This paper presents the role of clay portion in soil used to stabilize soils during alkaline activation with potassium-based alkaline activator. A 10 M potassium hydroxide solution was utilized to activate the soils with and without palm oil fuel ash (POFA) at a solution. Soils with and without POFA mixtures were tested using unconfined compression tests and microstructural analysis (using scanning electron microscopy and X-ray diffraction). Comparing the strength of the mixtures with and without POFA, the results presented that short-term compressive strength was higher for mixtures with POFA. However, after longer curing the admixtures of higher kaolinite content with POFA reached significantly higher strength levels than the admixtures without POFA. This work brings new insights to the soil stabilization by alkaline activation providing a relatively new avenue for effective utilization of aluminosilicate source materials with parent-treated soils. The clay minerals of hosted soil play an important role in soil stabilization with alkaline activation that affects the behavior of binder with hosted soil.

The feasibility of using palm oil fuel ash (POFA) as a precursor for alkali activation reactions, in combination with glass fibers as a discrete reinforcement, has been investigated. The experimental work was focused on the shear strength (using unconfined compression tests) and the tensile strength (using indirect tensile tests and flexural tests). According to the results, it was found that the peak stress increased and the post-peak behavior was modified from a brittle to a more ductile response depending on the amount of fiber reinforcement in the alkaliactivated mixtures. An analysis of the microstructures revealed that the most significant factor contributing to the enhanced behavior of the reinforced mixtures was the interaction between the geo-polymeric matrix and the fiber surface. The present work brings new insights to the soil stabilization industry by providing an effective method for enhancing the properties of soil treated by the alkali activation of POFA (a low-value agro-waste by-product) through the inclusion of glass fibers. This brings advantages over the traditional calcium-based binders (i.e., lime and cement) as their production involves the emission of carbon dioxide, one of the factors significantly contributing to global warming.

Abstract. There are several factors that affecting the shear strength and shear strength parameters (i.e. cohesion and friction angle). In this study, the effect of coarse material percentage was tested. Six different mixtures of soils (clay and sand) with different coarse material percentages (i.e. from 80 % to 30% of coarse material percentage) were tested via using direct shear test under different moisture content percentage. The results indicated that the shear strength and friction angle were decreased by the increment of the percentage of coarse materials (sand). However, the cohesion results showed unique behavior. The cohesion (at every moisture content values) increased with the increment of the percentage of coarse materials until specific point then it started to decrease with the increment of the percentage of coarse materials.

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