(739b) Alkali & Green Catalyst Activated Geopolymers Using Coal and Wood Fly Ash

Geopolymers are greener construction material alternatives to the commonly used Ordinary Portland cement(OPC) in terms of the carbon footprint apart from possessing suitable physiochemical & mechanical properties. Geopolymers however do need an alkaline activator, such as NaOH or KOH, which increases overall cost and manpower as it requires skilled personnel for process handling. Here, wood fly ash, a by product of wood combustion, which is alkaline in nature is used as an internal source of alkaline activator for geopolymerisation along with coal fly ash. The high calcium content of the ash mixture produces geopolymer–cementitious hybrid (GCH), which is a mixture of geopolymers and alkali activated cement (calcium hydrates). GCH is characterized for its morphology, size, porosity, surface groups, mineral content and also subjected to leaching tests as to check if heavy metal leaching ­­from wood fly ash has been controlled. Various factors such as water-to-ash ratio (w/a), method of curing, type of alkaline activator, sieving have been considered here through factorial experimental analysis with the leaching patterns of various elements such as Pb, Zn, Cr, As. Hg, Se being studied. The dominant factor for leaching was found to be the type of alkaline activator (i.e. Wood Fly Ash versus Na₂SiO₃) with the best formulation being 0.3DI_p_s (0.3 represents the w/a ratio, DI represents use of wood fly ash as the pure source of alkaline activator, “p” denotes that samples were precured and “s” denotes sieving) when compared to the Denmark leaching standards. This study points to the production of alkaline activated materials for construction without the use of an external activator where the final product exhibits controlled leaching as required especially when used in applications involving exposure to moisture or water bodies. To avoid the GCH formation, a follow up study is planned to produce purer geopolmers where the ratio of coal fly ash to wood fly ash will be varied (70-30,60-40 wt%). A green catalyst will be used to pretreat the coal fly ash as to increase it surface area and reduce the calcium content to prevent formation of calcium hydrates. The treated coal fly ash along with wood fly ash will be subject to green catalyst based geopolymerisation, with the formed structure tested for its geopolymeric nature through chemical analysis. Concrete would be cast out of the formed geopolymers using them in certain levels (eg: 5%) as cement substitutes along with OPC. Mechanical strength of the cast concrete would be analysed through standard testing methods with leaching properties of the final structure also studied through standard leaching techniques as to check for its suitability in different applications with pure OPC made concrete was used as control.