Nondestructive testing is when a group of techniques is used to evaluate materials, components, or a system without causing any damage to it. Nondestructive Testing doesn’t alter the article permanently, so it can save both money and time.
Ten years after being first published in 1989, the American Concrete Institute’s Design Standard 530 / American Society of Civil Engineers Standard 5, Masonry Building Code and Specification has only recently been adopted by the International Building Code (IBC) and will now become the adopted code of many States.
This design and construction specification was developed to assist design professionals in making masonry specification more consistent and reliable. This paper covers the new requirements dealing with quality control and assurance. Quality assurance is action taken by the owner or his representatives to ensure that the work undertaken is constructed in accordance with the written specifications. Quality control refers to requirements placed on the contractor in the form of construction testing and inspection.
With the adoption of ACI 530, architects no longer have an option of determining whether or not an inspection is required. All work must be inspected. Given the different nature of projects and corresponding level of inspection, some requirements are mandatory and some optional. However, a new level of masonry construction will be required to accommodate the code.
The use of non-destructive test methods such as infrared thermography or radiography of masonry construction provides an invaluable tool. This paper will detail the use of non-destructive testing for field verification inspections which assist in assuring that construction is in compliance with design specifications with regard to material, structural strength and thermal performance.
BUILDING ENVELOPE STRUCTURAL INSPECTION
To assist design professionals in making masonry specification more consistent and reliable, design and construction specifications have been developed. These standards are written in part to improve the level and method of inspecting masonry structures. Unlike past codes, in the new code the level of inspection depends on whether the facility is an essential or nonessential facility (as defined in the building code) and the design procedure.
While there is no substitute for visual inspection of masonry construction, the use of nondestructive testing techniques to supplement visual inspection can greatly enhance the quality assurance program. The intent of the standards is to assist contractors in bidding by reducing unknowns, help Architects in preparing uniform specifications and insure owners of more uniform quality in construction.
There are several methods of nondestructive testing which could be employed in quality assurance programs. However, for the purposes of this type of inspection there are two types of nondestructive testing which are reliable and cost effective and provide visual documentation of the test results. They are radiography and infrared thermography and both offer the ability to assist the visual component of code compliance inspections. There are advantages and disadvantages with each testing method. Specifically, with radiography the results are detailed, conclusive and visual. However, the cost and difficulty of operation, given safety and licensing concerns, are the major disadvantages. Infrared thermography has considerably less cost or operation limitations but the results are not as conclusive in locating the structural rebar within the block wall. To provide this information a second testing method such as electromagnetic testing may be required. Using the two tests in combination provides an excellent nondestructive inspection program to supplement visual inspections.
In conducting masonry inspections, the creation of a permanent well-documented record is valuable in avoiding potential controversy over the inspection findings. Therefore, the inspection method, verification of findings and presentation of the inspection data are key to the successful use of nondestructive testing as an inspection tool. Both radiography and thermography offer the ability to make visual the inspection results for review in establishing compliance with the building specifications.
There are several types of reinforced masonry construction including reinforced grouted cavity, reinforced solid, reinforced diaphragm and reinforced fin walls. The most common type of masonry wall used in one and multi- story commercial construction is hollow load bearing concrete block, which is partially reinforced. In a typical wall section, with vertical reinforcement consisting of reinforcement bars set in grout, these grouted vertical supports along with the bond beams become visible during an infrared thermograhpic survey or radiography x-ray.
Current code requirements for partially reinforced masonry walls limit the maximum spacing of vertical reinforcement to eight feet. Reinforcement must also be provided at both sides of openings and at each wall corner. Certain building codes require that horizontal reinforcement of at least 0.2 square inches in area be provided in bond beams at the top of footings, at the bottom and top of wall openings, at roof and floor levels, and at the top of parapet walls. Other code standards require reinforcement at these same locations but do not stipulate a minimum bar diameter.
To successfully accomplish this type of detailed building envelope inspection, the technician must be knowledgeable of construction techniques, materials, construction documents as well as the use of infrared thermography as it is used for the interpretation of building material thermal patterns. Finally, to achieve the greatest results from infrared building envelope inspections, the thermographer should work to overcome the confusion and possible resentment that can be created by such an inspection. A good program must educate the parties involved and work to build confidence so that the thermographer can become an integral part of the construction team.
When using thermography, the technician must address the vast amount of information which can be taken from an infrared building envelope inspection, laymen of thermography; the architect, engineer, contractor and owner need to have the data properly documented and presented in a report form which they can understand. Often the project architect will specify that an infrared inspection be performed on his building for a specific purpose, such as the verification of the insulation in the wall cavities. In performing the infrared inspection of this one specific item, the entire building envelope is being inspected and documented. This data can then be used to address not only the specified component but also other potential problems and provide assistance to solve them.
If x-ray radiographic evaluation is the test method selected, both sides of the building envelope will need to be accessible. Recent equipment improvements make the newer equipment much easier to use. Additionally, the advantage of providing a permanent record has improved with digital equipment. However, the safety issue remains and if gamma radiography is used the tests can be carried out only by firms who are licensed by the Nuclear Regulatory Commission and use technicians who have completed approved safety training. The test environment must be isolated as necessary to prevent radiation hazards.
The primary purpose of any construction inspection is to assure that the intent of the designer and owner has been fulfilled. For the nondestructive inspector to be effective in conducting building envelope inspections, he must become an integral part of the construction team. Given that masonry construction is a labor-intensive craft passed from generation to generation and primarily dependent upon site prepared materials, it is important that the inspector be professional and use tact when dealing with the contractor.
As part of the construction team, the inspector may want to discuss with the contractor the nature of the inspection and what are generally the results which can be expected from the type of nondestructive building envelope inspection which is being employed. This simple step will help avoid unnecessary confusion and assist everyone in performing his work in the most advantageous and profitable manner. At the same time, a discussion of inspection timing is valuable. Again, if possible, the inspector should gain the assistance of the site manager in notifying him of the exact time when the building can be inspected.
Depending on the type of building being inspected, new building codes are requiring an increased level of quality assurance inspections for new masonry construction. Both infrared thermography and radiography technologies have advanced to a point where they can greatly enhance the visual inspection of new construction. However, for the procedure to be useful, the assessment process must be relatively inexpensive and have the ability to coincide with a construction environment timetable.
Certainly not all new masonry construction will require inspection beyond visual. However, for the more complicated building, essential facilities, the use of nondestructive testing methods can provide a valuable addition to the quality assurance program. Further, the nature of what is being documented will influence the nondestructive test method chosen. If a whole building approach is to be taken then the use of thermography results in an inexpensive assessment procedure for identifying thermal and structural characteristics of the buildings. However if specific concerns involve the location and/or completeness of the structural rebar within the grouted solids of the masonry block wall, then the most appropriate test method would be radiography, and specifically x-ray evaluation of the wall section can best detect materials within the wall nondestructively.
As the new code is widely accepted and better understood, the addition of visual documented nondestructive testing to supplement visual inspection of new masonry construction will advance both methods of testing and further improved equipment to meet the demand of design professionals.
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