Evaluation of metakaolin pozzolan for cement in South Africa

This paper presents findings of an experimental study conducted to evaluate the performance of metakaolin (MK) for potential use as a supplementary cementitious material or cement extender in South Africa. In this study, various proportions consisting of 0%, 5%, 10%, 15% MK were incorporated into ordinary Portland cement CEM I 52.5 N, then used to prepare mortar mixtures. Various mechanical and durability properties were measured comprising flowability, compressive strength, pozzolanic activity with lime, drying shrinkage, alkali - silica reaction (ASR) and sulphate resistance. Analytical studies were done using X - ray diffraction and scanning electron microscopy. It was found that incorporation of 10%–15% MK into Portland cement led to improved flowability, compressive strength increase and lower drying shrinkage, while ASR and sulphate attack processes were effectively mitigated. Results showed that the MK extender satisfied ASTM C618 specified criteria for ‘Class N’ pozzolan. Incorporation of 15% MK into Portland cement also met the requirements categorising the blend as CEM II/A–P 42.5 N cement type of SANS EN 50197–1. •10%–15% MK in CEM I meets the ASTM C618 criteria for ‘Class N’ pozzolan.•CEM II/A–P 42.5 N cement type results from incorporation of 15% MK into CEM I.•MK maintains early – age strength and gives higher late – age strength gain.•MK significantly reduces drying shrinkage of mixtures.•Mixtures containing 10%–15% MK significantly mitigate sulphate attack and ASR.