Influence of axial loads on CO2 and Cl- transport in concrete phases: Paste, mortar and ITZ

In most studies concerning the influence of external loads on transport properties of concrete, concrete is assumed to be homogeneous and hence, differences in the transport properties of its components, which have various physicochemical properties, are not examined. The differences would be further changed, when there is load on the concrete. Therefore, the results obtained can seldom explain changes in the transport properties due to the applied loads and neither can they further enhance existing transport knowledge. An experimental study on carbonation and Cl- ingress in concrete components, viz., paste, mortar and the interface transition zone (ITZ), subjected to different levels of non-destructive axial tensile and compressive loads, was carried out. The results obtained indicate that there was an approximately linear relationship between the non-destructive load and the depth of carbonation. The external load had a significant effect on the CO2 and chloride transport process in the ITZ, where a large amount of calcium hydroxide crystals can be found; for the mortar and ITZ samples, the influence of load on the depth of Cl- ingress was more significant than on the carbonation, whereas the influence of the load on the ingress of CO2 and Cl- was similar in the interface-free paste sample. It is also found that comparing to tensile loads, compressive loads inhibited the transport of CO2 and Cl- at the later stage of exposure.