Modélisation des transports ioniques dans les milieux poreux saturés : application à la pénétration des chlorures dans les matériaux cimentaires

Dans ce travail, le problème du transport d'espèce ionique à travers les milieux poreux saturés a été documenté. Un modèle unidimensionnel basé sur l’approche multi-espèce est présenté. C'est la nouvelle version d'un modèle précédent, MsDiff, développé il y a quelques années dans notre groupe [TRU 00] qui décrit la diffusion d'espèce ionique avec l'équation de Nernst-Planck. Avec l’approche multi-espèces, il est possible de prendre en compte les interactions qui existent entre les espèces ioniques différentes dans la solution interstitielle du béton. Le schéma numérique du modèle est basé sur la méthode des différences finies avec des techniques de Cranck-Nickolson et de Lax-Wendroff. Afin de faire les simulations avec MsDiff, nous avons besoin des données d'entrée. Plusieurs essais ont été exécutés afin de les acquérire. Des essais standards d'immersion ont été effectués pour valider les résultats de MsDiff avec une attention particulière aux coefficients de diffusion des ions et aux interactions entre les chlorures et la phase solide du matériau. Quelques autres modèles existants ont été également essayés pour la comparaison avec les profils expérimentaux de chlorure. Des expérimentations ont été faites pour observer l'influence de la période d'exposition, de l'âge du béton à l'exposition et de la concentration de la solution environnementale sur la pénétration des chlorures. Enfin, les simulations afin de calculer le temps d’initiation de la corrosion ont été effectuées avec MsDiff en utilisant les données expérimentales déjà obtenues tout en utilisant différents critères adoptés par différents groupes de recherche.\ud Mots Clés : Chlore, pénétration, béton, multi-espèces, modélisation, corrosion\ud \ud \ud Here the problem of ionic species transport through concrete porous media has been documented. Chloride ions penetration in cementitious materials is one of the processes widely responsible for the degradation of concrete structures. Here, a one-dimensional model based on a multi-species approach of the ionic transport is presented. It is the new version of a previous model MsDiff developed a few years ago in our group [TRU 00] that describes the diffusion of ionic species with the Nernst-Planck equation instead of Fick’s laws. With a multi-species approach, it is possible to take into account the interactions existing among different ionic species in pore solution of concrete. The numerical scheme of the model is based on finite difference method with Crank-Nickolson and Law-Wendroff techniques. In order to run MsDiff, we need an input data. Several experiments were performed accordingly to provide experimental feedback to MsDiff. Standard immersion tests were conducted to validate the outcomes of MsDiff. Special attention is given to the diffusion coefficients of the ions and the interactions between the ionic species and the solid phase. In addition to MsDiff, some other existing models were also tried for the sake of comparison with the experimental chloride profiles. Certain experimentation was conducted to watch the effect of exposure period, concrete age at exposure and concentration in the environmental solution. In the end, the simulations were performed with MsDiff in order to calculate the chloride-induced corrosion initiation time using the experimental data already achieved while making use of different criteria adopted by different research groups.\ud \u

Evaluation of Steel Industrial Slag as Partial Replacement of Cement in Concrete

Cement is the most important ingredient in concrete, which acts as a binding material. It is evaluated that cement is the second largest industrial source of CO2 on earth. This demands a partial or full replacement of cement by an environment-friendly material. In this research industrial waste slag from a local Steel Mill, namely Mangla Metals was selected as possible replacement of cement. Some preliminary standard tests conducted on the slag showed its strong chances to be used as pozzolana. Slag used for this study was reduced to the particle size passing through ASTM standard sieve #100. Concrete specimens containing 10% and 20% replacement of cement by slag were prepared. The mechanical properties like compressive, split cylinder tensile and flexure strength were determined as per standard ASTM methods. Tests were conducted at 3, 7 and 28 days of concrete age. Results show a decrease of 14% in compressive strength, 7.5% in tensile strength and 10.5% in flexure strength for 10% replacement vis-à-vis control specimens at 28 days. For 20% replacement, the decrease in compressive, tensile and flexure strength are 25.5%, 29%, 31% respectively. Additionally, ASTM standard strength activity index test with finer slag particles passing through ASTM sieve #200 provided compressive strength more than that of control specimen. Based on the results, it is concluded that the industrial slag has the potential to partially replace the cement if slag is ground to the particles, passing through ASTM sieve #200. This could lead to a huge reduction of cement quantity in concrete and the environmental burden due to deposition of waste slag in landfills

Development of an Acid Resistant Concrete: A Review

This review paper addresses the measures taken to prevent or minimize the deterioration of concrete, which confronts an acidic environment. Primarily, the mechanism of reaction between alkaline concrete and acid is clearly demonstrated. The mechanism of reaction clearly sets guidelines as to how the chances of this disastrous reaction should be minimized or eliminated at all. The suggested preventive measures are two-fold i.e. the improvement of the basic microstructure of concrete and the provision of barriers against acids. Concrete can be made acid resistant using classical as well as novel techniques like nanotechnology.   There exists an immense need that these measures are recognized and implemented by the construction industry to put a stop to huge money losses

Fracture toughness and failure mechanism of high performance concrete incorporating carbon nanotubes

Cement and concrete composites are inherently brittle and exhibit very less tensile/flexural strength capacity as compared to their compressive strength. Use of thoroughly dispersed carbon nanotubes in the concrete matrix is one of the possible solution for enhancing mechanical properties in tension/flexure. In the present research work, small fractions of multiwall carbon nanotube (MWCNTs) i.e. 0.05 and 0.10 wt% of cement have been integrated into the cement concrete to study their effect on the mechanical properties of the resultant concrete mixtures. The enhanced performance of the whole mix lies on a single point that MWCNTs must be thoroughly disperse in the mixture. Hence, special arrangement through usage of high energy sonication along with amended acrylic based polymer (performing as a surfactant) was made to have a uniform dispersion of MWCNTs in the concrete mix. The testing of concrete samples includes i.e., flexure, splitting tensile and compressive strengths after 3, 7, 28 and 56 days of curing. After having comparison with the control mix cured for 28 days, it was observed that the addition of 0.05 wt% MWCNTs increased the splitting tensile strength by 20.58%, flexural strength by 26.29% and compressive strength by 15.60%. Through above results, which verify the increase in concrete mix strength after adding MWCNTs, these MWCNTs may be incorporated in the treatment of Nano/micro cracks completed through process of connecting, branching and pinning. Similarly, as proved in threepoint bending tests, MWCNTs also enhances the breaking strains as well as the fracture energy of the concrete mixes, besides, imparting increase to the strength. The investigations have shown that incorporating lesser amounts of MWCNTs i.e., 0.05 and 0.10 wt% of cement to the concrete mixes after insuring there complete dispersion, unusually improve their properties like mechanical strengths and fracture behavio

Activation of slag through a combination of NaOH/NaS alkali for transforming it into geopolymer slag binder mortar – assessment the effects of two different Blaine fines and three different curing conditions

This study investigates the effects of two different Blaine fineness and three distinct curing conditions on the physico-mechanical properties of a geopolymer-ground granulated blast furnace slag (GGBFS) binder mortar activated through a combination of NaOH/NaS alkalis. By ensuring constant curing and mixing conditions, geopolymer mortar (GPM) specimens were prepared and evaluated to determine their capillary water sorption, capillarity coefficient, and change in unit weight, alongside their compressive strength and flexural strength 3, 7, 28, and 56 d after production. It was found that the capillary water sorption decreased by approximately 50% as the curing temperature of the water increased from ambient temperature to 22 °C. The coefficient of capillarity remained constant across the geopolymer materials, irrespective of the Blaine fineness of the GGBFS. Furthermore, the increase in the unit weight, owing to the variation in the Blaine fineness of GGBFS, results in a reduction in the water sorption properties of GPMs. The GGBFS and alkali-based binders imparted a continuous increase in the compressive and flexural strengths. The results revealed that a Blaine fineness of 6000 cm2/g in the GGBFS under water-curing conditions imparted the most significant advantageous effect on the physico-mechanical properties of a GGBFS binder mortar activated through a combination of NaOH/NaS alkalis

improving the mechanical performance of cement composites by carbon nanotubes addition

Abstract: The addition of high performance nano materials like carbon fibers, carbon nanotubes, graphene etc. in the cement and concrete is gaining attention for achieving multifunctional composite materials with enhanced mechanical, physical and electrical properties. The nano-metric size range and the exceptionally high mechanical properties of carbon nanotubes possess very great potential for their utilization in cementitious composites for obtaining remarkable properties. Billions of ton of concrete is used every year in construction industry and its quantity may be reduced to a large extent only by improving the mechanical and durability properties. One way of achieving the enhanced mechanical properties of cement composite is the utilization of thoroughly dispersed carbon nanotubes in the composite matrix. In the present research, small fractions of multiwall carbon nanotube (MWCNTs) i.e. 0.05 and 0.10 wt.% of cement have been incorporated into the cement concrete and their influence on the mechanical properties of the resulting composites have been studied. It is a well-known fact that the uniform dispersion of the MWCNTs in the composite matrix holds the key for the performance improvement. Therefore, special attention was paid to this aspect and uniform dispersion of MWCNTs was achieved through the use of high energy sonication in the presence of modified acrylic based polymer (acting as a surfactant). The concrete specimens were tested in splitting tensile, flexure and compressive strength after 3, 7, 28 and 56 days of immersed water curing. It was observed that the addition of 0.05wt.% MWCNTs increased the splitting tensile strength by 20.58%, flexural strength by 26.29% and compressive strength by 15.60% as compared to the control mix at 28 days of curing. The strength enhancements for the concrete mixes containing MWCNTs may be regarded to the phenomenon of bridging, pinning and branching of the cracks at nano/micro level due to the presence of MWCNTs. Beside strength enhancements, it was also observed that the MWCNTs had tremendously enhanced the fracture energy and breaking strains of the concrete mixes as observed in three-point bending tests. The research concludes that very low amounts of MWCNTs incorporated in the cement concrete mixes improve their mechanical strengths and fracture behavior remarkably but the thorough dispersion of MWCNTs in the matrix have to be insured

Fracture toughness and failure mechanism of high performance concrete incorporating carbon nanotubes

Cement and concrete composites are inherently brittle and exhibit very less tensile/flexural strength capacity as compared to their compressive strength. Use of thoroughly dispersed carbon nanotubes in the concrete matrix is one of the possible solution for enhancing mechanical properties in tension/flexure. In the present research work, small fractions of multiwall carbon nanotube (MWCNTs) i.e. 0.05 and 0.10 wt% of cement have been integrated into the cement concrete to study their effect on the mechanical properties of the resultant concrete mixtures. The enhanced performance of the whole mix lies on a single point that MWCNTs must be thoroughly disperse in the mixture. Hence, special arrangement through usage of high energy sonication along with amended acrylic based polymer (performing as a surfactant) was made to have a uniform dispersion of MWCNTs in the concrete mix. The testing of concrete samples includes i.e., flexure, splitting tensile and compressive strengths after 3, 7, 28 and 56 days of curing. After having comparison with the control mix cured for 28 days, it was observed that the addition of 0.05 wt% MWCNTs increased the splitting tensile strength by 20.58%, flexural strength by 26.29% and compressive strength by 15.60%. Through above results, which verify the increase in concrete mix strength after adding MWCNTs, these MWCNTs may be incorporated in the treatment of Nano/micro cracks completed through process of connecting, branching and pinning. Similarly, as proved in threepoint bending tests, MWCNTs also enhances the breaking strains as well as the fracture energy of the concrete mixes, besides, imparting increase to the strength. The investigations have shown that incorporating lesser amounts of MWCNTs i.e., 0.05 and 0.10 wt% of cement to the concrete mixes after insuring there complete dispersion, unusually improve their properties like mechanical strengths and fracture behavior