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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.

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.

The combined use of chemical and mineral admixtures has resulted in a new generation of concrete called high-performance concrete (HPC). Understanding the roles of mineral admixtures, such as silica fume, fly ash, and slag depends on in-depth microstructural investigation of HPC at different ages. What is of major interest concerning these materials is their contrasting hydraulic behavior. Whereas silica fume and fly ash are pozzolanic, slag is strictly cementitious. The early strength of concrete increases when silica fume is incorporated, but the activity of slag and fly ash starts much later, and therefore, manifestation of changes in concrete properties, such as strength enhancement, also appears to be delayed. It is in this light that the roles of these admixtures, both individually and in combination, are described in terms of the development of HPC moisture.

Report presents the data on the effects of silica fume on mechanical and durability-related properties of high-strength concrete. High-strength concrete had a compressive strength in the range of 90 to 100 MPa. The compressive strength of high-strength concrete containing 8 percent silica fume was 25 to 30 percent higher than that of a corresponding concrete without silica fume. Both the splitting tensile strength and the modulus of elasticity of high-strength concrete increased as the compressive strength increased, but at a slower rate. The pore structure both in the cement paste and at the cement paste-aggregate interface in high-strength concrete containing 8 percent silica fume was very dense and homogenous due to the microfiller and pozzolanic effect of silica fume, leading to an improvement of the bond between cement paste and aggregates. Durability-related properties such as the chloride-ion permeability, the resistance to freezing-thawing, and the depth of carbonation of high-strength concrete with and without silica fume were also investigated with a special interest in the influence of curing condition at early ages on their properties. From the results, it was found that the use of silica fume in high-strength concrete led to a significant improvement of chloride-ion permeability, and no negative influence on the carbonation. However, the resistance of non-air-entrained high-strength concrete with and without silica fume to the freezing and thawing cycles was very sensitive to the lack of moist curing at early ages, and a poorly cured nonAE high-strength concrete containing 8 percent silica fume deteriorated more seriously.

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.