A sustainable permeable geoplymer pavement system

Coal bottom ash (CBA), a silica rich by-product of coal burning, has been primarily researched as a substitute in permeable pavements. This study investigates the effect of the treatment type and dosage of CBA as a binder replacement in cement paste. Grinding, soaking and burning of CBA were conducted prior to mixing in order to enhance its innate physical and chemical characteristics. Materials from two Malaysian power plants, Kapar (K) and Tanjung Bin (TB), were used to examine the source effect’ on the pozzolanic constituents of CBA.

Subsequently, the compressive strength of the produced cement paste was investigated. The total pozzolanic content (SiO2, Al2O3, and Fe2O3) in CBA from K amounts to 63%, whereas it is merely 50% for TB. The values of the compressive strength of cement paste involving CBA at different levels of binder replacement were compared to gauge the effect of the treatment type. The cement paste made with untreated (raw) At a liquid-to-binder (l/b) ratio of 0.35, the raw CBA samples showed relatively similar compressive strengths.

For both sources, however, the compressive strengths of the ground CBA cement paste samples surpassed those utilizing untreated CBA – signifying the positive impact of grinding on the cementitious properties of CBA. The compressive strengths for the ground K-CBA and TB-CBA at 50% cement replacement were 24.3 and 27.3 MPa, respectively. These strengths are adequate for basic structural application, e.g. concrete pavers. Burning and soaking CBA have somewhat improved the compressive strength. The positive preliminary results are indicative of the potential use of CBA, with other industrial waste (e.g. fly ash), as a geopolymer (cementless concrete) in permeable pavement systems.