Concrete Deterioration & Repair Baltimore MD/DC/VA

Concrete Restoration would like to provide all of its clients and potential clients with the following information on:

Parking Garage and Concrete Deterioration
and Detection Techniques

Most common types of concrete deterioration of parking structure slabs are due to:

What are the causes of concrete deterioration?

Cracking of concrete occurs primarily due to shrinkage of the concrete as it cures.  Cracks can also form as the concrete is saturated then freezes and thaws during the winter months repeatedly.  These cracks create an avenue for water to travel deeper into concrete and reach the reinforcement more easily.

The presence of chlorides in the concrete can occur from both internal and external sources. Internal sources are calcium chloride admixtures used during the winter months to accelerate the curing of the concrete.  External sources mainly occur from the application of de-icing salts.  During the winter months roadways are treated with de-icing salts and these salts are carried into the parking structure by vehicular traffic.

As the reinforcement corrodes, rust develops and the volume is greater than the original volume of the steel.  The volume change exerts pressure on the surrounding concrete. 

Over time this process continues until the pressure exerted by the rust results in a subsurface horizontal crack in the slab.  The horizontal crack is known as delamination and is not visible to the naked eye.  Eventually the delamination results in a spall due to the continued corrosion of the reinforcement and the forces of the freeze-thaw cycle.

Detection Techniques

Two common types of techniques used to detect delaminated areas of the slab, which may not be visible to the naked eye, are electromechanical sounding devices and chain dragging.  By far the economical and most commonly used technique is the chain drag.  A chain dragged over the surface of the slab produces a distinct hollow sound when the chain passes over a delaminated area.

If the degree of corrosion to the reinforcement is of concern, corrosion mapping should be undertaken.  Half-cell potential measurements serve as an important means of determining the probability of corrosion activity on the reinforcing steel of the structure. 

By the use of this technique, probable corrosion areas and the percentage of the total area subject to corrosion can be determined,

The amount of chlorides in the concrete can be determined by sampling the concrete at various locations and testing them for the concentration of chloride ions.  Dust samples are most typical sample type.  A drill is used to pulverize the concrete into a dust that is collected at different depths below the surface.  The chloride content at the level of the reinforcement is most important.  The American Concrete Institute or ACI has established 0.3% of chloride content in concrete, by weight of cement as the maximum chloride content for corrosion protection.

Recommendations

The ACI recommendation is a minimum of 2 inches of concrete cover over embedded reinforcement to reduce the amount of water and chlorides that reach the reinforcement.  Additionally, most specifiers recommend a concrete water/cement ratio that does not exceed 0.40.

It is also recommended that parking garages be washed down periodically.  It is recommended that this occur at least once a year, preferably in the spring after de-icing salts have accumulated in the garage and before that have a chance to permeate the concrete.  Additionally joints and cracks should be sealed to prevent the easy migration of chloride-laden water to reach the reinforcing steel or other parts of the structure.  The sealant should be periodically checked for deterioration and replaced as necessary.  Most sealants, under normal conditions, will last between three and five years.

Cracked concrete is not only found in parking garages.
As a matter of fact, we perform plenty of concrete block repairs as well as concrete sealing in Maryland, DC, and Northern Virginia.

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