Perspectives on Durability of Blended Systems with Calcined Clay and Limestone

Abstract

In the light of the increasing demand for cement in construction and dwindling reserves of cement-grade limestone, the blend of ground limestone and lower grade calcined clay has emerged as a potential candidate for large volume cement replacement. Studies of such ternary blended systems in paste and concrete reveal very interesting physical and chemical effects on the structure development, strength and durability performance. This paper describes the results of durability studies conducted at IIT Madras on concretes prepared with limestone calcined clay Cement, in comparison with ordinary Portland cement and fly ash-based cement. The focus of the study was to delineate the chemical and physical effects caused by the binder composition on durability indicators for chloride-induced corrosion. The experimental strategy involved the assessment of the pore structure evolution and electrical properties on cementitious pastes, along with measurement of the durability parameters based on moisture absorption, chloride migration and diffusion. The results from the study reveal the complex interplay of the various factors that lead to improved performance of the blended cementitious systems. The synergistic interactions of the blend of calcined clay and limestone impact the physical structure positively at early ages as opposed to fly ash systems, which require prolonged curing to realize their potential.