International Concrete Abstracts Portal

Sixteen agencies of the U.S. federal government have developed an interagency proposal for promoting the use of high-performance concrete and other materials for use in the nation's infrastructure. They are working jointly with the Civil Engineering Research Foundation (CERF) to enlist private sector support for sponsoring a research and development program aimed at getting the materials into use. CERF is drawing upon the technical community, such as that in ACI, to define the various research needs and studies that will lead to materials acceptance. Materials other than concrete are addressed in other parts of the total program. Workshops were held in the spring and fall of 1993 to develop schedules and priorities. A tentative cost for the concrete program is approximately $200 million over 10 years, which includes some technology transfer and which would be expected to be matched by some private sector funding.

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 use of high-strength lightweight concrete (HSLWC) in offshore oil and gas platforms is becoming more common. The constant wave action on these structures imposes continual fatigue loading on the concrete. Paper reviews previous research on both compressive and flexural fatigue behavior of HSLWC. The fatigue behavior of HSLWC is comparable or somewhat better than high-strength normal-density concrete (HSNDC) tested under the same conditions. The cyclic strain behavior of HSLWC is significantly different than for HSNDC and there is little change in strain behavior with increasing cycles of load until failure occurs. The fatigue life is reduced when the concrete is tested in submerged conditions. There is no significant difference between the S-N curves for reinforced and nonreinforced concrete. The mechanism that causes HSLWC to have comparable or better performance than HSNDC is attributed to the improved microstructure of the matrix-aggregate interface. This improvement reduces microcracking that typically leads to fatigue damage. The effect of crack blocking by sea salt depositions is discussed.

A 4-year study, conducted by a consortium of three universities, on the use of high-performance concrete in highway applications was recently completed. A major goal of this research project was to determine if high-performance concrete mixes could be successfully produced in the field. In addition, an evaluation was to be made of the long-term performance of this concrete under field service conditions. Field installations were constructed in five states for this purpose. Paper provides potential users of high-performance concrete with general recommendations and guidelines for production and placement.

Recently, there has been a great demand for high-quality concrete and concrete structures with high performance. In this context, silica fume is one of the most remarkable mineral admixtures that can give concrete high performance, such as high workability, strength, and durability. However, it is unclear as to the types of form silica fume takes in concrete, mortar, and cement paste. Some researchers point out that silica fume may be in high agglomeration. Therefore, it is very important to disperse silica fume in concrete effectively to get high-performance concrete. Consequently, this paper deals with the effect of physical treatment (ultrasonic homogenizer) and chemical treatment (superplasticizer) of silica fume on the properties of mortar. In this study, different silica fumes were used, one Japanese and five imported. The investigated properties of mortar were workability (flow values), compressive strength, and total pore volume. The study resulted in the following conclusions: 1) Silica fumes in the Japanese market were highly agglomerated in the natural state. This agglomeration of silica fume can be broken up by using some treatment methods, such as ultrasonic homogenizer and superplasticizer. 2) Physical treatment (ultrasonic homogenizer) before mixing mortar was useful to improve compressive strength and to decrease total pore volume of mortar containing silica fume. The use of superplasticizer could result in highly workable mortar. 3) The effectiveness of ultrasonic homogenizer treatment and that of superplasticizer treatment are different.