Concrete deterioration under alternate action of chemical attack environments

By micro-and macro-observations, this paper reveals the deterioration mechanisms of concrete under alternate action of carbonation and sodium sulfate solution attack (C-SA), and meanwhile, the single sodium sulfate solution attack (SA) is also done as comparison. The studies indicate: in both cases, the main attack product is ettringite, only in the first layer of case SA some gypsum is checked, and the thaumasite form of sulfate attack is not initiated in case C-SA; compared with single sodium sulfate solution attack, although the carbonation layer mitigates the extent of sulfate attack in limited exposure period, but 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.