Effects of Metakaolin as Supplementary Cementitious Material in Mortars for Construction Applications

Abstract

This work presents the effects of metakaolin as a supplementary cementitious material in mortars for construction applications. Kaolin from Teleku Bokazo was calcined at 650oC and partially used to replace Portland limestone cement to produce mortars and paste. The metakaolin was successfully used in a cement paste and its effect observed in the different cement replacements proportions. The replacements ranged from 10% - 35% by mass and characterised after 3, 7, 14 and 28 days of curing. Kaolin was characterized using X-ray diffractometer (XRD) with illite, kaolinite and quartz as the main crystalline phases. The metakaolin was also characterised using XRD with quartz as the main crystalline phase. Calcium silicate hydrate, calcium aluminium silicate hydrate, portlandite, calcite and ettringite were some of the hydrated compounds formed in the hydrated pastes. Fourier transform infrared spectroscopy was used to determine the functional groups of the hydrated cement products formed from the metakaolin cement paste. Other test including initial setting and water consistency were also carried out. Water consistency and setting times generally increased with increase in metakaolin addition. The optimum metakaolin replacement for flexural strength after 28 days curing was 15 and 20% whereas the compressive strength after 28 days curing was 20% metakaolin replacement. Generally, the metakaolin reduced the amount of water absorbed by capillary action for the 28 days cured mortar bars. The results suggest that 20% metakaolin replacements of Portland limestone possess characteristics that can be adopted for use in mortars for construction applications.