The ingress of chlorides in concrete under compressive or tensile loads

One common aggressive mechanism acting in reinforced concrete is chloride attack which induces steel corrosion. Although it has mostly been studied and analyzed separately it has been observed that loads acting on concrete may modify the deteriorating effect. In this research the effect that combined attack provokes on concretes made of ordinary Portland cement (OPC), high sulfate-resistance cement (SR) and blast furnace slag (BFS) cement is investigated. Five mixes were made with these materials, 2 of them using a type 52.5 N (OPC) cement, 2 replacing OPC by 50 and 70 % of BFS and 1 made of 52.5 N (SR) cement type. Cubic samples made with all binder types were exposed to a 3% by weight sodium chloride solution while applying a permanent splitting tensile load corresponding to 50 % of their breaking capacity. Prismatic samples (100 x 100 x 400 mm) made of OPC binder were exposed to a 3% by weight sodium chloride solution while maintaining a compressive load equal to 30 % of their maximum capacity. After the exposure time, ground layers were obtained from the samples to determine the chloride ingress into the concrete by means of potentiometric titration. To define chloride transport in concrete an error function solution was applied to Fick’s second law. In terms of their diffusion coefficient and chloride surface concentration in decreasing order of performance were found: the concrete with 70 % replacement by BFS, followed by the concrete with 50 % BFS substitution, then pure OPC concrete and finally the sulfate resistant cement concrete. Load levels of 30 % in compression and 50 % in splitting tensile testing, improved the resistance of concrete to chloride attack

On the quantitative thermogravimetric analysis of calcite content in hydrated cementitious systems

Calcite is a compound that is present in hydrated cementitious materials when carbonation of portlandite occurs or when limestone constituents are used. The quantification of its content in cementitious systems is then frequently necessary. Thermogravimetry (TG) measures the change in mass of a material (as a function of time) over a temperature range using a predetermined heating rate. It can be applied to estimate calcite content in the hydrated cement system, considering the temperature range at which it decomposes and releases carbon dioxide. However, the quantification is not easy because the onset of this decomposition is a function of many variables. The tangential method over the TG signal or the integration method over the derivative TG curve (DTG) are usually used to discount the background over the temperature range at which calcite decomposes. However, consistent underestimation of compounds is frequently described. The reasons for this are unclear and some hypothesis are discussed in this paper. Additionally, experimental quantitative TG of cement paste and aggregate containing calcite and diluted with low contents of analytical calcite are compared with the expected contents, as a calibration method regarding calcite content in the samples is given to improve the reliability of the results

Chloride penetration in concrete under compression or splitting tensile load representing 60-65 per cent of the ultimate load

A critical loading ratio is reached at 50% of concrete ultimate load. Beyond this point the presence of micro cracks exerts a big influence on the chloride transport. For compression the strain distribution in the sample developed micro-cracking system that is more or less homogeneously distributed in the sample. Therefore it is expected the same chloride profile regardless of the position. When combined splitting tensile load and chloride attack are acting on concrete, the main micro-crack system is located on the loading plane. This contributes to regular and alike shaped chloride profiles if they are taken from planes that are kept parallel to the splitting one. Prismatic samples (100 x 100 x 400 mm) made of OPC binder were exposed to a 3% by weight sodium chloride solution while maintaining a loading ratio equal to 60 % of the maximum capacity. Cubic samples (side = 150 mm) made of OPC and 50% BFS had similar chemical exposure while applying a permanent splitting tensile load corresponding to 65 % of their breaking capacity. After the exposure, ground layers were obtained from the samples to determine the total chloride ingress into the concrete by means of potentiometric titration and the effect of the load on the chloride ingress was assessed

Situación actual de la mediana mineria en el Ecuador. cambio de sistema de producción en la mina bonanza

DETALLA TRABAJO REALIZADO EN LA COMPAÑIA EXPOBONANZA S.A. Y EL PROBLEMA QUE SE PLANTEA ES LA PUESTA EN FUNCIONAMIENTO DE UN NUEVO SISTEMA DE PROCESAMINETO DEL MATERIAL QUE SALE DE LA MINA, EN VISTA DE QUE LA CAPACIDAD DEL MOLINO SE VE AMPLIAMENTE SUPERADA Y SE TIENE QUE ALQUILAR OTROS MOLINOS Y ES LO QUE ELEVA SUSTANCIALMENTE LOS COSTOS.Y PARA ELLO SE HA TRATADO DE LLEVAR UN DISEÑO DE INVESTIGACION DONDE SE TRATA DE ANALIZAR Y DEMOSTRAR QUE EL PROBLEMA ES FACTIBLE Y QUE ESTARIA LIMITADO SOLAMENTE POR RESTRICCIONES EN LA INVERSION Y LA BUSQUEDA DEL EQUIPO PESADO. SUS VENTAJAS SERIAN TENER CAPACIDAD DE PROCESAR MATERIAL DE MANERA CONTINUA , LA PRODUCCION SE DETENDRIA UNICAMENTE CUANDO TOQUE L

Recommendation of RILEM TC 246-TDC : test methods to determine durability of concrete under combined environmental actions and mechanical load

The combination of environmental actions and mechanical load has obvious synergetic effects on the durability of concrete. But these effects have been widely neglected so far. For a realistic service life prediction the effect of an applied mechanical load on chloride penetration has been taken into consideration as a first and important step in RILEM TC 246-TDC since 2011. This recommendation focuses on the test method to determine the effect of applied compressive stress and tensile stress on chloride diffusion. It includes detailed experimental procedure to receive consistent results of chloride profile and the apparent chloride ion diffusion coefficient of concrete under compressive and tensile stress

Test methods to determine durability of concrete under combined environmental actions and mechanical load: final report of RILEM TC 246-TDC

At present several methods are available to predict the durability of reinforced concrete structures. In most cases, one dominant deterioration process such as carbonation or chloride penetration is taken into consideration. Experimental results as well as observations in practice show that this is not a realistic and certainly not a conservative approach. In order to test more realistically, RILEM TC 246-TDC, founded in 2011, has developed a method to determine the durability of concrete exposed to the combined action of chloride penetration and mechanical load. In this report, a test method is presented which allows determination of realistic diffusion coefficients for chloride ions in concrete under compressive or tensile stress. Comparative test results from five different laboratories showed that the combination of mechanical and environmental loads may be much more severe than a single environmental load without mechanical loading. Modelling and probabilistic analysis also showed that the obvious synergetic effects cannot be neglected in realistic service life prediction

Examen de Tecnología Hormigon del 2009-2s de la 1° evaluación

Examen de TECNOLOGÍA HORMIGON del 2009-2S de la 1° Evaluació