Two-dimensional Inhomogeneous Model For Analyzing Durability Concerns Of Concrete Structures Subjected To Adverse Sulfate Attack

Adverse sulfate attack,been as a significant part of durability concerns,is going to deteriorate concrete structures through the formation of expansive substance,such as ettringite,led by reaction between ingressing sulfate ions and inherent calcium aluminates,causing the exceeding expansive strain and stress inside concrete structures,and accordingly resulting in initiation and development of cracks.Eventually,concrete structures will lose potential capacity to serve in sulfate environment.This thesis investigates deterioration mechanism and factors regarding sulfate attack diffusion-reaction behavior in concrete structures by means of launching adverse sulfate attack experiment and corresponding numerical simulation in parallel,thereafter,followed by corresponding durability analysis and service life prediction.The main research work described in this MSc thesis consists of following sections:1.An experimental method in terms of two-dimensional sulfate attack behavior had been presented in this thesis to launch corresponding experiment program.During the finished experimental work,sulfate content determination based on a sort of titration method by employing barium chloride and mechanical properties evaluation through MTS(Mechanical Test System)test were conducted jointly aming to collect experimental data of sulfate ingress and strain-stress response within 12 weeks of exposure in purpose of analyzing the effects of binder composition,curing durations,and coarse aggregate on sulfate attack behavior inside concrete.In accordance with the results,specimens made with HS cement registered strongest ability to resist sulfate ingress,and specimens made with GU cement performed best in MTS test with highest compressive strength.Further,aggregate totally should be favourable to impede transport of sulfate ions inside cement-based system,although sulfate ions would assemble somehow at the area in front of aggregate.2.The two-dimensional homogeneous and inhomogeneous Finite-Difference-Model were built and thereafter verified by experimental results in this thesis respectively,followed by corresponding numerical simulation in purpose of analyzing significance of potential factors including diffusion coefficient,inherent calcium aluminates content,external sulfate ions concentration,chemical reaction constant,aggregate characteristics such as size,location,shape and content for adverse sulfate attack.The results showed that it should be more reasonable to describe sulfate attack behavior inside concrete by taking aggregate into account as compared to homogeneous diffusion-reaction model adopted before.Note further that,aggregate size,location and content could generate enormous influence on diffusion-reaction behavior of sulfate ions inside cementitious system.3.A sort of durability analysis method with regard to concrete structures serving in sulfate environment were presented in this thesis,and the corresponding limit state function along with service life prediction model had been built thereafter,followed by a series of case study under varying sulfate environment and different material parameters.As per the numerical results,one can see that a decreasing diffusion coefficient and a dropping inherent calcium aluminates content should prolong the service life of concrete structures subjected to sulfate environment as they separately play the key role on diffusion behavior and reaction behavior of sulfate ions during attacking process.Note further that rising aggregate content within a reasonable range during concrete proportion design and strengthening cover thickness should be the effective and efficient way as well to improve concrete structures performance when serving in sulfate environment.