Study On Sulfate Transmission-Degradation Mechanism Of Concrete Under Long-term Soaking

The natural environment to which concrete structure is attached may contain a certain amount of sulfate. Sulfate enters into the inside of the concrete through a variety of ways, which not only worsens the concrete itself performance, but also reduces its ability to work with and protect reinforcing bars. Therefore, the study of sulfate attack mechanism and theoretical model provides an important theoretical foundation and basis for concrete life(re) design. For the purpose, this paper carry out a long-term soaking experimental study of concrete resistance to sulfate attack, and the following main conclusions and content are drawn:(1)This paper analyzes the deterioration law of C25 concrete strength with the change of corrosion age when the concrete is under the one-dimensional corrosion of 10% sodium sulfate; the study shows that strength increase of corroded concrete at the primary period is mainly caused by hydration and corrosion expansive products can improve concrete strength to a maximum extent of 4%, but their damage to concrete at later period is very markedly.(2)The sulfate ion distributions from the surface to the inner of C25 concrete at 1%, 5% and 10% sulfate concentration and of C50 and C70 concrete at 10% sulfate concentration are obtained through hierarchical slicing, solution titration and other chemical means; It analyzes the influence of different concentrations of sodium sulfate solution and concrete strength on the distribution and corrosion depth of sulfate ion inside concrete, and the analysis result shows that in different working conditions, the SO42- inside concrete has basically the same transmission deterioration mechanism, only evolution processes are different.(3)Carry out qualitative analysis on the microstructure morphology of corroded concrete and corrosion products by using microscopic test technology ESEM(environmental scanning electron microscope) and EDS(energy dispersive spectrometer), and the analysis result reveals the damage mechanism of sulfate on the microstructure of concrete and evolution law. And a deep macro-and micro combining analysis shows that deterioration of macro mechanical properties of concrete and the evolution of internal transport of sulfate ion in concrete are the reactions of microstructure change in the aspects of macro and transmission, and their performance are exactly consistent.(4)the paper takes the test result as guidance and takes diffusion theory as the foundation to build the transmission models of sulfate in the concrete under different working conditions, including concentration distribution model and crossion depth prediction model, and proves the rationality and applicability of these models through test data. In the end, the paper puts forward an average prediction model of corroded concrete and verifies this model through self-owned data and other literature data;meanwhile the damaged concrete section is simply but reasonably divided into uncorroded and corroded layers demarcated by the sulfate-induced corrosion depth of concrete, and calculate the average strength of concrete corroded layers, Consequently, a corrosion-depth-based deterioration model for concrete-corroded-layer strength isestablished was developed;in addition, based on the existing research of other scholars,this paper mathematically derives a distribution model of corroded concrete strength.