Pozzolanic and hydration properties of kamafugites and carbonatitic lavas as supplementary cementitious materials in Portland cement

Abstract

Kamafugites and carbonatites, being materials of volcanic origin with carbonates as their primary minerals, are relatively low in silica and alumina saturation. Their silica and alumina under-saturation is considered a limiting factor in pozzolanic reactivity; however, these materials are currently being utilised as supplementary cementitious materials in Portland cement in Uganda. This paper presents the findings of an experimental study into their pozzolanic and hydration properties. Pastes and mortars made from cement samples blended with test kamafugites and carbonatites were studied for water demand, setting time, heat of hydration and strength development. Results show carbonatites and kamafugites, because of their low saturation of silica and alumina phases, to have less pronounced pozzolanic properties. The results also show no dependence on reactive silica content for pozzolanic performance after 28 days of curing. The kamafugites and carbonatites accelerated early heat of hydration, reduced setting time, and increased water demand. Although the carbonatites are currently utilized in blended Portland cement as natural pozzolans under the EN 197-1 and ASTM C618 cement standards, they do not meet the minimum composition requirement and volatile elements (LOI) demanded by these standards.