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Calcium sulfoaluminate cement is a series of cements independently developed by China in the 1970s. It is made from bauxite, limestone, and gypsum as raw materials through low-temperature calcination (1300~1350℃), grinding, and other processes. This produces a hydraulic cementitious material with a series of excellent properties such as early strength, rapid hardening, freeze resistance, corrosion resistance, impermeability, expansion, autogenous stress, and low alkalinity. It can be applied in emergency repair and construction projects, seawater corrosion-resistant engineering, and engineering with large day-night temperature variations. According to "Calcium Sulfoaluminate Cement" (GB/T20472-2006), calcium sulfoaluminate cement is a hydraulic cementitious material made by the grinding of appropriate raw materials into clinker containing anhydrous calcium sulfoaluminate and dicalcium silicate as the major mineral components mixed with varying amounts of limestone and a suitable amount of gypsum. Calcium sulfoaluminate cement is categorized into rapid-hardening calcium sulfoaluminate cement, low-alkalinity calcium sulfoaluminate cement, and autogenous stress calcium sulfoaluminate cement. In recent years, to address the high cost and performance defects that limit the market application of calcium sulfoaluminate cement, research has begun domestically and internationally to develop calcium sulfoaluminate cement by incorporating solid waste or Portland cement, aiming to mitigate issues such as concentrated hydration heat, difficulty in controlling setting time, and slow strength development.
The advantages of calcium sulfoaluminate cement are evident, providing broad market prospects in fields such as marine engineering, low-temperature construction, rapid construction projects, and antique-style architectural engineering. Compared to the massive overall production and sales volume of over 2 billion tons of cement domestically, calcium sulfoaluminate cement is a niche product with a very low proportion in the domestic cement industry. According to statistics, the market size of calcium sulfoaluminate cement in China grew from 1.293 billion yuan in 2016 to 1.903 billion yuan in 2022.
Calcium sulfoaluminate cement clinker was first successfully trial-produced in hollow dry process rotary kilns with an annual output of 20,000-30,000 tons. Subsequently, production was progressively scaled up to shaft preheater kilns with an annual output of 90,000-100,000 tons and new dry process production lines with precalciner kilns with an annual output of 300,000 tons. Through technology investments and technology transfers, the production of calcium sulfoaluminate cement has continuously developed. By 1997, there were 15 calcium sulfoaluminate cement factories in China, producing nearly one million tons annually, forming the prototype of a new cement industry. After more than 20 years of market maturation, there are currently around 20 calcium sulfoaluminate cement factories in China with total production stabilizing at around 1.5 million tons.
Internal factors affecting the pricing of calcium sulfoaluminate cement products refer to the factors that producers can control when setting prices, such as costs and expenses, grade, raw materials, processes, human resources, and management levels. External factors affecting the pricing of calcium sulfoaluminate cement products are those that calcium sulfoaluminate cement suppliers cannot control but significantly impact pricing, such as market demand, industry types, competition, market development, and the environment. According to statistics, from 2016 to 2022, the average market price of calcium sulfoaluminate cement in China has generally been on the rise. However, due to multiple factors such as technological advancements and intensified market competition, the price of calcium sulfoaluminate may face certain downward risks. Therefore, promoting new product development and improving product performance will become important measures for leading companies to maintain high prices and sustain high profit levels.
Green and environmentally friendly building materials are a major trend in the development of road materials today. Calcium sulfoaluminate cement is made from high-quality bauxite and natural gypsum through calcination. Its production cost is high, and its raw materials are difficult to obtain, limiting its application and development. In contrast, the annual output of industrial waste in China increases year by year, leading to resource waste. Clearly, mixing industrial waste with calcium sulfoaluminate cement in large proportions is one effective way to address this issue. High-Belite calcium sulfoaluminate cement is made from low-grade bauxite and industrial waste residues. Compared to calcium sulfoaluminate cement, the clinker contains over 40% dicalcium silicate, offering advantages such as low energy consumption, low cost, rapid setting and hardening, micro-expansion, low shrinkage, freeze resistance, impermeability, and sulfate resistance, thereby improving the slow post-curing strength development of calcium sulfoaluminate cement. The research into high-Belite calcium sulfoaluminate cement significantly reduces the cost of calcium sulfoaluminate cement, providing a path for the development of early-strength green building materials.
Portland cement hydrates slowly, with low early strength but stable later strength development. Calcium sulfoaluminate cement hydrates rapidly, with high early strength but slow later strength development. By mixing Portland cement with calcium sulfoaluminate cement, it can delay the release of hydration heat, extend the setting time, and ensure stable post-curing strength development. Studies have found that mixing Portland cement and calcium sulfoaluminate cement at different ratios affects strength and setting time. When mixed in a 6/4 ratio, the setting time is moderate, the 6-hour strength of the cement system reaches its peak, and the late strength develops stably. Optimization of the ratio of Portland cement and calcium sulfoaluminate cement revealed that an 8/2 mixture achieves better overall performance. It was noted that the Ca(OH)2 gel formed by the hydration of Portland cement participates in the hydration process of calcium sulfoaluminate cement, promoting the formation of AFt and enhancing early strength. However, the early strength of this mixed cement is lower than that of calcium sulfoaluminate cement alone, requiring further research and improvement.
