Strength and permeability characteristics of road base materials blended with fly ash and bottom ash

Abstract

The Philippines has an extensive road network which handles most of its passenger and freight movements. Large volumes of aggregate embankment materials of good quality are required to primarily support these transport infrastructures, and this poses threat to the environment. Coal combustion by-products (CCPs) are seen to be its potential alternative mainly due to its vast production and disposal problems in the country. Representative samples of class C fly ash and bottom ash were gathered together with conventional road base materials. Fly ashes were substituted to act as fines; whereas, bottom ash substitutions were varied at different mixture ratios of 0%, 20%, 40%, 60%, 80%, and 100% of fine aggregates. Index properties (i.e. specific gravity, Atterberg limits, and maximum and minimum index densities), compaction characteristics, unsoaked and soaked California Bearing Ratios (CBR), and hydraulic conductivities were obtained for all the blends in order to produce empirical relationships with varying bottom ash content. Results show that the optimum strength can be produced at a blend of 100% bottom ash. However, permeability tests show a considerable decline in hydraulic conductivity with the addition of coal ashes to the typical aggregates. Thus, proper drainage must be carefully applied to these blended embankment materials so as to avoid substantial ingress of water.