Feasibility Studies of Using Ghanaian-Nyamebekyere Calcined Clay as Artificial Pozzolan


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Title: Feasibility Studies of Using Ghanaian-Nyamebekyere Calcined Clay as Artificial Pozzolan

Author(s): Albert Amatey Adjaottor, Mark Bediako, John Tristan Kevern, and Simon K. Y. Gawu

Publication: Materials Journal

Volume: 116

Issue: 2

Appears on pages(s): 127-132

Keywords: calcination temperatures; calcined clay; pozzolanic active phases; pozzolanic strength activity index; reactive phases; silicon intensity

Date: 5/1/2019

Calcined or partially calcined clay can be used to replace a significant portion of portland cement, which reduces the associated CO2 footprint, and in Western Africa, to use a locally available material. However, clay source properties influence thermal activation and ultimate pozzolanicity. In this study, clay from the Ashanti region of Ghana was thermally activated at calcination temperatures of 600, 800, and 1000°C (1112, 1472, and 1832°F). The raw clay and the calcined products were characterized in terms of mineralogy and silica intensity using X-ray diffraction (XRD) and solid-state silicon magic angle spinning nuclear magnetic resonance (29Si MAS NMR). The impact of the calcined clay material on portland cement was analyzed based on the pozzolanic strength activity index (PSAI). The influence of the calcined material on portland cement in terms of formation of polymerized phases including calcium aluminosilicate hydrates and lime consumption was determined using 29Si MAS NMR and thermal gravimetric analysis (TGA). The results of the study indicated that optimum calcination temperature of the clay was 800°C (1472°F), where more reactive pozzolanic phases were formed. The study concluded that the use of calcined clay at optimum calcination temperature together with portland cement improves the strength of mortar. The improvement in strength is consistent with the observed increased polarization between the reactive phases of the calcined clay and cement phases as well as the higher degree of pozzolanic reaction of portland and calcined clay mixtures at the hardened state compared to only portland cement.