The Evolution Of Micro-structure And Macro-mechanical Properties Of Concrete Material In Marine Water Attack

This paper is from the research on corrosion resistance of concrete in Binhai hydra-junction, Huaihe River Project. The evolution of micro-structure and macro-mechanical performance of concrete in marine water erosion were studied. A macroscopic constitutive relation of concrete with considering the internal pressure of void and the evolution of micro-damage in seawater erosion was proposed with the theories of continuum damage mechanics and micro-damage mechanics. Based on the macroscopic constitutive relation, a evolution model of concrete's module in seawater erosion was proposed.Firstly, the growth law of ettringite in mortar was studied by using of micro-experiments, and the quantity evolution of ettringite vs. erosion time was measured with the method of quantitative XRD (X-Radial Diffraction). The formation and growth law of ettringite crystal are observed in situation by Environment Scan Electron Microscope (ESEM) with the method of "Cold-Platform", and the evolution of micro-structure in mortar vs. erosion time in sulfate erosion with different concentration is observed regularly. The micro-experiments of the charter may be used to supply some reference basis for the micro-analysis of the fourth charter.Secondly, according to the accelerated and contrast corrosion test of common Portland cement sample, water cement ratio from 0.4 to 0.8, the evolution of the dynamic modulus, compressive strength, expansion and anti-fold intensity vs. erosion time were studied. The evolution mechanism of macro-mechanical performance is analyzed by ESEM, XRD, X-Energy Dispersive Spectrometer(X-EDS). The analytical results show that the evolution process of concrete's macro-mechanical performance due to sulfate erosion includes two aspects: one is a chemical problem viz. the reduce of concrete material's coherence results from the ettringite formation, which results in the decrease of strength; the other is a mechanical problem viz. with the formation of ettringite, the evolution of concrete's mechanical properties depend on the structural and mechanical properties of ettringite and theinteraction between ettringite and the materials, which results in the durability reduction and damage of concrete materials.Finally, the ettringite formation is considered as the internal pressure of void and the micro-damage of matrix, and the concrete materials is regardedas a two-phase composite------the void with internal pressure and the matrixwith micro-damage. A macroscopic constitutive relation of concrete with considering the internal pressure and the evolution of micro-damage was derived with the theories of continuum damage and micro-damage mechanics. Based on the constitutive relation, an evolution model of concrete's modulus in seawater erosion was proposed. Numerical results under the uniaxial loading indicate that the modulus of composite increases in seawater erosion to a peak in the initial stages, and then keeps on a constant, finally decreases rapidly. Curve-fitting results show that the model can simulate the experimental curves with some proper parameters. The influence of the void pressure on overall constitutive relation are also discussed under the uniaxial loading by the numerical method. Numerical result shows that the void pressure not only has some effect on effective modulus, but also can lead to an initial stress (or initial strain). With the increasing of void pressure, the modulus gradually decreases but the initial stress (or initial strain) is on the increase.Compared with other researchers, there are three main characteristics in this paper. The first is that the experimental method includes macro and micro aspects. The second is that the theoretical analysis includes qualitative describe and quantitative analysis. The third is that the evolution model of modulus is proposed based on continuum damage mechanics and micro damage mechanics. The present work as a basic research may be used to supply some guidelines and references for improving the attack resistance of concrete materials.