Performance and Mechanism of Alkali-Activated Complex Binders of High-Ca Fly Ash and Other Ca-Bearing Materials

摘要

Industrialization leads to the generation and release of large quantity of wastes into theenvironment.Processes that maximum utilization of wastes,as products,and minimizepollution in the environment are greatly needed.Complex binders were created fromhigh-Ca fly ash and other Ca-bearing materials activated by sodium hydroxide andsodium silicate solution.Hardened binders made only from high-Ca fly ash(CFA100%),fly ash with 40 wt%cement(CFA-C40%),fly ash with 10 wt%flue gas desulfurization(FGD)gypsum(CFA-G10%),and fly ash with 10 wt%water treatment residual(CFA-WTR10%)had better mechanical performance compared to the binders using other mixratios.Most of the synthesized products were non-crystalline as X-ray diffraction(XRD)analysis showed a broad diffuse halo.Using Fourier transform infrared spectroscopy(IR),asymmetric stretching of Al-O and Si-O bonds and Si-O-Si bending bandsappeared as the main peaks.Scanning electron microscope(SEM)pictures of theCFA100%,CFA-C40%,CFA-G10%,and CFA-WTR10%specimens also showedamorphous synthesis products were formed around the spherical fly ash particles.Further analysis using energy dispersive X-ray analysis(EDXA)indicated the mainproducts of the CFA100%,CFA-G10%,and CFA-WTR10%specimens weregeopolymeric gels.In the CFA100%and CFA-C40%specimens,calcium silicatehydrate(C-S-H)gel and geopolymeric gel were formed simultaneously.The bindingproperties of the amorphous alkali aluminosilicate geopolymer gel and C-S-H gelcontribute to the mechanical strength reaching 80.0 MPa(i.e.11,600 psi)of thecomplex binders.In conclusion,utilization of high-Ca fly ash and other Ca-bearingmaterials in alkali-activated complex binders is feasible.Additionally,compared toPortland cement,producing alkali-activated complex binders can also reduce the use ofmined raw materials and energy,and also reduce the release of greenhouse gases.These materials can be widely utilized in various applications such as in buildingmaterials and for solidification/stabilization materials,including other waste materials,thus making them more environmentally benign.