Nordine Leklou

Influence of various parameters on heat-induced internal sulphate attack

The work presented in this article studies the effects of some parameters that can be considered, a priori, as important in the appearance of delayed ettringite formation (DEF). The parameters studied are the nature of the binder, the water/cement (W/C) ratio, the preliminary microcracking (wetting–drying cycles) and the curing conditions. The results presented show that the chemical composition of cement is one of the main parameters controlling the appearance of DEF. The other parameters studied, (W/C ratio, wetting–drying cycles and temperature of curing water) principally modify the kinetics of the expansion: it seems that, the more favourable the conditions are to ionic and hydrous transfers, the sooner the expansion starts. Finally, the renewal of the curing water strongly affects the start of DEF. In one case of the study, the renewal of the curing water only accelerated the start of the expansion. In the second, it led to late starting of DEF (four years) whereas the same mixture cured continuously in water that was not renewed still had not expanded after more than five years. L’étude présentée dans cet article a pour objectif d’observer les effets de certains paramètres que l’on peut qualifier a priori d’importants vis-à-vis de l’apparition de la DEF. Les paramètres étudiés sont la nature du liant, le rapport E/C des mélanges, le préendommagement des éprouvettes (cycles d’humidification-séchage) et, enfin, les conditions de conservation des échantillons. Les résultats présentés montrent que la composition chimique du ciment est l’un des principaux paramètres contrôlant l’apparition de la DEF. Les autres paramètres étudiés (rapport E/C, cycles d’humidification-séchage et la température de l’eau de conservation des échantillons), modifient principalement la cinétique de l’expansion: il semble que plus les conditions sont favorables pour améliorer les transferts ioniques et hydriques, plus l’apparition des expansions est accélérée. Enfin, le renouvellement de l’eau de conservation affecte fortement le début de l’apparition de la DEF. Dans un cas d’étude, il n’a fait qu’accélérer le début de l’expansion. Dans un second cas, le renouvellement de l’eau de conservation a permis le déclenchement de la DEF au bout de 4 ans, alors que le même mélange conservé en permanence dans l’eau qui n’a pas été renouvelé n’avait pas encore montré de gonflement après plus de 5 ans.

Is alfa a vegetal fiber suitable for making green reinforced structure concrete

Many studies showed the interest of reinforcing composite materials with biofibers in the last decade. Producing more eco-friendly concretes, replacing synthetic fibers with natural and less expensive materials, is the main reason supporting these studies. Numerous plants have been investigated to reinforce concrete among which alfa has not been considered yet whilst it is made of cellulosic natural fibers with interesting stiffness and strength properties. In addition it is abundant and widely distributed around the Mediterranean basin and it grows without watering or use of any amendment. This study investigates the potential of alfa fibers to produce a green concrete with suitable mechanical properties. The results show that the use of alfa fibers allow to obtain a concrete less expensive, more eco-friendly and better from the mechanical point of view than when using polypropylene fibers, which makes of alfa a good candidate to produce sustainable concrete and green buildings.

Sensitivity analysis of the transient heat and moisture transfer in a single layer wall

Abstract The determination of the energy consumption of a building requires the computation of the coupled heat and mass transfers inside the wall. The existing models require the determination of the hygrothermal properties of the materials, and of the boundary and initial conditions, prior to computing numerically the temperature and vapour fluxes and the energy and mass balance of the building. However, the experimental measurements do not give accurate values, yielding a wrong estimation of the energy consumption. In order to determine the influence of the uncertainties on the values of the input parameters of the Kunzel model, we carried out a local sensitivity analysis (LSA) by varying by 5% the hygrothermal properties of the materials, the surface transfer coefficients and the initial conditions. The results of the LSA are treated by means of quartile boxes in order to identifiy the most influent parameters. The LSA is applied to two walls made of highly porous and hygroscopic materials: limestone and hemp concrete. The results show that the surface transfer coefficients and the adsorption isotherm are the most influential parameters. However, the conclusions are slightly different between the two materials, because of differences in the relative importance of transfer phenomena.