Core drilling remains the gold standard for verifying in-situ concrete strength. This article covers the complete workflow: sample extraction with diamond-tipped coring bits, laboratory compressive strength testing, and petrographic analysis for aggregate distribution.

We present data from a 12-story commercial building where core tests revealed a 15% strength deficit in upper-floor columns. The analysis led to a revised structural load plan and a targeted carbon-fiber wrapping retrofit. Compliance reporting requirements per ACI 318 are also outlined.

The extraction phase used 100 mm diameter diamond-tipped bits with continuous water cooling to minimize micro-cracking. Each core was logged for depth, orientation, and visible defects before being transported in sealed, padded containers. Laboratory testing followed ASTM C42 procedures, with moisture conditioning and end-grinding prior to compressive loading.

Petrographic examination of thin sections from the upper-floor cores showed uneven aggregate distribution and localized voids — consistent with poor consolidation during original placement. The 15% strength deficit compared to design specifications triggered a full structural reassessment. Our team modeled the reduced capacity and identified six columns requiring retrofit. Carbon-fiber wrapping was selected for its minimal added weight and rapid installation.

The final compliance report included core logs, stress-strain curves, petrographic micrographs, and a signed statement of findings per ACI 318-19 Section 5.6.5. The building owner submitted the report to the local building authority, and the retrofit was completed within the project schedule.