Time dependency study of chloride transport properties in modelling concrete durability

One of main concerns when modelling concrete durability with respect to chloride induced corrosion, it has to do with severity of damage caused, costs that arise from and more importantly, the increasing awareness of the number of reinforced concrete structures world wide that are prone to such type of damage. Moreover current practices in project planning demand further clarification regarding prediction of estimated service life, whether it is a new structure or an assessment of an existing one. To assess chloride penetration in concrete, current models rely on obtaining experimentally the diffusion coefficient at a given time. The challenge arises and practice codes demand enough precision in order to estimate with accuracy when a given structure will be needing maintenance intervention, so operational costs can be determined in order to maintain the desired serviceability over time. To better understand the time dependency of the diffusion coefficient and resulting service life prediction, current developments on modelling are analysed. A careful review demonstrates that in order to proceed further on modelling service life, it is needed to clarify the time frame of the parameters involved in which they remain valid and at the same time it is required to have a clear definition on the dimensional scale for which they preserve its validity. As so, to increase the desired reliability on output results, such time-scale transitions need to be investigated and addressed. An experimental campaign was carried on concrete samples made with ordinary Portland cement (OPC) with four different w/b ratios ranging from 0.40 to 0.78. Laboratory testing consisted on submitting concrete samples to the rapid migration test in a non steady state environment with different duration testing times for the same concrete composition. Testing aimed at the evaluation of ionic movement of chlorides due to applied electric field using a novel approach on determination of chloride diffusion in concrete. Results derived from testing, enable further developments on multi-scale modelling in order to support the redefinition of effective natural occurring diffusion in concrete due to chlorides and how it can be determined from accelerated migration tests