خصائص تثبيت التربة المعدلة بالاسمنت في تطبيقات الطرق

Characterization of Modified Cement-Soil Stabilization in Pavement Applications

Abstract

The rapid expansion of infrastructure projects in Iraq, especially in Karbala, has intensified the demand for sustainable soil stabilization solutions due to the prevalence of weak, sandy, and gypsiferous soils with low bearing capacity and high sensitivity to salinity, moisture, and freeze–thaw cycles. In light of the limitations associated with high-quality construction materials and the environmental and technical drawbacks of conventional Ordinary Portland Cement (OPC) stabilization, this study investigates the efficacy of a nanotechnology-based additive, RoadCem (comprising synthetic zeolite, alkaline earth metals, and specialized activators), for enhancing geotechnical properties. A comprehensive experimental program evaluated varying cement contents (4%, 7%, 10%) and RoadCem dosages (0.7%, 1%, 1.5%, 2%) for their combined effects on unconfined compressive strength (UCS), indirect tensile strength (ITS), elastic modulus, toughness, durability (wetting–drying), shrinkage, and microstructural evolution via scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results revealed that 1% RoadCem with optimized cement content produced the highest overall enhancements: UCS increased by 8–22% after 96 days of curing, ITS by 40–60%after 28 days of curing, elastic modulus by 25–40%after 96 days of curing, and toughness by 16–42% after 96 days of curing, while mass loss under wet–dry cycles declined by 7–15% and volumetric shrinkage was reduced by up to 40%. Analyses using XRD and SEM showed marked crystalline development and crystallite size growth (up to 4250 Å), a substantial reduction in full width at half maximum (FWHM, a measure of crystalline peak sharpness, down to 0.59), and greater XRD peak intensities compared to cement-only mixes. These changes reflect a dense, cohesive calcium silicate hydrate (C–S–H) gel network, uniform pore-filling, and strong encapsulation of soil grains, resulting in significantly improved microstructural integrity. Importantly, lower or higher RC doses did not yield further improvements and, at times, even led to inferior or less uniform structures. When the dosage exceeded 1%, improvements in UCS and other mechanical properties declined, in some cases dropping by about 3–5% compared to the optimal dosage. This reduction is attributed to the excess RoadCem causing agglomeration of gel phases and heterogeneity within the microstructure, creating weak zones. Conversely, using less than 1% RoadCem did not promote sufficient C–S–H formation, resulting in incomplete pore filling and weaker bonds. Thus, 1% RC was identified as the optimal dosage for maximizing structural and mechanical benefits. The data demonstrate that RC enables a reduction in required cement content (by up to 50% in some cases) without compromising performance, leading to lower costs and emissions. Notably, it allowed pavement layer thickness reduction by up to 30% to meet the same design criteria, translating into substantial material savings, faster execution, and better environmental outcomes. Maintaining an optimal moisture content of around 9% is critical for maximizing these benefits. The study recommends 1% RC, with careful cement and water adjustment for specific soils, as a superior engineering, economic, and environmental stabilization approach, and calls for additional research across broader soil types and climates to further support sustainable infrastructure solutions in Iraq and similar contexts.