Research On The Damage Of Concrete Under The Dry And Wet Cycles And Sulfate Attack

The durability of concrete involves resistance to corrosion, frost, carbonation, stress corrosion and so on in material subject have much extended and far-reaching meaning to be studied. However, in practice, several deterioration mechanisms exist in erosion environment, other factors have more or less infection to cauterization. Therefore, it is necessary to study the properties of the concrete subjected to more deterioration mechanisms. In seaside architecture and water conservancy, the degradation of concrete construction usually is the result of dry and wet cycles, and the concrete of sea level nearby is breached much easy. The sulfate attack is a extensive erosion of physical and chemical attack, combined with dry and wet cycles attack to be studied to avail significative reference on deterioration theory and practice of concrete construction.The macro-mechanical damage performance of concrete subjected to drying–wetting cycles and sodium sulfate attack in solution were investigated in this paper. Three water-cement ratio(0.4,0.55,0.7) of concrete specimens were placed in four different sulfate erosion solutions, 0%, 3%, 5% and 8% sodium sulfate concentration respectively. Compare and contrast single sulfate immersed test with sulfate attack& drying-wetting cycles double factors test, and the evolution damage model of the relative dynamic modulus of elasticity (Ed) of concrete is proposed based on continuum damage mechanics.For the degradation of concrete is a reflection of the micro damage mechanics, the micro-experiments include two contents, the one is the analysis of quantitative evolution of Ettringite vs. erosion time measured with the method of K value approximate calculation in XRD (X-Radial Diffraction), the second is observing the formation and growth law of Ettringite, sodium sulfate crystal etc. corrosive crystals and the evolution of concrete micro-structure in sulfate&D/W erosion in situation by ESEM (Environment Scan Electron Microscope).There are several conclusions in macro and micro aspects of sulfate&D/W erosion tests. The results of single sulfate immersed 440d test indicate the sulfate erosion is a chronically process and the evolution of Ed submit to early enhancing consistency, keeping and descending further, corresponding with the negative damage mechanics of concrete in test phase. There are certain interaction effect between the action of drying–wetting cycles and sulfate attack., especially in the high concentration solution. The degradation of concrete priority to sulfate attack.The distinctions of damage performance of concrete in sulfate&drying-wetting cycles tests are revealed by the different evolution damage models. The damage evolution equation of three differenr W/C concrete is fit in same curve, the expression is D = A+BT+CT², the change of damage slowly , and then the trend of accelerated increase later, the higher concentration the faster change, the W/C has small effect on damage.In the micro-experiments, the quantity of Ettringite in sulfate&frost tests is more than sulfate immersion, and improve obviously early till keeping later. The content range is 1.6% ².0% in small W/C ratio concrete and 3.0% in bigger. The effect of sulfate concentration and the interfacial crack extend rapidity along with the ratio increasing in ESEM. The primary corrosive crystal is ettringite to sodium sulfate attack, it have several different growth modality in different interspaces, the gelatinous crystals and fascicular crystals are also observed in small ratio micro- structure specimens, and that, a large volume of the minuteness needle crystals exist in broad voids or cracks in big W/C ratio specimens, and gypsum crystals also exist in high sulfate ion local. Furthermore, the physical erosion of Na₂SO₄ crystal inside or exterior of concrete also is distinct in sulfate&drying-wetting cycles circumstance. The significant influence of material configuration, void circumstance, and erosion medium etc. to the two damage mechanisms is complicated and need to be investigated farther.