Non-destructive evaluation techniques can be of significant value in historic preservation projects.

PRESERVATION
Tech Notes

Non-destructive Evaluation Techniques for Masonry Construction

Marilyn E. Kaplan
Preservation Architecture

Marie Ennis, P.E.
Einhorn Yaffee Prescott
Architecture & Engineering, P.C.

Edmund P. Meade, P.E.
Robert Silman Associates, P.C.

Introduction

   While non-destructive evaluation (NDE) techniques have been applied to historic preservation projects in Europe as well as in other countries for many years, their use in the United States has been relatively limited. Most of the American literature about NDE is in the fields of manufacturing and civil engineering works. In manufacturing, for example, dye penetrant tests, x-ray analysis, and ultrasonic techniques aid the evaluation of welds in pipes and pressure vessels. Civil engineers use impact echo testing for the evaluation of concrete bridge decks; ultrasonic methods to determine steel thicknesses in other bridge elements; and electromagnetic equipment to verify the placement of reinforcing bars in concrete structures.

   NDE techniques now need to be recognized for their potential value to engineers and architects who work on historic structures. Historic construction hidden from view may be successfully understood and conditions assessed while minimizing destructive probe work. The data obtained from conventional probe techniques are generally more limited in accuracy because the data is collected at discrete locations and must be interpolated to estimate the conditions at points between the probes. While it may not be possible to eliminate completely the use of conventional methods to confirm data, the amount of invasive work can be minimized by the implementation of NDE within historic preservation projects.

A variety of NDE techniques are available for use on historic masonry structures.

   NDE techniques are particularly useful in historic preservation because original structural drawings are often unavailable or are deficient in detail and do not reflect "as built" conditions. The location and size of framing members and load-bearing elements can usually be determined through NDE. The condition and integrity of a building's structural members can also be determined with the aid of NDE techniques, thus avoiding destructive probe methods, such as test pits, material removal, and core drilling. This is important since conventional probing not only destroys historic fabric, it can be disruptive to the users of the building, and often requires some degree of repair work to reinstate the previous appearance and integrity of the affected building component.

   NDE available for use on historic masonry structures include radar (also referred to as impulse radar), impact echo, ultrasonic pulse velocity, spectral analysis of surface waves, electromagnetic detection, infrared thermography and fiber optics. Recent work on the New York State Capitol and on Whig Hall at Princeton University (and detailed in the two case studies that follow) demonstrates the practical application of NDE in historic preservation projects

New York State Capitol Case Study