Tensile strength and durability performances-based evaluation of 3D-printed and mold-cast fibrous geopolymer composites produced at various alkaline activator combinations

Abstract

This study aimed to investigate the effects of the sodium silicate-to-sodium hydroxide ratio SH molarity and carbon fiber volume fraction on the tensile strength and durability properties of mold-cast and 3D-printed geopolymer composites including flexural and splitting tensile strengths ultrasonic pulse velocity water absorption sorptivity index and chloride penetration properties. For that purpose the ground-granulated blast furnace slag and fly ash were employed as alumino-silicate-rich raw material. In order to activate the alumino-silicate-rich raw material two sodium silicate/sodium hydroxide ratios of 1 and 2 and three sodium hydroxide molarities of 8M 10M and 12M were designated. Furthermore carbon fiber was incorporated into the geopolymer composites at three volume fractions: 0 % 0.3 % and 0.6 %. In total 18 nonfibrous and fibrous geopolymer composites were manufactured in two different ways: mold-cast and 3D- printed. The findings demonstrated that the strength and durability characteristics of 3D-printed specimens were inferior to those of mold-cast specimens attributed to the presence of weak interfacial bonds between layers. It has been observed that the incorporation of carbon fiber has the effect of improving tensile strength performance. Nevertheless the addition of carbon fiber led to a slight decrease in UPV values and an increase in water absorption and sorptivity index values. Also it adversely influenced the chloride penetration of geopolymer composites. The findings of the study also indicated that increasing the sodium hydroxide molarity had a positive impact on the strength and durability properties of the composites. Nevertheless it was observed that increasing the sodium silicate-to-sodium hydroxide ratio led to a decrease in both tensile strength and durability performances. Additionally the microstructure of the geopolymer composites was analyzed using scanning electron microscope (SEM) images.