Q. Use of PFA and GGBS?
Both PFA and GGBS are by-products of industry and use of them is ecologically friendly. Most significantly, with PFA and GBS adopted as partial replacement of cement, demand for cement will be severely reduced. As the manufacture of one tonne of cement produces about 1 tonne of carbon dioxide, environment could be conserved by using less cement by partial replacement of GGBS andPFA.
Conversely the use of PFA and GGBS as partial replacement of cement improves long-term durability of concrete in terms of resistance to sulphate attack, chloride attack and alkali-silica reaction. It follows that structure would remain to be serviceable for longer period, leading to substantial cost saving. Apart from consideration of long-term durability, use of GGBS and PFA results in the reduction of heat of hydration so that problem of thermal cracking is greatly decreased. The enhanced control of thermal movement also contributes to better and long-term performance of concrete.
In terms of development of strength, GGBS and PFA shared the common observation of lower initial strength development and higher final concrete strength. Henceforth, designers have to take into account the potential demerit of lower strength development and can make use of merit of higher final concrete strength in design.