Microstructural, mechanical and pozzolanic characteristics of metakaolin-based geopolymer

Abstract

The use of cement contributes to global CO2 emission and this leads to the depletion of ozone layer,
causing global warming. The quest to reduce or eliminate this problem has resulted in the discovery of metakaolin-
based geopolymer as an alternative to the use of cement in construction work. In this study, metakaolin obtained
as a result of kaolin calcination from some deposits in Nigeria; Ogun (Imeko), Edo (Okpela), Ondo (Ifon)
and Ekiti (Isan-Ekiti) were characterized and used to determine the compressive and flexural strength of metakaolin-
based geopolymer concrete (Mk-GPC). Cubes of 150 × 150 × 150 mm were used for the compressive strength
test and reinforced concrete beams of size 150 × 250 × 2160 mm were produced to test for flexural strength. A water-
absorption test was also carried out on Mk-GPC and the effect of ball-milling was assessed on the strength
properties. The results from the various tests showed that 800°C for 1 hour of calcination of kaolin gives best
combination of performance properties due to the presence of amorphous silica in metakaolin. Mk-GPC gave
higher compressive strength and at an early age than ordinary Portland cement (OPC) concrete. The water absorption
capacities of Mk-GPC were higher than the control samples. In the flexural strength test, the reinforced
beams failed in flexural-shear mode and the shear capacities at 28-, 56- and 90-day curing age of the beams were
between 0.656 and 0.938 MPa for Mk-GPC beams and between 0.563 and 0.844 MPa for the control beams. The
moment capacities for the beams were between 19.25 and 33.25 (×10³ kgm²/s²) for Mk-GPC beams and were between
22.75 and 28.0 (×10³ kgm²/s²) for the control beams. The study has revealed that metakaolin-based geopolymer
can serve as an alternative to cement for sustainable construction in the Nigerian construction industry.