Experimental study on gas permeability and desiccation cracking of fiber-reinforced compacted bentonite at high temperature

This study examined the evolution of gas permeability and desiccation crack patterns in compacted bentonite blocks reinforced with glass fiber at 150°C. Radial flow gas permeability tests were conducted to assess the deterioration of the sealing capabilities of both pure and fiber-reinforced bentonite blocks. X-ray computed tomography (CT) was also used to visualize internal desiccation cracks after each permeability test. Additionally, vertical air permeability tests were performed to further evaluate the sealing performance. The results showed internal desiccation cracks were formed in all specimens prepared by the dry-mixing method, but their size decreased with more fiber content. However, gas permeability exhibited no clear trend with fiber addition; instead, 2 % fiber content caused fiber clustering, which created voids that rather increased permeability of the bentonite block. On the other hand, the wet-mixing method significantly improved fiber distribution, resulting in lower permeability and fewer desiccation cracks compared to dry-mixing. Furthermore, major desiccation cracks were formed at the interfaces of the three-layer compacted bentonite blocks due to structural discontinuities. These inter-layer cracks may also weaken the integrity of the material. In this study, the wet-mixing method might lead to the dispersed clay structure, and thus, more uniform pore sizes. This led to a higher number of small, evenly distributed cracks. In contrast, the flocculated structure from the dry-mixing method created a rather heterogeneous pore network in the bentonite block, resulting in fewer but larger desiccation cracks. The results suggest that 1 % fiber content can help reduce cracks and maintain permeability. The wet-mixing and single-step compaction may further improve the sealing performance of bentonite blocks. • Internal desiccation cracks form in compacted bentonite blocks at 150°C. • Desiccation crack size decreases with the addition of glass fibers. • Terminal gas permeability shows no clear trend as fiber content increases. • Wet-mixing ensures uniform fiber distribution, lowering gas permeability and cracking. • Dispersed structure forms small and uniform cracks when dried at high temperatures.