Binary blended fly ash concrete with improved chemical resistance in natural and industrial environments

This study reports the enhanced chemical resistance of a blended concrete mix (CFNI) made with 40 wt.% fly ash, 2 wt.% nanoparticles, and 2 wt.% sodium nitrite inhibitor as partial replacement of cement against calcium leaching, acid and sulfate attacks. The concrete test specimens of four different compositions were fabricated and immersed in natural seawater, 3% sulfuric acid solution, and 10% magnesium sulfate solution for 120 days. Long-term chemical deterioration of the concrete systems is evaluated by assessing visual changes of the specimens and solutions along with the changes in percentage mass loss, compressive strength of the concrete, pH of the solution, and dimensions. The results indicate that CFNI concrete exhibits a superior resistance against chemical attack under all the three aggressive environments. Detailed chemical characterization of the specimens, carried out using XRD, FTIR, and thermogravimetric analysis, reveal a reduced CaO content, absence of deterioration phases like ettringite, brucite, and enhanced C-S-H content in the CFNI concrete. The addition of nanoparticles and inhibitors into fly ash concrete has lowered w/c ratio, increased surface pH, enabled conversion of soluble calcium hydroxide into insoluble calcium silicate hydrate, filled pores/voids, and reduced shrinkage and cracking. The compact microstructure of the CFNI prevented leaching and reduced the ingress of aggressive chemical ions into the concrete. Our results demonstrate that incorporation of nanoparticles and inhibitor into the fly ash concrete composition is ideally suited for the design of high-quality, low-permeable concrete structures that is the key for enhanced chemical resistance in natural and industrial environments.