Effect of Alkali Activators on Loess Geopolymer: Potential Waterproof Repair Material

Abstract

The possible utilities of geopolymers likely are due to their potentially high mechanical, physical, and durability properties that make geopolymers similar to ceramic materials. The similarity largely is because of a mineralogical and chemical composition silimar to that of ceramic materials. However, to produce effective similar properties, a measured dissolution of source materials in an adequate alkaline solution is required for geopolymerization. This paper examines the effects of sodium hydroxide (NaOH) and sodium silicate (${\mathrm{Na}}_2{\mathrm{SiO}}_3$ ) solutions on the properties of loess geopolymer and its effective use in ceramic tiles repairing. The experiments involved 8M concentration of sodium hydroxide and a combination of NaOH and sodium silicate with the same molarity at a ratio of ${\mathrm{SiO}}_2:{\mathrm{Na}}_2\mathrm{O}=2.5$ . Compressive and split tensile strengths of the loess geopolymer mortars (GPMs) were assessed at 7 and 28 days. X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron micrographs (SEM), and mercury intrusion porosimetry (MIP) analysis were carried out to determine the GPM behavior under alkali solutions as well as the correlation between its strength and structure. The resulting geopolymer loess was used to fill ceramic tile gaps. The experiment showed that the reaction and strength performance of loess geopolymer depended on the precursors and alkali liquids used. It was also established that the mixture of NaOH and ${\mathrm{Na}}_2{\mathrm{SiO}}_3$ not only reduced the pores in the loess based–geopolymer matrix but also had adequate mechanical behavior, effective adhesion, and durability for filling ceramic tile gaps.