Geopolymer stabilization of construction and demolition waste using water treatment sludge and silica fume for pavement applications

Abstract

ABSTRACT Sustainable management of construction and demolition (C&D) waste remains a critical challenge. This study investigates the geopolymer stabilization of C&D waste using a triple-waste system, including water treatment sludge (WTS, fixed at 10%) and silica fume (SF, varied 0–20%) activated by an alkaline waste effluent (NaOH solution, pH 13–14). The mixtures were cured under ambient conditions (i.e., 25°C) and evaluated through macro- and micro-scale tests, including unconfined compressive strength (UCS), California bearing ratio (CBR), ultrasonic pulse velocity (UPV), as well as scanning electron microscopy (SEM), X‐ray diffraction (XRD), and energy-dispersive X-ray spectrometry (EDS) analyses. Results demonstrated that the optimal mix (10% WTS + 15% SF) achieved a 56-day UCS of 2,250 kPa (630% improvement over untreated C&D), with secant modulus (E 50 ) increasing from 111 MPa to 1,260 MPa. The soaked CBR tests demonstrated a 235% improvement in bearing capacity, with the stabilized mixture achieving 87% CBR compared to 26% CBR for untreated C&D waste, meeting pavement subbase requirements. UPV values surged from 179 m/s to 1,550 m/s, confirming dense matrix formation. Microstructural analysis revealed enhanced calcium aluminosilicate hydrate (CASH) and sodium aluminosilicate hydrate (NASH) gel formations and particle bonding. However, the elevated optimum moisture content (OMC increasing from 7.4 to 11.65%) and reduced maximum dry density (MDD decreasing from 2.2 to 1.96 g/cm 3 ) may constrain field applicability in water-sensitive environments. This study advances sustainable waste valorization by integrating industrial by-products into low-carbon construction materials for pavement applications, though further research is needed to optimize moisture-density trade-offs for field implementation.

Topics & Concepts