Investigation of the potential use of dredged dam sediments as supplementary cementitious materials

Abstract

The disposal of dredged dam sediments often poses an environmental challenge. To address this issue, this study aimed to explore the potential use of dredged dam sediments as supplementary cementitious materials (SCMs). First, a simple identification procedure using chemical and geological data was proposed to facilitate large-scale identification. Second, dam sediments were used as partial cement replacements after being ground and calcined at 750°C for five hours. Four series of mortar samples were prepared, using pure Ordinary Portland Cement (OPC) and Portland Cement replaced by 10%, 20%, and 30% of calcined sediments. The contribution of calcined sediments to the development of mechanical strength was evaluated through the dilution and physical and pozzolanic effects from compressive strength tests. The results indicate that the proposed identification procedure is reliable, as confirmed by XRD and TGA/DSC analysis. The dredged dam sediments investigated are mainly composed of low-grade clay minerals associated with carbonates. In the early stages of hydration, calcined sediments influenced the hydration kinetics by their physical effect, as evidenced by the high amounts of portlandite observed in the XRD analysis. The pozzolanic effect becomes more pronounced between 28 and 180 curing ages, indicating the pozzolanic activity of 2:1 minerals, presumably enhanced by the presence of carbonate minerals. Both physical and pozzolanic effects increase proportionally with the replacement rate. In addition, the products of the pozzolanic reaction (C-S-H and C-S-A-H gels) differ from those of pure Portland cement in terms of structure and composition, as observed by SEM/EDS analysis, which explains the difference in cementing properties. Consequently, a replacement rate of 10% is deemed ideal for cement substitution.