Feasibility of using stabilized grouting wastes as a road foundation material

Cement-stabilized sand is widely used in road base construction, but its application is increasingly constrained by the shortage of natural sand. This study investigates the feasibility of reusing grouting waste (GW) as an alternative material in cement-stabilized road base mixtures. Seven GW samples collected from different sites in Belgium were characterized in terms of particle density, sand equivalent, methylene blue value, plasticity index, compaction behavior, mineralogical composition, and their 28-day unconfined compressive strength (UCS) was evaluated with cement contents of 4-12%. The results showed that the GW samples exhibited clear source-dependent variability, with lower particle density and sand equivalent, but higher methylene blue value and plasticity index than natural sand. Their optimum water contents ranged from 11.35% to 23.91%, indicating the need for source-specific moisture control. At 8% cement, the porosity of most cement-stabilized GW mixtures (29.9-36.9%, except GW F at 41.5%) was comparable to or lower than that of the cement-stabilized sand mixture (37.0%). The 28-day UCS of GW mixtures increased from 2.24–3.97 MPa at 4% cement to 5.01–9.33 MPa at 12% cement. With suitable cement dosage, all cement-stabilized GW mixtures satisfied the 28-day strength requirements of 4 MPa for road base materials in the Belgian specification, and some GW mixtures even developed higher UCS than the cement-stabilized natural-sand benchmark. The better-performing sources were associated with lower clay activity, favorable porosity, and possible residual cement-related contribution. A preliminary modified empirical framework was further proposed to describe the strength variation of cement-stabilized GW from different sources, increasing the overall correlation from R 2 =0.6435 to R 2 =0.8995. Overall, selected GW sources show preliminary laboratory-scale mechanical feasibility for road foundation applications, although durability, environmental compliance, and field validation remain necessary.