Abstract

Marginal soils are traditional stabilised with Portland Cement (PC) when used as a pavement material. The production of PC is however an energy-intensive process and emits a large amount of greenhouse gas into the atmosphere. Geopolymer is an environmentally friendly ‘green’ binder commonly used in building applications but rarely used in pavement applications. The application of geopolymer to marginal soil stabilisation is an innovative approach given the increasing scarcity of virgin quarry materials in many countries. This research investigates the effects of alkali activator and curing time on unconfined compressive strength (UCS) and microstructural characteristics of marginal lateritic soil (LS) stabilised with high calcium fly ash (FA)-based geopolymer, which is novel in the field of pavement geotechnics. The viability of using this stabilised material as a bound pavement material was also evaluated through laboratory evaluation tests. A liquid alkali activator was a mixture of sodium silicate (Na<inf>2</inf>SiO<inf>3</inf>) solution and sodium hydroxide (NaOH) solution at various Na<inf>2</inf>SiO<inf>3</inf>:NaOH ratios. The results showed that the UCS increased with the curing time and the 7-day UCS for all Na<inf>2</inf>SiO<inf>3</inf>:NaOH ratios tested meets the local national standard as pavement bound material for both light and heavy traffic roads. The maximum early strengths at 7 days of curing were found at Na<inf>2</inf>SiO<inf>3</inf>:NaOH of 90:10, where calcium silicate hydrate (C-S-H), cementitious products from high calcium FA and Na<inf>2</inf>SiO<inf>3</inf>, was found to play a significant role. The sodium alumino silicate hydrate (N-A-S-H) products, being time-dependent, however came into play after a longer duration. The maximum 90-day UCS was found at a Na<inf>2</inf>SiO<inf>3</inf>:NaOH ratio of 50:50. This study indicated that marginal LS could be stabilised by high calcium FA-based geopolymer and used as an environmentally friendly pavement material, which would furthermore decrease the need for high-carbon PC. The economical Na<inf>2</inf>SiO<inf>3</inf>:NaOH ratio for both light and heavy traffic pavement materials was suggested to be 50:50.