Solomon Solis-Cohen Elementary School Freeze Damage Investigation, Philadelphia, Pennsylvania
Overview: Surface cracking was observed on recently poured slab-on-deck concrete at the Solomon Solis-Cohen Elementary School in Philadelphia, Pennsylvania. GeoStructures performed petrographic laboratory analysis to characterize the extent of the cracking and to confirm whether or not the concrete was damaged by freezing weather conditions during curing.
Highlights & Related Services:
Core samples, both within and outside of the damaged zone, were obtained for comparative analysis. While surface observations suggested the crack systems to be hairline and shallow, polished thin sections oriented normal to the fracture system suggested otherwise.
Petrographic investigation revealed that the cracks traveled the entire depth of the core, thinning out to sub-millimeter thicknesses when they intersected layers of coarse aggregate. It was also observed that the crack systems were limited to the cement paste, migrating around particles of aggregate.
Despite the observed cracking, petrographic analysis did not reveal any other microstructural defects expected with freeze-damage. Instead, the observed system of cracking occurred around good-quality aggregate and within good-quality cement paste. This behavior is consistent with ‘thermal cracking’—differential stresses in the concrete slab as a result of warmer temperatures from below and colder temperatures on the unprotected surface— that which aligned with the history of site conditions.
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