Experimental investigation on the mechanical performance and microscopic characterization of desulfurization gypsum-reinforced ternary geopolymer

Abstract

Alkali-activation geopolymer material has been widely studied and applied in engineering due to its advantages of energy conservation and environmental protection. The geopolymer with the ground granulated blast-furnace slag (GGBS) and fly ash (FA) is the most common. This paper is aimed to incorporate the flue gas desulfurization gypsum (DG) into the GGBS/FA geopolymer to form a new ternary geopolymer. Thus, the unconfined compression tests are carried out to study the effects of the variations of GGBS and DG content and modulus of alkali activator on the compressive strength, then X-ray diffraction (XRD) and scanning electron microscope (SEM) are performed to analyze the chemical components of final products and microstructures to reveal the strength composition mechanism. Results show that the presence of calcium in GGBS and DG contributes to the C-(A)-S-H products while the polymerization reaction is impeded. The incorporation of DG can combine with active silicate to generate ettringite and fill the pores inside the geopolymer. In addition, the SO42- in DG can also promote the polymerization reaction. The double role of the above effects improves the strength of geopolymer. The lower alkaline condition leads to lower compressive strength due to the less polymerization gel products, while the contribution of high calcium content to the strength improvement is more pronounced. However, the DG content should be controlled to prevent the volume-filling effect and the produced ettringite shows excessive volume expansion.