The effect of metakaolin used as cement replacement on the properties of hardened cement paste

Abstract

The article analyses the effect of expanded glass production by-product rich in metakaolin on the properties of hardened cement paste. Portland cement CEM II/A-LL 42.5 N with the average particle size of 14.21 μm and metakaolin with the average particle size of 22.34 μm were used for the tests. Six cement paste compositions were formulated by replacing 0 %, 2 %, 4 %, 6 %, 8 %, 10 % of cement with metakaolin. Ultrasonic pulse velocity, compressive strength, flexural strength, water absorption and porosity of hardened cement paste specimens were measured at 28 days. The analysis of hardened cement paste microstructure (SEM) and physical and mechanical properties leads to the conclusion that the replacement of 8% of cement in the mix with metakaolin creates the densest microstructure that produces the highest values of compressive and flexural strengths and ultrasonic pulse velocity and the lowest values of closed porosity and water absorption rate. It was found that 8 % was the optimal ratio of cement replacement with metakaolin. Metakaolin can be added at 8 % by weight of cement in the production of modified high-performance concrete.