Samples collected in order to carry out a laboratory-based petrographic examination may be taken from a concrete structure or from a source of raw material such as aggregate, cement, mineral addition or an admixture. They will either have been selected to be representative of the material under investigation as a whole or selected specically to investigate some particular identied feature in the concrete or other material. In either case sufcient material needs to be collected for all the necessary laboratory tests to be carried out.