Calcined mixture of clay and limestone as a complex additive for blended Portland cement

摘要

The calcination of mixtures based on kaolinitic or polymineral clay and limestone with a calcite content of 99% at a temperature of 720-800℃ leads to the formation of C_2S, and increases the quantity of amorphous phase. At the same time, no free CaO is identified on the XRD pattern of calcined mixtures, hence demonstrating its binding by products of clay mineral decomposition - kaolinite for example - in new growths like C_2S or CA, and new growths in amorphous phase. The formation of accreting amounts of calcium silicates and aluminates in the calcined mixtures makes it possible to receive the complex additives for blended cement, replacing up to 20% of OPC with no loss of durability. The optimum parameters of calcined mixtures based on kaolinitic or polymineral clay and limestone arrived at by the method of mathematical experiment planning depend on the chemical and mineralogical composition, the physical and technological properties of the raw materials, and on the degree of component dispersion. The introduction of complex additives based on calcined mixtures of clays and limestone leads to the formation of an accreting amount of calcium hydrosilicates and hydroaluminosilicates of various composition, and of hydrocarboaluminate in samples with high carbonate content, hence decreasing the quantity of ettringite and portlandite.