【Sea River Civil Engineering Discussion】What is heat-resistant concrete?
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Heat-resistant concrete is commonly used in applications such as the foundations of industrial furnaces, the shells of blast furnaces, and chimneys. It can withstand temperatures ranging from 200 to 1300°C for extended periods of time, while retaining the required physical and mechanical properties at such high temperatures. Selection of aggregates for heat-resistant concrete: The main material in heat-resistant concrete is aggregate, which accounts for about 80% of the total material used in such concrete; it is therefore a key factor affecting the properties of heat-resistant concrete. The particle size of aggregates should neither be too large nor too small; they are generally classified into size ranges such as 5-8 mm, 3-5 mm, and 0-3 mm. A proper grading of aggregates allows them to pack more densely, reduces the amount of cementing material required, and maximizes the skeletal role of the aggregates, thereby improving the density of heat-resistant concrete and reducing its shrinkage rate. When selecting the type of aggregate, it is necessary to consider the heat resistance requirements of the application site. Commonly used materials include clay clinker, refractory brick particles, bauxite, corundum particles, ceramsite, and expanded perlite. Selection of binders for heat-resistant concrete: To ensure the heat-resistant properties of heat-resistant concrete, it is necessary to minimize the amount of binder used while still meeting the requirements regarding strength and heat resistance. At the same time, the binder should be chosen appropriately based on the highest temperatures that the heat-resistant concrete may be exposed to during use. Common binders include silicate-based binders such as silicate, aluminate, bauxite, sulfate, and phosphate binders. Slag Portland cement, ordinary Portland cement, or water glass are generally used as binders for heat-resistant concrete, and they can be divided into three categories: aluminate binders. High-alumina cement and pure calcium aluminate cement are generally used; these alumina-based binders can operate in temperature ranges of 800°C to 1200°C. Heat-resistant concrete prepared using bauxite binders, namely bauxite cement, can reach a maximum operating temperature of 1600 °C with phosphate binders. Phosphate binders do not possess binding properties at room temperature; rather, when heated to a certain temperature, some phosphates undergo decomposition-polymerization reactions, which endows them with strong adhesive properties that bind the aggregates together, thereby providing strength. As a binder in the formulation of heat-resistant concrete, phosphates can be used at temperatures up to 1600°C to 1700°C.
Selection of proportions for heat-resistant concrete: The formulation of heat-resistant concrete is not a random process; it must be carried out strictly in accordance with established requirements. When determining the concrete mix ratio, the following principles must be followed: ensure the minimum compressive strength required by the structural design of the project ； To meet and ensure the requirements for construction quality, concrete should have appropriate fluidity and good workability ； Concrete should possess good thermal stability and durability ； Try to minimize the amount of cement used, as an increase in cement usage leads to a lower load softening point and reduced fire resistance of the concrete ；
Precautions for the construction of heat-resistant concrete: During the production of heat-resistant concrete, it is necessary to ensure accurate mixing of ingredients and thorough mixing in order to maintain consistent quality of the concrete； When constructing heat-resistant concrete, it is necessary to follow the construction instructions strictly. Proper vibration must be applied; over-vibration should be avoided to prevent water from seeping out of the concrete mixture, thus ensuring uniformity in the quality of the concrete and avoiding the formation of surface cracks ； During winter construction, it is necessary to remove the ice accumulated on the rebar and inside the formwork ； The concrete once it has been poured should be covered promptly to maintain sufficient humidity and an appropriate temperature, thereby ensuring proper development of its strength ； Generally, water several times a day in the early stage, and extend the care period appropriately when the temperature is low.