Forensic Investigation of Deteriorated Concrete in Plantation East Culverts, City of Benbrook, Texas

Two underground concrete box culverts were installed below ground on Plantation Drive in the City of Benbrook, Texas, in 1991. The culverts consisted of precast segments with case-in-place (CIP) collars/bends. The concrete started deteriorating and spalling at several CIP bend locations as early as 1993. The concrete continued to deteriorate over the subsequent years. An investigation was launched herein to determine the cause and extent of the concrete degradation. The geotechnical investigation involved resistivity imaging, soil boring, and photo-ionic detection for exploring any soil contamination around the culverts that may enhance the concrete deterioration. Visual inspection of the deteriorated concrete helped to examine the clear concrete cover. Concrete cores were taken and tested for strength and deterioration. No soil contamination was observed at the site. The culvert water acidity was neutral. Therefore, the contamination in the underground tunnel/box culvert may not be related to the soil contamination or leakage from sewerage pipes around the culvert areas. The collected concrete core inspection and testing showed that most of the bend concrete is badly deteriorated. Although the strength of some of the more intact bends is acceptable, most of the bend concrete simply does not have sufficient strength, integrity, and ductility to effectively carry the service loads imparted on them. The rebars inside the cores were extensively deteriorated and lost much of their strengths and ductility. The visual inspection showed that the insufficient clear covers were used in the culvert wall and the slab; this was the likely cause of the premature concrete deterioration. On the basis of the investigation performed herein, immediate rehabilitation steps were recommended.