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 obtainedas 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 strengthtest 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 strengthproperties. The results from the various tests showed that 800°C for 1 hour of calcination of kaolin gives bestcombination of performance properties due to the presence of amorphous silica in metakaolin. Mk-GPC gavehigher compressive strength and at an early age than ordinary Portland cement (OPC) concrete. The water absorptioncapacities of Mk-GPC were higher than the control samples. In the flexural strength test, the reinforcedbeams failed in flexural-shear mode and the shear capacities at 28-, 56- and 90-day curing age of the beams werebetween 0.656 and 0.938 MPa for Mk-GPC beams and between 0.563 and 0.844 MPa for the control beams. Themoment capacities for the beams were between 19.25 and 33.25 (×10³ kgm²/s²) for Mk-GPC beams and were between22.75 and 28.0 (×10³ kgm²/s²) for the control beams. The study has revealed that metakaolin-based geopolymercan serve as an alternative to cement for sustainable construction in the Nigerian construction industry.
Highlights
The production of Portland cement involves the decomposition of limestone into lime (CaO) and CO2 by the addition of heat
Pozzolanic reactivity of metakaolin The graph shows the reactivity of metakaolin with Ca(OH)2 at different temperatures and reaction times (Fig. 2)
An increase in temperature from 25 to 100°C caused the percentage of Ca(OH)2 which reacted with metakaolin to increase from 0.45 to 0.68%
Summary
The production of Portland cement involves the decomposition of limestone (calcium carbonate) into lime (CaO) and CO2 by the addition of heat. This decomposition process is accountable for the release of a large amount of CO2 into the atmosphere as a result of the chemical reaction involved. The cement industry accounts for about 8% of the annual global CO2 emissions (Boden et al 2016, Andrew 2017) This is damaging to the environment, the search for alternative, more environmentally friendly cementitious materials such as geopolymers. The term ‘alkali activated materials’ are applied to a class of solid materials synthesized by the reaction of an aluminosilicate powder with an alkaline solution (Alonso & Palomo 2001). The use of an acid medium seems favorable, as some authors have demonstrated an increase of mechanical properties with acid-based geopolymers (Cao et al 2005, Perera et al 2008, Tchakouté & Rüscher 2017)
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