M.A. Climent

A test method for measuring chloride diffusion coefficients through nonsaturated concrete: Part I. The instantaneous plane source diffusion case

Abstract A test method is proposed for measuring chloride diffusion coefficients through nonsaturated concrete specimens with controlled water contents. The experimental setup used allows one to supply an initial limited amount of Cl − to the tested concrete surface. The procedure consists of submitting the surface of concrete specimens to interaction with the products of combustion of PVC, which contain mainly gaseous hydrogen chloride. This interaction yields a limited Cl − contamination of the concrete surface. After returning the specimens to their controlled humidity exposure conditions, the kinetics of Cl − transport from the surface inwards may be studied. The experimental Cl − concentration profiles determined at selected time intervals have been adjusted to a diffusion model of “instantaneous plane source,” which takes into account the particular initial and boundary conditions of the experimental procedure, for obtaining the corresponding diffusion coefficients.

Analysis of acid-soluble chloride in cement, mortar, and concrete by potentiometric titration without filtration steps

Abstract A potentiometric titration procedure that makes use of Gran’s method for end-point detection has been developed to analyze acid-soluble chloride in cement, mortar, and concrete, eliminating the filtration steps performed in habitual laboratory reference methods. The accuracy and reliability of the proposed analytical technique has been checked against a standard method, such as Volhard’s, by analyzing duplicate samples of cements, mortars, and concretes with varied chloride contents.

Bit shape geometric considerations when sampling by dry drilling for obtaining chloride profiles in concrete

When obtaining dust concrete samples by dry drilling to determine chloride content profiles, the common conical shape of the bit tip induces some problems for assigning the analyzed Cl− content of each sample to a fixed depth from surface, (which is necessary for applying Cl− transport models): the amount of concrete removed is not the same throughout the length of a single drilling step, and concrete coming from depths lower than the nominal drilling step is also obtained. It is proposed that each Cl− concentration in the profile should be assigned to the gravity centre of the solid sample really removed in each drilling step, instead of assigning it to the centre of the nominal drilling step. A simple method for calculating the gravity centre of each sample obtained by dry drilling, has been developed. The calculated values of Cl− diffusion coefficients from a Cl− content profile may be appreciably lower if the centres of gravity of the samples, instead of the centres of the nominal drilling steps, are used for the calculations.RésuméQuand on obtient, au moyen d’un forage à sec, des échantillons de béton pulvérisé destinés à établir le profil de concentration de chlorure, la forme conique de la mèche entraîne des problèmes dans l’assignation de chaque échantillon à une profondeur fixée, à partir de la surface, (cette assignation est nécessaire pour appliquer des modèles de transport de Cl−): la quantité de béton prélevé n’est pas la même à travers toute la longueur de chaque échelon du forage. D’autre part, on obtient aussi de la poudre de béton à des niveaux moins profonds que l’échelon nominal du forage. Pour cela, on propose d’assigner chaque concentration de Cl− du profil au centre de gravité de l’échantillon solide réellement obtenu à chaque échelon, plutôt que d’assigner cette concentration au centre de l’échelon nominal. On a développé une méthode simple pour calculer le centre de gravité des échantillons obtenus par forage à sec. Les valeurs issues du calcul du coefficient de diffusion de chlorure à partir d’un profil de concentration peuvent être appréciablement inférieures si l’on utilise pour ces calculs les centres de gravité des échantillons plutôt que les centres des échelons nominaux du forage.