Rule Out? Structural Cracking Structural failure Freeze-thaw cracking Reinforcement corrosion Dissimilar metals corrosion D-cracking Alkali-aggregate reaction

Rule Out?

Structural CrackingStructural failureFreeze-thaw crackingReinforcement corrosionDissimilar metals corrosionD-crackingAlkali-aggregate reaction

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Description of Problem:

Cracking, staining, exposure of aggregate in edge of concrete roof

Possible Contributing Factors:

Outdoor exposureUnprotected from rainPoor drip edge detail aboveNo drip detailing at bottom of fascia

The loss of cement paste and spalling on the fascia are suggestive of freezing damage to the surface of the concrete, and imply some poor curing practices during construction

The staining cracks behind suggest that water has penetrated into the concrete and is causing the corrosion of the reinforcement.

Consider Further

Structural Cracking failure

Freeze-thaw crackingReinforcement corrosion

D-cracking

Extensive further tests are not warranted in this instance. Some structural analysis to determine whether any of the cracks are structural in origin may be useful, but the solution to both freeze-thaw and corrosion problems in this instance is to make sure that water ceases to run down the edge of the roof structure. This can be accomplished by providing proper flashing details, including a drip edge at the edge of the roofing.

Rule Out?

Structural CrackingStructural failureFreeze-thaw crackingReinforcement corrosionShrinkage CrackingD-crackingAlkali-aggregate reaction




This 5 year old exterior column has been treated with a light sandblasting, which removed some of the cement paste from the surface, and made the column susceptible to water penetration. This treatment has exposed a zone of poorly consolidated concrete at the column base. There is an extensive pattern of cracking in the columns, which is unlikely to be of structural origin. The incomplete consolidation of the concrete would make it vulnerable to shrinkage or structural cracking. Corrosion damage cannot be ruled out due to the continuous access to moisture.

Consider Further

failure

Freeze-thaw crackingReinforcement corrosionShrinkage Cracking

Alkali-aggregate reactionng

Identification of the causes of damage to this column will require a testing program. Cores should be extracted from an inconspicuous location for petrography, to determine the extent of rock pockets and the presence of air entrainment. Half-cell potential testing of the reinforcement could rule out corrosion damage, while in-situ stress measurements could determine the likelihood of a structural origin for the vertical cracking.

Click for View of Shaft


Cracking of architectural column


Outdoor exposureUnprotected from rainPonding water at pedestalArchitectural treatmentPoor consolidation

Rule Out?

Structural CrackingStructural failureFreeze-thaw effectsReinforcement corrosionShrinkage crackingD-crackingAlkali-aggregate reaction





Spalling, exposed reinforcement in folded plate concrete roof


Outdoor exposureUnprotected from rainNo drip edge detail aboveNo roof membrane aboveInsufficient cover on reinforcement

The spalling on the fascia is suggestive of freezing damage to the surface of the concrete. However, the spalling could also result from expansion due to accumulation of products of corrosion within the reinforcement of the shell roof.

Both problems are exacerbated by the continual presence of water, due to the absence of a roof membrane and the edge detailing of the roof .

Consider Further

failureFreeze-thaw effectsReinforcement corrosion

D-cracking

Extensive further tests are not warranted in this instance. The solution to both freeze-thaw and corrosion problems in this instance is to make sure that water ceases to run down the edge of the roof structure. This can be accomplished by providing proper flashing details, including a drip edge at the edge of the roofing. It is probably of interest to determine the extent of the initiation of corrosion through half-cell potential testing of the reinforcement in the roof.

Rule Out?

Structural CrackingStructural failureFreeze-thaw crackingReinforcement corrosionShrinkage CrackingD-crackingAlkali-aggregate reaction





Cracking, staining, spalling of concrete around interior downspout


Water ingress around downspoutExterior exposureConcrete consolidtion

Although tbe basic problem here is obviously a leaking roof drain/downspout system, the initiation of concrete damage may be at a shrinkage crack, or a structural crack (the location is in a zone of stress concentrations), or may be due to freeze-thaw action. It apparent that corrosion of the reinforcement has initiated at this location.

Consider Further

Structural Cracking failureFreeze-thaw crackingReinforcement corrosionShrinkage cracking

D-cracking

Prior to undertaking repairs to these locations (all of the downspouts in this building are showing a similar pattern of damage), a delamination survey of the roof deck should be undertaken to estimate the areas of concrete requiring removal. The extent of corroded reinforcement should be investigated through half-cell potentials, and the extent of unsound concrete should be investigated through the use of a rebound hammer (ASTM C805) or other means.

Rule Out?

Structural CrackingStructural failureFreeze-thaw crackingReinforcement corrosionDissimilar metals corrosionConcrete qualityAlkali-aggregate reaction





Cracking, staining, exposure of aggregate in edge of concrete roof


Outdoor exposureUnprotected from rainPoor drip edge detail aboveDrip detailing at bottomConcrete cover

The spalling of the concrete cover at this location is due to some combination of freeze-thaw and corrosion effects, possibly exacerbated by poor concrete quality (lack of air entrainment, reactive aggregate, etc. The corrosion is already widespread, and is threatening the structural integrity of the beam.

Consider Further

Structural failureFreeze-thaw crackingReinforcement corrosion

Concrete quality -cracking

In addition to undertaking repairs of the obvious damage, it is necessary to investigate whether the concrete in this project in general is worth salvaging through petrographic analysis of cores extracted from damaged locations, and through in-situ cover and strength testing. The residual capacity of beams damaged to this extent also needs to be investigated by structural analysis.

Rule Out?






Map cracking of beam soffit in outdoor canopy; rust staining

In an area that is displaying significant problems with reinforcement corrosion and other water damage to concrete, the presence of cracking in this beam is particularly suggestive of corrosion, especially given the rust staining. However, the extent and character of the cracking, and the extent of the problems throughout the project may also suggest some problem inherent to the concrete.

Consider Further

failure


Alkali-aggregate reactioncracking

This area requires an extensive testing program to determine the extent of the issues. Petrographic analysis of specimens of the concrete should be undertaken to determine the source of some of the concrete problems. Other areas of concrete with inadequate cover on the reinforcement should be located with a cover meter. The extent of the corrosion activity should be surveyed, and the in-situ strength of the concrete at selected locations should be determined.


Outdoor exposureConcrete quality Inadequate reinforcement cover

Rule Out?






Cracking, staining, exposure of reinforcement in end of concrete beam


Outdoor exposureUnprotected from rainInadequate cover on reinforcementNo drip detailingPoor quality concrete

Water draining from the roof has penetrated the end of the concrete beam, causing freeze-thaw damage, and initiating corrosion of the reinforcement. It is also possible that a bearing failure has initiated at the top of the pier.

Consider Further

Structural failure (bearing) failure


D-cracking

Extensive further tests are not warranted in this instance. Some structural analysis to determine whether any of the cracks are structural in origin may be useful, but the solution to both freeze-thaw and corrosion problems in this instance is to make sure that water ceases to run down the edge of the roof structure. This can be accomplished by providing proper flashing details, including a drip edge at the edge of the roofing.

Rule Out?






Spalling of concrete on corner of column


Outdoor exposurepoor quality concrete (probably high w/c ratio)

The loss of cement paste and spalling on the fascia are suggestive of freezing damage to the surface of the concrete, and imply some poor curing practices during construction

The staining cracks behind suggest that water has penetrated into the concrete and is causing the corrosion of the reinforcement.

Consider Further

failure

Freeze-thaw cracking

D-cracking

Extensive further tests do not appear to be warranted in this instance. The tips of the corners are spalling due to penetration by moisture followed by freeze-thaw damage.

Rule Out?





This balcony area admits large volumes of rainwater without adequate provisions for removal of the water. As a result, the water permeates the concrete, causing staining, promoting freeze-thaw damage, and causing corrosion of the reinforcement. The problem is exacerbated by apparently poor quality concrete, and totally inadequate cover over some of the reinforcement.

Consider Further



D-cracking

This area requires a testing program to determine the extent of the issues. Petrographic analysis of specimens of the concrete should be undertaken to determine the source of some of the concrete problems. Other areas of concrete with inadequate cover on the reinforcement should be located with a cover meter. The extent of the corrosion activity should be surveyed, and the in-situ strength of the concrete at selected locations should be determined.


Cracking, staining, spalling, exposure of reinforcement in edge of concrete balcony


Outdoor exposureUnprotected from rainPoor drip edge details Lack of waterproofing or drainage of balcony slab

Rule Out?





This sidewalk area admits large volumes of rainwater without adequate provisions for removal of the water. As a result, the water permeates the concrete,, promoting freeze-thaw damage, and possibly causing corrosion of the reinforcement. The problem is exacerbated by apparently poor quality consolidation of the concrete.

Consider Further failure


D-crackingAlkali-aggregate reactionc

This area requires a testing program to determine the extent of the issues. Petrographic analysis of specimens of the concrete should be undertaken to determine the source of some of the concrete problems. The extent of the corrosion activity should be surveyed, .


Map cracking on exterior wall


Outdoor exposureUnprotected from rainimproper consolidationmoisture intrusion from sidewalk edge

Rule Out?





This canopy admits large volumes of rainwater without adequate provisions for removal of the water. As a result, the water permeates the concrete,, promoting freeze-thaw damage, and possibly causing corrosion of the reinforcement. The cracking has the characteristic pattern of D-cracking (freeze-thaw damage to the aggregate rather than to the cement matrix, but other factors must also be ruled out by testing.

Consider Further

failure


D-crackingAlkali-aggregate reactionc

This area requires a testing program to determine the extent of the issues. Petrographic analysis of specimens of the concrete should be undertaken to determine the source of some of the concrete problems. The extent of the corrosion activity should be surveyed, .


Map cracking on underside of canopy beam


Outdoor exposureUnprotected from rainmoisture intrusion from

roof above

Rule Out?





The diagonal cracks are characteristic of shearing forces in concrete, suggesting either uneven bearing on the bottom corner of the panel closer to the wall or pushing out of the wall. The most likely cause is differential expansion/contraction between the column enclosed by the panels and the wall.

Consider Further


Freeze-thaw cracking

This condition does not require an extensive diagnostic problem. The other columns should be monitored and a repair program should be initiated.


Diagonal cracking on precast concrete column enclosure


Outdoor exposureUnprotected from rainImproper provisions for expansion and contraction of underlying structure

Rule Out?

Structural CrackingStructural failureFreeze-thaw crackingReinforcement corrosionShrinkage crackingD-crackingAlkali-aggregate reaction




This column has been experiencing severe problems with cracking and spalling due to a combination of reinforcement corrosion and freeze-thaw action, exacerbated by low quality concrete. The column has been patched in several areas, including the exterior corner at the base shown here

.

Consider Further

failure

Freeze-thaw crackingReinforcement corrosionShrinkage cracking

The regularly spaced cracks are characteristic of shrinkage, and in fact, the material is shrinking visibly. It is highly probably that the patching material was over-watered, causing it to shrink on drying. Improper curing of the patch material may also have contributed to the problem. The underlying reinforcement corrosion has apparently not been addressed.


Map cracking in a concrete patch


Outdoor exposureUnprotected from rainimproper installation of patch

Rule Out?





The concrete in this beam appears to have been very poorly consolidated, as honeycombing is evident in this photogrraph. The cracking is suggestive of shrinkage. Shrinkage cracking in across dimensions as small as the depth of this beam is uncommon, and would imply a very high water-cement ratio or improper curing of the concrete, the latter being more likely in this case.

Consider Further

failure


Alkali-aggregate reaction

This area requires a testing program to determine the extent of the issues. Petrographic analysis of specimens of the concrete should be undertaken to determine the source of the problems, and to rule out reactive aggregate. The extent of the corrosion activity should be surveyed .


Cracking and rock pockets on end of canopy beam


Outdoor exposureImproper consolidation

Rule Out?





The pattern of cracking is suggestive of bending in the thin flange of the double tee along a diagonal axis. The cause appears to be the restaint of the flanges in the vertical and horizontal direction. As the supports of the tee settle, the flanges tend to be bent upwards.

Consider Further

Structural crackingfailure


No testing is warranted in this case. Drainage should be maintained the the development of the cracks should be monitored, especially for evidence of corrosion.


Diagonal cracks in flange of precast double tee in a parking garage.


Exposure to water, saltRestraint of vertical and horizontal movements

Rule Out?





The concrete in this four year old structure is generally of very poor quality, as evidenced by premature cracking and freeze-thaw damage. This crack has the appearance of a shear crack in a short cantilever bracket that is seriously overloaded. The crack may also be due to shrinkage of the concrete, or freeze-thaw action.

Consider Further

Structural crackingStructural failureFreeze-thaw crackingReinforcement corrosion

It is necessary in this case to rule out a structural effect that might precipitate a failure of the structure. This can be done by carefully examining the loading conditions on this bracket and determining whether large loads from the upper floor are being transferred directly to the short cantilever. It is also necessary to determine whether continuous reinforcing is present, especially in the top of the bracket. If a structural failure can be ruled out, it is still necessary to determine the extent of the corrosion and to arrest the further progression of the corrosion.


Vertical crack and staining of a short beam cantilever in a parking garage


Exposure to water and saltConcrete quality

Rule Out?





This crack results from transfer of beam loads to the corner of the panel, rather than the column that is designed to support the beam. The resulting overstress in the wall panel has caused the development of a shear crack.

Consider Further

Structural Cracking

Reinforcement corrosion

This crack does not appear to be severe, or to be associated with any impending structural failure. Monitoring of the development of the crack, or removal of a small amount of concrete and patching are sufficient. Consideration should be given to testing for the initiation of corrosion activity by testing half-cell potentials.


Diagonal crack in solid panel between columns and beam


Outdoor exposure

Rule Out?





The fact that the cracking is located adjacent to aluminum handrail posts is suggestive of galvanic corrosion due to the influence of reinforcing steel on the embedded aluminum. Freeze-thaw and corrosion of the reinforcement are other potential causes of the observed cracking that must be ruled out.

Consider Further

failure

Freeze-thaw crackingReinforcement corrosionDissimilar metal corrosion

This area requires a testing program to determine the extent of the issues. Specimens of the embedded aluminum should be examined for evidence of corrosion activity. The extent of the corrosion activity should be surveyed .


Diagonal cracks at anchorage for handrail posts on balcony


Outdoor exposureExposure to rainwater

Rule Out?





This beam has been previously repaired due to corrosion of the bottom reinforcement and delamination of the cover concrete from the bottom of the beam. A further longitudinal crack has developed in the top of the beam. The crack could be due to corrosion along the length of the top reinforcement, or it could signal the initiation of a more serious compression failure of the concrete in the top of the beam.

Consider Further

Structural cracking


This area requires a testing program to determine the extent of the corrosion, in particular to check for the presence of top reinforcement, and for evidence of corrosion activity in the top reinforcement. If corrosion is ruled out, it is necessary to consider the possibility that the cracking is a structural effect.


Longitudinal cracking at the top of a repaired concrete beam


Outdoor exposurePoor quality concrete

Documents

Rule Out? Structural Cracking Structural failure Freeze-thaw cracking Reinforcement corrosion Dissimilar metals corrosion D-cracking Alkali-aggregate reaction