IMPACT OF NANO-SILICA ON THE MECHANICAL BEHAVIOR OF GEOPOLYMER CONCRETE

Abstract

There is an enormous use of Portland cement concrete which presents serious environmental issues such as high levels of carbon emission, thus the use of sustainable alternatives such as geopolymer concrete (GPC). Nevertheless, GPC has exhibited irregular mechanical strength especially early-age strength that restrains its use to a greater extent. Although nano-silica has been funded in impacting positively into cementitious composites, its impact on GPC is not fully exploited particularly with regard to optimization of dosage and microstructural interactions. To fill this gap research was conducted to study the effect of nano-silica (0 4% by fly ash weight) on mechanical and microstructural properties of GPC. Controlled experimental design was undertaken, whereby compressive, tensile, and flexural strength tests as well as SEM and XRD tests were carried out. ANOVA, Tukey, HSD, and regression were used in statistical assessment. The findings showed that 3% nano-silica produced the maximum compressive strength (39.66 + 0.91 MPa, *p* < 0.001) which was 24.2 percent higher than that of the control whereas tensile and flexural strength were increased by 32.4 and 24.2 percent, respectively. By microstructural examination, more dense matrices with lower porosity (8.5 percent at 3 percent nano-silica as compared to 12.5 percent control) were observed. But the workability decreased in a linear manner as the dosages increased (slump: 81.22 +/- 2.03 mm to 69.01 +/- 1.49 mm). At 2 3%, the dosage provided the best combination between strength improvement and ease of handling, beyond which effects on agglomeration were found. These empirical results support the use of nano-silica in sustainable construction showing its effectiveness in enhancing the performance of GPC. The research can fill the existing severe knowledge gaps in nano-modified GPC, providing practical solutions in material optimization and low-carbon infrastructural construction.