One-part geopolymer binder by co-calcination of dredged marine sediment and oyster shell waste

One-part geopolymer eliminates the inconvenience of handling corrosive alkaline solution in conventional two-part formulation while retaining the advantage of low-carbon production. In this work, innovative one-part geopolymer binders produced from two ubiquitous marine wastes, namely dredged marine clay (31% quartz, 33% T-O-T clay) and oyster shell (93% calcite) via alkali fusion at 750 °C, are investigated, and the mechanisms underlying the thermal activation and synthesis process are discussed. The results show that upon co-calcination in Na 2 CO 3 environment, the crystalline structure of clay minerals in dredged marine sediments was disrupted due to the effectiveness of Na in breaking the bridging oxygens, resulting in the absence of Q 4 (0Al) silicon species. As the oyster shell content increases, the incorporation of Ca into the geopolymeric aluminosilicate network is enhanced, promoting a shift of silicon coordination towards more reactive states (Q 1 & Q 2 ). This is attributed to the preference of non-bridging oxygens for bonding with Ca than Na, leading to the reconstruction of the aluminosilicate network. With the inclusion of oyster shell up to 40 wt%, the compressive strength of the hardened one-part geopolymer paste was significantly improved from non-detectable to 22.6 MPa after 3 days of curing at 80 °C. These findings provide new insights into the synergistic utilization of aluminosilicate- and calcium-rich marine wastes in one-part geopolymer synthesis.