Deterioration Of Concrete Properties In Marine Environment Due To Erosion Of Multiple Factors

There are a large number of chloride ions, sulfate ions, and magnesium ions in seawater. Under attack of those ions, the mechanical properties will deteriorate, and the durability will decrease. Because of this reason, the close attention of researchers has been paid to the variation of mechanical properties of concrete engineering in marine environment. In this paper, the evolution in strength, modulus, and creep behavior of concrete materials due to seawater attack are investigated by considering multiple factors(chloride ions, sulfate ions, and magnesium ions) erosion and their couple influence.Usually, the reinforced steel bars will be attacked by chloride ions, and concrete is dominantly attacked by sulfate ions. In this paper, we investigate the influence of chloride ions on the sulfate attack. We detected the variation of compressive strength, dynamic elastic modulus and surface hardness variation of the concrete attacked by solution of sodium chloride, sodium sulfate, and sodium chloride-sodium sulfate solution, and obtained the evolution behavior of those mechanical quantities of the concrete. The effect of the chloride ions on the sulfate attack to concrete can be divided into three stages. In the first stage, the effect of the chloride was inhibiting the sulfate attack to concrete and this inhibition effect increased monotonically with time. In the second stage, however, the inhibition effect turns to monotonically decrease. Finally, the inhibition effect disappeared and the effect of the chloride turned to promote the attack of sulfate. This phenomenon revealed the effect of the chloride to sulfate attack was a suppression-reverse process.The mechanical properties of the concrete under attack of sodium sulfate and magnesium sulfate were studied in the third and fourth part in this paper. The attack mechanism of the magnesium coupling with sulfate was analyzed by detecting the dynamic elastic modulus and topography of the concrete. The damage of the concrete under magnesium and sulfate attack can be divided into three stages: I. The concrete pores were filled in the first phase. The fill of the concrete pores by ettringite and magnesium hydroxide enhanced the mechanical properties of concrete. Therefore, in this stage variation of mechanical properties is caused by "negative damage". II. Competitive mechanism exists due to filling effect of ettringite and magnesium hydroxide and weakened effect of micro-damage evolution. III. The damage evolution is dominant factor in degradation of concrete materials. The results confirm that adding fly ash not only leads to the decrease of C3 A, but also improves the internal structures of the concrete. Moreover, the damage deterioration of concrete is inhibited and the property of anti-sulfate attack was improved by fly ash.A new model of damage deterioration in concrete under sulfate attack.The dominant form of damage evolution in concrete under sulfate attack is nucleation, growth, and eventually coalescence. The driving force for micro-cracks expansion includes two aspects: far-field load and internal expansive force of erosion. Based on the tensile strength of the concrete, we provided a criterion for the micro-crack’s nucleation, and based on Bai’s model, we derived the equation of micro-crack nucleation rate, which relates to the driving force of damage. On the basis of assuming the micro-crack growth obeys Seaman extended equation, and combining with the equilibrium equation of the evolution of the micro-crack number density, we got the first-order ordinary differential equation of the micro-crack number density evolution on the characteristic line. Per the volume integral of the micro-crack, the new model of the degradation of concrete damage has been built. The parameters of this model are determined by the experimental results. The results of this research showed that the damage degradation model obtained in this paper can better reflect the evolution rule of concrete erosion damage.