Investigation of concrete mix variations and environmental conditions on defect detection ability using GPR S. Yehia a,n , N. Qaddoumi b , S. Farrag c , L. Hamzeh c a Department of Civil Engineering, American university of Sharjah, Sharjah, United Arab Emirates b Department of Electrical Engineering, American university of Sharjah, Sharjah, United Arab Emirates c American university of Sharjah, Sharjah, United Arab Emirates article info Article history: Received 7 August 2013 Received in revised form 10 March 2014 Accepted 16 March 2014 Available online 3 April 2014 Keywords: Bridge defects Dielectric constant Ground penetrating radar Mix variations abstract This paper presents an experimental investigation to evaluate the effects of mix variations, changes in temperature, and concrete maturity on defect detection ability using Ground Penetrating Radar (GPR) technique. Sixteen concrete specimens were prepared, eight of them with simulated bridge deck defects. Concrete type, defect type, size, and location were the parameters considered in the evaluation. Most defects were detectable by GPR under different environmental conditions in the different mixes. It was observed that defects with radius-to-depth ratio (R/d) as small as 0.15 can be detected. In all mixes, the detectable defects were visible at early and late concrete age. However, in lightweight concrete mix, defects were not detectable until 3 months after casting concrete. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Bridges are among the main elements in transportation systems that require continuous monitoring and maintenance. Concrete bridge decks are prone to deterioration, and therefore require frequent condition assessment. Typically, inspection processes rely on visual inspection of a facility, which is based on inspectors' experience and judgment. This is most likely inaccurate, especially judging the existence of sub-surface defects. In fact, historical evidence shows that bridge deterioration occurs mainly due to the formation and propagation of sub-surface defects [1–5]. Such defects can develop due to over-stressing, creep, fatigue, corrosion, or thermal expansion. Moreover, it is impractical to rely on core extractions along the span of the bridge since it is time consuming and labor intensive and might require bridge closure, significantly interrupting traffic, especially if it is a vital bridge. In addition, core extraction provides localized sub- surface information, and they may not necessarily represent informa- tion about an entire bridge. Therefore, Non-Destructive Testing (NDT) techniques provide an efficient and feasible method to detect defects in bridges in a quick manner as opposed to visual inspection and core extractions. Moreover, they can monitor the service life of bridges and indicate if immediate intervention is necessary. Several research efforts showed that the Ground Penetrating Radar (GPR) has a potential to be adopted versus other non-destructive techniques [3,6–9]. GPR proves to be an effective tool for accurate detection of bridge deck defects and it has been used in several applications [2,10– 20]. For instance, GPR could be applied to help detect deformation and corrosion [21]. In addition, it can help detect delaminated concrete layers, location of steel rebars, depths of cracks, and concrete cover thickness as well as asphalt density [22,23]. Apart from bridges, it can help detect leakage for pipes buried in soils [24]. There are several advantages to the use of GPR: fast, portable, safely applied and does not require safety precautions, and also does not require closure of the test location to carry out the test for security and health purposes unlike radioactive methods [10,11]. However, there are few limitations to the use of GPR: the results obtained by GPR are complex and not easy to interpret therefore training is required to be able to interpret the results. In certain cases, it is difficult to interpret the return signal, and destructive methods such as coring or drilling might be needed to help interpret the information [25]. There are several research efforts related to the application of GPR application as a NDT technique to assess concrete bridge conditions, for different structural elements. While most of the research efforts are devoted to defect detection, there is a need to thoroughly investigate the effect of material and environ- mental conditions variations on GPR performance. Thus, the current study investigates the effect of concrete mix variations and environmental conditions on concrete bridge deck defects detection using GPR. Several defects with different size and depth combinations were simulated and scanned. Moreover, the Effective Medium Theory (EMT) multi-phase composite model was used to estimate the dielectric constant of each concrete Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ndteint NDT&E International http://dx.doi.org/10.1016/j.ndteint.2014.03.006 0963-8695/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: syehia@aus.edu (S. Yehia). NDT&E International 65 (2014) 35–46