International Concrete Abstracts Portal

SP-145 In 1994, The Canada Centre for Mineral and Energy Technology (CANMET) in association with the America Concrete Institute, sponsored a third international conference on the Durability of Concrete This Special ACI publication presents the 65 conference papers accepter for publication. For Your Convenience, Durability of Concrete has been divided into two parts. Part 1, which contains 34 papers, covers the areas of: 1. Deicer Salt Scaling of Concrete 2. Freezing and Thawing Phenomenon 3. Performance of Concrete in Marine Environments 4. Corrosion of Steel to Fluoride-Ion Attach 5. And other Topics Part 2, containing 31 papers, covers the areas of: 1. Alkali-Aggregate Reactivity 2. Coatings for Concrete 3. Carbonation 4. High-Volume Fly Ash Concrete 5. Durability of Concrete

Petrographic examination and the South African mortar bar test have been performed at SINTEF--Structures and Concrete during the last 2 to 3 years to evaluate the reactivity of Norwegian aggregates to be used in concrete structures. Paper presents the relationships between these two test methods. The purpose of the petrographic examination is to identify, quantify, and group different rock types in an aggregate. These groups are: reactive (with known reactive field performance), potentially reactive, and innocuous aggregates. In Norway, further testing by the mortar bar test is recommended when petrographic examination indicates 20 percent of reactive or potentially reactive rock types in the aggregates. The mortar bar expansion after 14 days of exposure is used for the evaluation of potential expansivity of the aggregates. One main conclusion from the investigation is that mortar bar expansion increases to an upper level with increasing content of reactive rocks in the aggregates. Beyond a "marginal" amount of reactive rocks in aggregates, the mortar bar expansion increases no further. A significant difference in mortar bar expansion between different reactive rock types has not been found. The established limit of 20 percent of reactive rocks in aggregates appears, in most cases, sufficient for classifying aggregates as innocuous; however, no verification of the limit has been made.

The transport of ions related to the penetration of chlorides into concrete has been studied in the field by drilling 100-mm concrete cores from a marine bridge column. A 4-year-old concrete column in Sweden was selected. The concrete was of high quality (i.e., frost- and sulfate-resistant, with a low-heat, low-alkali portland cement with a maximum water-cement ratio of 0.40) according to new Swedish recommendations. Concrete cores were drilled from the submerged, splash, and atmospheric zones. Selective rinding from the concrete surface (profile grinding) revealed concentration profiles of acid-soluble chlorides, carbonates, sulfates, and water-soluble alkalies. Selected parts of the concrete surface were examined by SEM and thin-section microscopy for microstructural studies. Laboratory estimates of chloride diffusivities were carried out on 6-month-old laboratory concrete of similar mix proportions, and also on unexposed parts of drilled concrete cores. Chloride diffusivities obtained from laboratory exposure were then compared with the values obtained from the field concentration profiles, from both the bridge column and a field station, using Fick's second law of diffusion. Maximum chloride diffusivities calculated from the field profiles after 4 years of exposure were more than ten times lower than those obtained from the same concrete in the laboratory. Clearly, there are important mechanistic problems associated with laboratory procedures, resulting in serious misjudgments, if such laboratory tests are used for linear extrapolation of the service life for marine concretes.

The repair and rehabilitation of bridge decks in the western countries and reinforced concrete structures in the countries along the Arabian Gulf is a major challenge to civil engineers. The need for repair of these structures results from concrete deterioration caused mainly by reinforcement corrosion. The use of deicer salts in North America and Europe accelerates reinforcement corrosion in bridge decks. Aggressive environmental conditions in the Arabian Gulf are responsible for deterioration of concrete structures in this area. This investigation was carried out to evaluate the durability performance of various repair materials. The repair materials were exposed to thermal variations to evaluate their performance in arid environments, such as in the Arabian Gulf. Durability performance was evaluated by measuring water and chloride permeability, and resistance to reinforcement corrosion. Results indicate that the water permeability in all the repair materials was less than that in plain concrete. Water permeability was significantly increased in all the specimens that were subjected to thermal variations, compared to those cured in the laboratory temperature. Ordinary cement mortar specimens indicated higher chloride permeability and lower corrosion resistance than other repair materials and plain concrete, which could be attributed to its lower electrical resistivity in saturated condition.

Presents field data of up to 8 years on chloride penetration into concrete and consequent steel corrosion in a test structure exposed to an aggressive environment favoring rapid transportation of chloride ions into concrete. The structure consisted of reinforced concrete beams, slabs, and columns. Two types of concrete, one without salt and the other containing 0.5 percent NaCl by weight of concrete, were used in the construction. Parts of the structure were left exposed and unprotected, while the other half was protected with a highly elastic acrylic rubber coating previously subjected to intensive examination. The chloride contents in the structural members were determined regularly over a period of 8 years. In addition, the influence of the coating and the different salt concentrations on corrosion of the embedded steel were evaluated. It is shown that the acrylic rubber coating can almost totally protect the concrete from chloride penetration and consequent steel corrosion and maintain this protective effect for many years.