Influence of calcined clay pozzolana on strength characteristics of Portland cement concrete

The paper presents results of a study on concrete mixes containing two types of calcined clay pozzolanas obtained
from Mankranso and Tanoso for structural application. Mankranso sample is labeled Type I whilst Tanoso also labeled as type II.Both clay samples were analysed to determine their physical and geotechnical properties whilst the chemical composition of the calcined clay samples analysed. Portland cement was replaced with 0%-25%Type I and 0-30% of Type II pozzolanas to formulate binder pastes and concretes. Setting times and normal consistency test were determined on the formulated binder paste. Three grades of concrete (25N/mm2, 30N/mm2 and 40N/mm2) containing pozzolana were prepared and their workability, density, compressive strength and flexural strength investigated against the plain concrete. Concretes with clay pozzolana had delayed setting times and lower densities. They also exhibited a reduction in compressive and tensile strength development at early age (7 days), with an average drop of 6 percent in compressive strength for all grades. However, the compressive and tensile strengths beyond 28 days notably exceeded the control un-blended mixes. This study recommends up to 20% clay pozzolana content of both Types I and II for concrete grades of 25N/mm2, 30N/mm2 and 40N/mm2.