Non-steady state chloride migration and binding in cracked self-compacting concrete

We adopted a notch method to study the influence of crack width (macro level) on chloride transport and binding of cracked concrete under a non-steady state migration test. The results show that migration coefficient of cracked concrete increases with increasing crack width up to a critical value (0.43 mm), for the whole concrete or the area close to crack; the increase of migration coefficient could be independent from crack parameter when a critical crack width is reached. For chloride binding, Langmuir isotherms of cracked concrete samples exhibit the similar decreasing trend as crack width increases from 0.27 to 1.96 mm. The increased current value could be responsible for the trend based on the hypothesis of electric force

Halide binding by the purified halorhodopsin chromoprotein. II. New chloride-binding sites revealed by 35Cl NMR

Halorhodopsin is a light-driven chloride pump in the cell membrane of Halobacterium halobium. Recently, a polypeptide of apparent Mr = 20,000 has been purified that contains the halorhodopsin chromophore. Here we use 35Cl NMR to show that the purified chromoprotein possesses two previously unknown classes of chloride-binding sites. One class exhibits a low affinity (KD much greater than 1 M) for chloride and bromide. The second class exhibits a higher affinity (KD = 110 ± 50 mM) for chloride and also binds other anions according to the affinity series I-, SCN- greater than Br-, NO-3 greater than Cl- greater than F- , citrate. Both classes of NMR site remain intact at pH 11, indicating that the essential positive charges are provided by arginine. Also, both classes are unaffected by bleaching, suggesting that the sites are not in the immediate vicinity of the halorhodopsin chromophore. Although the chromoprotein also appears to contain the chloride- transport site (Steiner, M., Oesterhelt, D., Ariki, M., and Lanyi, J. K. (1984) J. Biol. Chem. 259, 2179-2184), this site was not detected by 35Cl NMR, suggesting that the transport site is in the interior of the protein where it is sampled slowly by chloride in the medium. It is proposed that the purified chromoprotein possesses a channel leading from the medium to the transport site and that the channel contains the high affinity NMR site which facilitates the migration of chloride between the medium and the transport site. We have also used 35Cl NMR to study chloride binding to purified monomeric bacteriorhodopsin; however, this protein contains no detectable chloride-binding sites

Evaluation of the migration coefficient, diffusion coefficient and the ageing factor according to the chloride ingress model described in the fib bulletin 34 applied to Belgian concrete mixtures

In this contribution the chloride diffusion model according to fib bulletin 34 is applied and evaluated on Belgian concrete [1]. The service life estimation according to chloride-induced corrosion is, inter alia, affected by the chloride migration coefficient or chloride diffusion coefficient. In addition, the time dependency of these parameters, reflected in the ageing exponent, has an even greater influence on the model. In a first part the different diffusion coefficients will be discussed. In a second part the parameters are calibrated to the Belgian concrete compositions. The chloride migration coefficient and chloride diffusion coefficient depend on the type of cement and vary according to different types of cement and w/c ratios. The ageing exponent is also dependent on the exposure class. Such a calibration is performed on the most commonly used types of cement in Belgium, which are Portland cement (CEM I) and blended cements (CEM III/A and CEM III/B). Distributions are proposed and evaluated based on available Belgian data and results from laboratory experiments. Finally the time dependency of the instantaneous diffusion coefficients and the time dependency of the apparent diffusivities are investigated

Supported ITZ modification efficiencies via surface coating nanoparticles on aggregate and its influence on properties

In order to modify the porous interfacial transition zone (ITZ) microstructure of concrete more efficiently, a method of coating aggregate surfaces by using several nanoparticles was evaluated in this study. The compressive strength, chloride penetration of sound, and pre-loading samples were assessed in relation to the type of coating materials used (slag, nano-CaCO3, and nano-SiO2) and the designed coating thickness (5, 10, and 15 mu m). The ITZ microstructure was quantitatively determined via Backscattered electron (BSE) image analysis. Results showed that the overall performance of concrete is highly dependent on the coating materials and the designed coating thickness. Increasing the coating thickness of slag and nano-SiO2 could improve the chloride penetration resistance but decrease the compressive strength. Using nano-CaCO3 to coat the aggregate leads to a significant reduction in the properties of the so-prepared concrete. Though coating inert fine particles around aggregate could disturb the initial particle packing and modify the ITZ, it is not able to improve the overall concrete properties. Coating aggregate could determine the ITZ microstructure, especially within the region that is around 30 mu m away from aggregate surface

Durability and service life of concrete repairs in the presence of cracks

Engineered Cementitious Composite (ECC) has been proposed to be one of the most promising repair materials due to its unique high ductility and tight crack width control. In concrete repairs, the shrinkage of repair materials is restrained by concrete substrate, and the repair material therefore often cracks. When ECC is used as repair material, the crack width is much smaller compared to normal concrete. The tight crack width of ECC retards the penetration of water and harmful substances and thus enhances the durability of concrete repairs. This paper is aimed to explore the chloride penetration in cracked ECC repairs and to assess the service life of the repair systems. Rapid chloride migration tests was conducted to investigate the chloride penetration profile. Based on the experimental results, the service life of repair systems was evaluated

Influence of concrete composition on chloride ingress and carbonation : analysis by means of an extended data-set

In 2015 an IWT-TETRA project, called DurOBet, was initiated focusing on service life design assessment according to different chloride diffusion and carbonation models applied on Belgian concrete mixtures. The main purpose of this research project is to develop a quantitative method for a service-life based design of concrete structures, more particular applicable for the Belgian concrete industry. In this way an improvement of the deemed-to-satisfy approach of the EN206-1 code can be established which is more reliable with regards to service life predictions of concrete structures. In the framework of this DurOBet project it was decided to develop an extensive database incorporating concrete related results on i) fresh properties, ii) hardened properties and iii) durability related properties such as porosity, permeability and more specifically on chloride ingress and carbonation. The data originate from numerous journal articles and conference papers, doctoral research projects and master thesis studies. At this time more than 100 papers or studies were investigated, reported between 1992 and 2016, generating a dataset of over a thousand unique concrete recipes, geographically spread but with focus on the concrete mixes applicable for the Belgian industry. Both traditional and self-compacting concrete mixes are incorporated into the database. This database is being used for the analysis of the durability related properties, such as the chloride diffusion and carbonation coefficient, and their relation with mix proportioning parameters of the concrete mixtures (cement or binder content, type of binder, water-to-binder ratio,…). The main focus of this paper is to highlight the framework of the database: the mix proportioning of the concrete mixes is being discussed and the origin of the concrete data (country, reference info, etc.). By means of data mining and some known relations with respect to the durability related properties, e.g. correlation between w/b-ratio and chloride diffusion coefficient, are being evaluated

Electrochemical migration of Sn and Ag in NaCl environment

The impact of chloride ion concentration on electrochemical migration (ECM) of tin and silver was studied by using an in-situ optical and electrical inspection system. It was found, that in both cases, dendrites grow not only in an electrolyte solution at low chloride concentration but also in an electrolyte at medium and high or even saturated chloride concentrations as well. According to the results, the migration susceptibility has decreased at low and medium concentration levels in both cases. However, the ECM susceptibility of Ag has increased, while the migration susceptibility of Sn was decreased at the saturated concentrations

Electrochemically induced precipitation enables fresh urine stabilization and facilitates source separation

Source separation of urine can enable nutrient recycling, facilitate wastewater management, and conserve water. Without stabilization of the urine, urea is quickly hydrolyzed into ammonia and (bi)carbonate, causing nutrient loss, clogging of collection systems, ammonia volatilization, and odor nuisance. In this study, electrochemically induced precipitation and stabilization of fresh urine was successfully demonstrated. By recirculating the urine over the cathodic compartment of an electrochemical cell, the pH was increased due to the production of hydroxyl ions at the cathode. The pH increased to 11-12, decreasing calcium and magnesium concentrations by >80%, and minimizing scaling and clogging during downstream processing. At pH 11, urine could be stabilized for one week, while an increase to pH 12 allowed urine storage without urea hydrolysis for >18 months. By a smart selection of membranes [anion exchange membrane (AEM) with a cation exchange membrane (CEM) or a bipolar membrane (BPM)], no chemical input was required in the electrochemical cell and an acidic stream was produced that can be used to periodically rinse the electrochemical cell and toilet. On-site electrochemical treatment, close to the toilet, is a promising new concept to minimize clogging in collection systems by forcing controlled precipitation and to inhibit urea hydrolysis during storage until further treatment in more centralized nutrient recovery plants