Baseline Condition Assessment...

Baseline condition assessment is not a routinely practiced form of quality assurance; however, it is truly the only way to compare the overall as-built condition of a structure to its future condition at various stages during its life.  One way to establish a baseline condition where "as-built factors" (variables in materials and workmanship that often hamper or adversely affect the accurate diagnosis of the condition of a structure) can be eliminated or minimized from consideration during a future evaluation is to perform measurements on a new structure identical to those that will be used for primary "screening" in the future to diagnose its overall condition. 

To establish a baseline condition assessment, only nondestructive evaluations are of value, and only those that continuously sample the deck along every centimer or meter of its length and width in the manner highlighted above warrant consideration.  That leaves only "full-coverage" methods, such as GPR, SASW and impact-echo, infrared (IR) thermography, or electrochemical analyses as candidates for this approach. 

GPR will accurately measure initial presence, pattern, and density of the reinforcement layout, including cover (depth) of reinforcement and any overlay properties.  Initial data can very easily be collected in such a manner that it will be identical in scope to data collected during a future deterioration-mapping process.  Additionally, it will provide repeatable and accurate condition assessment results in a more consistent fashion than any other NDT method at any stage of the life of a structure.  Collecting the data is rapid, fully nondestructive, and straightforward once an established methodology is developed and adhered to; the data can be obtained on decks with or without overlays that protect the concrete surface to establish their effect on its initial and future condition states.

When factoring in economics, objective capability and repeatability of the measurement, effective deck coverage, and ability to collect the baseline data without the absolute need for other NDT or destructive sampling, GPR is the only sensible instrument to use for this screening process.  It may be advantageous, however, to complement the GPR screening with diagnostic evaluations of a baseline nature in regions where the GPR or past experience reveals conditions (reinforcement depth, variations in depth and layout, or other heterogeneities not designed into the structure) typically indicative of potential problems in the future.  Those targeted areas can be measured, and the data obtained can be compared with future information gathered from those precise locations to supplement, verify, or otherwise improve a future GPR-based condition assessment