Non-steady State Chloride Migration and Binding in Cracked Self-compacting Concrete

We adopted a notch method to study the influence of crack width （macro level） on chloride transport and binding of cracked concrete under a non-steady state migration test. The results show that migration coefficient of cracked concrete increases with increasing crack width up to a critical value （0.43 mm）, for the whole concrete or the area close to crack; the increase of migration coefficient could be independent from crack parameter when a critical crack width is reached. For chloride binding, Langmuir isotherms of cracked concrete samples exhibit the similar decreasing trend as crack width increases from 0.27 to 1.96 mm. The increased current value could be responsible for the trend based on the hypothesis of electric force.

Chloride-binding capacity of mortars composed of marine sand subjected to external chloride penetration

In order to explore the interactional relations of internal chloride and external chloride-binding amongst the cementitious materials,the chloride-binding capacity of mortars composed of marine sand(MS)or washed marine sand(WMS)were investigated.Results indicate that more external chloride can penetrate and diff use more deeply into the WMS mortar than that in the MS mortar.This phenomenon suggests that the external chloride migration resistance due to WMS is lower than that caused by MS.The distribution trends of the bound chloride content in the two types of mortars are the same at diff erent immersion times.However,a signifi cantly decreased area of the bound chloride content exists at the border of the external penetration area(EPA)and the external unaff ected area(EUA)at the immersion ages of 3 and 7 d,and then it disappears gradually with immersion time.The WMS mortar can bind more external chloride,whereas the MS mortar can bind more internal chloride,at diff erent immersion times.The distributions of bound chloride conversion rate in the EPAs of the two types of mortars diff er across immersion times.The distribution fi rstly decreases,and then it increases at the immersion ages of 3 and 7 d.The distribution was from increase,then decreases,and increase again at the immersion ages of 28 and 56 d.The bound chloride conversion rate in the WMS mortar is aff ected more greatly by external chloride penetration than that in the MS mortar.The amounts of the Friedel’s salt tend to increase with prolonged immersion time.Finally,the penetration of external chloride can increase the amount of fi ne capillary pores smaller than 100 nm in the WMSmortar exposed for 56 d in the chloride salt solution(WMS-E)specimen.

Modelling of Time Dependency of Chloride Diffusion Coefficient in Cement Paste

A computer-based model and method was presented to predict the time dependency of chloride diffusion coefficients in cement paste. The HYMOSTRUC3D model was applied to generate a 3D representative elementary volume （REV） of cement paste. In the simulation of microstructure, both of cement hydration and chloride binding were considered. With the simulated microstructure of cement paste, the finite element method was applied to simulate the diffusion process of chloride through the saturated cement paste. Based on the Fick’s first law, the chloride diffusion coefficient can be calculated. In this method, the influences of age and w/c ratio on the chloride diffusion coefficient were evaluated. The simulated chloride diffusivities with various w/c at different time were compared to experimental data obtained from the literature. The experimental results indicate that the chloride diffusion coefficient decreases with the increase of time and the decrease of w/c ratio. The trend of simulated relationship （diffusion coefficient vs time, diffusion coefficient vs w/c ratio） fits very well with the experiments.

Effects of Steam Curing on the Resistance of Cementitious Materials to Chloride Penetration

The resistance to chloride penetration of cement-based material with different curing regimes was investigated by solution titration,XRD,LF-NMR and rapid chloride migration test.The results show that the curing regime has influences on the types and structure of the hydration products,which in turn affects their ability to bind chloride ions.The binding capacity of cementitious materials to chloride ions,porosity and chloride ion migration coefficient increased with the increase of water-cement ratio,while steam curing increased the porosity and chloride ion migration coefficient at the same time as it increased the chloride ion binding capacity of the materials.At lower water-cement ratios,the effect of steam curing on the resistance of cementitious materials to chloride ingress is negligible.