International Concrete Abstracts Portal

A high-performance concrete may posses satisfactory performance in many aspects other than compressive strength. In the context of in situ strength development, the performance of concrete at an early age is important. The temperature development, resistance to thermal cracking, early age engineering properties, and in situ strength development may all play a significant role in insuring satisfactory long-term performance. Describes the engineering properties of some very high-strength and high-performance concretes containing blast furnace slag with compressive strengths in excess of 80 Mpa under simulated "in situ" conditions of restricted moist curing and high-hydration temperatures. The influence of blast furnace slag content and the implications of the in situ development of engineering properties on performance are discussed.

Describes the development of a new type of high-performance concrete incorporating large volumes of ASTM Class F fly ash. Briefly, this concrete incorporates about 56 percent fly ash by weight of cement, and has a water-to-cementitious materials ratio of about 0.32. The portland cement and fly ash contents are of the order of 155 and 215 kg/m 3 of concrete, respectively. The flow slumps are achieved by the use of large dosages of superplasticizers. Because of the low cement content, the temperature rise in this concrete is low, and this concrete is ideally suited for concrete structures where excessive temperature rise is a concern. Also, the high-volume fly ash concrete has all the attributes of a high-performance concrete. It has excellent mechanical properties and demonstrates superior resistance to freezing and thawing cycling, chloride-ion penetration, sulfate attack, carbonation, and marine environment. Also, it has low permeability, and shows excellent performance in reducing potential expansion due to alkali-aggregate reaction.

Basic studies were conducted to develop high-performance concrete, with low-heat and high-strength characteristics under low-temperature environments, using blast furnace slag. The purpose of this study was to clarify the effects of slag fineness, slag content, gypsum content, limestone-powder content, and high-range water-reducing admixtures (HRWRA) on the strength development, adiabatic temperature rise, porosity, amount of Ca(OH) 2, and carbonation of concrete; and the effect of curing temperature on concrete strength development. As a result of this study, it was found that it is possible to produce high-performance concrete with low heat and high strength under low-temperature environments, by properly combining, and taking into consideration, their respective properties, granulated blast furnace slag, HRWRA, and other admixtures.

The time-dependent properties of high-strength concrete subjected to tensile and compressive loading have been studied experimentally and have been compared with those of normal concrete. Two kinds of load application were used during this investigation: loading with a constant strain rate and sustained loading. The range of strain rates is chosen between the so-called static and the creep strain rate limits. The ratio of adopted stress to 28-day prismatic strength in the sustained loading tests was chosen at 0.15, 0.35, 0.50, 0.75, 0.85, and 0.95. The research program mainly focused on the influence of the type of load application on the behavior of high-strength concrete in compression and tension. The phenomena observed in the experiments are interpreted by referring to a basic mechanism of rate sensitivity of concrete. The differences of the material structure between high-strength concrete and normal strength concrete are emphasized. In general, it is found that some properties of high-strength concrete in compression, such as strength and deformation characteristics, are more sensitive to the strain rate than those of normal strength concrete, whereas in tension, this tendency is less pronounced. On the basis of the test results, the long-term strength of high-strength concrete is defined.

Reports the moisture-induced shrinkage and swelling of high-strength concrete with 28-day cube strengths ranging from 81 to 107 MPa. The concrete mixtures consisted of hydraulic and blends of ordinary portland cement with 35 percent blast furnace slag content, silica fume, or fly ash in different proportions. The results showed that after 460 days of air-drying, shrinkage of high-strength concretes with 3-day water-curing is between 545 and 775 microstrains, depending on the binder materials used. The incremental shrinkage strains between 28 and 460 days for the concretes range from 215 to 285 microstrains. The highest proportion of drying shrinkage recovered was 69 percent of the 460-day shrinkage for concrete with 35 percent slag content, whereas, the control concrete showed the lowest recoverable shrinkage of 57 percent. Drying shrinkage after 100 days for concretes, which are water-cured for 460 days prior to drying, ranged from 39 to 67 percent of the corresponding shrinkage for similar concretes that are initially water-cured for only 3 days. Shrinkage of mature concrete having blended cement with 35 percent slag content is 240 microstrains, which is 39 percent lower than that for the control concrete with ordinary portland cement, although both concretes had compressive strength of about 105 MPa at the beginning of drying. The effect of partially replacing ordinary portland cement with silica fume decreased or increased the shrinkage of concrete, having 3-day water-curing, depending on the silica fume content. However, the shrinkage of concrete, having 460 days' water curing decreased when ordinary portland cement was replaced partially with silica fume up to 15 percent or with 5 percent silica fume and 5 percent fly ash.