FPrimeC Solutions Inc. was engaged by an iron and titanium manufacturing facility to perform non-destructive testing and evaluation (NDE) of a concrete slab-on-grade in an industrial building in Sorel-Tracy, QC. According to the client, the existing slab on grade floor structure has been experiencing sudden localized sinkholes and potholes at different locations, most likely due to voids and cavities underneath the slab-on-grade. The objective of this project was to evaluate the condition of the slab-on-grade and advise asset holders where greater chances of subsurface anomalies may occur.
The investigation was conducted in two different steps. Step 1 was non-destructive testing and evaluation of the slab on grade and involved hammer sounding and ground penetrating radar (GPR) to determine the location and extent of potential anomalies. Step 2 was the validation process and was performed by drilling boreholes at different locations to visually understand the subsurface condition, and to determine the depth and severity of potential anomalies (voids and cavities). Using this non-intrusive assessment with minimum intrusive validation, FPrimeC was able to provide accurate maps of potential voids and cavities underneath concrete slabs.
Step 1: Hammer Sounding and Ground Penetrating Radar
Hammer Sounding test was initially performed to identify the locations of potential subsurface anomalies, such as voids and cavities. The acoustic response of the slab was used to develop a primary map of potentially defective areas. Ground Penetrating Rebar GPR scanning using a high frequency equipment was conducted to assess the condition of the subsurface. The GPR scans were helpful in confirming and fine-tuning the results of the sounding map. Learn more about the available methods for scanning voids under slab here.
Step 2: Validation through Borehole Drilling
Eleven boreholes were drilled at different locations across the slab. The condition of the concrete slab, as well as the sub-surface condition was examined at each location. The examination of the boreholes validated the cavities and voids underneath the slab determined by the NDT’s, as their cavities ranged from 10mm to 275mm in depth.