The influences of sulfuric acid and magnesium sulfate attacks on pumice powder incorporated alkali-activated mortars with different sodium hydroxide molarities

Abstract

In this study, the mechanical properties and durability of the basaltic pumice-powder incorporated alkaliactivated mortars (AAM) were investigated against 5 % sulfuric acid and 5 % magnesium sulfate attacks. Basaltic pumice powder (BPP), ground granulated blast furnace slag, and F-type fly ash were used as binders. The BPP was replaced by fly ash and slag in equal proportions of 0 %, 10 %, 20 %, 30 %, 40 % and 50 %. Sodium silicate and sodium hydroxide (SH) were used as alkali activators with a silicate to hydroxide ratio of 2.5. In addition, 8 M, 12 M and 16 M SH molarities were utilized to investigate the effects of SH molarity on the resulting performances. Visual inspection, weight change, compressive strength, flexural strength, and ultrasonic pulse velocity (UPV) tests were performed to detect the differences due to the 5 % sulfuric acid and 5 % magnesium sulfate exposure at the macroscale. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were also performed to observe the changes at the micro-scale. The results showed that the average compressive strength decreased by 40 % and 25 %, flexural strength decreased by 32 % and 14 %, and UPV decreased by 24 % and 16 % due to the acid and sulfate exposure, respectively. Although higher mechanical strengths were obtained with higher SH molarities, the worst chemical resistance was found at 16 M AAM. The 12 M SH molarity proved to be the best SH molarity against chemical attacks. The incorporation of BBP also improved the chemical resistance, and the best chemical resistance was found for the AAM incorporated with 50 % BPP with an SH molarity of 12 M. The use of BPP has the potential to improve the chemical durability of AAM, and this potential increases with higher BPP replacement ratios. Thus, BPP materials can be utilized in structural applications against chemical attacks.