Effect of NaOH concentration and fly ash/alkaline activator ratio on the compressive strength of road base material

In this paper, a preliminary study is performed on the application of Class-C fly ash based geopolymer as road base material. The Class-C fly ash as a base material is collected from Manjung Coal-Fired Power Station, Lumut, Perak Malaysia. Geopolymer was produced by the reaction of fly ash with an alkaline activator (a mixture of Na2SiO3 and NaOH solutions). The effects of various NaOH concentration and fly ash/alkaline activator ratio to the strength of geopolymer paste were studied. The concentration of NaOH used in this study was 8 M, 10 M and 12 M. Various ratios of fly ash/alkaline activator (1.0, 2.0 and 3.0) and a constant ratio of Na2SiO3/NaOH at 2.5 were studied to define the maximum compressive strength. Tests were carried out on 50 × 50 × 50 mm3 cube geopolymer specimens and the test was conducted on the day-7 and day-28 for all samples. Results revealed that the 10 M NaOH concentration with the fly ash/alkaline activator of 3.0 is deduced as the optimum ratio, which exhibited the highest compressive strength at day-28 of testing.