Long-Term Performance Of Concrete Under Axial Compression Coupled Effects Of Sulfate Attack And Dry-Wet Cycle

As one of the important contents of concrete durability, sulfate attack on concrete, being many impact factors and great harmfulness, is a complex phenomenon which involves the effects of actions of physics, chemistry and mechanics. In practice, how to predicate the predetermined functions (e.g. safety, applicability, durability, etc.) of concrete structure suffered from couple effects of loading, single or double sulfate attack, requires the analysis of concrete long-term performance. However, test methods of concrete preformances under the coupled actions of the multi-factors have not been unified, such as creep test method of concrete under harsh environmental conditions has no corresponding standard to follow, which result in research achievement in lack of regularity and being commonplace disputed. These might cause deviations in research and unsafeties in engineering practice, to be solved.In the design of concrete structure, it is completely important to obtain the current state of material performances of concrete in service which are not constant in actual and differ from the concrete in28days in traditional design. The current statuses of concrete performances are affected by ambient environment, creep and damage, etc. At present, research on material performances of concrete under the combined actions are insufficiency and on beginning phase, the time-dependent behaviors of concrete suffered from coupled effects is still blank.In response to these circumstances, in this dissertation, experimental and theoretical studies are carried out on mechanical, durability and long-term performance of concrete under the coupled actions of axial compression, dry-wet cycle and shlfate attack. The main works are as follows:(1) Based on the comparison and analysis of pre-existing test mothod domestic and overseas, in combination of characteristics of concrete sulfate attack in engineering practical environment, testing programs for long-term performances of concrete subjected to coactions of axial compression, dry-wet cycle and sulfate attack are established.(2) Long-term properties and their relations with different immersion ways, stress levels and concentrations of sulfate solution of concrete exposed to multiple aggressions are experimentally studied. It is indicated that effects of combined factors on concrete performance are delayed or accelerated due to distinction between the alternative factors.(3) According to the general principle of the cellular automaton model, the evolution rules of the cells in concrete in time and space are proposed and the uncertainty of sulfate ion diffusion caused by inhomogenous in concrete are taken into consideration. A modified cellular automaton model is presented to simulate the diffusion process of sulfate ion in concrete under multiple corrosion factors.(4) On account of the concrete damage mechanics theory and the B3creep model, a modified B3creep model is presented to predict the time-dependent deformations of concrete under coupled effects of sustained loading and sulfate attack. Furthermore, in combination with the impact factor of drying and wetting cycle, a new creep model is established for prediction in the condition of dry-wet cycle and sulfate attack. All prediction models herein can agree well with the test data.(5) On the basis of concrete damage constitutive theory, a damage model of concrete suffered from sulfate attack is proposed which take the characteristics of concrete sulfate attack into account. In combination of the creep effects on concrete strength, modulus of elasticity and strain, a time-dependent stress-strain model of concrete under the coupled effects of axial compression, dry-wet cycle and sulfate attack is presented. This model can provide good predictions on the stress-strain relationship curves of the concrete and rational simulations on the failure propagation.