The Effect of Utilizing Fly Ash and Bottom Ash as a Replacement of Mineral Filler in Porous Asphalt Mixtures

Abstract

In the past decade, porous asphalt pavements have gained popularity as a stormwater best management practice because this unique asphalt can reduce spray and splash in wet weather, consequently reducing hydroplaning and increasing visibility. However, despite porous asphalt benefits, there are still some weaknesses, such as short service life than dense-graded asphalt due to its lower durability and strength. Coal ash is one of the most abundant industrial wastes and may be harmful to living things and human life if disposed of wrongly. The combustion of coal in the furnace in the power plant produces coal ash, consisting of fly ash and bottom ash. Hence, in this research, utilizing fly ash (class F) and dry bottom ash as a replacement of mineral filler to reduce the drainage value and improve the strength of porous asphalt mix was investigated. Laboratory specimens were prepared using 50 blows of Marshall Hammer per side by the Marshall mix design method. The bituminous binder used was performance grade PG 76, which complies with AASHTO Standard M320-02. The percentage of binder content in the range of 4.0% - 6.0% in increments of 0.5% was used to determine the Design Binder Content (DBC). The mix with both ashes was found to be 5 per cent of DBC. The DBC value for both mixtures was then used to evaluate the mixtures’ performance, which went through a binder drainage test, and rutting test. The performance results were then compared with the control porous asphalt mix using mineral filler. The control mixture and both modified mixtures show drain down values of 0.3%, 0.262%, and 0.167%, respectively. The replacement of both materials into the control mixture indicates that fly ash and bottom ash could increase the binder’s heat resistance and efficiently retain the binder in the modified mixtures. Meanwhile, after the completion of 8000 cycles in the rutting test, it could be seen that the rut depth measured for the mix with mineral filler was 1.6mm, 1.93mm for the mix with fly ash, and 2.04mm for the mix with bottom ash. The bottom ash mix’s higher rut depth value is likely due to the bottom ash characteristic with higher unburned carbon content, thus decreasing the strength mix. It is concluded that an investigation between both ashes in porous asphalt has the potential for the road industry in the future, leading to sustainable highway development.