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GPR bridge investigation

Reading bridge over river Thames

GPR is ideal as an NDT survey and investigation method for the investigation of bridge structures. It can be used to map reinforcement detail, locate post-tensioned tendons, determine general construction detail, thickness of construction and much more...

Objectives

The purpose of the investigation was to determine the reinforcement details (concrete cover, bar type and diameter and bar arrangement, spacing and cover) within the elements of the bridge including the road deck, main arch beams, transverse beams and longitudinal beams

Survey methods

Survey, testing and investigation methods included:

  • Ground Penetrating Radar (GPR) scanning of the various structural concrete elements. A GSSI SIR 3000 Ground Penetrating Radar system was used with 1.5GHz and 2.0GHz Palm antennas.
  • Breakouts were undertaken to establish reinforcement detail (bar type and diameter) and reinforcement distribution where GPR data was inconclusive.
  • Concrete core specimens were extracted, prepared, detailed, photographed and tested for strength and density in accordance with BS EN 12504-1:2009, BS 1881:Part 120:1983 (withdrawn), BS EN 12390-3:2009 and BS EN 12390-7:2009.

Survey findings

The reinforcement details of the bridge for all elements surveyed was successfully determined.
The main advantages of using GPR rather than more traditional methods such as Cover Meter or Ferroscan are:

  • Greater depth penetration
  • Better resolution
  • Ability to (typically) resolve 2 layers of reinforcement
  • Detection of non-metallic objects such as layer interfaces
  • Speed of site data collection

It is not possible to provide full details of all the results here, however the following images illustrate the capabilities and advantages of using GPR for Bridge Investigation surveys.

Reading Bridge - main arch beam

Reading Bridge - main arch beam

Concrete breakout to expose reinforcing steel

Concrete breakout to expose reinforcing steel and confirm GPR results

Concrete core

Concrete core extracted for laboratory testing

GPR radargrams

GPR radargram extracts, annotated to show detected features