International Concrete Abstracts Portal

In September 2000, the American Concrete Institute sponsored the ACI Fourth International Conference in Seoul, Korea. Sixty-two papers are included in this publication. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP193

The Hong Kong Mass Transit Railway Corporation, carrying a daily patronage of over 2 million, has a prime objective of providing a safe and reliable railway transportation system to the public in Hong Kong. The existing Urban Line System is situated mostly underground through soft, marine deposits and/or rock. The aggressive underground conditions in the coastal regions had resulted in various degrees of deterioration to the tunnel linings in a period less than 10 years from completion. The problem was most serious where precast concrete (PCC) lining was adopted because of the existence of segmental joints. A special method of repair was jointly developed by MTRC and Skanska International Civil Engineering AB. A robotic high pressure water jet system (hydrodemolition) is used to remove the surface delaminated concrete, and the surface repaired with a 75 mm layer of low permeability, fibre (polypropylene) reinforced shotcrete. Repair has to be implemented in the short time window during non traffic-hours each night with absolutely no disruption to the daily traffic.

Chloride ion is the main deterioration factor of concrete structures, mainly for external surfaces. These surfaces can be protected by paints, which may reduce the penetration of aggressive agents from external sources. A wide range of organic polymers are used as coatings for concrete and for each generic group a large number of formulations with different permeability against aggressive agents is possible. In order to understand the influence of paint composition on chloride ion penetration, acrylic latex paints with different pigment/binder ratios were studied. The objective of the study was also to evaluate the chloride penetration according to two methodologies. One, based on ASTM Cl202 “Electrical indication of concrete’s ability to resist chloride ion penetration” and the other, according to the previous method with modifications. The ASTM method allows us to obtain results in few hours; however, there are some controversies about this test and on the acceleration rate phenomenon. The tests were carried on applying paints on two different concrete substrates. The results not only show there is a correlation between paint composition and chloride penetration but also that the acrylic latex paints provide an effective barrier to this ion.

In this paper, electrodeposition method for repair of cracked reinforced concrete, based on the electrochemical technique, is presented. Electrodeposition means precipitation of material on the surface of an electrode by electrolysis. The aim of electrodeposition in a concrete repair method is to fill the cracks in concrete and to coat the concrete surface by electrodeposits of chemical compounds. Investigations on concrete specimens with drying-shrinkage cracks were conducted in this study. The specimens were immersed in a solution, then a constant current between the embedded steel in concrete and an electrode in the solution was applied for 2 weeks. The degree of crack closure and the amount of surface coating from the precipitation of electrodeposits were checked. The results indicate that electrodeposits formed on the concrete surface are able to close concrete cracks and to coat the concrete surface. In addition, the investigations show that the presence of electrodeposits led to improvement of the concrete watertightness and protection against detrimental materials. Therefore, it is considered that the electrodeposition method can be usefully applied as a repair technique for concrete with shrinkage cracks.

Electro-migration and diffusion of ions in electrolyte solution are theoretically described by the Nemst-Plank equation. Also, electro-migration and diffusion of ion can be related by using the Einstein’s equation in dilute solution. In concrete, however, the relationship between electro-migration and diffusion is still unclear, for the influence of the concentrations in pore solution is unknown. Previous work of the authors has shown that it is possible to assess the diffusion coefficients of chloride ion in an ordinary Portland cement mortar through conduction tests by following the Nemst-Plank equation, Debye-Huckel theory and electro-neutrality. This paper evaluates the adaptability of this method to mortars made of several binders, such as ordinaly Portland cement, high-early strength Portland cement, sulfate-resistant Portland cement, low-heat Portland cement, Portland blast-furnace slag cement, ordinary Portland cement with fly ash, ordinary Portland cement with silica fume. In these cases, the concentrations of calcium, sodium, potassium, chloride, and hydroxide ions are different from that of the ordinary Portland cement case. Thus, the adaptability of this method is confirmed in mortar made of a wide range of binders.