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.
SERVICE LIFE PREDICTION OF EXISTING CONCRETE STRUCTURES EXPOSED TO MARINE ENVIRONMENT
Deterioration of reinforced concrete structures due to chloride ingress followed by reinforcement corrosion is a serious problem all over the world. Service life predictions, both for existing and planned structures, are therefore of great importance. In the present paper, a practical model for predicting service life in existing structures is presented. The model is based on Fick's second law of diffusion combined with empirical results from existing structures and laboratory tests. The mathematical model may be utilized in different situations as described in the original report. This paper details the most common situations. The model can be used as it is; however, more data has to be collected to refine the model and thereby give better predictions in the future. Such data should be collected in a formal manner to fit into the model.
Economics of General-Purpose Assembly Robots
Summary A study of the comparative economics of various automatic assembly systems using general-purpose assembly robots is described. In the study, use is made of a “typical” candidate assembly whose profile is obtained from statistical analysis of actual products submitted by interested companies. It is shown that the choice of assembly system and the various parts presentation methods depends on three main factors, namely: the annual production volume per shift, the number of parts in the product and the equipment payback period.