Investigation of Inadequate Concrete Covers in a New Bridge Deck Using Ground Penetrating Radar
Transportation Research Board 93rd Annual Meeting
January 12, 2014
Hasan, Istiaque and Yazdani, Nur
The reinforced concrete cast in place deck of the SH114/SH170 Bridge near Roanoke, Texas, was recently completed. The bridge deck is 183 m (600 ft.) long and 12.2 m (40 ft.) wide with four spans. Due to possible construction errors, it was suspected that the concrete cover in the deck did not conform to drawings and specifications approved by the Texas Department of Transportation (TxDOT). So, a full scale non-destructive evaluation of the concrete covers in the deck surface was carried out using a Ground Penetrating Radar (GPR) equipment. A 2.6 GHz frequency ground coupled antenna was used with the GPR for increased data acquisition accuracy within the top portions of the deck. A total of 19 exploratory locations on the deck were identified using the GPR and were drilled to determine the actual clear covers. These results were used to calibrate the GPR readings for the concrete dielectric constant. Taking advantage of the rapid data collection ability of the GPR, the bridge deck was scanned and concrete cover values were determined from the radargram generated from the scan. The estimated covers were plotted on contour maps for each deck span, showing cover value distributions across the bridge deck. The results show that around 48% of the deck areas had inadequate concrete covers below the specified American Association of State highway and Transportation Officials (AASHTO) minimum value of 64 mm (2.5 in.). Moreover, some locations on the deck have excess clear cover ranging from 75 mm – 100 mm (3 in. to 4 in.). Based on the results, significant retrofitting of the bridge deck, such as additional overlay, is recommended before opening it to the traffic.