Mechanical Performance and Moisture Sensitivity of Sand–Clay Composite Stabilized with Gum Arabic as Partial Cement Replacement for Pavement Foundations

Abstract

Road construction requires foundation materials with high mechanical performance. Cement is the primary binder used to stabilize these materials, but its widespread use generates substantial CO2 emissions and environmental impacts. Reducing cement demand has therefore stimulated interest in sustainable stabilizers, particularly natural biopolymers such as Gum Arabic (GA). This study evaluates the mechanical performance of a sand–clay composite stabilized with Gum Arabic (GA) as a replacement for cement. The matrix material was formulated by litho-stabilizing a red clay soil with quarry dust and an optimal baseline percentage of cement. This reference cement ratio was systematically replaced with incremental doses of GA to quantify changes in mechanical properties, moisture susceptibility, and morphology via scanning electron microscopy (SEM). Because GA rendered standard curing (20 ± 2 °C) unsuitable, UCS and ITS were evaluated under room-temperature (RT, 25 ± 2 °C) and thermal plus room-temperature curing (TRT, 24 h at 60 °C followed by 25 ± 2 °C). Increasing the GA content progressively increased the Optimum Moisture Content (OMC) when SCC was treated with only 8% cement (SCC8 + 0) to 19.73% when SCC was treated with the same weight of GA without cement (SCC0 + 8). It also reduced the Maximum Dry Density (MDD) from 1.83 to 1.62 g/cm3. Under soaked conditions, the CBR decreased from 294% for SCC8 + 0 to 11% for SCC0 + 8, highlighting the strong effect of GA on moisture sensitivity. Under RT curing, UCS and ITS evolved differently with the curing age. At 28 days, UCS is 3.39 MPa for SCC8 + 0 and 2.94 MPa for SCC0 + 8, while at 28 days, the corresponding ITS value is 0.58 MPa, for both. At 90 days, ITS decreased to 0.51 MPa for SCC8 + 0 and increased to 0.71 MPa for SCC0 + 8. However, a major limitation emerged during moisture susceptibility testing, as all GA-bearing specimens collapsed under immersion. Thus, although mechanical testing indicates potential for partial cement substitution, this marked water sensitivity precludes direct road pavement implementation and underscores the need for further study to counteract these instability mechanisms.