5.3.2 Ground-Penetrating Radar (GPR

Figure 44. Defect index calculated based on IE dominant peak frequency

5.3.2 Ground-Penetrating Radar (GPR) GPR technology has been implemented to assess concrete quality. GPR can provide a qualitative assessment of concrete condition and describe potential concrete deterioration, delamination, and corrosive environment [63]. The GPR assessment is based on the measurement of attenuation of electromagnetic waves as they propagate through concrete layers. The condition index from the GPR surveys is calculated according to:

GPRindex=

����������×100+����������×70+����������×40+����������������×0 ������������

(12) where ����������, ����������, ����������, and ���������������� = areas with GPR signal attenuation (normalized dB) ranges of > -15, -15 to -17, -17 to -20, and <-20, respectively [64]. ������������ corresponds to the total surveyed area. Figure 45 below plots the variation of condition index for the different rounds of GPR data collection efforts from BEAST and compares it against the performance curve of the representative bridge. While the condition index decreases by the age of the bridge, it should be noted the variation is not significant and only changes between 99% and 100%. In addition, Figure 46 plots the estimation of defect index that was thoroughly discussed in the previous section. The range of defect index variation is somewhere between 16-21% and the trend in the data does not support the increase of defect index versus the increase of deck age. This conclusion was expected given that the level of moisture in the deck was not controlled due to the level of exposed brine solution. Therefore, the GPR results might hold some level of significant variability.

Figure 45. Condition index calculated based on GPR depth-corrected amplitude

Figure 46. Defect index calculated based on GPR depth-corrected amplitude

Alternatively, the GPR technology is able to detect the location of the rebar, resulting in the cover depth and its variation along the bridge length. Such measurements were also made during

the GPR data collection from the BEAST. Figure 47 below plots the estimated defect index for the GPR cover measurements. The results indicate that the increase in the defect index is wellcorrelated with the age of the deck. Figure 48 additionally plots the variation of average cover depth based on the measurements conducted in different rounds of data collections. Except for the first few datapoints (that could accompany some levels of uncertainty due to the level of moisture in the specimen), the results indicate a slight decrease in the estimated cover depth. This phenomenon could be associated with the decrease of cover mainly due to deterioration induced by a live load. No condition index was defined for the GPR – cover maps.

Figure 47. Defect index calculated based on GPR cover depth measurements