International Concrete Abstracts Portal

The current design recommendations for concrete deep beams given in the ACI Code, Canadian Code, CEB-FIP Model Code, CIRIA Guide-2, etc., are based on research results on normal strength concrete. As such, these design recommendations may not be directly applicable to deep beams made of high-strength concrete. A summary of the authors' recent research on the shear behavior of deep beams made of high-strength concrete is presented. Experimental results on the ultimate shear strengths of single-span, continuous, and slender deep beams as affected by the strength of concrete, shear-span-to-depth ratio, and slenderness ratio, are compared to various design methods. It is found that the ACI method is overly conservative for all cases, the Canadian Code method is unconservative for higher strength concrete, the CEB-FIP method gives somewhat scattered predictions, and the CIRIA Guide-2 is slightly unconservative for all cases. A minor modification on the CIRIA Guide-2 method is shown to yield a reliable method for all the cases investigated.

An experimental investigation was conducted on the shear behavior of deep beams made with steel fiber reinforced high performance concrete (HPC). Twenty-six beam specimens with various shear span-effective depth ratios, steel fiber contents, amounts of vertical and horizontal web reinforcements were tested under static loads. In addition to the strength test, extensive instrumentations were designed for the measurements of average strains of reinforced concrete in the shear span and strains of web reinforcements. The web-shear cracking initiated as the first inclined shear crack. About 30% increase in the inclined shear strength and 25% increase in the ultimate shear strength can be achieved with addition of 1 .O% steel fiber for specimens having a/d= 1 .5. The strain of vertical web reinforcements became negative and the horizontal web reinforcements were stretched to yield state for specimens having a/d ratios approach 0.5. The measured load-deformation relationships of reinforced concrete and strains of web reinforcements were compared with the prediction of the softened truss model of steel fiber reinforced concrete proposed by other investigators. Good correlation was found from the comparisons.

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.