Influence of fineness modulus of fine aggregate on the durability properties of alkali-activated slag composites: An exprimental and statistical study

The consideration of sustainability has become a very important factor, because of the negative impacts posed by the production of Ordinary Portland Cement (OPC). This study investigates the influence of fine aggregate fineness modulus (FM) on the durability properties of AACs exposed to harsh environmental conditions (high temperatures, sea water, and sulfate solutions). Furthermore, this paper aims to statistically derive and validate a linear model that can be utilized in predicting the compressive strength (CS) of AACs of ground granulated blast furnace slag (GGBFS) using ultrasonic pulse velocity (UPV) a non-destructive evaluation. The FM of 2.4, 2.8, and 3.2, which represent fine, medium, and coarse particle sizes of fine aggregate, respectively, were adopted in this study, with other parameters kept constant. GGBFS was activated with a combined alkaline activating solution of sodium silicate (Na₂SiO₃) and a 12 M concentration of sodium hydroxide (NaOH) in a 2 to 1 ratio. The CS, UPV, density, and microstructural morphology as well as statistical analysis investigating linear relationships between UPV and CS were all evaluated in different harsh environments. The results showed that specimens immersed in 7 % magnesium sulfate (MgSO₄)and sea water after 6 months exhibited an increase in densities, CS, and UPV, with 2.4 FM having the highest enhancements, followed by 3.2 FM due to void filling action. However, mixes containing 2.8 FM were more resistant to residual incremental change produced by 7 % MgSO₄ and sea water. The statistical analysis shows that; besides the simplicity and robustness of the linear model, it also gives a higher coefficient of determination compared to an exponential model, making it a better fit for the UPV and CS relationship.