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Effect of Curing Conditions on the Diffusion of Chloride into Concrete
abstract of my MSc thesis (in Persian)
 


Concrete structures are increasingly being deteriorated in Persian Gulf region, mainly due to the chloride-induced corrosion of the embedded steel. Severity of this environment in which the average temperature exceeds 40-50 °C and the relative humidity is about 60-70 % has made Persian Gulf one of the most aggressive environments in the world.

Initial curing, to which concrete is subjected prior to exposure to chloride environment, plays an important role in the rate of chloride penetration in it especially at early ages of exposure. Drying of cementious materials due to poor curing, particularly at surface, leads to restricted hydration in the surface layers and thus results in higher porosity and permeability. Since chloride ion diffuses through this part to reach the reinforcement, curing has an extremely important effect on the time of corrosion initiation in concrete. This issue would be more critical in the case of concrete containing silica fume replacement because the pozzolanic reaction is, in general, very sensitive to curing procedure.

This research presents laboratory and in-site obtained data of chloride diffusion parameetrs (diffusion coefficient, Dc; surface chloride concentration, Cs) into normal and silica fume concrete specimens cured in water for 0, 1, 3, 6 and 27 days an also use of one type of curing compound. The in site specimens were exposed to seawater in Persian Gulf Region in different exposure conditions: submerge, tidal and atmosphere
for 3 months. After the exposure period, total chloirde concentration was obtained at different depths from the surface. These results were curve fitted to Fick's second law of diffusion in order to obtain the diffusion parameters. They were also compared with the laboratory obtained data of these specimens, which immersed in 165 gr/lit NaCl solution according to NordTest standard method in laboratory for 5 months.

Evaluating the results of the values of Dc and Cs shows that although curing is a simple and cheap procedure, it can significantly result in the improvement and development of concrete characteristics specially the diffusivity of concrete in the surface layer. Based on the results, it is also proposed that the optimal moist curing times in terms of strength and durability for normal and silica fume concrete are 3 and 6 days, respectively.
 

 

This thesis was part of a national project supported by Management and Planning Organization of Iran in order to develop a model for durability based design of reinforced structure in the Persian Gulf region. This software that is called DuraPGulf simply uses a database of various parameters affecting the diffusion of chloride ion and estimates the time to corrosion initiation using Fick's second law of diffusion. This gives a basic idea to civil engineers about the importance of different factors in the service life of their designed concrete structure.
 

You can download the first version of DuraPGulf from here.
 

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