The effectiveness of fly ash and fly ash-cement mixtures as stabilizing materials for high plasticity clay

Abstract The increasing activity of burning coal as fuel for Steam Power Plants (PLTU) will increase the amount of fly ash waste, urging the industry to maximize waste utilizations as, for instance, a stabilizing material for high plasticity clay. This research examined the effectiveness of clay + fly ash and clay + fly ash + cement stabilization in increasing the strength of road subgrade. The results showed that fly ash and fly ash + cement improved clay properties, demonstrated by the value of unsoaked CBR (5.78%) and soaked CBR (3.11%) of unstabilized clay. Clay + 20% fly ash yielded optimum CBR value (23,13%), and stabilizing clay subgrade on a 50-meter section using 20% fly ash at a cost of IDR 18,329,675. The mix of 40% fly ash + 15% cement yielded optimal CBR value (42.70%) at a cost of IDR 18,359,435.00. The evaluation of soil properties and cost analysis, shows that the most efficient mixture variation is 40% fly ash and 15% cement for clay stabilization.