The 350,000-sq-ft concrete slab-on-ground at a facility owned by Industrial Development International (IDI) was designed with a thickness of 7 in. However, Pond, Robinson, and Associates (a firm retained by a potential buyer) had removed a number of cores that indicated an as-built thickness of 6 in. Investigators also observed voids beneath the floor at the core locations. A local testing and engineering firm reported that the floor was constructed on fill material measuring between 0 and 26 ft deep. Control joints were installed spaced about 17 ft in both directions. Some cracking had been attributed to loading by tilt-up crane outriggers. A sale of the property was scheduled within weeks of removing the initial cores, and concerns were raised about the thickness of the slab and stability of the base.
Pond, Robinson, and Associates hired CTLGroup to determine the overall slab thickness, presence of sub-slab voids, bearing capacity of the slab subbase, and potential differential settlement of the non-uniformly thick base material.
CTLGroup sent a team of engineers to the site within a week. They used Ground Penetrating Radar (GPR) to map the thickness of the entire floor slab nondestructively. The map indicated areas of significant underthickness. The team also located possible voids attributed to slab curling, and subcontracted with a local geotechnical firm to determine the bearing capacity of the base material.
Based on general site observations, CTLGroup was able to recommend additional joint treatment that would save the buyer an estimated $80,000. The site evaluation was completed within two days, and a verbal report was provided the day after returning to the office.