Durability and testing – Physical processes

Abstract

Concrete is well known to be strong in compression but weak in flexion and tension. However, by the use of steel reinforcing, often in combination with techniques such as pretensioning, and through appropriate structural engineering design methodologies, it is possible to compensate for this weakness by ensuring that the binder and aggregate of the concrete are subjected to minimal tensile load. This means that the relationship between compressive strength, flexural strength and other mechanical properties of concrete is used as an essential basis for civil and structural engineering design purposes. In practice, and with the current almost-universal use of Portland cement-based concretes in civil infrastructure applications, many of these relationships are codified in standards as empirical power-law relationships involving the 28-day compressive strength of the material, sometimes as the sole property used in the predictive equations or sometimes along with a small number of additional physical parameters. For example, the American Concrete Institute [1] specifies the prediction of elastic modulus as a function of compressive strength and concrete density, but an equation solely based on compressive strength is also provided, and is probably more widely used in practice. More sophisticated and more detailed theoretical models, or empirical correlations involving larger numbers of parameters, are often published in the academic literature, but are not in widespread application. An excellent discussion of phenomena and models for Portland cement concrete is presented by Neville [2], and the reader is referred to that text for further information.