Abstract
A sampling procedure, which avoids the need for wet cutting, has been developed for determination of compositional profiles of the pore liquid phase within concrete exposed to chloride ingress. The technique has been used to assess the effects on various concrete specimens of exposure to different regimes of chloride penetration and to compare them with those of salt, introduced as a constituent of the mix materials. The implications regarding corrosion risk to embedded steel are provisionally evaluated in terms of the ratio of chloride to hydroxyl ion concentrations in the pore solution. The significance of this parameter is to be considered in Part 2.
Resume
On exprime généralement en termes de contenu total de chlorure et de profondeur de carbonatation les critères qui déterminent le risque de corrosion dans le béton armé. On détermine par les procédures analytiques classiques la teneur totale en chlorure, et par les indications de pH telles que la phénolphtaléine, la profondeur de carbonatation. Ces méthodes sont imprécises du fait qu’une proportion variable de la teneur totale en chlorure peut exister sous forme insoluble comme celle de l’hydrate de chloroaluminate de calcium et que, d’autre part, le pH de l’électrolyte présent dans le béton que la phénolphtaléine indique comme étant alcalin, peut varier d’environ 10–14.
Afin d’obtenir une plus sûre indication du risque de corrosion à différentes profondeurs dans le béton exposé à des milieux riches en chlorures, on doit analyser la composition de l’électrolyte interstitielle en fonction de la distance de la surface exposée. Cet article, qui est le premier d’une étude en deux parties, décrit une approche expérimentale par laquelle on dispose d’échantillons de matériau avec solution interstitielle à différentes profondeurs dans des spécimens de béton exposés sans qu’on ait recours à un outil de coupe lubrifié. Cette technique appelée ‘crush-section’ élude par conséquent les risques potentiels de contamination de l’échantillon et de lessivage. On a procédé à une estimation des effets de l’exposition sur plusieurs types de béton à différents régimes de progression de sels. Les risques de corrosion en tant que fonction de la profondeur de pénétration et de la durée d’exposition sont provisoirement évalués en termes de variation des concentrations relatives de chlorure libre et d’ions hydroxyles dans la solution interstitielle.
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Page, C.L., Lambert, P. & Vassie, P.R.W. Investigations of reinforcement corrosion. 1. The pore electrolyte phase in chloride-contaminated concrete. Materials and Structures 24, 243–252 (1991). https://doi.org/10.1007/BF02472078
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DOI: https://doi.org/10.1007/BF02472078