Concrete petrography

Concrete petrography is most commonly carried out using an optical microscope to examine thin sections of concrete.

Thin-section concrete petrography is most suited to general examinations of concrete to determine aggregate type and to estimate the original water-cement ratio of the concrete and the overall mix proportions. Carbonation, sulfate attack and alkali-silica reaction are among the processes which can be readily identified using thin-section petrography.

One of the most useful applications of thin-section petrography is in the examination of aggregates to determine their susceptibility to alkali-silica reaction.

Thin section of concrete.

Other building materials

In addition to concrete, thin-section microscopy is used in the examination of a wide range of other building materials, including mortars, stone and brick. For example, sensitive restoration of old buildings requires the use of materials which are a close match with the originals. Thin-section microscopy is used to match sand for use in lime mortars and to match stone, so that colour and texture match the original as closely as possible. Sometimes, these techniques can be used to identify the actual source of the original material.

Thin section of concrete under oblique polars: the aggregate particle at the right is a chert particle (C) which has undergone alkali-silica reaction. Cracks containing alkali-silica gel extend from the chert into the cement paste (arrowed).

Concrete: concrete petrography / concrete by SEM / cement / chromium (VI)