Mechanical and microstructural properties of just add water geopolymer cement comprised of Thermo-Mechanicalsynthesis Sediments-Fly ash mix

Abstract

This study investigated the utilization of dredged sediments for the mix design of a just add water geopolymer (one-part geopolymer). For this purpose, four aluminosilicate sources were prepared, by volume substitution of fly ash by sediment, with ratios of 15, 30 and 50%. These mixtures were thermomechanically treated to increase their reactivity. Then, commercial anhydrous sodium silicates and sodium hydroxide powder (NaOH) were used to formulate geopolymers. Several mortar formulations have been prepared with a variation of SiO2/Al2O3 molar ratio between 3; 3.5; 4; 4.5 and 5 for each aluminosilicate source. The measurements of the mechanical strengths were performed at 7 and 28, days. An optimal mixture was obtained for each mixture. Indeed, the optimal SiO2/Al2O3 ratio was equal to 3.5 for FA, FA85SD15 and FA70SD30 and 5 for FA50SD50. Subsequently, a series of tests was carried out on the selected optimal mixtures, such as microstructural characterizations (Mercury Intrusion Porosimetry, SEM) and chemical characterizations (XRD, FTIR). The results have shown that the incorporation of sediments in mixtures can improve the mechanical performance of the geopolymers. The results of XRD, FTIR and SEM have shown that sediments can constitute a source of aluminosilicate by the formation of geopolymer gels and zeolite crystals as a secondary product. In addition, the Mercury Intrusion Porosimetry results showed that the substitution of fly ash by sediments could improve durability by reducing the pore size, which also explain the gain in strength with sediments incorporation.