The Trump International Hotel and Tower in Chicago pushes the capabilities of high-strength concrete. Self-consolidating concrete up to 16,000 psi was specified. The 92-story, 1134-foot structure (1362 feet including the spire) is the tallest structurally reinforced concrete building in the U.S. Crews topped off the building in August 2008.
One of the highest-strength concretes used in any large-scale commercial application has been concrete attaining a target compressive strength of 19,000 psi in the 58-story, 720-foot Two Union Square in Seattle.
Most authors writing about HSC usually spend an inordinate amount of time mulling over the question, “What is the best term to describe that which is not high-strength concrete?”
This truly has no best answer, and as a result, it is perpetually raised with each new work. Usually the first and most logical choice that comes to mind, the antonym of high is the one ruled out the quickest. Referring to non-high-strength concrete as low-strength concrete, though technically correct, is grammatically appalling.
Low-strength is frequently reserved in the industry to denote failure or deficiency. Following this, in relatively short order come the other choices: lower strength, normal strength, and conventional strength. Other terms I've used in the past have included regular strength and traditional strength, though, needless to say, these were ruled out almost as quickly as low-strength.
Perhaps the principal reason why so much time is spent deliberating this term is in the hope that readers do not come away believing that HSC is some sort of exotic or obscure material, which terms such as “normal” could tend to convey. Commercially available HSC is not new, and is neither exotic nor obscure.
HSC technology has been continually evolving for decades, and it has an extensive record of accomplishment with respect to both its mechanical and durability-enhancing properties. Though HSC may never come close to the volume of conventional-strength concrete produced, significantly more structures would benefit, both economically and technically if it were not perceived as something of an exotic or obscure nature.
After careful and lengthy consideration, the term conventional strength has been adopted to describe the type of concrete most commonly specified for civil and structural applications.High-performance concrete
Provided all performance requirements have been identified and satisfactorily addressed, HSC can be categorized under the much broader term high-performance concrete (HPC). Whether identified as HSC or HPC, there are two requirements both must satisfy. They must be constructible and durable. Just because concrete is strong is no guarantee that it will be durable.
Very often, the terms high-strength and high-performance are used interchangeably, which can make differentiating HSC and HPC a bit confusing. So what are the differences? Why are these terms used interchangeably? Perhaps the source of the confusion is that, in principle, high-strength is not a prerequisite for high-performance. In practice, strength commonly increases when steps are taken to improve most durability-related properties. When steps are taken to inhibit the ingress of injurious substances through reduced permeability, concrete strength increases, However, reducing permeability alone will not ensure durability.
Maybe the most important reason why the terms high-strength and high-performance are commonly used interchangeably is that permeability, generally considered the most important property influencing durability, goes hand-in-hand with strength. Both the coefficient of permeability and compressive strength are proportionally related to the w/b ratio. Decreases in permeability consequentially result in increased strength. There is perhaps another, more important reason why high-strength should not be considered a prerequisite for high-performance. The concrete industry has traditionally used strength as a surrogate for durability. Compared to durability, strength is much easier to measure. In some instances, durability correlates well with strength, particularly in cases where the durability property under consideration is proportional to the coefficient of permeability. In such cases, measures required for enhancing durability also result in higher strength.
In other cases, the opposite holds true; measures taken to produce high-strength can be detrimental to durability. For example, the durability of concrete subjected to cycles of freezing and thawing while saturated or in the presence of deicing agents depends much more on the quality of an entrained air-void system than on strength.