Papers by Keyword: Chloride Diffusion Coefficient

Abstract: This study investigated the influence of nanokaolin content on the behavior of cement mortar at various curing ages. The fluidity, chloride permeability, bending and compressive strength of cement mortar with various nanokaolin additives were examined. The addition of 0%, 1%, 2%, 3%, 4%, 5% and 6% nanokaolin were taken into consideration. The results showed that the addition of nanokaolin decreases the fluidity of cement mortar, and the fluidity the cement mortar decreases with the increase of nanokaolin additives. It is obtained that the addition of nanokaolin increases both the bending and compressive strength of cement mortar, and with the increase of nanokaolin additives, the bending and compressive strength of cement mortar increase. The addition of 4% nanokaolin can result in a significant low chloride permeability of cement mortar among the seven dosages. The chloride diffusion coefficient of the mortar with the addition of 4% nanokaolin was decreased by 18.93%, 12.68% and 31.05% at 7, 14 and 28 curing days, respectively.

Abstract: Concrete structures are generally subjected to serious deterioration under harsh environment, even though the concrete materials exhibit inherently higher durability than any other construction materials. The service life of concrete structures is directly affected by the durability performance under various conditions. In this regard, many studies have been conducted on the deterioration of concrete structures under various environmental conditions. However, previous studies were confined mostly to the deterioration of concrete structures under single deteriorating factor such as chloride ingress only or sulfate attack only, although real environment is actually a combination of such factors. The purpose of the present study is, therefore, to explore the effects of combined deterioration due to chlorides and sulfates in concrete structures. To this end, comprehensive experimental program has been set up to observe the chloride penetration behavior under combined deterioration conditions of chlorides and sulfates. The test results indicate that the chloride penetration is more pronounced for the case of combined attacks of chloride and sulfates than the case of single chloride attack. The surface chloride content is found to increase with time and this phenomenon is also more pronounced under the combined exposure of chlorides and sulfates. The present study may allow more realistic assessment of durability for such concrete structures which are subjected to combined attacks of chlorides and sulfates.

Abstract: The durability, microstructure and hydration products of concrete containing 0-6wt% metakaolin (MK) were studied by analytical techniques. The hydration products were calcium hydroxide (CH), ettringite and calcium silicate hydrate gels in the control concrete, and additional monocarboaluminate and hemicarboaluminate were identified in concrete containing MK. CH content decreased by 28 days hydration in concrete containing MK, due to the pozzolanic reaction between MK and CH. Chloride diffusion coefficient decreased with the increase of MK content. By addition of 6wt% MK, chloride diffusion coefficient decreased by 60%.

Abstract: The paper is focused on the evaluation of chloride ingress considering high performance and ordinary concrete mixtures. The effect of concrete maturing is investigated as well. The selected laboratory measurements are used for the description of resistance of concrete against ingress of chlorides. The Finite Element-based numerical model is applied in order to evaluate the effect of concrete type as well as the effect of aging.

Abstract: The effect of different layers of silane impregnation on chloride resistance of concrete materials at various curing ages is systematically discussed. The chloride resistance of two types of concrete specimens with surface silane impregnation has been investigated through the Rapid Chloride Migration (RCM) method. The testing results indicate that the chloride penetration can be effectively restrained by silane impregnation, and the chloride diffusion coefficients of samples are significantly decreased. After curing for 28 days, when compared to the untreated samples, the chloride diffusion coefficients of two types of concrete specimens both with two layers of silane impregnation decreased by 37.4%, 37.6% respectively.

Abstract: The correlation of chloride diffusion coefficient and concrete maturity value within 56 days of curing was investigated by the chemically combined water content method, rapid chloride migration (RCM) test and concrete maturity test, respectively. The experimental results showed the chloride diffusion coefficient of concretes decreased not only with increasing curing ages, but also with increasing curing temperature, which can promote the hydration degree of cementitous. There is a significant correlation between the chloride diffusion coefficient of indoor curing specimens and the concrete maturity value when expressed as a power function (R²=0.976), and the calculated values of concrete maturity for outdoor specimens which obtained by using the power function agrees well with the measured values, then it can use the measured concrete maturity value to predict the chloride diffusion coefficient of concrete. And then in this project, when the immersed tube tunnels were placed in seawater, the recommended value and the control value of concrete maturity was 21064°C•h and 13926°C•h, respectively. Furthermore, the ages of the tunnels placed in seawater can be appropriately adjusted by calculation when considering the external curing temperature and heat of hydration of cementious.

Abstract: The effect of stone powder content on the chloride diffusion coefficient and diffusion attenuation coefficient of chloride ion of mechanical sand (MS) concrete was studied. The results showed that the resistance to chloride ion permeability of MS concrete firstly increased and then decreased with the increase of the content of stone powder. The anti-permeability of the concrete which had moderate amount of stone powder was better than that of the natural river sand (NS) concrete. The diffusion attenuation coefficient of MS concrete was greater than that of the NS concrete, which was good for long-term durability of concrete structure.

Abstract: Cube crushing strength, resistance to chloride penetration and gas adsorption analysis of mineral admixture concrete are tested to analyze the effect of raw material on chloride diffusion coefficient and its regression relationship with concrete microcosmic pore structure index. Test results show that chloride diffusion coefficient at different age increased with the increase of water-binding material ratio, decreased with the increase of cement dosage and both appeared a good nonlinear regression relationship. Chloride diffusion coefficient at different age increased with the increase of concrete microcosmic pore structure index. 56d chloride diffusion coefficient has a good linear correlation with microcosmic pore structure index, and 84d chloride diffusion coefficient has a good nonlinear regression relationship with microcosmic pore structure index.

Abstract: The influence of mineral admixtures on workability of fresh concrete and chloride ion permeability resistance of hardened concrete for C50 self-compacting concrete was investigated by means of the Natural Immersion Test. The results showed that the chloride diffusion coefficient in fly ash concrete decreased first and then increased with increasing fly ash content in cementitious materials, when fly ash content was 30% or 40%, it got the lowest value at 28 days or 90 days, respectively. The chloride diffusion coefficient in specimens decreased with increasing the ground granulated blast furnace slag content in cementitious materials, but it changed little when the replacement was in ranges of 50% to 60%. Furthermore, for the specimens which replaced by fly ash and ground granulated blast furnace slag, the chloride diffusion coefficient decreased first and then increased with increasing the fly ash content in complex cementitious, and when fly ash content was 10% or 20%, it got the lowest value at 28 days or 90 days, respectively.

Abstract: In this paper, the effect of pore structure on the chloride ions ingress into concrete was investigated. The most probable diameter was measured by Mercury intrusion porosimetry (MIP) and the total porosity was measured by evaporative water method (EWM). The results indicate that the most probable diameter by MIP has better linear relationship with chloride diffusion coefficient than the total porosity by EWM, the most probable diameter has significant influence on chloride diffusivity, and the smaller most probable diameter will lead to higher chloride penetration resistance.