ABSTRACT
There are many reasons why a concrete structure may crack. It is, however, only rarely that AAR will be the cause of cracking in building, retaining or bridge structures. If founded on soft to firm clay or on loose to medium dense silt or sand, differential settlement is often the cause of structural cracking. Settlement may also cause cracking if the structure is founded on poorly, or unevenly compacted fill, or partly in cut and partly on fill. In semi-arid to arid climatic zones, cracking may result from differential expansion (or heave) of desiccated clays or clayey soils. Another cause of cracking could be differential shrinkage caused by the abstraction of water from the foundation soil by nearby vegetation, or swelling by the local addition of water by irrigation of nearby vegetation. In seismically active areas of the world, cracking may originate from seismic accelerations. A similar range of sources of movement could cause cracking in soil or water retaining structures, or in concrete structural pavements. Cracking could also be the result of plastic and/or drying shrinkage of the concrete, thermal contraction or frost attack.
