Compatibility between various Superpasticizers & Portland Pozzolona Cement

Workability of concrete is the major concern and interest of the construction engineers today. To achieve high workability, chemical admixtures like superplasticizers are required to be added to the concrete mix in the fresh state. Blended cements like PPC are being used quite commonly instead of OPC either due to the non-availability of the latter in the market or to improve the durability of concrete. Three brands of fly ash based PPCs were used to achieve two different grades of concrete, 25 and 40 MPa (M25 and M40). To achieve high workability in the fresh state and desired characteristic compressive strength in the hardened state, of the normal concretes, five different chemical admixtures namely, sulphonated naphthalene polymer(two different families), modified lignosulphonate, combination of ‘sulphonated naphthalene formaldehyde (SNF) and melamine’ and another combination of ‘SNF and lignosulphonate’ have been used in the present study, to investigate their compatibility with various brands of cement (PPCs). It was observed that for each and every type of chemical admixture considered in this research, the setting behaviour varied significantly from one brand of cement to another, though all the three brands of cement were of fly-ash based PPCs. The early age strength and slump loss were also found to be varied significantly. Hence, a strong case was made for studying the compatibility between various kinds of superplasticizers and cements (PPCs) before a suitable combination was used in concrete, especially when high workability and early strength were required.