Effect of raw clay type, fineness, water-to-cement ratio and fly ash addition on workability and strength performance of calcined clay - Limestone Portland cements

Workability and strength performance of blended cements with different replacement levels have been investigated for two calcined clay mineral additions (1:1 and 2:1 type) and mixtures with limestone. The effect of fly ash addition and different water-to-cementitious ratios was also evaluated. The results show that the SO3 content of the blended cements, and the ratio of calcined clay to limestone, can be optimized for maximum strength depending on the content of early soluble and total reactive alumina in the calcined clay. Workability is strongly affected by the calcined clay content, particularly for the 1:1 clay which greatly reduces the efficiency of superplasticizer (SP) required for achieving acceptable flow even at higher w/c ratios. On the other hand, delayed addition of the SP and/or the addition of fly ash significantly improve rheology of any binder containing calcined clay and maximize strength for same workability at a given clinker content in the paste.