Effect of zeolite and polypropylene fiber addition on cement stabilized soft clayey soils

Soft clayey soils generally have low bearing capacity and high settlement potential. Evaluating these types of soils in terms of their location and the stabilization of the existing conditions is economically important. Cement has been widely used in recent years to improve soil properties. However, cement has disadvantages such as its brittle structure, high production costs, and greenhouse gas emissions during production. Therefore, finding environmentally friendly, cost-effective, and sustainable new materials that can completely or at least partially replace cement is of great importance today. In this study, a high-performance, cost-effective, environmentally friendly, and more flexible binder was developed to strengthen soft clayey soils with low strength and low bearing capacity in the residential area of Bartın city. To achieve this goal, natural zeolite and polypropylene fibers were used in combination with Portland cement. In line with this objective, Portland cement was added to the natural soil at weight percentages of 0%, 2.5%, 5%, 7.5% and 10%, and the cement weight was replaced with zeolite at percentages of 0%, 20%, 40%, 60% and 80%. Artificial soil mixtures were prepared by adding polypropylene fibers at weight percentages of 0%, 0.25%, 0.50%, 0.75% and 1% to the soil-cement-zeolite mixtures. The maximum dry unit weights and optimum water contents of the prepared mixtures were determined using the Standard Proctor test. The obtained mixtures were compacted at the determined maximum dry unit weights to prepare the test specimens. The specimens were cured in a moist environment at 23±1°C for 3, 7, and 28 days, after which unconfined compression and indirect tensile tests were performed. Reference specimens were prepared using Portland cement under the same conditions and proportions. The obtained test results were compared with the results of the reference specimens to examine the strength improvements depending on the additive ratio and curing period, and optimal additive ratios were determined in the stabilized soil matrix. Additionally, selected series of specimens were subjected to SEM analysis to correlate microstructural changes with mechanical behavior. As a result, it was determined that the specimens containing 20% zeolite and 0.25% polypropylene fibers exhibited the highest resistance and strength against slight deformation compared to the cementitious mixtures.