Fly ash-based low-carbon cementitious material acting on highway semi-rigid base

Abstract

This invention relates to a fly ash-based low-carbon cementitious material for use in semi-rigid base courses of highways. The cementitious material is composed of the following components in parts by weight: 50-70 parts fly ash, 15-30 parts granulated blast furnace slag powder, 5-12 parts calcium carbide slag, 3-8 parts desulfurized gypsum, 1-5 parts sodium sulfate, 0.1-0.5 parts retarder, and 0.5-1.5 parts readily soluble sodium silicate. The preparation method includes: drying calcium carbide slag and desulfurized gypsum, then mixing and ball-milling them with fly ash, granulated blast furnace slag powder, sodium sulfate, retarder, and readily soluble sodium silicate to obtain the fly ash-based low-carbon cementitious material. The construction method includes: mixing aggregates with the cementitious material, spreading and compacting the mixture, and performing segmented curing. This invention solves the problems of difficulty in balancing early strength and crack resistance, and uncontrollable setting time in existing fly ash-based materials. It can replace cement, significantly reduce carbon emissions, and is suitable for the construction of semi-rigid base courses for high-grade highways and municipal roads.

Description

Technical Field

[0001] This invention relates to the field of road engineering materials, and more specifically, to a fly ash-based low-carbon cementitious material for use in semi-rigid base courses of highways, and its preparation and construction methods. Background Technology

[0002] Semi-rigid base courses for highways typically use cement-stabilized crushed stone or cement-stabilized graded aggregate as the main structural layer, with cement widely used as a binder. However, the decomposition of carbonates and the combustion of fuels during cement production generate significant carbon dioxide emissions, and the high cost of cement hinders the low-carbon development of road engineering. Fly ash, as an industrial solid waste from coal-fired power plants, possesses potential pozzolanic activity and can partially replace cement in base course materials. However, base course materials prepared solely from fly ash exhibit slow early strength development, typically failing to reach the unconfined compressive strength required for highway base courses within 7 days, and exhibit poor crack resistance, with prominent issues of drying shrinkage and thermal shrinkage cracking. Furthermore, fly ash-based materials lack sufficient resistance to erosion under dynamic water conditions and have weak resistance to freeze-thaw cycles, making it difficult to meet the durability requirements of high-grade highways and municipal roads for base course materials.

[0003] In recent years, significant progress has been made in the research of preparing road base cementitious materials using industrial solid waste. Patent application CN119176698A discloses a geopolymer-stabilized recycled aggregate road base material and its preparation method. It utilizes slag powder, fly ash, steel slag powder, and carbide slag to prepare the geopolymer cementitious material, using recycled brick-concrete aggregate as the aggregate and sodium metasilicate pentahydrate, sodium silicate, and sodium hydroxide as alkali activators to prepare a road base material utilizing all solid waste. Patent application CN121248200A discloses a cementitious material for roadbeds using solid waste from coal-fired power plants and its preparation method. It uses fly ash, slag, and desulfurization gypsum as the main components, with the addition of small amounts of other industrial solid waste. This is a low-carbon cementitious material made entirely from solid waste and can be applied to road base, subbase, or base course. In addition, CN114702294A discloses a solid waste-based ultra-slow-release gelling material, comprising 80-100 parts fly ash, 40-60 parts slag powder, 5-15 parts desulfurized gypsum, and 5-10 parts sodium silicate, which is suitable for application in stabilizing crushed stone base courses. CN118993592A discloses a fly ash-based road rock-forming agent, made of 55-70 parts fly ash, 15-20 parts slag powder, and 15-25 parts activator, mainly addressing the technical problems of poor drying shrinkage and easy cracking of existing modifiers. CN115368035A discloses a special cementitious material for low-carbon road base courses based on the synergistic activation of Ca²⁺ and Na⁺, prepared from 5-10 parts limestone, 15-26 parts fly ash, 65-80 parts blast furnace slag, and 5-20 parts dry-based calcium carbide slag, using sodium hydroxide as an alkali activator. It aims to solve the problem of easy cracking of road base courses when constructed with traditional silicate cement. CN113307595A discloses a geopolymer cementitious material for road base courses based on the synergistic effect of multiple solid wastes, using fly ash, slag, calcium carbide slag, and desulfurized gypsum as main raw materials. It is prepared through processes such as drying, grinding, and secondary mixing, resulting in significantly improved drying shrinkage.

[0004] The aforementioned studies demonstrate the application potential of industrial solid wastes such as fly ash in road base cementitious materials. However, existing technologies still have the following shortcomings: On the one hand, some technical solutions still require the addition of a certain amount of cement or lime, failing to completely eliminate reliance on traditional high-carbon emission cementitious materials; on the other hand, while improving early strength, existing fly ash-based cementitious materials often exacerbate shrinkage cracking or result in excessively short setting times, making them unsuitable for on-site paving construction requirements and unable to simultaneously meet the comprehensive needs of semi-rigid highway base courses for early strength, crack resistance, and construction setting time. Furthermore, the ability of existing technologies to control setting time under high-temperature construction environments needs further improvement. Therefore, there is an urgent need to develop a fly ash-based low-carbon cementitious material for semi-rigid highway base courses that can significantly replace cement while ensuring adjustable early strength, crack resistance, and construction setting time. Summary of the Invention

[0005] This invention aims to solve the problems of difficulty in achieving both early strength and crack resistance, and uncontrollable construction setting time in existing cementitious materials for semi-rigid road base courses. It provides a fly ash-based low-carbon cementitious material for semi-rigid road base courses that can replace cement, achieve synergistic improvement in early strength and crack resistance, and has an adjustable construction setting time, as well as its preparation and construction methods.

[0006] To achieve the above objectives, the present invention provides a fly ash-based low-carbon cementitious material for use in semi-rigid road base courses, characterized in that it comprises the following components in parts by weight: 50-70 parts fly ash; 15-30 parts of granulated blast furnace slag powder; 5-12 parts of calcium carbide slag; 3-8 parts of desulfurized gypsum; Sodium sulfate 1-5 parts; The retarding component is 0.1 to 0.5 parts. 0.5 to 1.5 parts of fast-dissolving sodium silicate.

[0007] Fly ash possesses potential pozzolanic activity, but its reaction rate is extremely slow, making it difficult to form sufficient cementitious products at room temperature. Granulated blast furnace slag powder, with its high calcium content and high activity index, can rapidly release calcium and silicate ions in the early stages of hydration, providing early strength. Calcium hydroxide, the main component of carbide slag, provides an alkaline environment to the system, promoting the deagglomeration of the glassy structure of fly ash and slag. Desulfurized gypsum provides sulfate ions, reacting with active aluminum to form ettringite. The formation of ettringite compensates for volume shrinkage during material hardening, thereby improving crack resistance. Sodium sulfate, as a strong electrolyte, accelerates the dissolution of calcium hydroxide and the dissolution of calcium ions in the slag, further accelerating the hydration reaction rate. Retarding components are used to regulate setting time, preventing paving and compaction from failing due to excessively rapid hydration. Quick-dissolving sodium silicate provides additional active silica, promoting the formation of geopolymer gels and enhancing the material's density and erosion resistance.

[0008] The ratio of fly ash to slag should be balanced. Too high a fly ash ratio will lead to insufficient early strength, while too high a slag ratio will increase costs and may exacerbate shrinkage. The amount of calcium carbide slag added needs to be matched with sodium sulfate and desulfurized gypsum. Too little calcium carbide slag will result in insufficient alkali activation, while too much may introduce free calcium oxide, leading to poor stability. The total amount of desulfurized gypsum and sodium sulfate should be controlled within a certain range. Excessive amounts will lead to excessive formation of ettringite, causing volume expansion, while insufficient amounts will fail to fully activate the fly ash. The dosage of retarder and readily soluble sodium silicate needs to be adjusted according to the ambient temperature during construction. At high temperatures, the dosage of retarder and readily soluble sodium silicate should be increased to prolong the setting time, while at low temperatures, the dosage should be reduced to avoid excessively slow setting. The proportions of all components in the entire system should work synergistically to match the formation rate of hydration products with the time window of the construction process, ultimately forming a hydraulic cementitious system mainly composed of CSH gel, ettringite, and geopolymer gel.

[0009] Preferably, the fly ash is Class F low-calcium fly ash with a specific surface area of ​​300 m². 2 / kg~500m 2 / kg, loss on ignition ≤8%. Class F low-calcium fly ash has a calcium oxide content of less than 10%, and its pozzolanic reaction mainly depends on external alkaline activation. The specific surface area is controlled at 300 m² / kg. 2 / kg~500m 2 Within the range of / kg, this is to ensure that the fly ash particles have a sufficient reaction interface, while avoiding excessive water demand or increased grinding energy consumption due to excessive fineness. Loss on ignition ≤8% is to control the content of unburned carbon. Carbon particles are porous and have strong adsorption properties, which can absorb additives and moisture, affecting the normal progress of the hydration reaction. If the specific surface area is less than 300m²... 2 / kg, coarse particles, insufficient reactivity, and difficulty in achieving early strength standards; if higher than 500m 2 / kg, if the particles are too fine, the specific surface energy increases, which can easily lead to an increase in the water demand of the mixture and an increased risk of drying shrinkage and cracking. F-type fly ash was chosen instead of C-type fly ash because F-type has stable components, is widely available, and there is no need to consider the stability risks caused by free calcium oxide. The technical solution is simpler and easier to promote in engineering.

[0010] Preferably, the specific surface area of ​​the granulated blast furnace slag powder is ≥600 m². 2 / kg, 28-day activity index ≥95%. Granulated blast furnace slag powder is a high-calcium, high-activity auxiliary cementitious component, with a specific surface area required to be ≥600m². 2 / kg is used to ensure that slag particles can rapidly dissolve calcium and silicate ions in the early stages of hydration, providing sufficient early strength. A 28-day activity index ≥95% means that the mortar strength of a 1:1 mixture of slag powder and cement is not less than 95% of the strength of pure cement mortar; this is a key indicator for evaluating the quality of slag powder. If the specific surface area of ​​the slag powder is less than 600 m², ...2 If the hydration rate is below 95%, the slag powder will not provide sufficient strength support within 7 days; if the activity index is below 95%, it indicates that the glass content in the slag powder is insufficient or that there are too many inert components, which will weaken its complementary reinforcing effect on fly ash. During the preparation process, when slag powder and fly ash are ground together, the finer slag particles can act as physical fillers, improving the particle size distribution of the cementitious material. At the same time, the calcium ions dissolved from the slag powder can promote the deagglomeration of the fly ash glass, achieving synergistic hydration of both.

[0011] Preferably, the calcium hydroxide content in the carbide slag is ≥80%, and the moisture content is ≤5%; the desulfurization gypsum is dihydrate or hemihydrate gypsum, with a sulfur trioxide content ≥40%. Calcium carbide slag is a waste residue produced by the chlor-alkali industry, and its main effective component is calcium hydroxide. The requirement of a calcium hydroxide content ≥80% is to ensure sufficient concentration of the alkaline activator. If the content is too low, the amount of carbide slag added needs to be increased, but excessive carbide slag will introduce more inert impurities. The moisture content ≤5% is to prevent material adhesion and equipment blockage during the grinding process, and to avoid water consumption of additives. Desulfurization gypsum is a byproduct of wet desulfurization in coal-fired power plants, and its main component is dihydrate or hemihydrate calcium sulfate. The requirement of a sulfur trioxide content ≥40% is to ensure an effective supply of sulfate ions. If the sulfur trioxide content is too low, the amount of desulfurization gypsum needs to be increased, but excessive gypsum will lead to excessive formation of ettringite, causing expansion and cracking. During the preparation process, both carbide slag and desulfurized gypsum need to be pre-dried at a temperature of 100℃ to 110℃ to avoid the gypsum from dehydrating and turning into anhydrous gypsum due to high temperature, thus reducing its activity.

[0012] Preferably, the retarding component is a mixture of sodium gluconate and citric acid in a mass ratio of 1:1 to 3:1. Both sodium gluconate and citric acid are organic retarder agents. Their mechanism of action is to form complexes with calcium ions in the system, inhibiting the nucleation and growth of calcium hydroxide crystals, thereby delaying the appearance of the hydration exothermic peak. The combination of the two has a better retarding effect than a single component because sodium gluconate has a stronger complexing ability for calcium ions, while citric acid, in addition to complexing calcium ions, can also adsorb onto the surface of unhydrated particles to form a protective film. The mass ratio is 1:1 to 3:1, with a higher proportion of sodium gluconate because sodium gluconate is more stable in alkaline environments and has less impact on later strength. If the retarding component dosage is less than 0.1 parts, the retarding effect is not obvious, and the mixture may have already begun to set before paving; if the dosage is greater than 0.5 parts, excessive retarding will lead to a severe decrease in early strength, prolonging the time before traffic can resume. In high-temperature construction environments, the dosage of the retarding component can be appropriately increased, but should not exceed the upper limit of 0.5 parts.

[0013] Preferably, the modulus of the rapidly soluble sodium silicate is 1.0 to 1.5. Rapidly soluble sodium silicate is a water-soluble silicate, and its modulus refers to the molar ratio of silicon dioxide to sodium oxide. A modulus of 1.0 to 1.5 falls within the low modulus range, indicating rapid dissolution and the ability to quickly release active silicate ions, which react with calcium and aluminum ions in the system to form CSH gel and geopolymer gel. The addition of rapidly soluble sodium silicate can significantly improve early strength and enhance the material's density and erosion resistance. However, rapidly soluble sodium silicate also accelerates the hydration reaction, shortening the setting time. At ambient temperatures above 30°C, the hydration reaction rate accelerates; without increasing the dosage of retarder and rapidly soluble sodium silicate, the setting time may be shortened to less than 2 hours, failing to meet the time delay requirements for on-site construction. Therefore, increasing the dosage of rapidly soluble sodium silicate to 1 to 2 parts, in synergy with the retarder, ensures both early strength and extended setting time. If the amount of fast-dissolving sodium silicate exceeds 2 parts, it will lead to excessive alkalinity and increase the risk of drying shrinkage and cracking; if it is less than 1 part, the effect of improving early strength will not be obvious.

[0014] This invention also provides a method for preparing the above-mentioned fly ash-based low-carbon cementitious material for use in semi-rigid road base courses, comprising the following steps: drying carbide slag and desulfurized gypsum at 100℃~110℃ until the moisture content is ≤1%, then mixing them with fly ash, granulated blast furnace slag powder, sodium sulfate, retarding components, and readily soluble sodium silicate, and ball milling for 30 minutes~45 minutes to achieve a loose density of 1±0.2g / cm³ for the resulting cementitious material. 3 The ball milling process ensures uniform mixing of the components and, through mechanical force, rearranges the particles, reduces porosity, and densifies the powder, thereby improving the bulk density of the cementitious material and the uniformity of subsequent hydration reactions. Loose bulk density is an important parameter characterizing the packing state of powders, and is controlled within 1 ± 0.2 g / cm³. 3 Within this range, sufficient density is ensured while avoiding an increase in water demand due to excessive grinding.

[0015] The core of this preparation method is an integrated process of "drying first, then mixing and grinding". Calcium carbide slag and desulfurized gypsum contain a large amount of free water. If they are ground directly without drying, the moisture will cause the material to adhere to the grinding media and liners, reducing grinding efficiency. Furthermore, the moisture will react with readily soluble sodium silicate, affecting its dispersion. The drying temperature is controlled at 100℃~110℃ to remove free water while preventing the dihydrate gypsum from dehydrating into hemihydrate or anhydrous gypsum, as dihydrate gypsum has the highest solubility and the best activation effect. The ball milling time is 30~45 minutes, ensuring thorough mixing and achieving the required fineness while avoiding over-grinding that would increase energy consumption and water demand. All solid components are fed into the mill at once. Compared to the process of grinding separately and then mixing, this method is simpler and can achieve uniform dispersion of each component particle, avoiding segregation due to differences in specific gravity.

[0016] Preferably, the specific surface area of ​​the fly ash-based low-carbon cementitious material after ball milling is 450 m². 2 / kg~550 m 2 / kg, the specific surface area was determined according to GB / T 8074-2008 "Determination of Specific Surface Area of ​​Cement - Blaine Method". Specific surface area is a key parameter characterizing the fineness of cementitious materials, directly related to the hydration reaction rate and strength development. It should be noted that the specific surface area of ​​fly ash raw material is 300–500 m² / kg. 2 / kg, while the overall specific surface area of ​​the cementitious material is limited to 450–550 m². 2 The overall fineness is relatively high (approximately 0.5 kg / kg). This is because granulated blast furnace slag powder, carbide slag, and desulfurized gypsum are easier to grind than fly ash during ball milling, resulting in a higher overall fineness of the mixed powder compared to the original fly ash, thus achieving higher reactivity and density. This method controls the specific surface area of ​​the ball-milled cementitious material to be around 450 m² / kg. 2 / kg~550m 2 / kg is an optimized range determined after comprehensively considering grinding energy consumption, water demand, early strength, and long-term durability. If the specific surface area is less than 450m²... 2 / kg, the particles are relatively coarse, the hydration reaction is insufficient, and the 7-day strength is difficult to reach above 3.5MPa; if it is higher than 550m 2 The particle size is too fine, significantly increasing the water demand of the mixture, leading to increased drying shrinkage and compaction difficulties. The Blaine method, as specified in GB / T 8074-2008, was used to determine the specific surface area. This method uses a Blaine air permeability meter, is simple to operate, and has good reproducibility, making it a common method for testing materials in the cement industry and road engineering. During the preparation process, the specific surface area can be adjusted by controlling the ball milling time; the longer the ball milling time, the larger the specific surface area. However, after 45 minutes, the increase in specific surface area slows down, while energy consumption increases significantly. Therefore, 30–45 minutes is the economically reasonable process window.

[0017] This invention also provides a construction method for a semi-rigid highway base course based on the above-mentioned fly ash-based low-carbon cementitious material acting on a semi-rigid highway base course, comprising the following steps: Step 1, Mixing: Dry mix the aggregate with the above-mentioned fly ash-based low-carbon cementitious material for 30 seconds, then add water and wet mix for 60 seconds. The amount of water used for mixing is 5% to 7% of the total mass of the aggregate and cementitious material. Step 2, paving: Paving is carried out using a paver with a loose paving coefficient of 1.25 to 1.35. The time from adding water and mixing to the completion of compaction should not exceed 4 hours. Step 3, Compaction: Compact the material into shape; Step 4, Segmented Curing: From day 1 to day 3, cover with moisturizing geotextile to keep the surface moist and prohibit passage; From day 4 to day 7, continue to cover with moisturizing geotextile, and allow light water trucks to pass at a speed of ≤5 km / h; After day 7, allow natural curing until 28 days.

[0018] The core innovation of this construction method lies in the segmented curing process and the control of the delay time. Dry mixing for 30 seconds ensures thorough mixing of the cementitious material and aggregates, followed by wet mixing with water for 60 seconds to prevent clumping of the cementitious material and ensure the slurry evenly coats the aggregate particles. The water content is controlled based on the optimal moisture content determined by compaction tests, with a deviation of no more than ±1%. This is because too low a moisture content results in a loose mixture that is difficult to compact, while too high a moisture content easily leads to the formation of springy soil during compaction and increases shrinkage cracks. The loose paving coefficient of 1.25–1.35 is determined based on the compaction characteristics of this material; a coefficient that is too small results in insufficient compaction thickness, while a coefficient that is too large increases the workload of leveling. The time from adding water and mixing to the completion of compaction should not exceed 4 hours. This is based on the setting characteristics of this material at room temperature. After 4 hours, the mixture begins to initially set, and compaction will damage the already formed cementitious structure, leading to a decrease in strength. Segmented curing is key to this method: From day 1 to 3, cover the surface with moisture-retaining geotextile and keep it moist, prohibiting traffic. During this stage, the hydration reaction is just beginning, requiring sufficient moisture to prevent shrinkage cracks. From day 4 to 7, continue covering, but allow light water trucks to pass at a low speed of ≤5 km / h. At this point, the material has gained some strength, and minor disturbances will not damage the structure; the water trucks also help retain moisture. After 7 days, allow natural curing. By this time, the hydration reaction has entered a stable period, and the impact of environmental humidity is reduced. This segmented curing method ensures early hydration conditions while avoiding the impact of prolonged traffic closures on the construction schedule.

[0019] Preferably, for construction environments with temperatures exceeding 30℃, a cementitious material with a retarding component dosage of 0.4–0.5 parts is selected. This extends the initial setting time to 5–6 hours, and the time from adding water and mixing to compaction can be extended to 6 hours. In high-temperature environments, the hydration reaction rate accelerates significantly. Without adjusting the formula, the initial setting time of the mixture may be shortened to less than 2 hours, making on-site paving and compaction impossible. This method increases the retarding component dosage to 0.4–0.5 parts, utilizing the calcium ion complexation and surface adsorption of sodium gluconate and citric acid to inhibit hydration heat release and control the initial setting time to 5–6 hours. Simultaneously, the allowable construction delay time is extended to 6 hours to accommodate the time requirements of transportation, paving, and compaction under high temperatures. It is important to note that the retarding component dosage should not exceed 0.5 parts, otherwise it will lead to excessive reduction in early strength. Furthermore, during high-temperature construction, the watering frequency should be appropriately increased to keep the aggregate and base surface moist and reduce the adverse effects of moisture evaporation on hydration.

[0020] Preferably, the compaction is achieved using a combination of vibratory roller and rubber-tired roller. The specific process is as follows: first, one pass of static compaction with a vibratory roller; then two passes of weak vibration with a vibratory roller; followed by two passes of strong vibration with a vibratory roller; and finally, one pass of finishing compaction with a rubber-tired roller. The vibratory roller uses high-frequency vibration to rearrange the mixture particles, increasing density; the rubber-tired roller uses a kneading action to seal surface pores, making the surface more dense and smooth. One pass of static compaction is for initial stabilization of the paving layer, preventing excessive vibration from shifting the mixture. Two passes of weak vibration initially compact the mixture, two passes of strong vibration achieve the designed compaction degree, and the final pass of finishing compaction with the rubber-tired roller eliminates wheel tracks and seals the surface. Insufficient compaction will result in insufficient base course bearing capacity; excessive compaction may cause aggregate breakage or surface undulation. This compaction process is matched to the material's setting characteristics and should be completed before the mixture initially sets.

[0021] Preferably, the aggregate is a skeleton-dense gradation crushed stone. A skeleton-dense gradation refers to a gradation type where coarse aggregates form a skeleton-interlocking structure, while fine aggregates and cementitious materials fill the skeleton voids. Compared to a suspended dense gradation, a skeleton-dense gradation has a higher internal friction angle and load-bearing capacity, while also providing better drainage performance. The strength of the cementitious material of this invention is slightly lower than that of cement, therefore, it needs to be combined with a skeleton-dense aggregate gradation to compensate for its mechanical properties. Specific requirements for the skeleton-dense gradation can be found in the relevant provisions of the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20, which features a higher coarse aggregate content and a lower fine aggregate content, thereby reducing the amount of cementitious material used and lowering costs and carbon emissions. If other gradation types, such as continuous dense or open gradation, are used, the performance advantages of this cementitious material may not be fully utilized.

[0022] The technical mechanism of this invention lies in the following: A multi-component composite activation system composed of fly ash, slag powder, carbide slag, desulfurized gypsum, and sodium sulfate, under the synergistic effect of an alkaline environment and sulfates, causes the glassy structure of fly ash and slag powder to depolymerize and repolymerize, generating a hydraulic cementitious product mainly composed of CSH gel, ettringite, and geopolymer gel. Specifically, slag powder provides early calcium and silicon sources, carbide slag provides the alkaline environment, desulfurized gypsum and sodium sulfate provide sulfate ions, and fly ash provides aluminum and later-stage activity. The retarding component controls the hydration rate through complexation of calcium ions and surface adsorption, while readily soluble sodium silicate supplements active silicon and promotes geopolymer formation. The synergistic effect of each component within a defined mass fraction ensures rapid early strength formation while inhibiting drying shrinkage cracking through the expansion compensation effect of ettringite. The segmented curing process during construction further optimizes the hydration environment. Moisturizing curing on days 1-3 prevents early water loss and cracking, while semi-open curing on days 4-7 promotes later strength development, thus fully meeting the comprehensive requirements of semi-rigid highway base courses for strength, crack resistance, erosion resistance, freeze-thaw resistance, and construction setting time.

[0023] Compared with the prior art, the present invention has the following beneficial effects: From a compositional perspective, the technical advantage of this solution lies in its five-element composite activation system consisting of fly ash, slag powder, carbide slag, desulfurized gypsum, and sodium sulfate. This system can replace cement and significantly reduce carbon emissions. The complementary activity of slag powder and fly ash solves the problem of low early strength caused by fly ash alone. The synergistic activation of carbide slag and sodium sulfate ensures an alkaline environment and sulfate supply. The addition of desulfurized gypsum promotes the formation of ettringite, achieving shrinkage compensation. The combined use of retarder components and readily soluble sodium silicate allows the setting time to be adjusted from 3 to 6 hours, adapting to different construction temperatures and transportation distances.

[0024] From a process perspective, the technical advantages of this solution lie in its integrated preparation process of "drying first, then mixing and grinding," and its segmented curing and construction process. The drying process ensures grinding efficiency and gypsum activity, and a ball milling time of 30-45 minutes achieves a specific surface area of ​​450 m². 2 / kg~550m 2 Precise control of / kg. In the segmented curing process, the fully enclosed moisturizing curing on days 1-3 and the semi-open curing on days 4-7 not only ensure early hydration conditions but also shorten the time of traffic closure, demonstrating good engineering adaptability.

[0025] From a performance perspective, the cementitious material obtained in this scheme, when used for semi-rigid highway base courses, achieves an unconfined compressive strength of 3.8–4.2 MPa after 7 days, meeting the early strength requirements of high-grade highway base courses. Its 28-day drying shrinkage coefficient is more than 40% lower than that of cement-stabilized crushed stone, significantly reducing cracking. The erosion resistance rate is ≤0.8%, exhibiting superior erosion resistance compared to cement-stabilized crushed stone. The strength loss rate after 5 freeze-thaw cycles is ≤15%, meeting the freeze-thaw resistance requirements for highway base courses in seasonally frozen areas. The construction delay time can reach 4 hours, and under high-temperature conditions, this can be extended to 6 hours by adjusting the dosage of the retarding component, demonstrating good construction adaptability. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to specific examples. However, it should be understood that these embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0027] General Implementation Examples A fly ash-based low-carbon cementitious material for use in semi-rigid highway base courses, its preparation and construction method are as follows: S1. Raw Material Preparation: Weigh the following components by weight: 50-70 parts fly ash, 15-30 parts granulated blast furnace slag powder, 5-12 parts calcium carbide slag, 3-8 parts desulfurized gypsum, 1-5 parts sodium sulfate, 0.1-0.5 parts retarder, and 0.5-1.5 parts readily soluble sodium silicate. The fly ash is Class F low-calcium fly ash with a specific surface area of ​​300 m². 2 / kg~500m 2 / kg, loss on ignition ≤8%; specific surface area of ​​granulated blast furnace slag powder ≥600m² 2 / kg, 28-day activity index ≥95%; calcium hydroxide content in carbide slag ≥80%, moisture content ≤5%; desulfurized gypsum is dihydrate gypsum or hemihydrate gypsum, sulfur trioxide content ≥40%; retarding component is a mixture of sodium gluconate and citric acid, with a mass ratio of 1:1 to 3:1; modulus of readily soluble sodium silicate is 1.0 to 1.5.

[0028] S2. Drying: Dry the carbide slag and desulfurized gypsum at 100℃~110℃ until the moisture content is ≤1%.

[0029] S3. Grinding and Mixing: The dried carbide slag, desulfurized gypsum, fly ash, granulated blast furnace slag powder, sodium sulfate, retarder, and readily soluble sodium silicate are mixed and ball-milled for 30 to 45 minutes to obtain a loose density of 1 ± 0.2 g / cm³ for the resulting fly ash-based low-carbon cementitious material. 3 The specific surface area of ​​the cementitious material after ball milling is 450 m². 2 / kg~550m 2 / kg.

[0030] S4. Aggregate preparation: Use dense-graded crushed stone as aggregate.

[0031] S5. Mixing: Dry mix the aggregate and the above-mentioned fly ash-based low-carbon cementitious material at a mass ratio of 100:4 to 100:6 for 30 seconds, then add water and wet mix for 60 seconds. The amount of water used for mixing is 5% to 7% of the total mass of the aggregate and cementitious material.

[0032] S6. Paving: Paving is carried out using a paver with a loose paving coefficient of 1.25–1.35. The time from adding water and mixing to compaction should not exceed 4 hours. For high-temperature construction environments, a cementitious material with a retarding component of 0.4–0.5 parts can be used, in which case the time from adding water and mixing to compaction can be extended to 6 hours.

[0033] S7. Compaction: A combination of vibratory roller and rubber-tired roller is used for compaction. The specific process is as follows: first, use a vibratory roller for static compaction once, then use a vibratory roller for weak vibration twice, then use a vibratory roller for strong vibration twice, and finally use a rubber-tired roller to finish the surface once.

[0034] S8. Segmented curing: From day 1 to day 3, cover with moisturizing geotextile to keep the surface moist and prohibit passage; from day 4 to day 7, continue to cover with moisturizing geotextile and allow light sprinkler trucks to pass at a speed of ≤5 km / h; after day 7, allow natural curing until day 28.

[0035] Example 1 A fly ash-based low-carbon cementitious material for use in semi-rigid road base courses, its preparation and construction method at room temperature (20℃) are as follows: S1. Raw Material Preparation: Weigh the following components by weight: 60 parts fly ash, 20 parts granulated blast furnace slag powder, 8 parts carbide slag, 5 parts desulfurized gypsum, 3 parts sodium sulfate, 0.2 parts retarder, and 1 part readily soluble sodium silicate. The fly ash is classified as Class F low-calcium fly ash with a specific surface area of ​​400 m². 2 / kg, loss on ignition 5%; specific surface area of ​​granulated blast furnace slag powder 650m² 2 / kg, 28-day activity index 96%; calcium hydroxide content in carbide slag 85%, water content 3%; desulfurized gypsum is dihydrate gypsum, sulfur trioxide content 42%; retarding component is a mixture of sodium gluconate and citric acid, with a mass ratio of 2:1; modulus of readily soluble sodium silicate is 1.2.

[0036] S2. Drying: Dry the carbide slag and desulfurized gypsum at 105℃ until the moisture content is ≤1%.

[0037] S3. Grinding and Mixing: The dried carbide slag, desulfurized gypsum, fly ash, granulated blast furnace slag powder, sodium sulfate, retarder, and readily soluble sodium silicate are mixed and ball-milled for 38 minutes to obtain a fly ash-based low-carbon cementitious material. The specific surface area of ​​this cementitious material after ball milling is 500 m². 2 / kg, loose bulk density is 1.05g / cm³ 3 .

[0038] S4. Aggregate preparation: Use dense-graded crushed stone as aggregate.

[0039] S5. Mixing: Dry mix the aggregate and the above-mentioned fly ash-based low-carbon cementitious material at a mass ratio of 100:5 for 30 seconds, then add water and wet mix for 60 seconds. The amount of water used for mixing is 6% of the total mass of the aggregate and cementitious material.

[0040] S6. Paving: Paving is carried out using a paver with a loose paving coefficient of 1.30. The time from adding water and mixing to compaction should not exceed 4 hours.

[0041] S7. Compaction: A combination of vibratory roller and rubber-tired roller is used for compaction. The specific process is as follows: first, use a vibratory roller for static compaction once, then use a vibratory roller for weak vibration twice, then use a vibratory roller for strong vibration twice, and finally use a rubber-tired roller to finish the surface once.

[0042] S8. Segmented curing: From day 1 to day 3, cover with moisturizing geotextile to keep the surface moist and prohibit passage; from day 4 to day 7, continue to cover with moisturizing geotextile and allow light sprinkler trucks to pass at a speed of ≤5 km / h; after day 7, allow natural curing until day 28.

[0043] Example 2 A fly ash-based low-carbon cementitious material for use in semi-rigid road base courses, its preparation and construction method at 25℃ are as follows: S1. Raw Material Preparation: Weigh the following components by weight: 55 parts fly ash, 25 parts granulated blast furnace slag powder, 10 parts carbide slag, 6 parts desulfurized gypsum, 2 parts sodium sulfate, 0.3 parts retarder, and 0.5 parts readily soluble sodium silicate. The fly ash is Class F low-calcium fly ash with a specific surface area of ​​350 m² / g. 2 / kg, loss on ignition 6%; specific surface area of ​​granulated blast furnace slag powder 700m² 2 / kg, 28-day activity index 97%; calcium hydroxide content in carbide slag 82%, water content 4%; desulfurized gypsum is hemihydrate gypsum with sulfur trioxide content 41%; retarding component is a mixture of sodium gluconate and citric acid in a mass ratio of 1.5:1; modulus of readily soluble sodium silicate is 1.0.

[0044] S2. Drying: Dry the carbide slag and desulfurized gypsum at 100℃ until the moisture content is ≤1%.

[0045] S3. Grinding and Mixing: The dried carbide slag, desulfurized gypsum, fly ash, granulated blast furnace slag powder, sodium sulfate, retarder, and readily soluble sodium silicate are mixed and ball-milled for 42 minutes to obtain a fly ash-based low-carbon cementitious material. The specific surface area of ​​this cementitious material after ball milling is 520 m². 2 / kg, loose bulk density is 1.08g / cm³ 3 .

[0046] S4. Aggregate preparation: Use dense-graded crushed stone as aggregate.

[0047] S5. Mixing: Dry mix the aggregate and the above-mentioned fly ash-based low-carbon cementitious material at a mass ratio of 100:4.5 for 30 seconds, then add water and wet mix for 60 seconds. The amount of water used for mixing is 5% of the total mass of the aggregate and cementitious material.

[0048] S6. Paving: Paving is carried out using a paver with a loose paving coefficient of 1.28. The time from adding water and mixing to compaction should not exceed 4 hours.

[0049] S7. Compaction: A combination of vibratory roller and rubber-tired roller is used for compaction. The specific process is as follows: first, use a vibratory roller for static compaction once, then use a vibratory roller for weak vibration twice, then use a vibratory roller for strong vibration twice, and finally use a rubber-tired roller to finish the surface once.

[0050] S8. Segmented curing: From day 1 to day 3, cover with moisturizing geotextile to keep the surface moist and prohibit passage; from day 4 to day 7, continue to cover with moisturizing geotextile and allow light sprinkler trucks to pass at a speed of ≤5 km / h; after day 7, allow natural curing until day 28.

[0051] Example 3 A fly ash-based low-carbon cementitious material for use in semi-rigid highway base courses, its preparation and construction method at 35℃ are as follows: S1. Raw Material Preparation: Weigh the following components by weight: 65 parts fly ash, 15 parts granulated blast furnace slag powder, 6 parts carbide slag, 4 parts desulfurized gypsum, 4 parts sodium sulfate, 0.45 parts retarder, and 1.5 parts readily soluble sodium silicate. The fly ash is classified as Class F low-calcium fly ash with a specific surface area of ​​450 m². 2 / kg, loss on ignition 4%; specific surface area of ​​granulated blast furnace slag powder 620m² 2 / kg, 28-day activity index 95%; calcium hydroxide content in carbide slag 88%, water content 2%; desulfurized gypsum is dihydrate gypsum with sulfur trioxide content 43%; retarding component is a mixture of sodium gluconate and citric acid in a mass ratio of 2.5:1; modulus of readily soluble sodium silicate is 1.4.

[0052] S2. Drying: Dry the carbide slag and desulfurized gypsum at 110℃ until the moisture content is ≤1%.

[0053] S3. Grinding and Mixing: The dried carbide slag, desulfurized gypsum, fly ash, granulated blast furnace slag powder, sodium sulfate, retarder, and readily soluble sodium silicate are mixed and ball-milled for 32 minutes to obtain a fly ash-based low-carbon cementitious material. The specific surface area of ​​this cementitious material after ball milling is 470 m². 2 / kg, loose bulk density is 0.95g / cm³ 3 .

[0054] S4. Aggregate preparation: Use dense-graded crushed stone as aggregate.

[0055] S5. Mixing: Dry mix the aggregate and the above-mentioned fly ash-based low-carbon cementitious material at a mass ratio of 100:5.5 for 30 seconds, then add water and wet mix for 60 seconds. The amount of water used for mixing is 7% of the total mass of the aggregate and cementitious material.

[0056] S6. Paving: Paving is carried out using a paver with a loose paving coefficient of 1.32. The time from adding water and mixing to compaction should not exceed 6 hours.

[0057] S7. Compaction: A combination of vibratory roller and rubber-tired roller is used for compaction. The specific process is as follows: first, use a vibratory roller for static compaction once, then use a vibratory roller for weak vibration twice, then use a vibratory roller for strong vibration twice, and finally use a rubber-tired roller to finish the surface once.

[0058] S8. Segmented curing: From day 1 to day 3, cover with moisturizing geotextile to keep the surface moist and prohibit passage; from day 4 to day 7, continue to cover with moisturizing geotextile and allow light sprinkler trucks to pass at a speed of ≤5 km / h; after day 7, allow natural curing until day 28.

[0059] Comparative Example 1 The difference from Example 1 is that granulated blast furnace slag powder, desulfurized gypsum and sodium sulfate are not added to the raw materials. The raw materials consist only of 70 parts fly ash, 15 parts carbide slag, 0.2 parts retarding component and 1 part quick-dissolving sodium silicate.

[0060] Comparative Example 2 The difference from Example 1 is that: no desulfurized gypsum and sodium sulfate are added to the raw materials, and the raw materials consist of 60 parts fly ash, 25 parts granulated blast furnace slag powder, 12 parts carbide slag, 0.2 parts retarding component and 1 part quick-dissolving sodium silicate.

[0061] Comparative Example 3 The difference from Example 1 is that no carbide slag is added to the raw materials, which are composed of 65 parts fly ash, 25 parts granulated blast furnace slag powder, 8 parts desulfurized gypsum, 5 parts sodium sulfate, 0.2 parts retarding component and 1 part quick-dissolving sodium silicate.

[0062] Comparative Example 4 The difference from Example 1 is that the curing process is changed to spreading and compacting the soil, then continuously covering it with a moisture-retaining geotextile for 7 days, prohibiting any vehicle traffic, and then allowing it to cure naturally after 7 days without segmented curing.

[0063] Comparative Example 5 The difference from Example 1 is that no mixture of sodium gluconate and citric acid is added to the raw materials as a retarding component, and only 1 part of readily soluble sodium silicate is retained.

[0064] Comparative Example 6 The difference from Example 1 is that the specific surface area of ​​the fly ash used is 250 m². 2 / kg, other components are the same.

[0065] Comparative Example 7 The difference from Example 1 is that the ball milling time is shortened to 20 minutes, and the specific surface area of ​​the cementitious material after ball milling is 380 m². 2 / kg, loose bulk density is 0.70g / cm³ 3 .

[0066] Comparative Example 8 The difference from Example 1 is that the ball milling time was extended to 60 minutes, and the specific surface area of ​​the cementitious material after ball milling was 580 m². 2 / kg, loose bulk density is 1.25g / cm³ 3 .

[0067] Comparative Example 9 The difference from Example 1 is that the maintenance process is changed to a fully enclosed moisturizing maintenance for days 1-7, prohibiting any vehicle passage, without segmentation, and water trucks are not allowed to pass through from days 4-7.

[0068] Comparative Example 10 The difference from Example 1 is that the construction environment temperature is 35°C, but the amount of retarding component in the raw materials is still 0.2 parts, not increased to 0.4-0.5 parts.

[0069] Comparative Example 11 The difference from Example 1 is that, after preparing the raw materials, ball milling was not performed; instead, the components were manually stirred and mixed in a container for 5 minutes. The resulting mixture had a specific surface area of ​​280 m². 2 / kg, loose bulk density is 0.50g / cm³ 3 .

[0070] Comparative Example 12 The difference from Example 1 is that the ball milling time is shortened to 5 minutes, and the specific surface area of ​​the cementitious material after ball milling is 320 m². 2 / kg, loose bulk density is 0.55g / cm³ 3 .

[0071] The detection methods are shown in Table 1: Table 1 Detection Methods

[0072] Table 2 Performance data for examples and comparative examples

[0073] The background technology of this invention reveals a key problem commonly found in existing semi-rigid road base cementitious materials: cement-based cementitious materials have high carbon emissions and high costs, while fly ash alone can partially replace cement, but its early strength development is slow, usually failing to reach the unconfined compressive strength required for the base layer within 7 days, and its crack resistance is poor, with prominent problems of drying shrinkage and thermal shrinkage cracks. Furthermore, fly ash-based materials have insufficient resistance to erosion under dynamic water action and weak resistance to freeze-thaw cycles. Existing activation methods for fly ash with low activity often exacerbate shrinkage cracking while improving early strength, or result in excessively short setting times that cannot meet the process requirements of on-site paving construction, making it difficult to simultaneously satisfy the comprehensive requirements of semi-rigid road base layers for early strength, crack resistance, erosion resistance, and construction setting time. The embodiments of the present invention construct a five-element composite activation system comprising fly ash, granulated blast furnace slag powder, carbide slag, desulfurized gypsum, and sodium sulfate, and combine it with the synergistic regulation of retarding components and readily soluble sodium silicate, as well as a segmented curing process, to successfully achieve the synergistic effects of rapid early strength formation, significant reduction in both drying shrinkage and thermal shrinkage coefficients, improved erosion resistance and freeze-thaw resistance, and adjustable construction setting time. Its theoretical advantages lie in the fact that slag powder provides early calcium and silicon sources, which complement the later pozzolanic reaction of fly ash; carbide slag provides an alkaline environment to promote the depolymerization of glass; desulfurized gypsum provides sulfate ions to react with active aluminum to generate ettringite, and the expansion effect of ettringite compensates for volume shrinkage, thereby inhibiting drying shrinkage cracks; sodium sulfate, as a strong electrolyte, accelerates the dissolution of calcium hydroxide and the dissolution of calcium ions, further accelerating the hydration reaction rate; the retarding component controls the hydration process through complexation of calcium ions and surface adsorption, and the fast-dissolving sodium silicate supplements active silicon to promote the formation of geopolymer gel. The two work together to make the setting time flexibly adjustable from 3 to 6 hours; in the segmented curing process, the first three days are fully enclosed and moisturized to prevent early water loss and cracking, and light sprinkler trucks are allowed to pass at low speed from the fourth to the seventh day, which not only ensures the hydration conditions but also shortens the time of traffic closure. In each embodiment, the overall performance is optimal when the ratio of fly ash to slag powder is appropriate and the ratio of activator is coordinated. Appropriately increasing the proportion of slag powder and reducing the amount of readily soluble sodium silicate results in a slight decrease in early strength but an extended setting time, making it suitable for construction over long distances. Increasing the amount of retarding components and readily soluble sodium silicate in high-temperature environments can extend the setting time to 5 to 6 hours, ensuring the feasibility of high-temperature construction.

[0074] Compared with the embodiments, each comparative example failed to achieve the aforementioned synergistic effect due to the absence or deviation from any key technical feature. Comparative Example 1 lacked granulated blast furnace slag powder, desulfurized gypsum, and sodium sulfate. The carbide slag and readily soluble sodium silicate alone could not provide sufficient early calcium source and sulfate ions, making it difficult to fully activate the fly ash activity. This resulted in extremely low early strength, and without ettringite to compensate for shrinkage, severe drying shrinkage cracks occurred, significantly reducing erosion resistance and freeze-thaw resistance. Comparative Example 2, although retaining slag powder and carbide slag, lacked desulfurized gypsum and sodium sulfate. Without sulfate ions participating in the reaction, sufficient ettringite could not be generated. Although the slag powder provided some early strength, the drying shrinkage coefficient increased significantly, and the erosion resistance was insufficient, indicating that the expansion compensation effect of ettringite is indispensable for suppressing shrinkage. Comparative Example 3 lacked carbide slag, resulting in insufficient alkalinity in the system. The glassy structure of fly ash and slag powder was difficult to effectively depolymerize, leading to slow hydration and significantly lower early strength. Simultaneously, the rapid hydrolysis of readily soluble sodium silicate in the low-alkaline environment resulted in an excessively short setting time, preventing paving and compaction. This demonstrates that alkaline activation is a prerequisite for the normal operation of a multi-component system. Comparative Example 4 employed full-closed curing for 7 days without segmentation. Although early strength was not significantly affected, the lack of appropriate disturbance and water replenishment in the later stages of curing resulted in a higher drying shrinkage coefficient than the segmented curing example. Furthermore, the excessively long traffic closure time was detrimental to project progress, indicating that segmented curing achieved a better balance between ensuring hydration conditions and shortening the closure time. Comparative Example 5, without adding retarder components, relied solely on readily soluble sodium silicate to accelerate hydration. The initial setting time was less than two hours, and the mixture began to solidify during transportation and paving. By the time of compaction, it had lost its plasticity, resulting in severely insufficient compaction and a significant decrease in strength. This confirms the crucial role of retarder components in controlling the construction window. The fly ash used in Comparative Example 6 had a specific surface area of ​​less than 300 m². 2 / kg, with coarse particles, a small reaction interface, and extremely slow pozzolanic reaction, even with the same formulation, it is impossible to form sufficient strength within 7 days. Furthermore, the mixture has poor workability and low compaction, indicating that the fly ash fineness must reach a threshold to ensure activity. Comparative Example 7, with a ball milling time shortened to 15 minutes, had a specific surface area of ​​only 380 m². 2 / kg, below 450m 2 / kg, with a loose density of only 0.70g / cm³. 3 The loose particle packing led to increased water demand and decreased compaction of the mixture. Simultaneously, the uneven distribution of hydration products resulted in lower early and later strengths compared to the example, and an increased shrinkage coefficient. This indicates that specific surface area and loose density are crucial parameters for ensuring the uniformity and compactness of the mixture. In Comparative Example 8, the ball milling time was extended to 60 minutes, achieving a specific surface area of ​​580 m². 2 / kg, above 550m 2 / kg, loose density 1.25g / cm³, excessively fine particles significantly increased water demand, raised the optimum moisture content of the mixture, increased drying shrinkage cracks after compaction, and significantly increased grinding energy consumption, indicating that a higher specific surface area is not necessarily better; a balance must be struck between activity and workability. Comparative Example 9, cured in a fully enclosed environment for 7 days without water truck access, similar to Comparative Example 4, also showed a high drying shrinkage coefficient, further verifying the positive effect of moderate disturbance and water replenishment in the later stages of segmented curing on inhibiting drying shrinkage. Comparative Example 10, at a high temperature of 35℃ without increasing the amount of retarder, showed a drastic acceleration in the hydration reaction rate, shortening the initial setting time to 1.5 hours. The mixture had already begun to set before compaction was complete, resulting in low compaction and poor strength, indicating that the amount of retarder must be adjusted simultaneously during high-temperature construction to control the setting time within the workable range of 5 to 6 hours. Comparative Example 11, without ball milling, only simple mixing, had a specific surface area of ​​only 280m². 2 / kg, with a loose bulk density of only 0.50g / cm³ 3 The components are extremely unevenly distributed, and there is no mechanical interlocking between particles, making it difficult for the hydration reaction to proceed effectively. This results in a 7-day strength of less than 1 MPa, a compaction degree of only 88.5%, and a drying shrinkage coefficient as high as 520 × 10⁻⁶. -6 The material exhibits extremely poor resistance to erosion and freeze-thaw cycles, indicating that ball milling and densification are fundamental to ensuring the performance of cementitious materials. Comparative Example 12, with a ball milling time of only 5 minutes, has a specific surface area of ​​only 320 m². 2 / kg, loose bulk density 0.55g / cm³ 3 Although there was some mixing effect, it was far from meeting the standard; the particles remained loose, with a specific surface area of ​​only 320 m². 2 / kg, the activity was not fully activated, and the strength was significantly lower than in the example, confirming that the ball milling time must reach more than 30 minutes to achieve a loose packing density of 0.8–1.2 g / cm³. 3 The preferred range. The results of these comparative examples collectively demonstrate that the technical solution of the present invention is an organic whole with interconnected links and precisely coordinated parameters. Its five-element composite activation system, synergistic regulation of retarding and fast-dissolving sodium silicate, fineness control of fly ash and cementitious materials, and segmented curing process are all indispensable for simultaneously achieving the early strength, crack resistance, erosion resistance, freeze-thaw resistance and construction adaptability required for semi-rigid road base courses, thus systematically solving the long-standing contradictions in the background technology.

Claims

1. A fly ash-based low-carbon cementitious material for use in semi-rigid base courses of highways, characterized in that, It consists of the following components in parts by weight: 50-70 parts fly ash; 15-30 parts of granulated blast furnace slag powder; 5-12 parts of calcium carbide slag; 3-8 parts of desulfurized gypsum; Sodium sulfate 1-5 parts; The retarding component is 0.1 to 0.5 parts. 0.5–1.5 parts of fast-dissolving sodium silicate; The fly ash is Class F low-calcium fly ash, with a specific surface area of ​​300–500 m². 2 / kg, loss on ignition ≤8%; the specific surface area of ​​the granulated blast furnace slag powder is ≥600m². 2 / kg, 28d activity index ≥95%; the calcium carbide slag contains ≥80% Ca(OH)2 and ≤5% moisture; the desulfurized gypsum is dihydrate or hemihydrate gypsum with SO3 content ≥40%; the retarding component is a mixture of sodium gluconate and citric acid in a mass ratio of 1:1 to 3:1; the modulus of the readily soluble sodium silicate is 1.0 to 1.5; The preparation method of the fly ash-based low-carbon cementitious material includes the following steps: Carbide slag and desulfurized gypsum were dried at 100℃~110℃ until the moisture content was ≤1%. Then, they were mixed with fly ash, granulated blast furnace slag powder, sodium sulfate, retarder, and readily soluble sodium silicate, and ball-milled for 30~45min until the loose density of the resulting fly ash-based low-carbon cementitious material was 1±0.2g / cm³. 3 ; The specific surface area of ​​the fly ash-based low-carbon cementitious material is 500±50m². 2 / kg.

2. A construction method for the fly ash-based low-carbon cementitious material as described in claim 1 in a semi-rigid base course of highways, characterized in that, Includes the following steps: (1) Mixing: The aggregate and the fly ash-based low-carbon cementitious material according to claim 1 are mixed at a mass ratio of 100:4 to 100:6, and then water is added for mixing, wherein the amount of water used for mixing is 5% to 7% of the total mass of the aggregate and cementitious material; (2) Paving: Paving is carried out using a paver, and the time from adding water and mixing to the completion of compaction shall not exceed the preset maximum allowable time; (3) Rolling: Rolling and shaping; (4) Segmented maintenance: Days 1-3: Cover with moisture-retaining geotextile, keep the surface moist, and prohibit passage; Days 4-7: Continue to cover with geotextile, and allow light water trucks to pass at low speeds; After the 7th day, allow it to rest naturally until the 28th day.

3. The construction method of the fly ash-based low-carbon cementitious material in a semi-rigid base course of highways according to claim 2, characterized in that, The preset maximum allowable time is 4 to 6 hours.

4. The construction method of the fly ash-based low-carbon cementitious material in a semi-rigid base course of highways according to claim 2, characterized in that, When the ambient temperature during construction is above 30℃, the dosage of the retarding component in the fly ash-based low-carbon cementitious material is 0.4 to 0.5 parts, and the preset maximum allowable time is 6 hours; when the ambient temperature during construction is below 30℃, the dosage of the retarding component in the fly ash-based low-carbon cementitious material is 0.1 to 0.4 parts, and the preset maximum allowable time is 4 hours.

5. The construction method of the fly ash-based low-carbon cementitious material in a semi-rigid base course of highways according to claim 2, characterized in that, The compaction is carried out by a combination of vibratory roller and rubber-tired roller. The specific process is as follows: first, the vibratory roller is used for static compaction once, then weak vibration twice, strong vibration twice, and finally the surface is finished with a rubber-tired roller once.

6. The construction method of the fly ash-based low-carbon cementitious material in a semi-rigid base course of highways according to claim 2, characterized in that, The phrase "allowing light-duty water trucks to pass at low speeds" means that the water trucks can pass at a speed of ≤5km / h; the loose paving coefficient is 1.25 to 1.35.

Images