The Magic of Investigative Petrography: The Practical Basis for Resolving Concrete Problems

Investigative petrography, based upon past and present applications, includes information developed using a broad variety of analytical methods. The analytical data needed to be obtained is initially identified using microscopical evaluations. That initial data, plus subsequently developed data, evaluated in the light of the nature of materials behavior, provides a better understanding of causes of materials performance.

Two case histories are presented which follow analytical investigative procedures used to identify the causes; in one case, of low concrete strengths, and in the other, of extensive cracks and curling of slabs-on-grade.

The low strengths were caused by exposure of the concrete to sub-freezing temperatures. The petrographic studies provided evidence of the early freezing, exonerated other factors, and subsequent studies for admixture contents provided evidence linking the admixture dosage to the freezing phenomenon. The cracks and curling resulted because of interference of a chemical component of an admixture to the timely hydration of the expansive component of Type K shrinkage-compensating cement. The petrographic procedures used to identify the causes of these problems are presented.