, and its direct use can easily interfere with the cement hydration process. Although fly ash has pozzolanic activity, it is highly inert at room temperature and requires effective activation to participate in the cementitious reaction. If the two are used in isolation, not only will it be difficult to exert a synergistic effect, but it may also exacerbate material performance fluctuations due to insufficient activity or poor compatibility.

[0006] Traditional approaches treat expansion control and solid waste utilization as two separate objectives, resulting in a severe disconnect between expansion behavior and contraction processes in the temporal and spatial dimensions. Furthermore, the amount of solid waste incorporated is limited by the activity bottleneck and difficult to overcome. Even some studies that have attempted to combine multiple expansion sources have failed to solve secondary problems such as weak interfacial bonding between expansion products and the matrix and coarsening of the pore structure, leading to compromised material density and durability. Summary of the Invention

[0007] To achieve the aforementioned objectives, this invention provides a high-crack-resistant cement-based composite material and its preparation method. The high-crack-resistant cement-based composite material achieves a unified approach by constructing a two-stage expansion compensation mechanism, synergistically activating industrial solid waste components, and introducing a carbonization-wet curing synergistic maintenance system. This results in dynamic matching of the entire shrinkage-expansion process, denser and strengthened microstructure, and efficient resource utilization of industrial by-products. This material system, while meeting the stringent requirements for base strength and durability in high-grade infrastructure projects, significantly inhibits early microcrack formation, improves impermeability, freeze-thaw resistance, and long-term service stability, and also possesses significant low-carbon environmental benefits.

[0008] The high crack-resistant cement-based composite material of the present invention is composed of the following components in parts by weight: 100 parts silicate cement, 25-32 parts activated fly ash, 12-18 parts modified titanium gypsum, 3-5 parts composite expansion agent, 0.8-1.2 parts regulator, 60-75 parts fine aggregate, 110-130 parts coarse aggregate, and 38-42 parts water. The activated fly ash is fly ash that has been surface-modified with triethanolamine and mechanically activated, and has a specific surface area greater than 650 m². 2 / kg, residue on 45μm sieve is less than 5%; The modified titanium gypsum was dried at 105℃ for 2 hours and then ground to a specific surface area greater than 400 m². 2 The titanium gypsum powder, with β-type calcium sulfate hemihydrate as the main phase, has a CaSO4·0.5H2O content higher than 85% and a total impurity content of Fe2O3 and TiO2 of less than 8% per kg. The composite expanding agent is composed of magnesium oxide expanding agent and calcium sulfoaluminate expanding agent in a mass ratio of 1:1.2-1.5. The magnesium oxide expanding agent contains more than 80% active MgO and has a particle size D50 of 5-8 μm, while the calcium sulfoaluminate expanding agent contains more than 70% C4A3S phase and has a specific surface area of ​​350-400 m². 2 / kg; The regulating agent is a composite composed of a polycarboxylate shrinkage reducer and nano-silica sol in a mass ratio of 3:1. The polycarboxylate shrinkage reducer has a solid content of 40% and a weight-average molecular weight of 25,000-30,000. The nano-silica sol has a SiO2 content of 20% and an average particle size of 15 nm.

[0009] In a preferred embodiment of the present invention, the method for preparing the activated fly ash includes: Unprocessed fly ash and 0.3% (by weight) of triethanolamine were fed into a planetary ball mill and ground for 30 minutes at 400 rpm. The resulting product was immediately sealed in a moisture-proof container and stored as activated fly ash. This process disrupts the vitreous network structure of the fly ash through mechanochemical action. Simultaneously, triethanolamine molecules adsorb onto the newly formed surface, reducing surface energy and promoting the exposure of active sites for subsequent hydration reactions, enabling the fly ash to effectively participate in pozzolanic reactions at room temperature.

[0010] The preparation method of the modified titanium plaster includes: Industrial titanium gypsum was dried at a constant temperature of 105℃ for 2 hours in an electrically heated drying oven to remove free water and some of the water of crystallization; then it was fed into a Raymond mill system to grind it to a specific surface area of ​​400-450 m². 2 / kg; then add the aforementioned composite expanding agent at a mass ratio of (12-18):(3-5) into a twin-shaft paddle mixer, and premix for 10 minutes at a speed of 30 r / min to form a uniform expanding mixture. This premixing step ensures that the sulfate ions in the titanium gypsum and the aluminum and magnesium phases in the composite expanding agent form multi-source expansion reaction centers during the subsequent hydration process, avoiding excessively high local concentrations that could lead to abrupt expansion changes.

[0011] The preparation method of the high crack resistance cement-based composite material of the present invention includes the following steps: Step 1, Raw material pretreatment: Prepare activated fly ash and expanded mixture separately, as described above; Step 2, dry mixing stage: Put silicate cement and activated fly ash into a forced planetary mixer and dry mix for 2 minutes at a speed of 60 r / min to make the cementitious components initially dispersed evenly; then add fine aggregate and coarse aggregate and continue to dry mix for 3 minutes to form a uniform aggregate-cement skeleton system. Step 3, wet mixing stage: Add the expansion mixture, the regulating agent and the calculated amount of water to the dry mixture in sequence, and wet mix for 5-8 minutes at a speed of 90 r / min. Control the slump of the fresh mixture to be 10-20 mm and the spread to be 280-320 mm to ensure that the workability meets the requirements of paving and compaction construction. Step 4, molding and vibration: Pour the wet mixture into a standard test mold or engineering template, and vibrate it for 90 seconds using a high-frequency vibrating table at a frequency of 50Hz and an amplitude of 1.0mm to fully compact the mixture and remove internal air bubbles. Step 5, Carbonization-Wet Curing Synergistic Maintenance: Immediately after demolding, place the specimens in a carbonization curing chamber and cure them for 3 days under conditions of CO2 concentration of 20%-30%, relative humidity of 60%-70%, temperature of 20±2℃, and normal pressure; then transfer them to a standard curing chamber and continue curing them for 28 days under conditions of temperature of 20±2℃ and relative humidity ≥90%.

[0012] In the aforementioned carbonization-wet curing synergistic process, the carbonization stage on days 1-3 plays a crucial role: the activated fly ash slowly releases Ca in an alkaline environment. 2+ The ions react with CO2 that permeates into the pores of the material to form CaCO3(am), and the reaction formula is: Ca 2+ +CO2+H2O→CaCO3(am)+2H + The generated CaCO3(am) is deposited at the nanoscale in the transition zone of the cement stone-aggregate interface and on the capillary walls, effectively filling micropores, refining the pore size distribution, and enhancing the interfacial chemical bonding strength; simultaneously, this reaction consumes some of the Ca in the pore fluid. 2+ Appropriately lowering the local pH value can inhibit excessive growth of ettringite and prevent early expansion stress concentration.

[0013] During the subsequent wet curing stage, the cement clinker minerals continue to hydrate, generating CSH gel and calcium hydroxide; simultaneously, the calcium sulfate hemihydrate in the modified titanium gypsum gradually dissolves, providing SO4. 2- Ions react with the C4A3S phase and unhydrated C3A in the composite expanding agent to form ettringite, resulting in the first stage of expansion. Meanwhile, the active MgO in the composite expanding agent slowly hydrates in the later stage of hydration (after 7 days) to form Mg(OH)2, expanding in volume by about 148%, forming the second stage of continuous expansion. This two-stage expansion mechanism is precisely coupled with the material shrinkage process in the time dimension: in the early stage (1-7 days), expansion dominated by ettringite compensates for plastic shrinkage and autogenous shrinkage, while in the later stage (7-28 days), expansion dominated by Mg(OH)2 compensates for drying shrinkage, thereby achieving full-cycle volume stability control.

[0014] The polycarboxylate-based shrinkage reducer in the regulating additives suppresses shrinkage stress caused by capillary negative pressure by reducing the surface tension of the pore fluid; the nano-silica sol consumes Ca(OH)2 through a pozzolanic reaction to generate additional CSH gel, while its nanoparticle filling effect further densifies the microstructure. The synergistic effect of these two agents reduces the total porosity of the material from 35% in conventional cement-based materials to below 22%, with the proportion of harmful pores (>50nm) decreasing by more than 60%.

[0015] In another preferred embodiment of the present invention, the coarse aggregate is basalt crushed stone with a particle size of 5-10 mm, a crushing value ≤12%, and a needle-like and flaky particle content ≤8%; the fine aggregate is manufactured sand with a fineness modulus of 2.6-2.9, an MB value ≤1.0, and a stone powder content of 5%-7%. The aggregate gradation adopts a continuous gradation design to ensure a dense skeleton structure, reduce the amount of cementitious materials used, and improve crack resistance and toughness.

[0016] In engineering applications, the material of this invention is suitable for structural components with stringent requirements for crack resistance, impermeability, and long-term durability, such as pavement layers of large bridges, protective layers on the water-facing side of hydraulic dams, shear walls of high-rise buildings, and urban underground utility tunnels. When applied in bridge engineering, the material effectively blocks the intrusion of chloride ions and moisture due to its early absence of visible cracks and its dense interface transition zone, thus slowing down the corrosion process of reinforcing steel.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention solves the imbalance problem of the strength-crack resistance-durability triangle in existing cement-based materials by integrating solid waste activation, two-stage expansion compensation and carbonization-wet curing synergistic maintenance technology. It breaks through the technical bottleneck of insufficient timeliness of single expansion source and low activity utilization of industrial solid waste, and provides a new generation of cement-based composite materials with high performance, high durability and high environmental friendliness and its industrially feasible preparation method. Detailed Implementation

[0018] This invention provides a high-crack-resistant cement-based composite material and its preparation method. By constructing a two-stage expansion compensation mechanism, synergistically activating industrial solid waste components, and introducing a carbonization-wet curing synergistic maintenance system, it achieves a unified approach to dynamic matching of the entire shrinkage-expansion process, microstructural densification and strengthening, and efficient resource utilization of industrial by-products. This material system, while meeting the stringent requirements for base strength and durability in high-grade infrastructure projects, significantly inhibits early microcrack formation, improves impermeability, freeze-thaw resistance, and long-term service stability, and also possesses significant low-carbon environmental benefits.

[0019] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0020] Example 1: 100 parts silicate cement; 28 parts activated fly ash; 15 parts modified titanium gypsum; 4 parts composite expansion agent (magnesium oxide: calcium sulfoaluminate = 1:1.3); 1.0 part regulator; 68 parts fine aggregate; 120 parts coarse aggregate; 40 parts water; carbonization curing for 3 days (CO2 concentration 25%). Preparation process: triethanolamine modification of fly ash + mechanical activation; premixing of titanium gypsum and expansion agent; dry mixing of cementitious materials and aggregates, wet mixing of expansion mixtures, additives and water; high-frequency vibration molding; carbonization-wet curing synergistic curing for 28 days.

[0021] Example 2: 25 parts activated fly ash; 12 parts modified titanium gypsum; the remaining formula and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0022] Example 3: 32 parts activated fly ash; 18 parts modified titanium gypsum; the remaining formula and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0023] Example 4: Composite expanding agent magnesium oxide: calcium sulfoaluminate = 1:1.2; other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1.

[0024] Example 5: Composite expanding agent magnesium oxide: calcium sulfoaluminate = 1:1.5; other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1.

[0025] Example 6: 3 parts of composite expanding agent; the remaining formula and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0026] Example 7: 5 parts of composite expanding agent; the remaining formula and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0027] Example 8: 38 parts water; the rest of the formula and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0028] Comparative Example 1: 4 parts of single calcium sulfoaluminate expansive agent; fly ash not activated; titanium gypsum not modified; the rest of the formulation is the same as in Example 1; Preparation process: No solid waste activation step; direct mixing of all raw materials; standard wet curing for 28 days (no carbonization curing).

[0029] Comparative Example 2: No composite expanding agent; the rest of the formulation is the same as in Example 1; Preparation process: No expansion agent added; standard wet curing for 28 days (no carbonization curing).

[0030] Test method: Crack resistance test: Test the 28-day drying shrinkage rate according to the standard; observe the crack width; evaluate the crack resistance toughness using fracture energy test.

[0031] Mechanical and durability performance testing: 28-day flexural strength and compressive strength are tested; the impermeability grade is determined by the water seepage height; after 25 freeze-thaw cycles, the strength loss rate and mass loss rate are calculated.

[0032] Microstructure testing: Observe the thickness of the transition zone at the cement stone-aggregate interface; test the total porosity and the proportion of harmful pores; analyze the distribution of carbonization products and expansion products.

[0033] Test data comparison table 1:

[0034] Test data comparison table 2:

[0035] Examples 1-8 showed a drying shrinkage rate of ≤0.028% and a crack width of ≤0.04mm, which were far superior to the comparative examples. Comparative example 1 had insufficient time-dependent expansion agent, and comparative example 2 had no expansion compensation and extremely poor crack resistance, confirming that the dual-stage expansion and solid waste synergy are the core of crack resistance.

[0036] Increased solid waste content (Examples 2→1→3) resulted in decreased shrinkage and improved crack resistance due to the filling of pores by solid waste hydration products; increased expansion agent content (Examples 6→1→7) enhanced expansion compensation and reduced crack width; carbonization curing promoted the formation of CaCO3(am), densed the interface transition zone, and improved impermeability and strength.

[0037] Examples 1-8 balance crack resistance and strength, with flexural strength ≥ 8.1 MPa, impermeability grade ≥ P12, and freeze-thaw loss rate ≤ 10%; the comparative examples, due to their loose microstructure, show a significant decrease in strength and durability, failing to meet the requirements of high-level engineering projects.

[0038] Examples 1-8 use 30%-43% solid waste, reducing carbon emissions by more than 20%; the process is compatible with existing building material production equipment and is suitable for harsh scenarios such as bridges and underground pipe corridors, extending the service life of the project.

[0039] The composite material described in this invention solves the contradiction between crack resistance and durability of traditional cement-based materials through two-stage expansion compensation and solid waste synergistic activation. Different parameter combinations can achieve a balance between high performance and environmental benefits, making it suitable for high-level infrastructure construction.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cement-based composite material with high crack resistance, characterized in that, It consists of the following components in parts by mass: 100 parts of silicate cement; 25-32 parts activated fly ash; 12-18 parts of modified titanium plaster; 3-5 parts of composite expanding agent; 0.8-1.2 parts of regulatory agent; 60-75 parts fine aggregate; 110-130 parts coarse aggregate; 38-42 parts water; The activated fly ash is fly ash that has been surface-modified with triethanolamine and activated by mechanochemical processes. The modified titanium gypsum is a titanium gypsum powder with β-type calcium sulfate hemihydrate as the main phase, which has been dried and ground, and its CaSO4·0.5H2O content is higher than 85%, and the total impurity content of Fe2O3 and TiO2 is less than 8%. The composite expanding agent is composed of magnesium oxide expanding agent and calcium sulfoaluminate expanding agent in a mass ratio of 1:1.2-1.5, wherein the active MgO content in the magnesium oxide expanding agent is higher than 80%, and the C4A3S phase content in the calcium sulfoaluminate expanding agent is higher than 70%. The regulating agent is a composite material composed of a polycarboxylate shrinkage reducing agent and nano-silica sol in a mass ratio of 3:1, wherein the polycarboxylate shrinkage reducing agent has a solid content of 40% and the nano-silica sol has a SiO2 content of 20%. The coarse aggregate is basalt crushed stone; the fine aggregate is manufactured sand with a stone powder content of 5%-7%. The modified titanium gypsum and the composite expanding agent are premixed at a mass ratio of (12-18):(3-5) to form an expanding mixture; The curing method for the high crack resistance cement-based composite material is carbonation-wet curing combined curing: immediately after demolding, the specimens are placed in a carbonation curing chamber and cured for 3 days under conditions of CO2 concentration of 20%-30%, relative humidity of 60%-70%, temperature of 20±2℃, and normal pressure; then transferred to a standard curing chamber and cured for 28 days under conditions of temperature of 20±2℃ and relative humidity ≥90%.

2. The high crack resistance cement-based composite material according to claim 1, characterized in that, The activated fly ash is obtained by feeding raw fly ash and 0.3% of triethanolamine by mass into a planetary ball mill and grinding for 30 minutes at a speed of 400 r / min. The resulting product is then sealed and stored in a moisture-proof environment.

3. The high crack resistance cement-based composite material according to claim 1, characterized in that, The premixing of the expanded mixture is completed in a twin-shaft paddle mixer.

4. The high crack resistance cement-based composite material according to claim 1, characterized in that, The coarse and fine aggregates are designed with continuous gradation to form a dense skeleton structure.

5. A method for preparing a high-crack-resistant cement-based composite material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1, Raw material pretreatment: Prepare activated fly ash and expanded mixture separately; Step 2, dry mixing stage: Put silicate cement and activated fly ash into a forced planetary mixer and dry mix evenly, then add fine aggregate and coarse aggregate and continue to dry mix evenly. Step 3, wet mixing stage: Add the expansion mixture, regulator and water to the dry mixture in sequence, and wet mix evenly; Step 4, molding and vibration: pour the wet mixture into the test mold and vibrate it using a high-frequency vibration table; Step 5, Carbonization-Wet Curing Synergistic Maintenance: Immediately after demolding, place the specimens in a carbonization curing chamber and cure them for 3 days under conditions of CO2 concentration of 20%-30%, relative humidity of 60%-70%, temperature of 20±2℃, and normal pressure; then transfer them to a standard curing chamber and continue curing them for 28 days under conditions of temperature of 20±2℃ and relative humidity ≥90%.

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