Cracking is a common problem in concrete construction. Homeowners see it in basement fl oors, garage fl oors, and basement walls. Cracks occur in sidewalks, dams, bridges, and retaining walls. Any crack is a reason for concern and warrants a thorough inspection and investigation.
Pattern cracking
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| Image courtesy: American Geosciences |
Pattern cracks are common. These cracks tend to be short and uniformly distributed throughout a concrete surface. Pattern cracking can have two causes: It can indicate restraint of contraction on the surface layer by the backing or inner concrete, or it can be due to an increase in the volume in the interior concrete.
You may hear pattern cracking referred to as map cracks, crazing, checking, or D-cracking. D-cracking is often found in the lower part of a concrete slab, usually near a joint in the concrete. If you find moisture accumulation, you could find D-cracking.
Isolation cracks
Isolation cracks appear as individual cracks. This type of cracking indicates tension on the concrete. The tension is usually perpendicular to the cracks. An individual crack can run in a diagonal, longitudinal, transverse, vertical, or horizontal direction.
Crack depth
Crack depth is categorized into four terms: surface, shallow, deep, and through.
Crack width
Crack width ranges from fine to medium to wide. Fine cracks are typically less than 0.04 inch wide. A medium crack would be between 0.04 to 0.08 inch. Wide cracks exceed 0.08 inch.
Crack activity
Crack activity has to do with the presence of a particular factor causing a crack. Determining crack activity is necessary to determine a mode or repair. If the cause of a crack is causing more cracking, then the crack is active. Any crack that is currently moving is considered active. If a specific cause for a crack cannot be determined, the crack must be considered active.
Dormant cracks do not have current movement. Some cracks are considered dormant when any movement of the crack is minimal enough to not interfere with a repair plan.
Code enforcement officers have the authority to require the results of strength tests of cylinders cured under field conditions.
When preparing to pour concrete, installers must do the following:
● Clean all equipment.
● Make sure no debris is in the concrete.
● Make sure no ice is in the concrete.
● Clean the forms.
● Make sure any filler units that are in contact with the concrete are well drenched.
● Make sure there are no deleterious coatings or ice on the reinforcing materials.
● Make sure there is no water in the path of the concrete installation without the consideration and approval of a code officer.
● Make sure no unsound material is present.
When concrete is mixed, it must be mixed to a uniform distribution of materials.
ALL CRACK OCCURRENCE
Cracks can occur before or after concrete cures. The cracking can be structural or nonstructural. It may be hard to determine whether a crack is structural or nonstructural by visual inspection only. A full analysis by a structural engineer is normally required to make a full determination of the type of cracking that is encountered.
Structural cracks tend to be wide. Their openings can increase as a result of continuous loading and creep of the concrete. As a rule of thumb, any crack that could be structural in nature should be treated as a structural defect and receive a full evaluation from appropriate experts.
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Related articles:
☞ How to Prevent Plastic Shrinkage Cracking of Concrete?
☞ Cracks in Concrete Floors
☞ How to Repair Cracks in Concrete Floors?