Discussion of the evolution of the chloride migration coefficient of Portland cement concrete tested by the rapid chloride migration (RCM) test at long-term curing periods up to 5 years
Chloride-induced corrosion of reinforced concrete is one of the main deterioration mechanisms leading to shortening of the service life of concrete structures. Therefore, assessment of the resistance of concrete to chloride ingress plays an important role in predicting the service life of such structures. The Rapid Chloride Migration (RCM) test is one of the accelerated test methods commonly used in Europe. It is commonly assumed that for a properly cured Portland cement concrete without degradation, the chloride migration coefficient should decrease with increasing curing age due to on-going hydration and microstructure densification. However, recent experiments show that the rapid chloride migration coefficient of Portland cement concrete decreases at early curing age, but increases at later curing ages up to 5 years. In this paper, the evolution of the rapid chloride migration coefficient of Portland cement concrete during long-term curing periods up to 5 years is discussed. The test conditions for the RCM test and the test results obtained from RCM tests are described. Finally, possible causes for the increase in DRCM that occurred during late curing of the samples are investigated in order to explain this increase.
Chloride Transport in Concrete - Measurement and Prediction
This doctoral work has been carried out to try to classify the basic theories involved in chloride transport in concrete, and at the same time to develop a measurement method and a prediction model for concrete structures submerged in sea water. Chloride binding accompanies almost all the transport processes and has a significant influence on chloride transport. It has been found that the chloride binding capacity non-linearly decreases as free chloride concentration increases. The relationship between bound and free chlorides may be simply expressed by the Freundlich equation. Diffusion is one of the main transport mechanisms, especially when the pores in concrete are filled with water. A concept of "intrinsic diffusion coefficient" with the dimension m 2_x per second has been proposed to evaluate chloride diffusion through the pore solution in concrete. This intrinsic diffusion coefficient facilitates the comparison between different test results and the modelling for predicting chloride penetration. Under the action of an external electrical field, the chloride transport process can be greatly accelerated. The rate of migration is theoretically related to the diffusion coefficient. Therefore, the chloride diffusion coefficient can be quickly determined through a migration test. The CTH rapid method for determining the chloride diffusion coefficient has been developed based on the theory of diffusion-migration. Among different rapid methods the CTH method is theoretically clearest and experimentally simplest. Numerical approach is a better way for modelling of such a complicated transport process. A windows based program ClinConc has been developed for this numerical approach. In this numerical model most of the factors affecting chloride penetration have been considered. The main input data in the program include concrete mix design, workmanship and exposure conditions. The only parameter which must be measured is the chloride diffusion coefficient by the CTH rapid method. The chloride penetration data obtained from both laboratory and field studies were used to test the model. The preliminary results show that the predicted chloride profiles correspond fairly well with the measured data, in spite of different exposure conditions and durations.
Determination of Optimal Ball-Burnishing Parameters for Plastic Injection Moulding Steel
The objective of this study is to determine the optimal plane ball-burnishing parameters for plastic injection moulding steel PDS5 on a machining centre by utilising the Taguchi’s orthogonal array method. The design and manufacture of a burnishing tool are described. Four burnishing parameters, namely the ball material, burnishing speed, burnishing force and feed, were selected as the experimental factors in Taguchi’s design of experiments to determine the optimal burnishing parameters which have the dominant influence on surface roughness. The optimal burnishing parameters were found after carrying out the experiments specified by Taguchi’s L18 orthogonal table, by the analysis of variation, and by a full factorial experiment. The optimal plane burnishing parameters for the plastic injection moulding steel PDS5 were a combination of a tungsten carbide ball, a burnishing speed of 200 mm/min, a burnishing force of 300 N and a feed of 40 μm. The surface roughness Ra of the specimen can be improved from about 1 μm to 0.07 μm by using the optimal burnishing parameters for plane burnishing.