Elevated-temperature performance of alkali-activated nano concrete: The role of sustainable nanomaterials

Concrete, widely used in construction, presents sustainability issues due to its significant environmental footprint. An eco-friendly substitute, alkali-activated concrete (AAC), significantly lowers carbon di-oxide (CO 2 ) emissions and energy requirements. In comparison to conventional Portland cement (OPC), AAC demonstrates superior fire resistance, ensuring structural integrity in elevated temperature environments. The inclusion of additives further enhances AAC's durability and thermal properties. This research explores the impact of nano- fly ash (nFA), nano-ground granulated blast furnace slag (nGS), and nano-bentonite (nBT) on the properties of alkali-activated nano concrete (AANC) when subjected to high temperatures. While there is substantial research on conventional concrete, AANC, especially its high-temperature performance, remains under-explored. This study addresses this gap by examining how these nanomaterials (NM) affect the workability, mechanical properties, and thermal stability of AANC. The study shows that increasing the content of nFA, nGS, and nBT leads to a reduction in slump values, signifying decreased workability. Optimal levels of nFA and nGS significantly improve the mechanical strength due to enhanced particle packing and microstructural compactness. However, excessive amounts of these NM result in strength reduction due to particle agglomeration. nBT exhibits a complex relationship with compressive strength (CS), with an optimal dosage beyond which strength decreases. Elevated-temperature tests showed that nGS12 specimens had the highest CS at ambient temperature. Residual compressive strength (RCS) increased up to 400 °C but sharply declined at 600 °C and 800 °C. nGS specimens demonstrated superior thermal performance, while nBT specimens experienced significant strength loss. Flexural strength (FS) and splitting tensile strength (STS) significantly decreased with increasing temperature, with nBT-blended AANC showing the largest crack widths. Microstructural analysis through X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated substantial changes at elevated temperatures, such as increased porosity and gel phase decomposition. Thermogravimetric analysis (TGA) analysis indicated reduced weight loss (WL) in nanomaterial-enhanced AANC, suggesting better thermal stability. These findings highlight the need to optimize nanomaterial content to achieve a balance between mechanical performance and thermal stability in AANC.