GGBS is a hydraulic cement formed from iron production and has high glassy content for reaction with OPC. The chemical composition of GGBS is almost similar to OPC. GGBS is an industrial pozzolan, different from natural pozzolans like PFA and silica fume. The granulated blast-furnace slag has to be grinded before they are mixed with OPC to form PBFC and HSPBFC. The proportions of GGBS to OPC for the two products are as follows:-
In fresh concrete, PBFC/HSPBFC produces higher workability.
PBFC/HSPBFC is very efficient in lowering the heat of hydration and hence can be use for mass concreting to reduce thermal cracking. It is also used to improve the durability if concrete to chloride penetration, resistant to sulphate attack and minimize alkali-silica reaction (ASR). PBFC/HSPBFC is available in 50kg bags and in 1.5MT bulk bags.
PFA is the lighter and finer fraction of the ash resulting from the combustion of pulverised coal in the production of energy. The ash is extracted by filters and electrostatic precipitators. PFA particles are hard, glassy spheres which impart a ball-bearing lubricating effect to plastic concrete, therefore enhancing workability, placeability, finishability and pumpability while reducing bleeding and segregation.
Due to its slower rate of hydration, PFA is use in replacement of cement (in the range of 20% to 30%) to generate less heat resulting in reduce thermal cracking when concreting massive structures like raft foundations, transfer beams, dams etc.