Mobility of chloride through cement-based materials underpartially saturated conditions
Résumé
This work presents two complementary techniques to study 36Cland stable chloride diffusion through unsaturated cement-based materialsfor saturation degrees (Sw) ranging from 0.18 to 1. The first techniqueis based on steady-state through-diffusion method where suction (up to 9MPa) is controlled using osmosis process. In the second technique, indiffusionexperiments are performed by putting into contact a spikedfresh-cement paste with a CEM-V-A-hardened-cement paste (HCP) sample(initial water to cement ratio of 0.4) having a given water saturationimposed by saline solution method. After a controlled diffusion time, the36Cl activity profiles within the samples are acquired by means of theabrasive peeling method and 36Cl activity is determined by liquidscintillation counting (LSC) technique. The application of the firsttechnique resulted in data showing a sharp decrease of the effectivediffusion coefficient (De) (by a factor of ten) between the experimentsdone on the fully-saturated HCP sample and the HCP sample at Sw = 0.85.Moreover, duplicate in-diffusion experiments carried out on HCP samplespartially-saturated at Sw = 0.86 provided 36Cl De range well bracketingthe one determined by the first approach at Sw = 0.85. Four other indiffusionexperiments were thus performed on HCP samples with saturationdegrees down to 0.18. Interpretation of the experimental results showed avery small decrease of De values for Sw from 0.74 to 0.41 and a sharpdecrease for Sw from 0.41 to 0.18. Lastly, comparison with the diffusivebehavior of tritiated water (HTO) through unfully saturated CEM V-A HCPsamples clearly indicated that diffusion of chloride was more affected bydesaturation than HTO. Its ionic form restricted chloride to the liquidphase whom continuity is broken when dehydrating is strong enough.