Durability of concrete — Degradation phenomena involving detrimental chemical reactions

Abstract

While interacting with its service environment, concrete often undergoes significant alterations that often have significant adverse consequences on its engineering properties. As a result, the durability of hydrated cement systems and their constituent phases has received significant attention from scientists and engineers. Cement paste deterioration by detrimental chemical reactions is discussed. First, the mechanisms that govern the transport of ions, moisture and gas are described. Then, different chemical degradation phenomena are reviewed. Microstructural alterations resulting from exposure to chlorides and carbon dioxide are discussed. Sulfate attack from external sources is described including processes resulting in the formation of ettringite and thaumasite. The mineralogy of Portland cement is sensitive to temperature and thermal cycling, particularly during the early hydration period.

Introduction

The good durability of Portland cement compositions in normal service environments has long been recognized. However, cements and concretes made with cement binders can be attacked and, as a result, exhibit a reduced service life. Most of the adverse conditions are recognized from experience and have been the subject of numerous examinations of field concretes as well as laboratory studies. Not surprisingly, research and testing have focused on the areas of underperformance.

The concept of a “service life” is not new. The ancient world used stone, brick, tile and, from Roman times onwards, concrete, because of their permanence. Today, cement and Portland cement concrete are widely used and comprise the world's major structural material.

Although modern cements are much improved in properties, the high and rising cost of construction and the economic cost and disruption associated with replacement and renewal, especially of major infrastructure facilities, placed new pressures on ensuring durable construction. Again, these pressures are not new but have intensified particularly in view of the relatively high carbon penalty associated with cement production and use.

The perceived problems arising from limited performance have long been the subject of investigation. Most of this has been empirical in nature although often employing sophisticated statistical controls. We have also seen the rise of modeling, as a way of predicting durability and compressing the time factor without distortion of the underlying mechanisms.

Thus the art and science of durability are in a state of great activity with the development of a variety of approaches. This is healthy. But we have so much of significance to report that this review can only capture selected aspects of current research.