Nondestructive Concrete Characterization System

OBJECTIVE: Develop a small, portable, low power field device that can estimate the strength and thickness, to 6 feet, of reinforced concrete structures and identify and locate metal contained therein. DESCRIPTION: Reinforced concrete structures impede the movement of military personnel in a variety of military missions. Non-destructive evaluation (NDE) of the structural characteristics (e.g., material strength, level of reinforcement, thickness) of these structures is important for calculating the amount of charge that must be placed to breach the structure. NDE remains an application requirement in order for missions to remain stealthy. Several techniques have been considered for NDE of reinforced concrete in order to test for defects and deterioration. Techniques such as ultrasound require a transmitter probe that presents short duration high voltage pulses into piezoelectric crystals, and their expansion produces a pressure pulse that administers a broadband field into the concrete. Such systems can be large, require significant power, and are expensive, rendering them impracticable for tactical applications. Conversely, ground penetrating radar is another NDE technique that has also been used extensively to interrogate concrete that may overcome these deficiencies. Currently there are no methods when combined and simple to use to close this need for breaching. While concrete can withstand significant compressive stresses, its tensile strength is approximately an order of magnitude smaller than the compressive strength. Historically, this issue has been addressed by reinforcing concrete with reinforcing bars, rebar, and/or fibers to improve tensile strength. Recent advances in manufacturing high strength concrete mixes, such as those by Lafarge, have rendered current approaches to assessing strength and thickness of concrete (and thus charge size) less accurate. A simple, low power, small and accurate alternative utilizing ground penetrating radar (GPR) technology is sought. GPR has commonly been used for interrogating the ground in a nondestructive fashion in order to assess the presence of objects of interest (landmines, pipes, IEDs) buried below the surface. There are several geophysical companies who utilize GPR for a variety of interrogation applications, including locating rebar in concrete to aid excavation, location of utilities and pipes, forensics and graveyard surveying, etc. The proposed concept for structural assessment of reinforced concrete must operate in a variety of conditions with high accuracy and rapid analysis time. Systems that leverage currently fielded Army systems are preferred, and a detailed proof of concept plan is critical. PHASE I: Develop the hardware and software design that supports the interrogation technology needed to estimate relevant structural parameters such as reinforced concrete thickness up to six feet, concrete strength over a range of 3,000 to 30,000 psi, density of reinforcement, and presence of fiber reinforcement. In addition, the approach should be able to locate metal substructure. The approach should demonstrate the ability to estimate these parameters in controlled proof-of-concept experiments with an accuracy of one foot in thickness and +/- 3,000 psi in strength over a variety of structures. In addition, the impact of reinforcement additives such as composite or metallic fiber should be assessed and design issues to address any confounding issues should be put forth. Power consumption and estimated system weight must also be addressed and should be within a factor of two of similar Army deployed equipment. The existence of metal objects should be detected and located to =/- one foot on the wall surface and the density of reinforcement and fiber-reinforcement estimated. PHASE II: Develop and field test the proposed system for estimating relevant structural parameters and metal substructure. Optimize the design and algorithms for performance, weight, and power consumption. Develop and engineer hardware and software to meet program goals. Conduct field-testing to validate performance on a variety of representative structures to assess accuracy, time-of-measurement, and identify potential operational limitations of the final hardware. Preference should be given to extending the capability of already deployed Army systems to support multiple functions. PHASE III DUAL USE APPLICATIONS: Describe the "vision" or "end-state" of the research. Include one or more specific Phase III military applications and/or supported S&T or acquisition program as well as the most likely path for transition of the SBIR from research to operational capability. Additionally, the Phase III section must include (a) one or more potential commercial applications OR (b) one or more commercial technology that could be potentially inserted into defense systems as a result of this particular SBIR project. The proposed technology has potential use in numerous applications within the Department of Defense and the commercial sector. The technology could be used for the Department of Homeland Security as well as state and local authorities, and potentially HAZMAT response teams. REFERENCES: 1. ASTM C 1383-04, Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact Echo Method ; 2. Pristov, E., Dalton, W., Piscsalko, G., and Likins, G. Comparison of Impact-Echo with Broadband Input to Determine Concrete Thickness. Proc. NDE Conf. on Civil Engin., August, 2006; 3. www.geophysical.com; 4. www.groundradarcarolina.com KEYWORDS: Ground Penetrating Radar, Concrete Characterization, IED Detection, Mine Detection