Structural concrete slab systems are common structural members in commercial and industrial building structures. Hardened concrete materials are strong in compression and relatively weak in tension, and are used to withstand compressive loading in structures. Cracks in concrete occur when tensile stress exceeds the strength of concrete in tension. Some factors that may result in cracks in concrete slab include subgrade soil movement, plastic or drying shrinkage, overloading, and poor workmanship. Significant cracks prompt the project stakeholders to question the integrity of the structure and to retain investigation teams to determine the extent of defects or distresses, identify potential causes, and assist in developing a remediation plan.
Non-destructive evaluation (NDE) techniques have been gaining interests in field assessment activities. Properly conducted NDE shortens the time of assessment, saves cost, and provides information that is not visible to human eyes. The authors have served in many projects of structural assessment and realized the lack of knowledge on NDE techniques in the market. It is the intent of this study to discuss the advantages and limitations of using NDE techniques in the assessment of structural slabs. The present study consists of several project case studies of investigating reinforced concrete slab-on-grade systems affected by subgrade soil movement, a reinforced concrete floor slab, a composite steel deck floor exhibiting significant surface cracking, and a reinforced concrete pad foundation subjected to fire damage and overloading. The NDE techniques used in the investigation include:
• Floor relative elevation survey.
• High-frequency ground penetrating radar survey.
• Impulse response test.
• Ultrasonic echo tomography.