International audienceThis study examined the effects of traversing cracks of concrete on chloride diffusion. Three different concretes were tested: one ordinary concrete (OC) and two high performance concretes with two different mix designs (HPC and HPCSF, with silica fume) to show the influence of the water/cement ratio and silica fume addition. Cracks with average widths ranging from 30 to 250 mu m, were induced using a splitting tensile test. Chloride diffusion coefficients of concrete were evaluated using a steady-state migration test. The results showed that the diffusion coefficient of uncracked HPCSF was less than HPC and OC, but the cracking changed the material behavior in terms of chloride diffusion. The diffusion coefficient increased with the increasing crack width, and this trend was present for all three concretes. The diffusion coefficient through the crack D-cr was not dependent of material parameters and becomes constant when the crack width is higher than similar to 80 mu m, where the value obtained was the diffusion coefficient in free solution

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Concrete from deconstruction can have a second life in the form of recycled concrete aggregates (RCAs). They unfortunately have poor properties (high porosity and water absorption coefficient (WAC)) with respect to natural aggregates. Accelerated carbonation was implemented to improve the RCA properties and to increase their use by storing carbon dioxide (CO2) in the cement matrix and thereby reduce their environmental impact. This paper aims to perform a parametric study of a process for accelerated carbonation of RCAs to store the largest possible amount of CO2 and improve their properties. This study highlights the fact that each of these parameters affects CO2 storage, with an optimum water content for the maximum CO2 uptake depending on the nature and the source of the RCAs. This optimum is related to the RCA water absorption coefficient by a linear relationship. The results show that accelerated carbonation reduces the water absorption coefficient by as much as 67%. Finally, carbonation also decreases porosity, as observed by mercury intrusion porosimetry, by filling the capillary pores.

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Previous literature indicates a decrease in the mechanical properties of various concrete types that contain recycled aggregates (RA), due to their porosity and to their interface of transition zone (ITZ). However, other components of the RA concrete microstructure have not yet been explored, such as the modification of the new paste (NP) with respect to a reference concrete. This paper deals with the microstructure of the new paste of self-compacting concrete (SCC) for different levels of RA. The water to binder ratio (w/b) was kept constant for all concrete mixtures, and equal to 0.5. The SCC mixtures were prepared with percentages of coarse RA of 0%, 30%, 50% and 100%. Mercury intrusion porosimetry test (MIP) and scanning electron microscope (SEM) observations were conducted on the new paste of each concrete. The results indicated that the porosity of the new paste presents a significant variation for replacement percentages of 50% and 100% with respect to NP0 and NP30. However, RA contributed to the refinement of the pore structure of the new paste. The amount of macrospores the diameter of which is in the 50–10,000 nm range was reduced to 20% for NP50 and NP100, while it was about 30% for NP0 and NP30, attributed to the water released by RA. Compressive strength loss for SCC50 and SCC100 concretes are both influenced by porosity of RA, and by the NP porosity. The latter is similar for these two concretes with the 26% increase compared to a reference concrete.