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Title

Evaluating Concrete Building Facades

Author

Jay H. Paul

Jay H. Paul is the CEO of Klein and Hoffman, Inc. in Chicago.

Laying the groundwork for a sucessful repair program
Engineers often are retained to oversee the repair of high-rise, concrete-framed buildings. They must identify defective and damaged areas of the façade, determine their cause, and develop details to correct them. Engineers also prepare an estimate of the cost of the repair program.

Building owners often order a façade evaluation because of poor appearance or water infiltration, but these may be just symptoms of a larger problem. On high rises, many problems cannot be seen from the ground, balconies, or other accessible vantage points. Therefore, perform a hands-on inspection from suspended scaffolding or other appropriate access equipment.

Repairs usually are prioritized in descending order of importance:
1. Eliminate potential safety hazards
2. Correct structural deficiencies
3. Minimize water and air infiltration
4. Upgrade appearance

Should you inspect the entire facade?
The greater the area of facade inspected, the more accurate will be the estimate of the work required. But inspecting the entire facade is too costly and unnecessary. If all of the typical areas are covered, inspecting about 20% of the facade usually is sufficient.

Types of concrete deterioration
Spalling and delaminations
Spalls and delaminations are usually the result of internal pressure caused by corroding reinforcing steel. Spalls are areas where concrete has broken away from the wall. Delaminations are areas where the concrete has lost bond with the reinforcing steel. Delaminations can be detected by tapping the concrete with a hammer. A hollow sound indicates a delaminated area. Record the boundaries of the delaminated areas. Then remove or temporarily secure delaminated concrete found during the inspection.

Spalls and delaminations on the building facade may be only warnings of more extensive structural damage extending into the building. Repairs inside the building are more expensive, often requiring shoring and bracing of windows or walls and protection of interior spaces from dust and weather.

Cracking
Cracks may appear for a variety of reasons: corrosion of reinforcing steel, drying shrinkage, thermal movement, or structural stress. Selecting the proper repair technique depends on the reason for the cracking. For example, if the crack was caused by drying shrinkage, then it is likely that the crack will eventually stabilize. In this case, applying a rigid repair material may be suitable. However, the cracks may be caused by more serious structural damage to the facade and will continue to grow. In this case, it is necessary to determine and correct the underlying cause of the cracking.

Shrinkage cracks that are perpendicular to slab edges, especially under masonry spandrel panels, often are a source of water infiltration. Such cracks usually go beyond the wall line and serve as a conduit for water.

Determining causes of deterioration
In order to specify appropriate repairs, you must understand the cause of the damage. For example, it is not enough to know that spalls and delaminations were caused by rebar corrosion. Engineers must determine why the rebar corroded and specify repairs to prevent recurrence.

Deterioration often is caused by one, or a combination, of the following:

Inadequate materials
Construction errors
Design errors

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Caption: On high rises, many problems cannot be seen from the ground, balconies, or other accessible vantage points. Therefore, perform a hands-on inspection from suspended scaffolding or other appropriate access equipment. If all of the typical areas are covered, inspecting about 20% of the facade usually is sufficient.

Inadequate materials
Sometimes the building façade deteriorates because of poor quality concrete. To determine concrete quality, take cores from various locations for evaluation.

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Caption: Portable thin wall coring machine used to take samples for petrographic examination. Knowing the quality of the concrete allows you to predict whether further deterioration is likely.

It’s a good idea to take cores from both deteriorated areas and those that appear to be undamaged. Differences in the concrete may give clues to the reason for the deterioration. To minimize structural damage to the facade, avoid coring through reinforcing steel. Whenever possible, minimize the visual impact of coring by removing concrete from inconspicuous locations.

Petrographic examination and other laboratory tests help determine the cause of deterioration and provide other useful information. Some common tests include:

Chloride content
High levels are common in buildings constructed in winter months before the mid-1970s. At that time, calcium chloride was permitted for use in accelerating concrete curing in cold weather. High chloride levels indicate an increased likelihood of rebar corrosion.
Air content
This information is helpful in cases where concrete has suffered from freeze-thaw damage rather than rebar corrosion. Problems caused by severely corroded rebar require removing concrete until the rebar is exposed regardless of the concrete’s condition. Repairs for freeze-thaw damage, which generally does not go as deep, require removing less concrete.
Carbonation
Although carbonation usually occurs to a depth of less than one inch from the surface, if it reaches the reinforcing steel, the potential for corrosion increases substantially.
Moisture penetration
Estimates of moisture penetration furnish data on the effectiveness of existing coatings or sealers on the concrete surface (Figure 2).
Aggressive aggregates
Sealers and coatings may help reduce deterioration caused by reactive aggregates.
Concrete mix design
Knowing the mix design of the parent concrete helps when choosing a repair material. Proper detailing to ensure the maximum benefits calls for matching patch materials as closely as possible to the parent concrete.

There’s often no immediate cost-effective solution to the problem of poor quality concrete. Coatings or sealers can be applied to reduce the permeability of the concrete and slow deterioration of the facade. But, more than anything, knowing the quality of the concrete allows you to predict whether further deterioration is likely. This information provides an indication of the expected life of the building and helps the owner plan and budget immediate and future repairs.

Construction and design errors
Construction errors occur when what is actually built deviates from the original specification or prevailing standard detailing of the time. Although construction defects usually cannot be completely corrected, efforts must be made to alleviate their detrimental effects. Design errors occur when mistakes are made in the original specification.

A typical construction error is insufficient concrete cover over reinforcing bars. Rust stains on slab edges or columns may indicate inadequate concrete cover. Misaligned columns from one level to another are usually a clue that the reinforcing cage was improperly positioned (Figure 3). Also, electrical conduit placed too close to slab edges can promote spalling. Wherever possible, the thickness of the repair concrete should be increased to provide increased to provide proper coverage.

Premature removal of slab shoring can cause excessive deflection in beams. Deflection can cause distorted window frames, problems with window seals, and cracked masonry. Honeycombing or segregation of the aggregate often results from concrete placement problems in small or substantially reinforced columns. Design errors may include an absence of drips under slab edges or expansion and control joints that are spaced too far apart.

Balconies present special challenges
Balconies carry the potential for a number of problems that can mean costly repairs. Some of the more common items to examine are: corrosion of handrail anchorages and reinforcing steel and water infiltration. Dissimilar metals such as aluminum handrail anchorages in contact with steel reinforcing bars often result in corrosion, as well as the eventual failure of the anchorage.

Corrosion of the base of the post or embedded sleeves is also a typical defect. Both situations require that the structural integrity of the railing system be restored before it becomes a threat to public safety. In the cast of dissimilar metals, steps should be taken to impede interaction by using either coatings or compatible metals.

Spalling, especially on the top side of balconies, generally occurs as a result of corrosion of improperly placed reinforcing steel. Cracked and spalled concrete on the edges or bottom surface can pose a safety hazard, requiring an emergency removal program. If there is extensive corrosion on the top reinforcing of a cantilevered balcony, the required repairs can be involved and expensive. Some jobs require removal of large areas of the slab inside the building. Check existing coatings and surface finishes. Slab coverings such as tile or indoor/outdoor carpeting can trap moisture and salts, creating an environment conducive to corrosion. The same can be true of inappropriate membranes and coatings.

In addition to spalled concrete, there are several other factors that can promote water infiltration. Lack of sills under balcony doors, poor drainage, improper pitching of the slab’s top surface, and incorrect detailing of the door unit can lead to serviceability problems.

Inspect existing repairs
Inspect and evaluate existing concrete patches carefully for signs of failure such as rust stains, cracking, delamination, or displacement. Repairs usually fail near the edges of the patch or at the adjacent parent concrete.

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Caption: This concrete patch is failing near the bond line. Replace all failed previous repairs and carefully document the locations of old repairs that will remain. This way, they will not be mistaken as part of the new work.

The condition of existing repairs can provide information about whether to replace remaining patches. Replace all failed previous repairs and carefully document the locations of old repairs that will remain. This way they will not be mistaken as part of the new work. Identify the use of vapor barrier coatings that may have trapped moisture in the concrete and need to be removed.

Estimating the cost of a repair project
After completing the hands-on inspection, prepare a report with conclusions about the cause of deficiencies and repair recommendations. Based on the findings, it is possible to quantify the scope of work and develop an opinion of cost for the repair program. When preparing an estimate, consider the cost of similar work performed on previous projects. Other factors can have a major impact on repair costs. Building elements such as mansard roofs, cornices, bay windows, wall projections, or balconies can make scaffold rigging difficult and add significantly to repair costs. Other factors to consider when preparing a cost estimate include:

Availability of elevators
Allowable working days and hours
Nearby trees and power lines
Potential problems with sandblasting
Location of public areas such as walkways. driveways, plazas, and swimming pools
Required temporary protection canopies
Available electric power
Required construction schedule
Time of year work is to be done

Consult with contractors specializing in facade repair to assist in identifying special considerations and estimating the cost they might add to a project.

When discussing a proposed repair program, the client should understand that in most cases concrete repairs have a given life span. Further deterioration next to concrete repair patches should be anticipated. Although using good repair techniques and providing a protective system such as a sealer or coating can extend the life of the repairs, future concrete maintenance will be required.

Inform the owner of any problems that might not be corrected. This often includes water infiltration problems that might continue because certain defects, such as faulty windows, defective wall flashing or roof-related problems, will not be corrected in the proposed repair project.

Recommend a pilot repair program
Before beginning a full-scale facade restoration program, repair and test a pilot area. A pilot program allows you to improve the quality of concrete repairs and possibly extend their life. Perform tensile-bond tests on patches to evaluate surface preparation and repair materials.

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Caption: Apparatus for measuring permeability on-site provides information on the effectiveness of existing coatings or reveals the need for additional surface protection.

Occasionally, petrographic analysis of cores taken through patches is done to evaluate the effectiveness of the bond between the repair and parent concrete.

Another benefit a pilot program offers is that the client can see the appearance of completed concrete repairs before the start of the project. Some repair patches must be built out at some locations to achieve adequate cover of the reinforcing steel. Coatings can help hide color differences between the old and new concrete, but patches often can be seen through the coatings because their finish differs from adjacent concrete.

Furthermore, some people find certain coatings objectionable because of their texture, color, or shiny appearance. A pilot repair program reduces the potential of surprises for the owner.

Educating the owner before repair helps avoid problems that may arise because of unrealistic expectations. The most successful facade repair projects are those in which the engineer clearly communicates to the owner a description of the program, its cost, and the resulting building appearance. The key to providing that information is a hands-on inspection. This useful tool will serve both engineer and owner well.

Inspecting other facade elements
Masonry defects
Check masonry panels to see if they are dislodged, crushed, or warped. They may be improperly anchored. Anchorage problems can be solved by installing additional mechanical supports or, when necessary, rebuilding the masonry panel. It often helps to have the contractor expose internal wall construction during inspection.

Study the design documents to see if any details have been overlooked. Sometimes masonry elements are designed without flashing or weep holes, or flashing has been improperly installed. We often find caulking over weep holes or in from of thru-wall flashings at the bottom of masonry infill panels. Both situations trap moisture and increase the potential for deterioration or water infiltration.

Window Systems
Inspect the window systems adjacent to the concrete and masonry under investigation. Water often enters buildings through window-related defects and is often misconstrued as resulting from faulty facade repair work. One way to avoid this problem is to spray the window units with water to see if they leak. The engineer should inform the owner about a faulty window system, because it may cause continued problems even after a successful concrete repair program.

Caulking
Deteriorated caulking and sealants often allow water to enter the building. Carefully check the condition of the caulking for signs of poor adhesion, splitting, loss of resiliency, or degradation. Also inspect the sealants on window components and masonry.

Identify the type of existing caulking – it may be that a different material is more suitable. For example, silicone caulking may provide better results on nonporous surfaces. However, it should be used with care on concrete because of possible staining. Also, some caulks are harder to remove than others which will increase the cost of repairs. For example, caulk that hardens over time, such as acrylic latex and certain moisture-cure polyurethanes, can be particularly hard to remove.