Characterization of some clay deposits in southwest Nigeria for use as supplementary cementitious material in cement

Abstract

Supplementary cementitious materials (SCMs) contribute to the properties of concrete through pozzolanic and hydraulic activities. Clay is an SCM used to replace part of clinker to reduce cost, CO2 emission, and make concrete durable. Nigeria has deposits of clay with pozzolanic potential when calcined and in finely divided form, thus, reducing the overdependence on Ordinary Portland Cement in concrete production. The chemical, mineral, morphology, calcination efficiency and physical properties were analyzed using X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA/DTA), particle size distribution, Brunauer–Emmett–Teller (BET), and specific surface area (SSA) by nitrogen adsorption methods. The Strength activity index (SAI) of calcined clay samples from Owode-Ketu (OK), Imotoyewa (IM), and Ifonyintedo (IF), in Ogun state-Nigeria were investigated. Compressive strength was determined by partially replacing cement in steps of 10 wt% from 0 − 40 wt% in a mortar test. Results revealed that IF clay has the highest plasticity with 52% of clay content, and the plasticity Index of 27%. Kaolinite was the dominant mineral with values greater than 35 wt% on the XRD trace, consistent with BET values above 31.22 m2/g. The oxides (SiO2 + AI2O3 + Fe2O3) satisfy the minimum requirement of “Class N pozzolan”. TGA/DTA established calcination temperatures of 600 °C, 650 °C, and 700 °C for IF, OK, and IM clays respectively at 2 h. These results agreed with FTIR data. The SAI of calcined clay (C-IF, C-OK, and C-IM) were 122%, 120.2%, and 118.8%, consistent with all the analytical results. Thus, these clays are useable in cementitious blends.