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

An underground concrete structure in Japan was severely damaged. The structure was located in a soil that contained considerable hydrogen sulfide and the effects of various microorganisms could not be disregarded. In this study, several types of bacteria in the soil around the structure were isolated and cultured, and simulation tests of mortar deterioration were performed to clarify effects of bacteria on concrete deterioration. Hydrogen sulfide-producing bacteria or sulfur-oxidizing bacteria or both were used. Calcium ion was dissolved out of mortar soaked in the culture medium inoculated with hydrogen sulfide-producing bacteria. The value of pH was decreased and the quantity of hydrogen sulfide was increased in the culture medium as growth of the bacteria proceeded. Since this dissolution of calcium ion from mortar was not observed in the control medium, metabolites of these bacteria could be one of the reasons. From the results of TG-DTA, CaCO 3 content in the mortar surface increased and Ca(OH) 2 content decreased. This is because carbon dioxide produced by the bacteria caused carbonation of the mortar. It has already been established that concrete can be severely damaged by anaerobic bacteria, but this study suggests that concrete can also be damaged by metabolites of aerobic bacteria.

Abrasion resistance of 10 concrete mixes with compressive strength ranging from 0.24 to 0.42 MPa was evaluated. Mixes studied contained silica fume, fly ash or natural pozzolan, and addition of superplasticizer in some cases to reduce mixing water. Concrete workability remained constant. Tests were carried out following a Portuguese standard similar to a Brazilian standard and German Standard DIN 52108, using the Dorry apparatus. Porosity and compressive strength of concrete were also determined. The main conclusions are as follows: 1) cement replacement by mineral admixtures always reduced the abrasion resistance at rates between 10 and 25 percent, while less satisfactory results were obtained with condensed silica fume concretes; 2) addition of superplasticizer increased the abrasion resistance about 25 percent; 3) abrasion resistance varied inversely with water-cement ratio, cement paste volume, and concrete porosity; 4) general correlation was poor between abrasion resistance and compressive strength, indicating a strong influence from cementing material type, mainly in the case of silica fume; 5) there was evidence that poor performance of condensed silica fume concrete can be ascribed to self-desiccation; 6) even the worst results obtained in this test series were equivalent to abrasion resistance at least six times higher than that of ordinary concrete with 20 MPa compressive strength.

In 1980, dead-burned dolomite particles removed from a cement kiln were inadvertently distributed in aggregates that were later used in concrete. These particles were of coarse aggregate size (38 mm) and contained approximately 55 percent calcium oxide (CaO) and 35 percent magnesium oxide (MgO). When this contaminated aggregate was used to make concrete in 1980, it caused some relatively large popouts (up to possibly 230-mm-diameter). Subsequent periodic visual evaluations of this contaminated concrete were performed to verify the acceptability of the concrete and the durability of popout repairs. To the authors' knowledge, only one structure was removed and repaired. In 1989, another such incidence occurred, but this time the portland cement was contaminated with smaller (<9.5-mm) dead-burned dolomite particles with approximately the same proportions of CaO and MgO. Paper reports on how data developed from the 1980 incident was extended for use in evaluating the concrete contaminated in 1989, and how instrumentation was used to effectively determine the actual volume of dead-burned dolomite in the contaminated concrete and degree of hydration of the particles. Such information is being used to predict the long-term effects of the contamination.

The European prestandard for concrete, ENV 206, includes durability requirements framed principally in terms of maximum water-cement values for various exposure classes. Minimum cement contents are also given, but the values are relatively low. No minimum concrete strength grades are included, and no distinction is made between cements of different strength classes or different types. It is clear that the variety of cement types specified in the European prestandard for cement, ENV 197-1, will produce a wide range of concrete strengths when fulfilling the limiting specification requirements for a given exposure category. Previous work has suggested that, although water-cement ratio may be the most suitable specification parameter within a single cement type, strength should also be specified if comparable concrete durability is to be achieved with a range of cement types. To test this proposition, two series of concrete mixes were prepared with a variety of cements, including slag, fly ash, and limestone filler: one series had equal cement contents and water-cement-ratio and the other had equal strength grade and workability. The results to date show that durability, as measured by permeability, carbonation, and freeze-thaw resistance, is not equal for all cements at the same water-cement ratio, and suggest that concrete strength grade is a better specification parameter if similar durability is required from the wide range of cement types defined in ENV 197-1.