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Masonry Wall : Nabisco, New Philadelphia Plant, PA

Infrared Analysis
Investigation: 11/91

Table of Contents

  1. Abstract

  2. Evaluation

  3. Illustrations


The basic tool of ABACUS Infrared Wall Survey is the Agema Thermovision 450 Infrared Thermal Measurement and Imaging System, using the state of the art Electro-optical scanning mechanism, the new SPRITE infrared detector, video interface and control electronics and microprocessors for video output. The infrared camera converts electromagnetic thermal energy radiated from an object into electronic video signals. These signals are amplified and transmitted to the video processing part of the camera where the signals are further amplified and the resultant image is displayed on the viewfinder. The camera senses the intensity of thermal radiation from the object surface, and displays a monochrome image whose density corresponds to the radiation intensity. The radiant energy levels are interpreted as surface temperatures.

The north, east, south and west exterior walls of the Nabisco Plant were wetted using fire hoses in the afternoon of November 13, 1991, for the purpose of creating a thermal differential profile on the surface. This procedure would provide distinct heat patterns that would be associated with a non-uniform substrate. The wetting procedure consisted of allowing water from hoses to run down the exterior walls until soaked. The water was sprayed from ground level, from intermediate roof levels,, and from the tower roof, providing full coverage of all wall surfaces. Once the surface of the walls have dried (approximately 2-3 hours), the infrared survey commenced.

The walls were scanned at night. Scanning at night allows for sufficient cooling of the surfaces and eliminates solar reflection. Because a crack in the masonry wall will absorb more water than solid masonry, it has a reservoir of coolant (water) trapped behind it. As the residual water stored behind a crack continues to evaporate, it cools the surface in the immediate vicinity of the opening. These "cool" spots are quite visible to the infrared camera.

Upon request, certain portions of the thermal information obtained during the scan can be videotaped for further analysis. This information is later digitized using the new Data Translations High Resolution Frame Grabber, which digitizes the real-time video signal for further processing by the IRIS Image Processing Computer System. The thermal image signal is broken down into a 16 color temperature scale, and temperatures/colors are assigned to the radiational intensities of the image.

The information can now be presented as colorized thermograms, with different colors representing different surface temperatures. Variables that can affect the thermal radiation include wind velocity, cloud coverage and material density. A color bar along the bottom of the thermograms indicate temperatures in ascending degrees with warmer areas at the right of the bar.

Corresponding visible light photographs help to orientate the thermograms, as well as give clues to water entry points.

Anomaly areas seen during the survey are marked on the site elevations, with thermograms and visible light photographs corresponding to the markings on the drawings. The areas indicated represent findings identified during the IR survey. Please note that the findings of the infrared survey can only be accurate and representative for the time of the survey.

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This report provides Nabisco with two evaluation studies that can be used to determine the overall condition of the masonry at the Philadelphia plant. This section of the report will not discuss specific details of the findings since that information exists in the markings on the elevation drawings and in the Illustrations Section of this report.

By using those two components of the report, elevation drawings and illustrations, a more clear picture of the existing conditions will be seen. The evaluation section of this report will discuss the findings in broad terms that are supported by the additional specific images this report has produced.

The most important conclusion that can be drawn f from this survey is that roof leaks are the most significant contributor to the deterioration of the masonry walls. In nearly all cases, where excessive water was f found in the wall, the problem appeared to begin at the roof line.

This condition became even more critical on the north elevations where due to a lack of solar gain, these walls have less of an opportunity to dry out. The cumulative

effect of the moisture creates a saturation condition which leads to metal corrosion and freeze/thaw damage. This condition is not limited to the north elevation, but the symptoms appear more serious on these walls.

The severity of the wall damage is also a function of the extent of the roof leak above the wall. Significant water absorption was noted in all elevations as specific locations.

The apparent lack of an internal drainage system and weep tubes further aggravate a water absorption problem within the masonry walls. on numerous locations water can be seen accumulating above windows and floor lines when viewed by the infrared camera. This prolonged exposure to water at these locations will deteriorate the wall at a rate that will increase with exponential speed the longer the problem is ignored.

The walls throughout the building were observed to absorb some amount of water through the mortar joints. This would not normally be a problem because of the hollow core design of the masonry unit. But when combined with moisture from other sources, such as roof leaks and wall cracks, compounded by a lack of a drainage system, deterioration of the masonry walls will occur.

Although the report does find numerous defects with respect to moisture absorption in the masonry, the overall condition is satisfactory . With an effective short and intermediate term restoration program, much of the masonry remains quite serviceable, and can be so for many years into the future.

An overall plan should be developed that incorporates these three major components in order or priority:

Repair all defective roofing - This is the most important priority. The cost for completing this work should not exceed 25% of the costs that will be incurred if the roof continues to be neglected. Consider masonry repairs, structural deck replacement and energy loss.

Restore defective masonry - Repair cracked mortar joints, replace caulking where needed. Look for metal corrosion in walls particularly at window lintels and louvers.

Apply a water repellent to the masonry - This material should be a penetrating type that does not create a film and allows for 100% water vapor transmission.

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During the infrared survey of the Nabisco Plant, thermal data was recorded on videotape and later processed to create the following thermograms. Each set of photographs depicts one sample area as a colorized thermogram, and a visible light photograph.

The colorized thermogram depicts moisture affected wall components as changes in color.

The visible light photographs are taken from the same location as their corresponding thermograms and depict the same field of view. Some areas combine two or three colorized thermograms for one visible light photo.

Refer to the elevation drawings for the location of anomaly areas on the walls. Each thermographic set is labeled Al-25, Bl-25, and Cl-20.

Colorized Thermogram (CT)-This colorized thermogram shows a uniform thermal pattern on the wall. The parapet is seen in red and pink. The only water entry points seen here are the red patterns between the windows. The small wall penetrations above the windows are most likely taking on some water (see red arrow).

CT (#1)-This overview of the wall section shows a large later entry point at the corner of the wall. The leak occurs at the top of the wall, with the opening either at the gravel stop or a leak in the roof at that point.

CT (#2)-The red patterns in this thermogram show water coming out of the mortar joints. Dry joints are seen in yellow.
VL-The vent stacks show up as white in the infrared image.

CT #1-The areas marked by arrows #1 and #3 in this thermogram are probable water entry points in the masonry. Arrow #2 is a cool spot created by the window louver.

CT #2-Arrow #4 in this thermogram shows a more diffuse moisture pattern in the wall to the left of the window, indicating a larger opening in the mortar joint (s).

VL-The arrows in this picture correspond to the numbered arrows in thermograms 11A#1 and 11A#2.

CT-This thermogram is taken on the north elevation of the tower. There are two areas of concern. The irregular red pattern between the top row of windows indicate water is entering the parapet at or above the roof line and moving down the wall. The second concern is the amount of small water entry points dispersed throughout this elevation. This pattern indicates minor mortar debonding at numerous locations. The large irregular blue and red pattern at the bottom right is a piece of roof mounted equipment.

VL-This photo corresponds to the area seen above.

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