Thermally activated clay and biomass mixtures as supplementary cementitious materials for sustainable construction in Ghana

The concept of sustainable development is probably one of the most significant gifts of the 21st century to human kind in pursuit of benign environment, sound economic growth and a peaceful society. Many researchers have reported that there is gross lack of respect for the ecosystem and other factors that support quality of life for human beings and this seriously threatens mankind in this millennium on earth. Currently the global emphasis on sustainability has urged many engineers to design products and provide services that incorporate the concepts of sustainability. The cement industry is among the industries whose activities have negative impact on sustainability due to its huge economic, ecological and societal footprint. In recent times the cement industry has become fully aware of these negative impacts and has currently positioned itself to address these footprints. This study sought to formulate cementitious materials as partial replacement of cement estimated to have lesser footprint on the economy, environment and society compared to the use of only Portland cement for construction. The formulated cementitious materials were prepared using clay and waste biomass at different replacement levels by mass of clay powder. The waste biomass used for the study included palm kernel shells, rice husk, maize cob and sawdust. Thes biomass materials were selected because of their elemental silica and calorific values which had the potential to impact positively on the properties of calcined clay. Formulated clay and waste biomass were used to form pellets which were thermally activated in an electric furnace and used to replace Portland cement at percentages between 10% and 40% by weight. The experimental approach for this study was segmented into six different phases and they included biomass characterization, optimum temperature of clay calcination and iii  dosage determination, maximum clay/biomass mixture and optimum dosage determination, influence of calcined clay and clay/biomass mixture on Portland cement hydration and pozzolanic reaction, durability studies and sustainability analysis. The maximum clay/biomass mixture and optimum dosage increasing effect determination were performed using the compressive strength machine whereas the thermogravimetric analyzer and the nuclear magnetic angle machine were used to investigate the influence of calcined clay and clay/biomass on cement. Durability studies performed in this work focused on shrinkage and sorptivity analysis. The results from the study showed that complete calcination of clays was achieved at 800oC, and therefore attained optimum performance in terms of strength. The maximum strength activity indices obtained for mortar mixtures involving Portland cement and calcined clay/biomass mixture were at 20% and 1.5% replacement of clay with palm kernel shells and sawdust respectively whereas that of rice husk and maize cob were at 2% replacement by weight of clay. 20 wt% calcined clay, calcined clay/palm kernel shells, calcined clay/maize cob and calcined clay/sawdust, and 30 wt% of calcined clay/rice husk pozzolans produced the optimum strengths. At optimum values, thermogravimetric and MAS NMR analysis were performed using their formulated binder paste. The thermal gravimetric analysis showed that calcined clay/rice husk paste mixture indicated a higher degree of pozzolanic reaction than the calcined clay paste mixture at all periods. The degree of pozzolanic reaction of the other calcined products remained sluggish at earlier periods however indicated a consumption pattern higher than the calcined clay paste system. At 28 days calcined clay/palm kernel shells and clay/sawdust mixtures showed similar lime consumption pattern like calcined clay paste system. The analysis by the MAS 29Si and iv  27Al NMR also indicated the formation of increased polymerized materials and stable monosulphates respectively, confirming strength enhacement of cement-pozzolan system than only Portland cement system. The results obtained from the shrinkage studies indicated insignificant effect with regards to Portland cement and calcined clay mortar mixtures. However, with sorptivity analysis, there were significant effects with regards to the type of calcined products used for the mortar mixture formulation. Generally, all the calcined products showed a lower initial and secondary sorptivity coefficient values than the control which indicated a higher resistance to ingress of ions. Calcined products that included clay/palm kernel shells and clay/maize cob indicated a higher sorptivity coefficient values than calcined clay mortar mixture whereas that of calcined clay/rice husk and clay/sawdust had lower initial and secondary sorptivity values. The study showed that the use of the supplementary cementitious materials investigated could save between 9% and 14% on cement utilization which will mean a significant cost reduction of cement importation. Moreover, the inclusion of the selected biomass in the supplementary cementitious materials (SCMs) production could also save the country between $0.12 million and $1.59 million depending on the type of biomass.

Source: KNUST