Chapter 4: Chemical deterioration mechanisms

This chapter reviews the range of mechanisms that result in the chemical degradation of concrete. Concrete, if correctly formulated, cast and cured, can endure for millennia in one environment but may completely degrade in a few years or even months in another. Thus, a ‘durable concrete’ is one that can resist the forces that would cause premature deterioration in the particular environment it is exposed to. The assumption that using the right strength, cement content and water-to-cement ratio will ensure that the concrete is durable can be misleading, as it must also possess properties appropriate to its local environment and to the external and internal factors that can influence its ability to resist deterioration. With real-world concrete structures, investigations typically show that several mechanisms act together to produce the observed deterioration, although usually only one is the initiator or the predominant decay mechanism. Specific deterioration types and mechanisms described include weathering and leaching, acid and alkali attack, sulfate attack, delayed ettringite formation, salt attack, alkali-aggregate reaction and corrosion of the steel reinforcement.