Evaluating the mechanical and microstructural properties of high-performance sustainable concrete utilizing nano-silica and recycled seashell with addition of steel fiber

This study investigates the utilization of seashell powder (SSP), a calcium-rich byproduct from coastal ecosystems, as a partial substitute for ordinary Portland cement (OPC) in high-performance concrete. This study seeks to assess SSP as a sustainable binder that diminishes carbon emissions while preserving or enhancing concrete performance. There was a planned experiment with SSP replacement levels of 6.5%, 7.5%, and 9%, as well as two doses of nano-silica (NS) of 2% and 3%. This study used slump flow (65–100 mm) and compaction factor tests to check the fresh properties. These tests showed that higher replacement levels made the material less workable. This study looked at mechanical performance by measuring compressive and splitting tensile strength. The SSP9NS3 mix had the highest compressive strength of 63.62 MPa after 56 days, and the tensile strength of all the mixes was between 2.44 and 5.15 MPa. Durability tests showed that chloride penetration was much lower and density was much higher. SEM analysis showed that the microstructure was better and interfacial bonding was better because of the combined effects of SSP and NS. The sustainability assessment showed that the embodied carbon went down by 17.5% and the cost of making it went down by $8.85/m³ compared to the control mix. The combination of seashell powder and nano-silica not only made the material stronger and longer-lasting, but it also had less of an effect on the environment. The best mix was SSP9NS3, which was made up of 9% SSP, 3% NS, and 1.5% steel fibers. These results show that SSP could be a good alternative to cement that is better for the environment, especially in coastal areas where there is a lot of seashell waste. They also suggest that more research is needed on how it works in large-scale applications and how long it lasts in harsh conditions.