A DEVELOPMENT OF CLAY-BASED GEOPOLYMER BINDER FROM SELECTED LOCALLY SOURCED KAOLINS

Abstract

Cement is one of the major construction material needed for the built environment in the world. It is one of the major constituents in concrete and mortar . While cement is a good and very useful material for construction works, it also poses a threat to the environment. The cement Industry is responsible for 8% of the world total carbon dioxide ( CO2) emissions which is the major cause of the ozone layer depletions that leads to global warming. In order to alleviate the problems associated with cement manufacturing ,the world need to focus on another material that would perform optimally as cement, this is where geopolymer comes into play. To this end,this research was designed to develop a kaolin –based geopolymer binder through the synthesis and characterization of selected materials with a view to contributing to the development of an ecofriendly alternative material for construction purposes in Nigeria. Geopolymer .The study selected kaolin from Ejigbo in Lagos Akure in Ondo State and research work focused made used of kaolin from Lagos, Akure in Ondo State and Auchi in Edo State for the development of geopolymer binder together with sodium silicate and sodium hydroxide as alkaline activator. Laagba silica sand and Laagba palm kernel shells were used as fine and coarse aggregates respectively. The three kaolin samples were calcined at 700.3oC using a gas kiln, and each sample was synthesized using the alkaline activators using a line blending procedure to have an optimal sample in the first stage of the experiment. The chemical compositions of the sourced materials meant for the experimental work were done at the Engineering material development Institute at Akure in Ondo State using X-ray fluorescence Spectrometer ( XRF) .The results of the X ray fluorescence showed the three kaolin samples contained the essential oxides( Al2O3, SiO2 and Fe2O3) that are required in a pozzolan for the synthesis of geopolymer binder/ concrete. The experimental work was in three stages. The first stage of the experiment was the synthesis of geopolymer binder using the three metakaolin samples with the alkaline activator, the second stage was the research work was the addition of fine aggregates to the optimum sample gotten from the first stage of the experiment, while the third stage of the work was the addition of coarse aggregates to the optimum sample in the second stage , all these were done using the line blending procedure. Ordinary Portland cement ( OPC) was used as the control in each stage of the experimental work. The geopolymer concrete specimens were casted using a PVC pipe with dimension 50mm*50mm, and the curing was done at ordinary temperature. Tests like the compressive strength test, water absorption capacity, sulfate attack test were done on the concrete samples. The best blending (NaOH: Na2SiO3) for Auchi samples in the first stage was ratio 2:8 and 3:7), and for the second stage of the research work, Lagos and Akure Kaolin failed in all the blendings ; they failed to solidify after 28 days of casting, while Auchi kaolin showed promising outcome between the metakaolin and Laagba silica sand. The ratios 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, while the blending of ratio 3:7, 2:8 and 1:9 failed to solidify after 28 days of casting. All the samples that could not achieve strength did not undergo compressive strength tests. The third stage of the research work encompassed the blending of the good samples in stage 2 with the Laagba PKS, still using the line blending procedures. All the specimens failed in the three metakaolin samples. All the geopolymer samples crumbled before 28 days. The average compressive strength recorded for the geopolymer concrete samples was 13.7N/mm2, while the average water absorption capacity of the geopolymer concrete was 0.51% after 28 days curing period. This research can be adopted as a policy document for the government on the replacement of the ordinary portland cement (OPC) partially or fully with geopolymer binder for construction purposes in Nigeria.