Methods and Recommendations For Concrete Sampling

Petrographic data typically include: degree of cement hydration, estimation of water-cement ratio, extent of paste carbonation, presence and estimation of amount of pozzolans, extent of reinforcement corrosion, evidence of alkali-aggregate reaction, sulfate attack, or other chemical alteration, identification of potentially reactive aggregates, evidence of improper finishing, estimation of air content by comparison with known standards, evidence of early freezing, causes of cracking, premature finishing, and other items.

 

Data are derived from polished slabs, thin sections (15-25 microns thick), powder mounts, and fracture surfaces studied microscopically.

 

Nominal three- to four-inch (76.2-101.6mm) diameter cores are recommended. Where possible the samples should represent the range of material conditions, typically from severely deteriorated to relatively undamaged areas nearby.

 

Companion cores are necessary for chemical tests such as cement and water contents (ASTM C 1084), chlorides, sulfates, infrared spectroscopy, each at additional charges.

 

The petrographic report commonly includes a discussion of the principal findings and conclusions, illustrated with color photomicrographs, and data forms. An audio-video tape of the microscopical findings can be prepared if requested. Fluorescent epoxy is used for microcrack detection. Multiple-sample prices may apply to samples from the same mix design and source. Turnaround time is approximately three to four weeks depending on the number of samples and workload.

 


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