Investigating the use of Kaolin Clay and Volcanic ash as precursors for Geopolymer cement in concrete blocks.

Abstract

Concrete blocks comprise of quarry dust, water and binder. Cement, as a binder, is the most expensive input into the production of concrete blocks. This has necessitated producers of these blocks to produce them with low OPC content that will be affordable to people and with much gain. Cement production is also an energy and resource-intensive process that uses kiln temperatures between 1400 and 1500 °C and emits a significant quantity of greenhouse gases (CO2) into the environment. Many scholars are now interested in the new cement technology known as geopolymer cement. Geopolymer cement produces strengths up to 70 MPa without using calcium carbonate (limestone) in the production process. Finely ground pozzolanic aluminosilicate materials, including fly ash and blast furnace slag, kaolinitic clays, and agricultural waste products like rice husk ash, are used in the production of geopolymer cement. When these aluminosilicates are combined with alkaline solutions, a cementitious binder is created. This cement technology also offers a greener option for disposing of industrial waste like slag in highly industrialized nations. This study was done to explore the use of geopolymer cement in the production of GPC blocks to address the issues of high carbon dioxide emissions and costly building materials through producing a cheaper and sustainable alternative to OPC blocks. Kaolin clay was sourced from Bushenyi District whereas volcanic ash from Rubanda District. Volcanic ash and Kaolin clay were ground to form fine cementitious material using a ball mill at UIRI to increase the surface area available for reaction. Kaolin clay was calcined at a temperature of 7500C for 2 hours which is way less than the 1500oC necessary for the formation of OPC clinker. A 22 factorial design was used to attain the optimum design mix ratios for production of solid GPC blocks with Sodium Silicate solution to sodium hydroxide ratio and alkaline solution to binder ratio as the variable parameters. Strength tests were carried out on geopolymer mortar cubes with the 7-day compressive strength as the performance parameter. Sodium hydroxide to Sodium Silicate and alkaline solution to binder ratio had significant impact on the strength of the binder. Mix 1 which obtained a compressive strength of 8.33MPa was used to cast Volcanic based blocks whereas mix 4 which obtained 20.0 MPa was used to cast Metakaolin based blocks. Mix 1 (for Volcanic ash) and Mix 4 (Metakaolin Clay) had the highest SiO2/Al2O3 initial molar ratio that facilitates the geo-polymerisation process. In addition to the GPC blocks, control blocks made out of CEM Type IV B were also cast. Compressive strength, density grade and water absorption tests were carried out for comparison. All the blocks were classified as grade A with respect to their densities at 3 days. Both GPC blocks had lower water absorption values at three days as compared to the control blocks. Compressive strength tests were carried out at 3, 7 and 28 days. Metakaolin clay and volcanic ash-based blocks attained 7.22 MPa and 3.39 MPa respectively at 28 days. Whereas the control blocks attained 11.87 MPa at 28 days of testing. The GPC blocks generally attained lower compressive strength values which can be attributed to curing method used in this study.