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.

A significant proportion of Australian infrastructure is located in a zone that is close to or in direct contact with seawater. At most of these locations, the coastal environment is coupled with high ambient temperatures and large diurnal temperature ranges, conditions that are conducive to promoting corrosion of steel reinforcement in concrete structural elements. Users of concrete are thus always looking for ways to maximize concrete performance for long-term use under these aggressive conditions. The options available in terms of binder systems for concretes in a marine environment have increased in recent years. There are currently available a range of cements and blended cements that include fly ash, slag, and silica fume, which have a place in specifications for marine concrete applications. To provide technical data for potential specifiers and users of such concrete types, a collaborative CSIRO-CSR research and development project was initiated to consider the performance of a range of concretes for marine environments. Concretes considered had a water-binder ratio of 0.35 and included both portland and blended cements. Paper reviews current standards on specifications of concrete for marine environments and goes on to present some recently produced Australian data for different concretes reflecting potential performance. Techniques considered include chloride-ion penetration of concrete based on charge transfer measurements, chloride-ion penetration through concrete, and some mechanical properties of concrete. Conclusions are drawn as to the suitability of certain concrete types under marine conditions.

The Strategic Highway Research Program (SHRP) awarded a contract to North Carolina State University (NCSU) to investigate the use of high-performance concrete (HPC) in highway pavements and bridge structures. The goals of the project were threefold. First, a number of HPC mixtures were developed for highway applications. Second, laboratory testing of the HPC mixtures was conducted. Finally, a number of field test sites were constructed and monitored. Three different classes of HPC were established for this research. These are very early-strength (VES), high-early-strength (HES), and very high-strength (VHS) concrete. Two types of VES and VHS concrete were developed. The VES mixture was developed for use primarily as a rapid repair material where time is critical and cost is a lesser concern. The HES mixture was developed for bridge deck construction where deterioration due to freezing and thawing and steel corrosion is a major problem. The HES mixture can also be used for repair where cost is important and time is a lesser concern. The VHS mixture was developed for use in bridge structures where high-long-term strength is needed rather than rapid strength gain characteristics. Paper summarizes the development of the mixture proportions for the three classes of HPC. Included in the paper are the strength and serviceability requirements for the mixtures. Recommendations are made for adapting the HPC mixtures for local conditions.

One of the techniques proposed to improve the durability performance of concrete in aggressive environments is to use quality concrete. Much research has shown that cement composition also has a significant effect on concrete durability in sulfate-bearing soils/groundwaters and in chloride-corrosive situations. High C 3A cements have been found to be superior in terms of protection against corrosion of reinforcement, although they have a lower sulfate-resistance performance. In many situations, such as marine and Sabkha environments, chlorides and sulfates occur concomitantly and operate against concrete durability simultaneously. This study has been carried out to evaluate the sulfate resistance and chloride penetration performance of high-strength concrete. Two high-strength concrete mixes in the range of 60 to 75 MPa were designed first by using a superplasticized concrete of 0.36 water-cement ratio (w/c) and second by replacing 10 percent cement by silica fume. The control for comparison is a 25 Mpa concrete made with a 0.58 w/c. Type I portland cement has been used to provide higher chloride-binding capacity and, hence, better corrosion protection. A mixed sodium and magnesium sulfate environment has been used to evaluate sulfate resistance. High-strength concrete made with silica fume blending showed the best sulfate resistance in a sodium sulfate environment and the worst performance in a magnesium sulfate environment. Also, the normal 0.58 w/c ratio of 300 kg/m 3 cement content mix showed 1.5 times better performance than the 0.36 w/c ratio 450 kg/m 3 cement factor mix in magnesium sulfate environment. High-strength concrete showed three to four times better performance against chloride penetration compared to normal strength concrete. Use of 10 percent silica fume further improved resistance against chloride penetration.

A full factorial experimental design was used to investigate the effects of the following variables on cylinder strength: end preparation (sulfur capping versus grinding), cylinder size (100 versus 150 mm diameter), type of testing machine (1.33-MN capacity versus 4.45-MN capacity), and nominal stress rate (0.14 versus 0.34 MPa/sec). Two levels of strength were used (45 and 90 Mpa), and three replicates were tested for each run. Specific gravities were measured to check on the consistency of cylinder fabrication. Statistical analyses indicated that all the factors had significant effects on the measured compressive strength. On average, the 100-mm cylinders resulted in about 1.3 percent greater strength, the faster stress rate produced about 2.6 percent greater strength, the ground cylinders were 2.1 percent stronger, and the 1.33-MN testing machine resulted in about 2.3 percent greater strength. There were significant interactions among the factors, so that the effects were greater than the average values for particular factor settings. For example, the effect of end preparation depended on the strength level. For the 45-Mpa concrete, there was no strength difference due to the method of end preparation, but for the 90-MPa concrete, grinding resulted in as much as 6 percent greater strength in certain cases. Analysis of dispersion indicated that the 100-mm cylinders had higher within-test variability, but the differences were not statistically significant. Recommendations for modifications to testing standards are provided.