ABSTRACT
This chapter examines why engineering materials age and what are the key ageing mechanisms in the context of built infrastructure. Ageing is reflected by responses by individual materials within built components, while contributing to the ageing of the overall infrastructure over a period of time. It explains the mechanisms of ageing and provides the reader relevant sources of background references, which provide greater detail. The mechanisms of ageing are: Physical interaction; Biological; Structural degradation; Chemical; Mechanical; and Electrochemical. A broad range of physical actions degrade engineering materials. Abrasion is caused by solids and/or liquids mechanically rolling or sliding over a material thereby leading to wear. Freeze-thaw leads to damage of porous materials located in cold climates, and it is characterised by saturated water within the capillary pores being exposed above and below the freezing point. Porous materials, including masonry, stone and concrete, are vulnerable to damage due to salt crystallisation in the exposed pores.
