Petrographic examination is the definitive method for the measurement of carbonation depth in concrete. However petrographic examination provides much more information than just carbonation depth and can be used to assess the extent of weakening of the concrete as well as the original condition of the concrete.
Historically, an important part of the assessment of the residual strength of concrete containing HAC has been the measurement of its degree of conversion. However the measurement of the degree of conversion of HAC concrete is no longer considered useful as the results cannot be used to form an opinion of the quality of the concrete.
It is important to know the depth of carbonation when assessing the potential for the development of reinforcement corrosion in concrete. The definitive method for the measurement of the depth of carbonation in HAC concrete is petrographically using thin sections.
Petrography can be used to form an opinion of the overall quality of the concrete and also to detect evidence for deterioration as a result of moisture penetration or chemical attack. The electron microprobe is a valuable tool in investigating chemical attack in HAC concrete as the products of many forms of chemical attack in HAC concrete are too fine to identified using the petrological microscope.
Two photomicrographs showing uncarbonated HAC paste on the left side of the field of view and carbonated HAC paste on the right side of the field of view