Research And Evaluation On The Deterioration Of Concrete Subject To Multi-factor

Deterioration mechanism of cement based materials in single factors was studied by many domestic and foreign scholars. Actually, the deterioration of reinforcement concrete is a process that interaction between physical, chemical, electrochemical and mechanical. Research on durability in single factor is hard to reflect the deterioration process of concrete structure in service. The aim of this paper is to investigate the deterioration mechanism of reinforcement concrete subject to multi-factor.Deterioration mechanism of concrete during three factors of freeze-thaw cycles, external flexural loading, and chloride salt attack and four factors of stray current corrosion, freeze-thaw cycles, external flexural loading, and chloride salt attack were studied respectively. Test equipment for concrete deterioration in multi-factor was invented; deterioration mechanism of concrete matrix in double factors and multi-factor, probability and states of steel corrosion in concrete during multi-factors, and evolution of strain in concrete matrix and reinforcement were studied by measured the mass loss, dynamic elastic modulus, ultrasonic parameters, corrosion potential and strain of reinforcement concrete. The results are as fellows:1. The presence of chloride salt increased the degree of saturation and permeability of the specimens which responsible for concrete deterioration whether during in three combination factors or double factors. The mass loss is more sensitive than that of dynamic elastic modulus for concrete deterioration. During three factors, the higher the applied external flexural load the rapid the deterioration, external flexural load accelerated the deterioration of reinforcement concrete.2. During four factors, cracking of steel corrosion is the main reason for reinforcement concrete deterioration. Scaling and external applied flexural loading is secondary. The results of ultrasonic characteristic parameters show that velocity decreased, amplitude decreased, propagation time increase, and period increase. Waveform from sharp become to plain. Ultrasonic can be used to qualitatively determine concrete deterioration.3. Potential of reinforcement decreasing during the combination of freeze-thaw cycles, chloride salt attack and external load. The rust result in cracking along the reinforcement is the main reason for concrete deterioration. The accumulated irreversible damage of concrete matrix is greater than that of reinforcement during the effect of freeze-thaw cycles, chloride salt attack and external load. The base line of concrete strain curve rising with the number of freeze-thaw cycles increase. Deterioration of concrete in freezing process is higher than that of in thawing process when applied 0.3 external loading. Strain of reinforcement keep at relatively stable range and no strain shift phenomenon was found. Strain evolution of concrete matrix is move to the negative direction first and the move to positive direction, at the same time, strain amplitude increase and degree of concrete matrix damage increase gradually.4. The invented test equipment can not only exert accurate external flexural loading but also to maintain long term load steady, to achieve any combination of three factors of freeze-thaw cycles, chloride salt attack and external flexural load at will, to gather signal of strain, load, temperature and resistivity of the specimens during the deterioration process, is a qualitative change from loading device to test equipment.