Using PC clinker as aggregate-enhancing concrete properties by improving ITZ microstructure

Abstract

The interfacial transition zone (ITZ) in a concrete microstructure is a region of high porosity and low binding materials at the interface of cement paste and aggregate that causes significant reduction in compressive and flexural strengths and considerable increase in permeability of the concrete. Extensive research activities have been devoted to reduction of the ITZ, to avoid its negative effects on concrete properties. This research introduces reactive aggregate concrete (RAC), formed by partial replacement of natural aggregate with Portland cement (PC) clinker of the same size as a reactive aggregate in the concrete mix to reduce the ITZ and improve the concrete properties. After determining the optimum replacement level based on 28 and 60 d compressive strengths, the developed RAC was characterised by measuring its workability, setting time, compressive and flexural strengths, for varying age, water absorption, open-pore volume and chloride penetration depth. Microstructural studies of the ITZ were also performed using scanning electron microscopy. In all measurements, normal concrete was also considered for comparison purposes. The results confirm 121% and 33% enhancement in 7 and 90 d compressive strengths accompanied with 53, 19 and 22·4% reductions in 28 d chloride penetration depth, open-pore volume and water absorption, respectively.