Enhanced strength and microstructure of dredged clay sediment-fly ash geopolymer by mechanochemical activation

Abstract

A low reactivity dredged high plasticity clay rich in quartz and alumina was obtained from an intercoastal waterway in southeast Texas and mechanochemically treated with fly ash and sodium silicate and used to manufacture a geopolymer mortar. The treated dredged clay and fly ash precursor was activated with a liquid sodium hydroxide solution. Ten different mixes were considered to study the effects of mechanochemical treatment, mixing procedure, and fly ash replacement dosage. The compressive strength, the reactivity during thermal curing, degree of polymerization, and microstructure and morphology were investigated using isothermal calorimetry, Fourier-transform infrared spectroscopy, nano-indentation, and optical and scanning electron microscopy. Co-grinding fly ash, sodium silicate, and dredge clay enhances the bulk reactivity and dispersion of the blended precursor which enhances the connectivity of the geopolymer, intensifies the polymerized structure, increases compressive strength, and lowers the matrix pore size surface area despite increased water demand and some physical interferences from the dredge clay sediment. The efficacy of the mechanochemical treatment will largely depend on the quantity and reactivity of the fly ash present in the geopolymer. The inert dredge high plasticity clay sediment serves as an effective filling agent in geopolymer systems up to 50% replacement. However, the mechanochemical treatment of a blended fly ash-dredge clay system is most effective in increasing compressive strength (by ~ 30 MPa) when the inert dredge clay sediment is less than or equal to 25% of the total precursor mass.