An experimental study to examine the effect of fiber and natural pozzolan on the failure characteristics of a cement-treated sand

Incorporating zeolite for the enhanced treatment of the cement-treated sands, apart from environmental benefits and saving cost and time, results in the improvement of pozzolanic reactions and hence, the failure mechanisms over time. Besides, reinforcing these samples with fibers can be a further contribution to mitigate the brittle behavior along with increasing the strength characteristics of the base soil. The main focus of the current study is to investigate the changes of the stress-strain (q–ε) relationships and the micro-character of the zeolite-cement treated sands with and without fibers subjected to the drained behavior. In this regard, the samples were prepared with cement content of 4%, zeolite contents of 15, 30, 45 and 60% (cement replacement) and fiber content of 0.5%, considering the relative density of 50% and 56 days of curing time. The consolidated drained (CD) triaxial tests with confining pressures of 50, 100 and 200 kPa and SEM analysis were performed. Crucial geotechnical parameters, obtained from the q–ε curves, like maximum strength (qmax), failure strain (εf), brittle index (BI), secant modulus (E50), cohesion (C) and internal friction angle (ϕ) were evaluated. The results indicated that concurrent use of fiber and zeolite substantially modified the high brittle index and low failure strain of the cement-treated sands. In fact, zeolite incorporation in the mixture enhanced the post-peak behavior while post-peak stresses in cement-treated sands experienced a dramatic drop. Besides, observational analysis from SEM micrographs confirmed that pores were roughly filled up in the optimum zeolite content and more tension resistance were witnessed in the fiber-reinforced samples. Furthermore, fibers in the zeolite-cement treated samples exposed to less tension rather than cement-treated ones. Zeolite fully covered the fibers and helped them to provide more resistance, hence, prevented the complete failure and improved the strain-hardening characteristics.