Impact of plasticity characteristics on wet-dry response of fiber reinforced clays

Hydrological changes affect clays used as landfill cover, liner and embankments due to wetting-drying (W-D) cycles, adversely affecting their engineering behavior. This study assessed impact of plasticity characteristics on W-D response of unreinforced and fiber-reinforced clays. Four different mixtures of kaolinite and bentonite have been used to assess a wide array of plasticity. Compositions have been mixed with 0.1, 0.2, 0.3, 0.4, 0.6 and 0.9% polypropylene (PP) fibers 6, 12 and 18 mm in length and subjected to six W-D cycles. To analyze pictures of cracks for geometric dimension determination, Image J software together with Scanning Electron Microscopy (SEM) for visual examinations have been used. Results show that unfavorable effects of W-D cycles intensify with increase in clay plasticity and inclusion of fibers significantly reduced the detrimental effects through reduction of the area, length, width and number of cracks and helped maintaining integrity of samples even after six cycles. Additions of up to 0.3% fibers proved very effective with 12 mm being the optimum length. Fiber inclusion proved more effective in controlling cracking in high compared to low plasticity clays. Longer fibers proved more effective in low plasticity and shorter fibers with larger numbers in high plasticity clays. In high and low plasticity clays cracks formed after the 1st and the 3rd W-D cycles respectively and number of cracks grew with increase in W-D cycles. SEM showed fibers create a 3-dimensional network in clays that bind particles, resist tensile stresses and prevent rise in number and size of cracks.