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 hydroxide, sodium chloride and concrete superplasticiser is also reported. Compressive strength up to 7 days at 60 °C was determined. Results show that 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 a 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.

► Low calcium fly ash activated with a sodium-based solution to enhance soil properties for earth construction. ► No significant improvement with sodium chloride or superplasticiser. ► There are optimum liquid:solid and alkali:ash ratios and alkali concentration in terms of maximum strength. ► Microstructure is significantly affected which can be related to strength increase. ► Mixture consistency allows dispensing any compaction energy, only vibration is necessary.