Heavy metal encapsulation and performance assessment of novel binary blended geopolymer concrete incorporating blast furnace slag sand for safe and sustainable construction practices

The use of industrial waste in construction materials leads to the release of harmful heavy metals, posing risks to health and the environment. This study aims to create a safe and eco-friendly binary blended geopolymer concrete (GPC) by using fly ash (FA) and ground granulated blast furnace slag (GGBS) as binders, along with replacing natural fine aggregates (NFA) with blast furnace slag sand (BFS). A 50:50 ratio of FA to GGBS was used in all mixes, with BFS replacing NFA at levels from 0 % to 100 %. Among all mixes, the 50 % BFS mix (G50S50) showed the best performance. It reduced the leaching of arsenic, chromium, and selenium by over 90 %, keeping all values below the limits set by the U.S. Environmental Protection Agency. This mix achieved the highest compressive strength of 46.26 MPa, which is better than traditional concrete. It showed excellent durability with low water absorption (3.59 %), lesser voids (3.29 %), and high density (2489 kg/m³). To ensure statistical reliability, Shapiro-Wilk, Kolmogorov-Smirnov, and Anderson-Darling normality tests were conducted, supported by sensitivity analysis and principal component analysis (PCA), which confirmed robust correlations between leaching, durability, and strength. Microstructural analyses using FESEM, EDS, XRD, Raman spectroscopy, water contact angle, and surface roughness revealed refined pore structure and effective immobilization of heavy metals. Collectively, the findings provide the first comprehensive evaluation of FA–GGBS binary blended GPC with BFS sand, demonstrating its potential as a safe, durable, and environmentally sustainable construction material.