The emission of carbon dioxide gas from the cement manufacturing industry has raised concerns about global warming. Geopolymer concrete (GC) is gaining attention as a sustainable and environmentally friendly alternative to traditional cement concrete. The current study focused on using local clay to synthesize and characterize metakaolin-based GC with varying percentages of nanosilica (NS) (1.5%, 3.0%, 4.5%, 6.0%, and 7.5% by weight of MK content) using NaOH/sodium silicate. The geopolymer specimens were cured at room temperature for 28 days, and their workability, compressive, tensile, and flexural strengths were measured to evaluate the influence of NS on the concrete’s mechanical properties. The study found that the compressive, tensile, and flexural strengths of the GC increased gradually up to 6.0% NS, but any further increase in its ratio resulted in a reduction in mechanical characteristics. The study concludes that the addition of 6.0% NS in metakaolin (MK)-based GC produces the highest mechanical properties, improving the compressive strength of the GC mix by 34.3% compared to the control GC mix and improving the flexural and split tensile strengths by 39% and 37%, respectively, compared to control GC strengths. Furthermore, the statistical analysis confirms nano-silica’s significant impact on geopolymer concrete’s mechanical properties, emphasizing its role in improving performance and sustainability as an alternative to cement-based materials.

The study investigated how simulated notches within concrete-filled steel tube (CFST) columns affect their mechanical performance. It aimed to understand the impact of notch length, orientation, and location within the steel tubes on the behavior of these circular columns. Study conducted compressive tests on a total of 32 CFST specimens, varying in thickness (3 mm and 6 mm) and filled with High-Strength Concrete (HSC) or Normal-Strength Concrete (NSC). Four control specimens without notches served as reference points. Results indicated that CFST columns with notches exhibited reduced mechanical performance compared to those without notches. Notch parameters played a crucial role in this reduced performance. Notch length and orientation had a more significant influence than notch location. It also highlighted that the thickness of the steel tube was a paramount factor, surpassing the importance of concrete type. In summary, the study emphasized that presence of notches in CFST columns significantly impacted their load-bearing capacity, buckling behavior, and failure modes. Length and orientation of notches were identified as critical factors, with steel tube thickness being a dominant factor in determining overall mechanical performance of these columns. These findings provide valuable insights for structural engineers and designers working with CFST columns in various construction applications.

The global growth of concrete is a strong indication of the urgent need for sustainable construction materials to reduce carbon footprints and reuse industrial waste. In this work, we study the combined effect of mixing two industrial by-products, silica fume and mill scale. The concrete mixes were prepared with combined substitution levels of 0, 20, 25, and 30%. Fresh properties were evaluated by slump, flow table, and compaction factor tests. Hardened performance was studied by compressive, flexural, splitting tensile, and non-destructive ultrasonic pulse velocity (UPV) tests. The long-term chemical durability of the combinations was studied by exposure for 91 days to magnesium sulfate (MgSO₄), sulfuric acid (H₂SO₄), and NaCl conditions. The performance of the trial indicated that a moderate replacement level of 20% is optimum for the fresh properties, resulting in the highest slump and flow values due to paste modification and improved particle packing. The result of non-destructive testing showed that the mix with 25% replacement achieved the highest UPV, which means the microstructure was highly dense and the interfacial transition zone was improved. The modified mixes exhibited better resistance against the mass loss of sulfuric acid when exposed to aggressive chemical environments than the control mix. The maximum acid resistance was found to be highest in the 30% substitution due to the decreased reserves of Ca(OH)₂. The 25% mix showed the best microstructural density and steady long-term development of compressive strength under sulfate and marine conditions. However, the high replacement (30%) resulted in a high dilution of cement clinker and a major decrease in mechanical performance and workability. The study shows that, in general, a replacement rate of 20% to 25% provides a good compromise between environmental sustainability and waste management, on one hand, and good mechanical performance and chemical durability, on the other, concerning modern concrete architecture.