Development of lightweight geopolymeric materials using coal fly ash and WastePaper

Abstract

The increase in population results in the intensification of coal combustion for power generation. The exponential population growth in South Africa results in an increase in unused process by-products such as coal fly ash (CFA) and wastepaper. In power plants, by-products such as fly ash is extracted from the exhaust gases and disposed to landfills. The demand for and consumption of paper in daily life is increasing every year, leading to paper disposal problems. Waste paper has drawn interest from to researchers as a reinforcement material for geopolymer due to its properties such as lightweight, affordability, availability, and toughness. Non-load bearing materials are currently manufactured from gypsum and wood, but these materials are relatively expensive due to the additional costs incurred by the addition of nonflammable constituents. CFA and waste paper which are currently causing disposal problems might provide an alternative and cost-effective route to manufacturing non-flammable, lightweight, low cost and high strength non-load bearing geopolymeric materials. The chief aim of this study is to develop lightweight, high strength geopolymeric material using waste materials such as waste paper and CFA. Specifically, the objectives of this study are to evaluate the compressive strength, weight, tensile strength, water absorption and shrinkage of the reinforced geopolymer synthesized using different characterization techniques. In addition, the impact of waste paper on CFA ratio, NaOH molarity and curing temperature on compressive strength, geopolymer weight, water absorption and shrinkage properties will be investigated in order to determine the optimum conditions for the synthesis of reinforced geopolymers. Characterization of the geopolymer by x-ray diffraction, x-ray fluorescence, and electron microscopy scanning were included in this analysis. This study will lead to the development of cheap, lightweight, high strength construction material by making use of waste paper and fly ash which is currently constituting an environmental nuisance. The result of this research could find application in the construction industries. No aggregates, sand or cement were used in any of the formulations developed in this study. Waste paper content was varied from 10 % to 40 %. The optimum waste paper content was found to be 20 % as the geopolymer weight was 0.856 kg, compressive strength between 3.8 MPa and 4.5 MPa; the water absorbed after 30 minutes of immersion was 0.360 L and the shrinkage percentage was found to be between 18 % and 20 %. The geopolymer product had a mass varying from 0.91 to 1.2 kg per 100 mm3 and density of 600 - 1000 kg/m3. The operating cost was calculated, and it was determined that for a 5 000 kg/year production, one geopolymer costs ZAR 31.70 and at 160 000 kg/year the block costs about ZAR 5.02. The optimum formulation used consisted of 2.4 kg of CFA, 0.6 kg of WP, 1.80 kg of H20, 0.64 kg of Na2SiO3 and 0.32 kg of NaOH. The mixture was mixed for a total time of 45 minutes and the hydraulic pressure used for moulding was 5 MPa. The geopolymer was cured for less than 60 hours and aged for 7 days prior to any tests. Partitioning wallboard manufactured using this formulation weighed 35 kg/m2 and the lightweight brick manufactured weighed 1.1 kg at 220 mm in length, 110 mm in width and 49 mm in depth. It was concluded that the materials can be used for non-load bearing construction material and should be installed at 1 m above ground level to avoid moisture absorption from the ground.