Recycling of Fly ash-Slag based Geopolymer Cement

Abstract

Fly ash/slag based Geopolymer cement is a material presenting potential of becoming a low-carbon alternative to ordinary Portland cement. With respect to sustainability the potential of recycling it after the end of its life, in OPC and GPC matrix mortars is investigated at the present thesis. The fabrication of OPC and fly ash/ slag based GPC mortars incorporating 0%, 25% and 50% fine recycled aggregate deriving for the same type of GPC binder took place. The mixes with the same replacement percentages and fine recycled aggregate deriving from OPC binder were produced to be used as comparatives. For both aggregate types, strength of the original binder, density, water absorption and alkali silica reactivity were tested. In comparison to OPC aggregates, GPC aggregates demonstrated lower density and higher water absorption, while they proved not to be prone to induce ASR expansion. The flow, density, compressive and flexural strength, water absorption and drying shrinkage of the resulting mortars were investigated. Gradual reductions in flow and density were observed with increasing replacement levels, with GPC aggregate presenting a less severe effect. The influence of GPC aggregate on water absorption, compressive and flexural strength of the OPC mortars proved to be similar to that of OPC aggregate, causing slight downgrading regardless the replacement level. Its effect on drying shrinkage was negligible in contradiction to that of OPC aggregate. In GPC mortars water absorption, compressive and flexural strength exhibited an enhancing effect with GPC aggregate replacement. On the contrary, drying shrinkage was negatively affected resulting to significantly high values. OPC aggregates replacement led to significant downgrading on most of the GPC mortar properties. Water absorption, drying shrinkage, flow and density of mortars appeared to be essentially dependent on the replacement percentage of natural by recycled fine aggregate.

Date of Award	8 Dec 2015
Original language	English
Awarding Institution	University of Bath
Supervisor	Andrew Heath (Supervisor)