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It is important to have an accurate understanding of the chloride permeability of concrete, especially in the case of RC structures that are susceptible to reinforcement corrosion. The Rapid Chloride Permeability Test (RCPT, AASHTO T-277 831) has often been used during the past several years for a quick evaluation of the chloride permeability of concrete and for comparing the performance of different concrete mixtures. Presents a summary of some of the valuable experimental results published and also briefly discusses the authors' own experience with this method, gathered during a research program presently underway to monitor the chloride permeability of various concretes at different levels of hydration under varying conditions. A study of the literature reveals that AASHTO T-277 has been used for a large variety of concrete mixtures, including those using supplementary cementitious materials, curing conditions, etc., and several attempts have been made to relate the coulombs (obtained using AASHTO T-277) to other parameters and characteristics of concrete, such as resistivity, pore structure, etc. Some of the results from the authors' study included in the paper also show that it may be better at times to work with other voltages than 60 V, and an appropriate conversion factor can be determined to compare the results at different voltages. Further, it was found that, in general, the coulombs decrease as the compressive strength increases, and concrete containing supplementary cementitious material gives lower coulombs at a given strength, which reduce further as the replacement level increases. Paper also discusses some of the possible applications of AASHTO T-277 as a tool for quality control, inspection, and design in concrete engineering.

Concretes containing either latex, Class F fly ash, ground granulated blast-furnace slag, silica fume, or, in some cases, combinations of these ingredients generally are found to have lower permeabilities than concretes containing only portland cement as the cementitious material. Concretes with low permeability provide high resistance to penetration by chlorides or other aggressive ions, which is essential for insuring their long-lasting performance when exposed to aggressive chemical attack while in service. The tests conducted show that either the rapid chloride- permeability test (AASHTO T 277 or ASTM C 1202) or the ponding test (AASHTO T 259) (used for periods longer than the standard 90 days) can be used to differentiate the permeability of different concretes. General agreement in the findings of the two tests with respect to chloride permeability is expected, provided that the concretes compared have been exposed to similar conditions and periods of exposure, and that possible interferences with the results of the rapid test have been eliminated.

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.