Using Non-destructive Testing to Find Unknown As Built Conditions of a Concrete Retaining Wall | New York, USA
Services Applied by VCS Engineering
Summary
NDT Division performed a non-destructive evaluation of a concrete retaining wall supporting a state highway in Hammondsport, NY. Ground Penetrating Radar (GPR) was used to map the reinforcing details and measure concrete thickness along the full height of the wall. Impact Echo/Pulse Velocity (IE/PV) testing was completed at the top of the wall to determine its total height, including the portion extending below grade. IE/PV testing was also carried out across the wall’s face to collect surface wave velocities and estimate the in-situ concrete compressive strength.
Results showed strong correlation between the IE/PV strength estimates and laboratory compression testing, and GPR confirmed that no steel reinforcement was present in the structure.
Scope
NDT Division was contracted to determine the geometric configuration and overall condition of a concrete retaining wall structure to get a comprehensive assessment if the wall could be preserved. This retaining wall holds up a portion of a state highway in Hammondsport, NY. The wall exhibited signs of deterioration and spalling was visible at/around the pour joints. The owner of the wall had no drawings or plans showing the designed or as-built conditions. The owner wanted NDT Division to determine the existing dimensions and condition of the wall. The required dimensions included: thickness, height, back batter and if any steel reinforcing was present. The owner also wanted to know the integrity/strength of the concrete and to identify any areas of internal cracking or voids that might be present.
NDT Division conducted nondestructive testing with ground penetrating radar (GPR) and impact echo/pulse velocity (IE/PV) equipment to determine the requested dimensions and concrete condition assessment. Using GPR, NDT Division was able to scan the wall to assess the steel reinforcing in the wall and determine the wall thickness over the full height and show the battered slope of the back face. The IE/PV data was also collected from the top to determine the height of the wall. Data to determine the concrete compressive strength was calculated from the surface wave velocities at many locations. NDT Division also used a core drill to extract concrete material samples to be sent to a lab for compressive strength verification testing.
Solution
The overall wall height, thickness and batter was confirmed by the IE/PV testing by measuring the thickness frequencies from the front wall face to the back of the wall. Data was collected along the full height of the wall (top to the bottom). Concrete compressive strength results from the IE/PV testing on the entire wall face correlated well with the lab testing and confirmed weak concrete (less than 3000 PSI) in many locations. During concrete core extraction NDT Corp discovered that the coarse aggregate used in the wall was on average 3” rounded river stone and was not well bonded. This resulted in cores breaking apart shorter than the desired length for compression testing. NDT Division was able to use a larger core barrel to extract proper length cores despite the poorly bonded aggregate. GPR indicated there was no reinforcement in this wall.