Because of the limited tensile strength and brittleness of ultra high performance concrete, it was natural for researchers to investigate the use of steel fibers to overcome these deficiencies. The characteristics of each of the three major types of ultra high performance fiber-reinforced concrete are described, and the current state of the research into each type is summarized.

If the dumping height is too large for the construction procedures, mixture, and reinforcement congestion, the most evident defects are honeycombs. To provide a tool to define an acceptable dumping height that will assure that the amount of honeycombing is within a permissible limit, the Concrete Casting Committee of the Instituto del Cemento y del Hormigón de Chile (ICH) developed Technical Specification ET 002-05, “Dumping Height of Concrete when Casting Vertical Elements.” This performance specification allows greater dumping heights that can lead to greater productivity without compromising the quality of the product.

Advocates of mixtures containing well graded combined aggregates argue that such mixtures have optimized packing and minimal voids and therefore minimize the cementitious paste required for a given workability. Opponents of well graded combined aggregates argue that they don’t necessarily lead to optimized performance, but might actually cost more. In an effort to resolve the controversy, a study was conducted at the National Ready Mixed Concrete Association Research Laboratory to determine whether well graded combined aggregates improve aggregate packing density and concrete performance. A summary of the research report is provided in this article.