Vol: 1 Issue: 1
MICROSTRUCTURAL DEVELOPMENTS IN PLAIN AND SLAG-BLENDED CEMENTS
Joseph O. Ukpata
1. INTRODUCTION
The microstructure of cement paste comprises hydrated phases, anhydrous phases and pores with pore water. The hydrated phases are dominated by calcium silicate hydrate (C-S-H) gel and calcium hydroxide (CH), both products of tricalsium silicate (C3S) and dicalsium silicate (C2S) hydration, which are the most abundant phases, constituting about, 75-90% in normal cements. These phases are also known to be the main strength controlling phases at early and later ages respectively [1, 2]. In ground granulated blast-furnace slag (slag)-blended cements, these phases still occur but with the C-S-H modified to C-A-S-H and more reduced quantity of CH because of its consumption during slag’s pozzolanic reaction [3, 4].
The porosity of cement systems affects the transport of aggressive substances with grave implications for durability. However, transport of fluids through cement systems is dependent on the number of interconnected pores rather than total porosity. It has been shown in Power’s model the volumetric changes that affect porosity due to continuous hydration of plain cement at 20°C. It showed how the gel spaces occupied by gel solid and gel water increased with time, while capillary spaces (pores, air and water) reduced with time [5]. Microstructures of mortars and concretes also include interfacial transition zone (ITZ), with potential to contribute to the pore network of the matrix [6-9]. ITZ can affect the transport of destructive chemicals significantly.