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 study, the construction conditions of OS-treated CFA were simulated in the laboratory, and the degree of induced water repellency was investigated through contact angle measurements. A class F CFA from a coal-fired electric power plant ash impoundment and a commercially available OS were used. Besides CFA geotechnical and geochemical characterisation, samples were prepared by post-compaction treatment of CFA with OS solutions applied by spraying, which simulates a field irrigation truck. Results indicate that a 7% volume concentration of the OS solution is appropriate for construction purposes. However, the degree of water repellency, as measured by using contact angles, is strongly dependent on the water content of the compacted CFA. This suggests that the contractor should compact the CFA first, then apply truck-mounted jet drying or a similar technique 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 the compacted CFA.