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

An efficient energy management in office using bio-inspired energy optimization algorithms

Energy is one of the valuable resources in this biosphere. However, with the rapid increase of the population and increasing dependency on the daily use of energy due to smart technologies and the Internet of Things (IoT), the existing resources are becoming scarce. Therefore, to have an optimum usage of the existing energy resources on the consumer side, new techniques and algorithms are being discovered and used in the energy optimization process in the smart grid (SG). In SG, because of the possibility of bi-directional power flow and communication between the utility and consumers, an active and optimized energy scheduling technique is essential, which minimizes the end-user electricity bill, reduces the peak-to-average power ratio (PAR) and reduces the frequency of interruptions. Because of the varying nature of the power consumption patterns of consumers, optimized scheduling of energy consumption is a challenging task. For the maximum benefit of both the utility and consumers, to decide whether to store, buy or sale extra energy, such active environmental features must also be taken into consideration. This paper presents two bio-inspired energy optimization techniques; the grasshopper optimization algorithm (GOA) and bacterial foraging algorithm (BFA), for power scheduling in a single office. It is clear from the simulation results that the consumer electricity bill can be reduced by more than 34.69% and 37.47%, while PAR has a reduction of 56.20% and 20.87% with GOA and BFA scheduling, respectively, as compared to unscheduled energy consumption with the day-ahead pricing (DAP) scheme

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

Effect of Phosphorus and Sulfur on the Yield and Nutrients Uptake of Wheat

A field experiment was conducted to study the effect of phosphorus and sulfur on the yield and nutrients uptake of wheat at New Developmental Research Farm (NDF)  Malakandher, University of Agriculture, Peshawar in Rabi season during 2011-2012. The experiment was laid out in randomized complete block design (RCBD) with three replications. Phosphorus was applied  at the rate of 60, 90 and 120 kg ha-1 as DAP where as sulfur was applied at the rate of  45, 60 and 75 kg ha-1 as ammonium sulphat  along with control ( no fertilizer) and a treatment of just N and K  as basal dose (120 + 60 kg ha-1). The results showed that biological yield increased significantly (p≤0.05) over control when P and S were applied at the rate of 90-45 kg ha-1where as significantly higher grain yield was recorded in treatment receiving 120 kg P and 45 kg S along with a basal dose of N and K, Significantly highest straw yield of 4245 kg ha-1 was noted in treatment receiving 90 kg P along with 45 kg S ha-1. The soil samples collected at anthesis stage and post harvest stage showed that the P and S contents were significantly affected and the higher values were noted in plot receiving the maximum level of the respective fertilizer i.e P and S but the trend of increase was not consistent with respect to the amount of P and S applied. The P and S content in leaves indicated that higher level of S (75 kg ha-1) resulted in significantly low uptake of P and vice versa indicating their antagonistic effect with each other. This antagonistic effect was displayed in the yield whereby maximum grain yield was obtained where higher dose of P along with lower level of S was applied.

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

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