Wick action in mature mortars with binary cements containing slag or silica fume – The relation between chloride and moisture transport properties under non-saturated conditions

Moisture and ionic transport under non-saturated condition is an important, but poorly understood transport phenomena particularly for mature systems containing supplementary cementitious materials. This paper investigates the moisture and chloride profiles of 3-year old mortars containing Portland cement (OPC), slag and silica fume (SF) after long-term (30–48 months) wick action exposure in 1.09 M NaCl solution. Moisture profiles were measured with 1H NMR relaxometry and chloride profiles with microXRF. The measured profiles were discussed in relation to moisture dependent material properties such as chloride diffusion coefficients, moisture diffusion coefficients, and desorption isotherms. Results show that the combination of different cementitious materials, e.g. the cementitious binder, is the key factor affecting chloride penetration depth. The cementitious binder also strongly affects chloride diffusion coefficient, moisture diffusion coefficient and chloride binding properties, which are all important parameters for the prediction of chloride ingress

Estudio del contenido de humedad en un material en base cemento midiendo su impedancia y su gamma-densitometría

The local water content in cementitious material depends on the equilibrium between its atmospheric environment and its bulk properties. So, the moisture profile in material can vary with time. The object of this study is to follow the change of this profile by measuring the electrical impedance of the material with pairs of small wires embedded at different depths. This method was applied to young cement paste specimens. The results obtained show that this method is quite satisfactory. The best frequency to be applied, is about 50 or 100 Hz. These results were compared with those obtained with gamma-densitometry.El agua contenida en los materiales en base cemento depende del equilibrio entre la atmósfera que le rodea y las propiedades de la matriz sólida. Por lo tanto el perfil de humedad en los materiales puede variar con el tiempo. La finalidad de este estudio es seguir los cambios en dicho perfil, a través de la medición de la impedancia eléctrica del material con varios pares de pequeños conductores situados a diferentes profundidadades. Este sistema se aplicó a diversas muestras de pasta de cemento Jóvenes. Los resultados obtenidos nos hacen ver que el método es satisfactorio, debiendo aplicarse a una frecuencia de 50 a 100 Hz. Dichos resultados se compararon con los obtenidos a través de la gammadensitometría

1H NMR relaxometry as an indicator of setting and water depletion during cement hydration

International audienceProton nuclear magnetic resonance relaxometry has been used to detect setting and microstructure evolution during cement hydration. NMR measurements were performed since casting, during setting and until hardening (from 0 to 3 days). The mobility of water molecules was assessed by an analysis focused on the diagram of longitudinal relaxation time T1 generated by an Inversion Recovery sequence. The initial stiffening of the solid network was identified by an analysis of the relaxation rate 1/T1. The kinetics of water depletion was investigated by using a simple one-pulse acquisition sequence. In parallel, conventional techniques (Vicat needle and temperature monitoring), as well as numerical simulations of hydration, were used to complement and validate these NMR results. Cement pastes and mortars with different water-to-cement ratios made of grey or white OPCs were tested. Furthermore, the effects of the addition of sand, super-plasticizer and silica fume on the hydration kinetics were investigated. © 2012 Elsevier Ltd

Une meilleure compréhension du gel des matériaux cimentaires en présence de sel pour un béton durable

Ce texte présente les méthodes d'essais de caractérisation de résistance au gel actuellement applicables en France. Ces essais en place depuis 10 à 20 ans ont largement contribué à l'amélioration de la prescription et de la durabilité des bétons face à la résistance au gel en présence de sels. Dans une deuxième partie, la distribution et la répétabilité ainsi que la méthode d'analyse du résultat de l'essai d'écaillage XP P18-420 sont évalués au travers d'un nombre significatif d'essais sur des bétons composés d'un ciment de Portland avec un agent entraîneur d'air