Deterioration mechanism and pore structure characteristics of concrete under the coupling effect of SO₂ and CO₂

Abstract

Concrete structures in industrial corrosion environments experience prolonged exposure to SO₂ and CO₂, leading to premature failure. This study conducted indoor simulation experiments to investigate the effects of SO₂ and CO₂, both individually and in combination, on concrete. By examining substance distribution within the neutralization zone, including pH values, ion concentrations, and microscopic morphology, the coupling degree of SO₂ and CO₂ effects was analyzed. The long-term corrosion effects of SO₂ and CO₂ were investigated to elucidate the deterioration mechanisms in concrete. Additionally, using nuclear magnetic resonance (NMR) technology and fractal theory, the relationship between pore fractal dimensions and the compressive strength of the corroded layer was explored. The findings reveal that under the combined effects of SO₂ and CO₂, CO₂ predominantly drives concrete neutralization, with the neutralization depth proportional to the square root of corrosion time. The distribution of corrosion products reveals that the coupled action of SO₂ and CO₂ mutually inhibits their diffusion into the concrete interior. Initially, corrosion products include plate- and rod-like gypsum crystals and cubic calcite. The rod-like and plate-like gypsum crystals grow close to and parallel with the calcite crystals. Subsequently, the corrosion products transform into large prismatic gypsum crystals, which aggregate perpendicular to the silicate matrix. When these crystals form at grain boundaries or within narrow pores, they generate substantial crystallization pressure on the silicate matrix, inducing microcracks and increasing concrete porosity. As porosity increases, the fractal dimension (Dc) of large and capillary pores significantly rises, thereby amplifying the heterogeneity of the pore structure. Consequently, the compactness of the concrete decreases, leading to a pronounced reduction in its strength.