Reliability assessment of concrete under external sulfate attack

The variability in characteristics of concrete material, such as pore size and chemical composition, has significant impact on the long-term performance of concrete structures under sulfate attack. This paper presents a reliability-based numerical model for assessing the long-term corrosion behaviour of concrete subject to sulfate attack. Using a reliability approach, the model can describe the reactive transport behaviour of sulfate ions and concrete degradation process. Specially, the variables in pore characteristics in interfacial transition zone (ITZ) and concrete chemical composition were quantified using a large amount of experimental data to determine the time-dependent reliability index (β) under long-term sulfate attack. The results show that the filling of ettringite and monosulfate after sulfate attack could modify the physical pore structure of ITZ at early stage. The time for concrete to reach the reliability index limit state shorten remarkably with the increase of sulfate concentration. For example, a four-fold increase of sulfate concentration (e.g. from 57 mol/m3 to 14.25 mol/m3) could shorten the time to reach the reliability index limit (i.e. β = 4.7) by 70 %. In addition, aggregate surface treatment especially with silica fume could improve the reliability of deteriorating concrete significantly by prolonging the time to reach the reliability index limit by 40 % in this study.