Arif, E 2016, 'Development of value added products from sugarcane boiler ashes: utilisation in cements, mortars and concretes', MA thesis, Southern Cross University, Lismore, NSW.
Copyright E Arif 2016
Sugar-cane bagasse ash (SCBA), from combustion of bagasse fibre at co-generation sugar-cane mills, is an aluminosilicate waste material suitable for studies in concrete as a pozzolanic supplementary cementitious material and/or a filler. The use of waste materials as supplementary materials in concretes reduces the problems associated with waste disposal and helps to reduce the environmental impact of the cement industry. The use of waste materials as fillers also alleviates waste disposal and reduces the environmental impacts associated with mining natural resources. However, SCBA must be high in amorphous silica to be pozzolanic and have a small particle size (< 63 μm) to be an effective filler material. The SCBA from a high-efficiency co-generation boiler contains high amounts of silica (78.498%) which is substantially crystalline α-quartz rather than amorphous. The mean particle volume was 56.963 μm hence may be a suitable filler. Pozzolanic reactivity of the SCBA in lime-SCBA pastes confirmed the SCBA had little to no pozzolanic activity. Cement pastes made with partial replacement of cement with the SCBA showed pozzolanic strength gains at 5% replacement. However, at higher replacement levels the comparative strengths were lower than controls, hence the filler effect of the SCBA contributes to strength gain through pore refining. Compressive strengths of standard mortars with partial cement replacement confirmed that the SCBA acts primarily as a pore filler. Hence, the SCBA as a filler replacing sand in concretes up to 20% (by weight of the cement) improved concrete 7, 14, and 28 day strengths. The 90-day strengths were also improved except for the 20% SCBA concrete but was still above the target strength of 40 MPa. The 28 day flexural strength of concretes increased with increasing SCBA. Drying shrinkage of the SCBA concretes improved particularly at 5% replacement level. The SCBA had a large proportion of irregular and porous particles and an LOI of 7.150% hence superplasticizer was required to maintain workability in SCBA concretes. The SCBA pore refining effect improved the acid resistance of standard mortars and concretes submerged in a 1% sulphuric acid solution. However, the Rapid Chloride Penetrability Test (RCPT) test suggests increased permeability to chloride ingress but is possibly a misleading result from interference from SCBA and/or superplasticizer. The use of high volumes of unprocessed SCBA in concretes as filler is a promising solution to SCBA waste disposal and environmental impacts of sand mining. Further the use of low volumes of SCBA as supplementary cementitious materials lessens the environmental impact of concrete and provides alternative income for the sugar-cane industry.