Nomograph modelling of hydraulic conductivity for landfill soil liner using boiler ash-based geopolymer / Atiqah Najwa Zainuddin

The study investigates a green technology geopolymer as an additive in enhancing the properties of landfill soil liner. Soil liners are used to contain waste in modern landfills. Essentially, the liner system isolates the landfill contents from the surrounding environment and protects the soil and groundwater from pollutants originating from the landfill. Liner requires low hydraulic conductivity (1x10-9 m/s) and adequate shear strength. Laterites are of great interest because of their abundance, availability, and easy workability. Despite the source of laterite in construction, the soil type is hard, impenetrable, and has high permeability. Geopolymer can be considered the key factor that could enhance laterite's properties in the performance of hydraulic conductivity. Geopolymer paste consists of palm oil boiler ash mixed with an alkaline solution of sodium hydroxide and sodium silicate. Boiler ash is another industrial waste product from the combustion of coal. In this study, laterite mixed was mixed with different percentages of boiler ash-based geopolymer (GeoPOBA) to improve the properties of soil liner application. This research aims to determine the optimum percentage of geopolymer mixed with laterite as an additive and reduce the value of hydraulic conductivity. Laterite was mixed with 5, 10, 15, and 20% of GeoPOBA by weight. The test carried out were divided into physical properties (particle distribution test, Atterberg test, specific analysis, and shrinkage test), chemical (structural morphology, chemical oxides, and pH test), and engineering properties (compaction and compressive strength) of original laterite and the mixture with geopolymer. Mixture samples for hydraulic conductivity were tested using falling head compact at dry, wet, and optimum moisture content ranging from -2 and +2 of the optimum moisture content with standard proctor test. Result shows the addition of GeoPOBA as additives in laterite has significantly given positive results on soil strength and chemical alteration in geopolymerization. As GeoPOBA is mixed with the laterite, the hydraulic conductivity of laterite soil decreases from 3.08 x10-8 to a range 3.00 x10−8 m/s to 5.05 x10-9 m/s. Sample above 15% of Laterite-GeoPOBA meet the requirement in designing a soil liner that gives low hydraulic conductivity, at less than 1 x10−9 m/s. The increases in GeoPOBA content are associated with a decrease in hydraulic conductivity, leading to a significant reduction in hydraulic conductivity. An empirical model with nomograph was successfully develop from this study. The empirical model and nomograph in predicting hydraulic conductivity, k, were developed as alternative guidelines for engineers to design landfill soil liners without conducting laboratory testing that takes a long time and can reduce the cost and time. As an added benefit, GeoPOBA as an additive in laterite could help reduce the environmental impact of boiler ash produced by palm oil production.