Track 3: Conservation of modern and post-modern heritage
New nondestructive evaluation equipment, approaches, and analytical techniques are being developed to complement current condition assessment technology. Several new methods for diagnosing material distress and as-built conditions will be presented,providing a brief overview of each including current status of the technology, applications, and typical results. Some of these techniques are currently available for use, and others are reaching final development stages.
New equipment for ultrasonic imaging came on the market in early 2017. The transducer array system uses ultrasonic pulse echo technology to create a 2-dimensional image of subsurface conditions in concrete, stone, and other building materials. This method requires only single-sided access and has proven capable of locating subsurface cracks, delaminations, voids, and other distress in historic concrete and stone.
Conventional radar systems are limited to discrete microwave frequencies at each scan. Several manufacturers have developed multifrequency or broadband radar systems, combining good penetration of low frequency signals with enhanced resolution of high frequency signals with a single scan. These systems are useful for evaluating distress and other subsurface conditions in mass historic brick and stone masonry construction.
Infrared thermography has been used for several decades to image temperature distributions at building surfaces as an indicator of subsurface conditions and moisture. Data is typically presented as a series of discrete planar images, related to position on the building using companion visible light photographs. A new visualization approach we are calling infragrammetry maps infrared images onto surface models developed using standard photogrammetric techniques. The method has been used for art conservation for several years and has recently been applied to building conservation. Results permit users to interact with 3D surface temperature models, simplifying interpretation and cross-correlation with other methods.
The presenter has been working with researchers at the University of Nebraska – Omaha on a project to develop a new method for evaluating reinforcement corrosion in concrete construction. The technique introduces ultrasonic waves into reinforcing bars, where the bar acts as a wave guide to transmit energy deep into concrete members. Ultrasonic energy leaking off the bar into surrounding concrete provides early indications of reinforcement corrosion, prior to crack formation, giving designers advanced warning of impending corrosion issues.
The presenter is working with researchers at New York University to develop an imaging technique for identifying salt type and concentration throughout building facades using hyperspectral imaging. This global method obtains underlying spectral information for every point in an image on a pixel-by-pixel basis. Images are collected from dozens to hundreds of feet from the building, offering the potential to better understand the impact of contaminants over an entire building’s exposed surfaces, the evolution of potential damage, and the ability to directly analyze areas that are difficult to physically sample.