Beetroot Juice Additive in Chloride Brines Reduces Damage of Concrete Exposed to Freeze–Thaw Cycles

This work investigated whether and how a common agro-based additive, beetroot juice, alters the detrimental effects of chloride brines on the durability of cement concrete, by evaluating the frost resistance of ordinary portland cement concrete in various chloride brines. The presence of beetroot juice greatly slowed the ingress of ${\mathrm{Cl}}^{-}$ ions and mitigated the leaching of ${\mathrm{Ca}}^{2+}$, thus effectively mitigating the scaling-induced mass loss, strength reduction, and gas permeability change of the concrete. The microscopic investigation, including scanning electron microscopy, Fourier-transform infrared spectroscopy, and electron probe microanalysis, also proved that beetroot juice mitigated the degradation of C-S-H gel and C-A-S-H gel on the concrete surface and inhibited the formation of oxychloride and trichloroaluminate crystals, as confirmed by the lower $\mathrm{Na}(\mathrm{Mg})/\mathrm{Ca}$ and $\mathrm{Na}(\mathrm{Mg})/(\mathrm{Si}+\mathrm{Al})$ molar ratios in the deicer-weathered concrete. This study sheds light on the mechanistic roles of beetroot juice in improving the frost resistance of concrete in chloride-laden cold regions.