Reduced wettability in compacted coal fly ash due to organosilane treatment

Organosilane (OS) treatment for water repellency has gained attention as a mechanism for mitigating leaching and for possible beneficial reuse of coal combustion residuals, particularly coal fly ash (CFA). However, little effort has been devoted to understanding the interaction between OS-treated CFA and water under conditions representative of field applications. In this paper, construction conditions of OS-treated CFA are simulated in the laboratory, and the degree of induced water repellency is investigated via contact angle measurements. A class-F CFA from a coal-fired electric power plant ash impoundment and a commercially available organosilane were used. In addition to CFA geotechnical and geochemical characterization, samples were prepared by post-compaction treatment of CFA with OS-solutions applied via spray, which simulates a field irrigation truck. Results indicate that a 7% volume concentration of OS solution is appropriate for construction purposes. However, the degree of water repellency, as measured by contact angles, is strongly dependent on the compacted CFA’s water content. This suggests that the contractor should compact the CFA first, then apply truck-mounted jet drying or similar, and finally spray the OS-solution on the surface. Results also demonstrate that about 84% of the treatment accumulates in the upper 5 cm of compacted CFA.