Statistical Study of the Effect of the Composition on the Strength of Supersulphated Cements

Abstract

ABSTRACTSupersulphated cements (SSC) are environmentally friendly binders that incorporate several raw materials, including byproducts. A systematic study was considered opportune considering the wide range of formulations found in the literature. The effect of the type and proportioning of components in the strength of SC was investigated using the Taguchi method to optimize the experimental work and to define the optimal conditions. The factors were: [A] %blast furnace slag (82.5-90%), [B] CaSO4 - alkaline activator ratio (1:0, 3:1, 1:1, 1:3 and 0:1), [C] type of CaSO4 (5 types) and [D] type of alkaline activator (portland cement, Ca(OH)2, KOH and NaCO3 and 2 combinations of these). Pastes were prepared and characterized for up to 28 days at 20°C. In general, for all values of [A] the best strength was for levels of [C] at 3:1, followed by the 1:1 and 1:0 ratios. The optimal conditions using the 28 day strength consisted of [A]= 82.5%, [B]= 3:1, [C]= flyorgypsum and [D] = portland cement, which developed excellent strength from day one and 35MPa. X-ray diffraction showed ettringite and C-S-H formation from the early ages. The microstructures showed dense matrices of reaction products well bonded to partially reacted slag grains, which in some cases showed rims of hydration products.