You are here

Nondestructive Evaluation (NDE)-based Condition Assessment of Sub-surface Concrete with Limited Access

Description:

OBJECTIVE: Develop and demonstrate a man-portable capability to rapidly assess the condition of concrete with reinforcing bars and wire that encases on sides and bottom of an in-ground large scale box-like steel structure with access to only the interior surfaces. Detect typical failure modes, such as cracking / spalling of the concrete, corrosion of the rebar, and related degradation modes for the concrete. The thickness of the concrete is typically on the order of 6 inches. The concrete is located behind an approximately 0.5” steel liner and there is no direct access to the other surface as it is sub-surface, typically under local soil with limited barrier between the two. There is access to the internal box-like structure for placing sensors and other related equipment, provided it is portable and can be removed between assessments. In addition to assessing the condition of the concrete, the approach could assess the moisture/temperature content along the exterior of the concrete provide the information can be directly correlated to the assessment and potential degradation of the concrete. For this to occur, the methods how these data and conditions are correlated must be systematically described. This approach will assess and analyze any trends in the material degradation as a function of spatial location and time of the assessment. A final configuration of the approach includes the ability to generate reports automatically via a simplified or generic interface for simple translation into a digital data storage system. 

DESCRIPTION: The Air Force has storage systems that are capable of securely storing items in an underground vault. Some of the storage systems have been in the ground for over 20 years and have experienced variable temperature and/or humidity environments. The storage system includes a large area steel box that is lined along its exterior with concrete. Access to the interior of the structure is possible by removal of the lid of the box and there relatively simple access to all internal surfaces of the steel box. External access to the structure is not possible. Currently, there is no capability to rapidly assess the condition of the concrete as there is no external access to the concrete and it is hidden from visual view by the steel. The objective is to develop an NDE-based system that can be placed inside the steel liner and provide the capability to detect materials degradation in the concrete, such as cracking, spalling, and corrosion of the rebar. There is no pre-determined method to be used and all options are open to consideration. If ionizing radiation methods are used, including neutron-based methods that are sensitive to water, safety aspect and portability aspect relative to the structure of interest needs to be addressed. This approach should be for the four walls of the vault as well as the concrete floor material. Note that at a few locations and typically no more than once per each wall it is possible to core through the concrete to place a source or detector in the soil outside of the vault without digging down around the vault. However, this access cannot be assumed to be possible at all locations. Alternative approaches are being considered, such as the use of environmental monitoring devices that can be placed into the soil next to the concrete to infer the presence of damage from monitoring the soil conditions, such as humidity and temperature. For these indirect approaches, there must be a viable method to establish the link between the condition of the soil as a function of time and the degradation of the concrete. In addition, there is a desire to map any detected materials degradation as a function of location and to track any changes as a function of time. The preferred approach generates digital data that can be stored and exported via a neutral format to enable its translation into a digital data storage system. 

PHASE I: Phase I shall show the feasibility of an NDE-based system to detect degradation of concrete with a capability to determine the presence of corrosion in 20 percent (objective) / 10 percent (threshold) of all rebar in the concrete (assume 6 inch spacing of the rebar). Detect a volume fraction of 10 percent (objective) / 5 percent (threshold) of volume fraction of cracks in the through-thickness direction of the total volume of concrete. Detect the presence of spalling that removed 10 percent (objective) / 5 percent (threshold) of the total through-thickness of the concrete. The total area of coverage of all the concrete volume should be 100 percent (objective) / 70 percent (threshold). Note that it is possible to core through the concrete to outside of the vault at a maximum of one location per wall. Modeling can be used to support the feasibility demonstration as needed. The approach must be demonstrated on representative damage found in concrete. The technical approach must show potential to assess 800 square feet of concrete that is 6 inches thick in 4 hours or less. The technical approach must address weight and access issues to place the assessment system into the desired locations to enable that assessment to be performed in the desired time allocation. The system must include an approach for spatially mapping the location of concrete degradation and storing this information via an automated reporting function that is exportable in a neutral data format. 

PHASE II: Phase II shall demonstrate a prototype system that can meet the intent required for Phase I and demonstrate the integrated concrete degradation tracking system with an automated reporting capability. It is anticipated that final demonstration will occur at a government facility to be determined during Phase I to ensure the system can meet all required performance parameters in a representative working environment. In addition, the system must be shown to be operated by an Airmen with application specific training with the objective of minimizing the overall amount of specialized training to use the system. 

PHASE III: Similar storage systems with limited access exist in analogous Military and commercial structures. The desired capability will have applications to assess the presence of concrete degradation in similar liners and related geometric configurations in a rapid and quantitative manner. 

REFERENCES: 

1: V. M. Malhotra and N.J. Carino, eds., Handbook on Nondestructive Testing of Concrete, 2nd Ed, ASTM International, CRC Press, New York, 2003

2:  R.J. Wheen, "Nondestructive Testing of Concrete," Build. Sci., Vol. 9, 157, Pergamon Press

3:  J. Hola, K. Schabowicz, "State-of-the-art non-destructive methods for diagnostic testing of building structures – anticipated development trends," Archives of Civil and Mechanical Engineering, Vol. X, 3, 5, (2010).

4:  Ryzewski, K., Herringer, S., Bilheux, H., Walker, L., Sheldon, B., Voisin, S., . . . Finocchiaro, V. (2013). Neutron Imaging of Archaeological Bronzes at the Oak Ridge National Laboratory. Physics Procedia, 43, 343-351. doi:10.1016/j.phpro.2013.03.041

KEYWORDS: Neutron Tomography, Neutron Radiographs, Aging And Surveillance, Steel, Concrete 

CONTACT(S): 

Dr. Eric A. Lindgren (AFRL/RXCA) 

(312) 785-6994 

eric.lindgren@us.af.mil 

US Flag An Official Website of the United States Government