Soil stabilisation using alkaline activation of fly ash for self-compacting rammed earth construction

This paper studies the effectiveness of alkaline activation of low-calcium fly ash on the improvement of residual granitic soils to be used on rammed-earth construction. Different liquid:solid ratios, alkali concentrations and Na2O : ash ratios were tested. Effect of calcium hidroxide, sodium chloride and concrete superplasticiser is also reported. Compressive strength up to 7 days at 60ºC was determined. Results show that, in terms of mechanical strength, there is an optimum value for the activator:solids ratio and the alkali concentration, and that a decrease in the Na2O:ash ratio results in strength increase. No improvement was observed with the sodium chloride or the superplasticiser, while the calcium produced only a short term increase in strength. SEM/EDS analysis were used to analyse microstructural development, showing that strength is fairly related to the Si:Al and Na:Si ratios