International Concrete Abstracts Portal

In general, the structural member using high-strength concrete is accompanied by high brittleness, which may result in the unexpected dangerous failure. For economy and safety, high-strength concrete may be used for compressive members (vertical members) and low-strength concrete for flexural members (horizontal members). ACI 318-89 recommends that when the specified compressive strength of concrete in the column is greater than 1.4 times that specified for the floor system, the column concrete shall extend 600 mm into the slab from column face to avoid unexpected failure. The structural behavior of beam-column joints with two different compressive strengths of concrete for the beams and the columns has not been investigated adequately. ACI-ASCE Committee 352 recommends that for joints that are part of the primary system for resisting seismic lateral loads, the sum of nominal moment strengths of the column sections above and below the joint ( M c), calculated using the axial load, which gives the minimum column moment strength, should not be less than 1.4 times the sum of the nominal strengths of the beam sections at the joint ( M b). Thus, those recommended values should be examined before high-strength concrete can be used with confidence and convenience in structural members. The results showed that the ACI 318-89 extension distance of 600 mm is safe at least for members up to 300 mm in total depth, and the 2h (h is overall depth of the beam) extension distance was found to be safe also for members under flexural loading with a column-to-beam flexural strength ratio of 1.8.

Reports data from a comparative, long-term study of several blended cements. The study compared the performances of five different binder systems for strength and for properties related to durability. It was found that both ground granulated blast furnace slag (ggbs/slag) and silica fume (microsilica) were very efficient in improving durability and impermeability. The two materials combined with OPC in a triple blend showed better performance than either on its own, and in this combination, silica fume compensated for much of the delayed strength development in slag cement concretes. Paper gives a thorough summary of the results obtained during the first 30 months of the project.

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.