Concrete spalling can be triggered by several causes:
The most prominent cause in south Florida is primarily attributable to the brutal environment of South Florida, particularly along the coast. The air has a high content of humidity, and also a high content of calcium chloride (salt). Most buildings are constructed of either pre-cast or poured-in-place concrete. In both cases, concrete is a porous substance. When the "skin" (paint surface) of the building is not waterproof, the concrete absorbs the moisture and the salt from the air and the ground. This causes the steel reinforcing bars ("rebar") to rust. When steel rusts, it expands. This then causes the concrete to break away from the building, commonly known as "spalling." Surface cracking can be generated by the reaction between atmospheric carbon dioxide and the alkalis present in the concrete mix itself. These surface cracks can then admit rainwater.
Improper concrete finishing operations can contribute to the premature spalling of concrete surfaces. If water is added to the freshly laid concrete surface to increase its workability, it could result in a weakening of that surface concrete. This could lead to the weakened surface section delaminating from the stronger concrete below and thus admitting more water to react with the reinforcing steel. If a concrete surface is trowelled while the initial bleed water is present, a similar result could occur.
SPALLING: Why use us?
Design Center has been repairing spalling for the past 15 years in the FL Keys. Design Center belongs to the International Concrete Repair Institute. We use recommendations from ICRI engineers.
We do small to big jobs.
SPALLING: Why it is a problem
Concrete spalling can result in a variety of undesirable outcomes:
Spalled surfaces can lead to rapid degradation of reinforcing steel which would jeopardize the integrity of structures and necessitate costly repairs. Spalls are also unsightly and indicate a lack of maintenance on the part of owners.
Remediation of spalling is a tedious and expensive process:
Here at Design Center (a JC Construction Company), an engineer overseas the design and remediation of the concrete restoration. At times, hidden corrosion problems may be more invasive than seen through inspection and may require additional repair. Possible shoring of existing structures must be evaluated and put in place before any demolition is performed. Demolition consists of sawcutting the perimeter of damaged areas taking care not to cut any existing rebar. Small chipping guns are used to remove the damaged concrete, usually deep enough to provide about one inch of clearance behind existing reinforcing steel so that the new patching material will have a good bond to the reinforcing steel.
The steel is then scrapped with wire brushes to remove all rust. Replacement of bars with some section loss may be required. After the bars are prepared, a zinc coating may be required by the engineer. The existing concrete surface requires preparation in the form of cleaning and application of a bonding agent or keeping continuously wet for a specified period of time. Several patching compounds are available including specialty concrete materials or standard concrete mixes. Application will depend on the size, thickness and location of the area to be repaired. It may require a standard formed and poured concrete repair. Most contractors use dry packed or trowelled-on patch method, we prefer the standard formed and poured concrete method.