Stress-State-Dependent Reinforcement of Cement-Stabilized Soil Using Waste Brick Powder and Glass Fiber

Cement-stabilized soil is widely used for ground improvement but suffers from brittleness and low tensile strength. This study investigates combined modification of cement-stabilized soil with waste brick powder (WBP, 5%) and glass fiber (GF, 0–2.0%) to enhance mechanical performance and microstructural integrity. Unconfined compressive strength (UCS), splitting tensile strength (STS), and qualitative scanning electron microscopy were evaluated at 3, 14, and 28 days. Results reveal stress-state-dependent reinforcement: UCS peaked at 2.0% GF with gains of 18.1%, 7.3%, and 9.1%, while STS maximized at 1.5% GF (43% increase), declining 14.3% at 2.0% due to fiber agglomeration. Post-peak ductility improved markedly, with the residual strength ratio increasing from 12.4% to 43.2% and the ductility index from 1.18 to 1.85. Microstructural analysis suggests that uniform fiber dispersion enables crack bridging and interfacial load transfer, whereas agglomeration creates localized weak zones. Preliminary assessment indicates that WBP substitution may avoid approximately 85 kg CO2eq per cubic meter by valorizing construction waste. These preliminary laboratory findings suggest potential stress-state-dependent dosage trends for sustainable cement-stabilized soil composites, pending further validation.