Papers by Keyword: Chloride Penetration

Abstract: The aim of this research is to investigate hardened state properties of Self Compacting Concrete (SCC) containing low calcium based fly ash. The mixtures were prepared using various proportions of Class F fly ash ranging from 0% to 30% cement replacement. Water to powder ratio is 0.38 – 0.39 and powder content was kept constant at 540 kg/m3. Properties investigated were strength properties (compressive strength and splitting tensile strength), and durability properties (complete immersion water absorption, apparent volume of permeable voids (AVPV), sorptivity, and RCIPT tests. These tests were done at various days. Results showed that fly ash replacement of up to 30% gave acceptable strength and durability properties for medium strength SCC.

Abstract: Finite difference method (FDM) is used to numerical stimulation analysis for chloride diffusion in concrete. By numerical computing, comparison of chloride content profile in different concrete members with different sectional shapes is made. Calculation and comparison show the chloride content prolife in rectangular and circular section has obvious difference. If the side length of rectangular section is equal to the diameter of circular section, as well as the material property and environment, the chloride content in rectangular section is higher than that in that in circular section. In the calculation example, the chloride content at the depth of reinforcement of circular section is about 50-60% that of rectangular section. This tendency is more remarkable in less section dimension, as well as less cover thickness. With the increasing of section, the ratio of difference becomes to be less until to a constant value. In durability design and service life prediction of concrete structures, the section shape and dimension influence should be taken to consideration.

Abstract: A study was made into the resistance in frost-thaw cycles and chloride penetration of silica-fume concrete by simulating the characteristics of the marine environment and using the R-value evaluation method. The results show that as a result of mixing silica fume in concrete, the R-value increases by 52.1%; the composite use of silica fume and air-entraining agent with an adequate mixing amount can increase substantially the comprehensive property of concrete in resisting frost-thaw cycles and chloride penetration, with the magnitude of R-value increase being as high as 174%~ 284% and the silica mixing amount being best at around 10%.

Abstract: The mechanism of concrete durability under uniaxial compressive load has been studied through chloride penetration experiments in this contribution. It has been found that there is a good corresponding relationship between chloride penetration resistance of concrete and the applied compressive stress level. With increasing of the applied compressive load, chloride penetration depth and content both decreased firstly. After the compressive load up to a critical level, they began to increase quickly. The apparent diffusion coefficient and chloride concentration at the surface also increase with the same rule. It is shown that chloride penetration of concrete is a complex process. So the effect of mechanical load should be considered as an important factor for prediction of service life of reinforced concrete structures in marine environment.

Abstract: In order to investigate the effects of polyvinyl alcohol (PVA) fibers on the performance of concrete, such as strength, crack resistance, permeability and chloride penetration properties, experimental research were carried out in this paper . Three types of fiber reinforced concretes with 0, 0.5%, 1.0% volume fractions were designed with the same water to cement ratio of 0.43. Flat band method was used to evaluate the cracking resistance, while AutoCLAM and ASTM C1202 were adopted to measure the permeability of concrete. The experimental results showed that the workability and the compression strength decreased as PVA adding volume increasing. However, the tension and the bending strengths increased for PVA fiber concrete. The number of cracks induced by the shrinkage of concrete was reduced by adding more PVA fibers. The permeability and chloride penetration ascended as PVA volume increasing. However, all the parameters with regards to strength, crack resistance, permeability and chloride penetration for fiber reinforced concrete were more reasonable than those for the specimens without PVA fiber. In additional, a very good correlation between the permeability and the electric flux was found in this paper, that means both AutoCLAM and ASTM C1202 could be used for concrete penetration test.

Abstract: The purpose of this study is to identify and quantify the effect of the mixing features of concrete such as size of coarse aggregate, high strength and steel fiber reinforcement on chloride penetration through micro-cracks. In examining the effect of size of coarse aggregate on chloride penetration through cracks, the cracks should not impact on chloride penetration directly, although small size of coarse aggregate can lead to complicated micro-cracks in concrete. On the contrary, chloride should easily penetrate through micro-cracks concentrated at the surface of coarse aggregates. In examining the effect of high strength concrete on chloride penetration through cracks, high strength concrete has an excellent performance to resist with chloride penetration. If cracks are generated in high strength concrete, however, its performance is reduced up to the level of ordinary concrete.

Abstract: This experimental research was to investigate the chloride penetration and consolidation behavior of OPC and coal gangue added cement. By comparing the results of two kinds of cement, results showed that the chloride consolidation of gangue added cement is higher than OPC. The chloride consolidation increased with more gangue added. The coal gangue is helpful to impede the chloride ingress until the added content reach 30%. The more gangue content decreased the fluid of mortar. And this increased the porosity of harden pastes. Furthermore the corrosion behavior of steel bar in OPC and G30 samples were conducted. Corrosion potential of gangue added cement moved positively comparing with OPC. These indicated that the propriety gangue content was helpful to steel bar protection.

Abstract: With the rapid consumption of natural resources, there is a growing concern about sustainable development. More than 6 billion tons of concrete are produced annually for various construction purposes with limited life expectancy. In addition, increasing cost of construction and demolition of concrete structures in densely populated areas is a great concern for the future. One of the best solutions to tackle these challenges is to increase the life expectancy of the structures. Residential structures and important civil structures are typically designed for a life span of 50 and 100 years respectively. However, the life expectancy of structures can be increased to several hundred years with careful planning and proper design. Cost of the concrete materials is not a considerable amount compared to the total cost for construction of reinforced concrete structures. Doubling the concrete materials cost may only increase the total construction cost by few percent but it can increase the life expectancy of structures significantly. In this work, a comparison between ultra durable concrete mixes with normal high strength concrete in terms of cost, mechanical and durability aspects is presented. Ultra durable concrete has superior qualities which makes it a favourable construction material for future structures.

Abstract: The total porosity of high performance concrete specimens after different level uniaxial tensile loading were measured to reflect the damage degree of mechanical load to the microstructure of the concrete. Meanwhile, considering the environmental characteristics of the ocean tidal zone, chloride penetration tests of the concrete were carried out with salt solution capillary absorption method. Based on the profile of chloride measured from specimens, chloride diffusion coefficients of the concrete under uniaxial tensile load with different levels are determined further by Fick’s second law. Results show that both of total porosity and chloride diffusion coefficient of the concrete are increased significantly after short-term tensile loading. And the evolutions of the porosity and chloride diffusion coefficient are similar with the development of micro-cracks under uniaxial tensile load.

Abstract: The influence of fly ash as cement replacement on pore structure, chloride penetration and frost resistance of recycled concrete is investigated by evaporable water test, chloride natural diffusion test, and freeze-thawing test. The experimental results indicate that adding fly ash to recycled concrete can decrease its porosity and improve its pore size distribution. Chloride penetration resistance of recycled concrete is enhanced firstly and then reduced with increasing of fly ash content. The best proportion replacing cement with fly ash is 20%. Fly ash content has a certain influence on the frost resistance of recycled concrete, and the frost resistance of recycled concrete only has been improved when the proportion of fly ash replacing cement achieves more than 20%.