Abstract
By micro- and macro-observations, the study reveals the deterioration mechanisms of concrete under alternate action of carbonation and sodium sulfate solution attack (C-SA) comparied with the single sodium sulfate solution attack (SA). The studies indicate that in both cases, the main attack product is ettringite, some gypsum is checked only in the first layer of case SA, the thaumasite form of sulfate attack is not initiated in case C-SA. Compared with the single sodium sulfate solution attack, although the carbonation layer mitigates the extent of sulfate attack in limited exposure period, the alternate action of carbonation and sulfate attack still leads to strength degradation to some extent. The effect of carbonation on sulfate attack for longer exposure period deserves further research.
Highlights
Deterioration of cementitious systems exposed to sulfate salts is the result of sulfate ions transport through the pore system, chemical reaction with the hydration product, generation of stress due to the creating of expansive reaction products and the mechanical response of bulk material due to the stresses (Ferraris et al, 2006)
Our researches depend on the following background to investigate the multi-factors action cases: some concrete structures lying in fluctuation region of sulfate-rich water discharged from chemical plant suffer from carbonation when no water, which is referred as the action of both carbonation and sulfate attack
Based on the previous researches have finished discussing concrete deterioration mechanisms under single carbonation action (Li et al, 2006), the study studies the mechanisms of concrete under alternate action of carbonation and sulfate attack compared with the single sulfate attack
Summary
Deterioration of cementitious systems exposed to sulfate salts is the result of sulfate ions transport through the pore system, chemical reaction with the hydration product, generation of stress due to the creating of expansive reaction products and the mechanical response (typically spalling and cracking) of bulk material due to the stresses (Ferraris et al, 2006). Micro-observations include the analysis of attack products by thermal analysis method and the determination of sulfate-ion content from surface to interior by chemical titrating method The thaumasite form of sulfate attack will generate white halo on the concrete surface, but with careful observations to the specimens
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