The Compressive Strength Indices of Calcined Clay-Cement Blended Concrete as a Function of Calcination and Cement Replacement Level Using Locally Sourced Clay

Abstract

Cement is highly valued primarily for its enhanced rate of hydration when compared to its predecessors. Its production process, however, is of adverse effects economically and mostly environmentally. Amidst the existing research routes for solving the problems associated with cement production, partial cement replaceability using sustainable supplementary cementitious materials appears to be gaining the most attention. However, the present research gap exists in the limited potential of the available materials in terms of availability or structural efficiency. As such, the abundance of local clay as well as its siliceous nature, in addition to the established structural properties of kaolinite (calcined Kaolin), suggests to the researchers that the index properties of clay, when properly optimized, could result in more efficient material with enhanced performance in concrete as a partial supplementary cementitious material. In the research, locally-sourced clay calcined at 450, 600, 750, and 900^oC were pulverized to pass through 150µm and used to replace Portland cement at 15%, 30%, 45%, and 60%. Results obtained indicated optimum calcination temperature for local clay to fall between 600 and 700^oC, yielding a compressive strength range of 15 – 22 MPA and 19 – 28MPA for 7 and 28 days, respectively. However, a more comprehensive range of cement replaceability was observed for clays calcined between 750 - 900^oC at a reduced mechanical index. As such, it is recommended that local clays be calcined between 600 and 700^oC, pulverized and sieved to pass through 150µm, and used to replace a maximum of 30% cement (by mass) for optimum efficiency and structural performance of calcined clay-cement blended concrete.