CONCRETE DETERIORATION MECHANISMS UNDER SIMULTANEOUS SULFATE ATTACK AND LOAD ACTION

摘要

The deterioration mechanisms of sulfate attack of concrete under sustained loading and wet-dry cycling are investigated based upon micro-and macroobservations. The sulfate-ion concentration in the sodium sulfate test solution was 50000mg/L with the corresponding mass fraction being 6.9%. Three loading levels of 20%, 40% and 60% of ultimate flexural load were investigated and the load was mechanically applied to the specimens under four-point bending. Micro-observation was the determination of the sulfate-ion content profile using the modified barium sulfate gravimetric method (chemical titration method). Macro-observation was the measurement of the flexural strength change. Test results showed: the tensile stresses can increase diffusivity by initiating or developing microcracks; the compressive stresses are small compared with the concrete compressive strength, so the any effect on ion transport properties are not observed; under simultaneous sulfate attack and flexural loading, deterioration is aggravated as the loading level increases, and this is characterized on the macroscale by increased strength degradation.