Fig 1 Sources of durability problems (ref 2). Fig 2 Typical concrete durability problems (ref 3). Fig 3 Variations of concrete quality across a section (ref 4).

Concrete serves in all environments, each of which has its own particular set of effects on concrete and/or reinforcement. Deterioration is inevitable but the engineer is concerned with the rate at which concrete degrades. This can be defined as,

This suggests that the estimation of potential durability requires a knowledge of the concrete characteristics and of the exposure environment. The factors affecting concrete durability are shown in Figure 4. These factors are diverse and extensive and more often than not several will occur concurrently. Overall, these factors may be divided into four broad categories:

1. Internal material failure, eg ASR, HAC conversion. 2. Fluid and/or ion ingress from the environment which may attack concrete and/or

reinforcement, eg chloride ingress, carbonation, sulphate attack. 3. Direct wear and impact, eg abrasion, cavitation. 4. Mechanical disruption due to excessive strains, eg thermal load, flexural cracking,

wetting and drying, frost action.