International Concrete Abstracts Portal

In most existing standards and guidelines, durability of reinforced concrete structures is covered by prescriptive requirements. For corrosion initiated by carbonation, this may include requirements on w/cm, type and content of cement, compressive strength, concrete cover etc. Future requirements will probably be performance based, defined according to a probabilistic approach. However, today we don’t have the appropriate information on the correlation between carbonation rate and factors like w/cm, type and content of cement and environmental situation, especially air humidity and CO2 concentration. Therefore, requirements in standards are still prescriptive. However, the pre- scriptive specifications within codes and standards may be based on testing of existing structures and using a probabilistic approach when analysing the results. A probabilistic approach to the process of defining prescriptive requirements for concrete exposed to carbonation, is presented. The approach is based on the philosophy given in the European standard EN 1990 (1) "Basic of Structural Design," which means that the "failure" reliability Z is calculated as the difference between a resistance against "failure" R (e.g., concrete cover) and an environmental load or action F (e.g., time dependent carbonation depth). Both resistance and load are expressed in a probabilistic way. The new European standard EN 206-1 (2) is used as example, but the presented principle may be used in other situations.

The main objective of this research was to investigate the properties of ternary and binary blends incorporating silica fume, metakaolin, and electric arcfurnace steel slag produced in Libya (LSS). The properties investigated include workability, chloride-ion penetration, and compressive strength. The penetration of chloride-ions was studied using the Rapid Chloride Permeability Test Method, in accordance with the procedures prescribed by AASHTO T277-83 [5]. The study also looked at the effect of the amount of pozzolanic content on the observed trends. It was established that ternary and binary mixtures could differ significantly in both their fresh and hardened properties. The ternary blends exhibited some positively complementary properties, which were not observed in the binary mixtures. Significantly, the ternary blends incorporating metakaolin were found to have greater improvement in strength and chloride-ion penetrability compared to those mixtures incorporating the other two pozzolans used.

Concrete structures on the western coast of Norway are exposed to a harsh environment, mainly wind and sea water. The concrete should be designed in order to sustain attach from the environment and especially reinforcement corrosion, which is the most serious type of damage on coastal concrete structures. Several major Norwegian research projects have taken place in order to improve durability by correlating relevant durability parameters to environmental exposure, material composition, structural geometry and details. The most important factors to resist deterioration are thickness of the concrete cover and the concrete composition. This paper reviews some of the results from these projects, and concentrates mainly on the binder type. Attention is paid to the addition of silica fume and use of a fly ash portland cement, introduced in Norway in the late 70's and early 80's, respectively. Laboratory testing (several methods), in-situ exposed specimens and long-term in situ experience clearly demonstrate the beneficial effect on the chloride-ion intrusion from the addition of pozzolans to the binder. The results have lead to improved practical recommendations and regulations concerning concrete composition for structures in Norway exposed to chloride-ions.

This paper examines the test results from a research program that evaluated the performance of epoxy coatings as a corrosion prevention method. In this study, laboratory tests were performed on small-scale precracked reinforced concrete specimens containing epoxy-coated reinforcement. A total of six different epoxy coatings with four duplicate bars for each coating type were evaluated. The concrete specimens were subjected to a simulated marine environment for more than five years and corrosion current density of the steel reinforcement was measured using Linear Polarisation Resistance technique. At the end of the testing period it was found that epoxy coating is an effec- tive method to prevent corrosion of steel reinforcing bars in cracked high w/c concrete. It was also found that pretreatment of the steel surface before the coating application enhances the effectiveness of epoxy coatings as steel corrosion prevention measure.

In the frame of a European sponsored Brite-Euram research project program, long-term exposure tests are conducted. Notched cubes are used to test the effect of exposure to different environments for different periods of time. The different environments are: outside exposure; alternatively drying and wetting for one week in lab environment; wetting in demineralised or chloride water and drying in CO2 environment. Reference testing is done after 6, 12 and I8 months. To assess the mechanical behaviour, the wedge splitting test is performed. The electrochemical testing is done on the same types of cubes in which fibres are embedded. The comparison is made between fibres bridging the crack and fibres fully embedded in the concrete. Afterwards fibres are taken out and analysed with the microscope. This is done for the cubes mechanically tested and for the cubes electrochemically tested. No decrease of strength could be found after the 18 months of exposure. The electrochemical measurements on the sensors show negligible corrosion. This is confirmed by the microscopic analysis. Maximum measured corrosion depth is 16um.