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A major driving force for specification development, whether for a cement or other material, is a need for enhanced and more predictable performance. A prescriptive specification reduces the risk of poor performance by keeping the composition and other conveniently measurable characteristics of a product close to those of a product which has performed well. Although it is harder to develop and apply, a performance specification can be a valuable complement to a prescriptive one; apart from being less restrictive, its development focuses attention explicitly on the definition and the measurement of performance.
Neither prescriptive nor performance specifications necessarily require scientific understanding of factors affecting performance, and so a third approach is proposed—a predictive specification based on scientific understanding. In the case of cement and concrete, it can be foreseen as a result of the continued strengthening of the materials science base of the technology combined with developments in computer simulation of the behavior of cementitious systems. While these developments arc taking place, improvements must continue to be sought in the prescriptive and performance specifications to make sure they are as good as they can be. The desired improvements and the research needed to achieve them must be defined, and support for the research must be provided. For the near term, some suggestions for improving the existing portland cement specifications, ASTM C 150, are offered. They concern minimum strength levels, strength uniformity, and improvement of compound composition calculations.
Openaka Corp., Inc., Denver, CO
National Institute of Standards and Technology, Gaithersburg, MD
Stock #: CCA10596J