Concrete Defects

Do you understand the causes of concrete delamination and how you should approach it?  There can be many causes of concrete delamination but for most cases, it all starts with Carbon Dioxide.  Concrete normally contains moisture at levels of 2 to 4 %.  When Carbon Dioxide makes its way into the concrete, it combines with the moisture to start Carbonation, which begins the process that attacks the rebar in reinforced concrete. This process which is commonly known  as Carbonation is the reduction of the alkalinity of concrete, caused by the absorption of the carbon dioxide and the moisture in the concrete. Normally in concrete, the reinforcing steel is protected by the high alkalinity (pH above 10) of the concrete surrounding the Rebar.  The chances of corrosion are increased when the pH falls below 10. The rebar close to the surface are more subject to the effects of carbonation and as such are affected by the corrosion.

As the Carbonation process starts the attacks on the rebar, the rebar it allows corrosion products to form which cause corrosion of the rebar, these corrosion products expand greatly.  As the corrosion products expand, the pressure of the expansion causes the concrete to crack and begin to spall.  As cracks form more moisture enters the concrete and the process accelerates.

Standards such as the ICRI dictate how repairs have to be made, however there are alternative approaches that can be utilized for repairs.  Many times making repairs even following the standards can set up  a scenario that can cause the acceleration of additional concrete problems.  When you make a repair, let’s say, a 2’ by 4’ repair in a concrete slab you are making that repair with clean non corrosive concrete, assuming of course that you have followed standard practice and that you have not added and special inhibitors to the concrete.   

This clean concrete will cause a reaction over time with the former concrete that surrounds it and that may contain large amounts of chlorides or other impurities including the standard amount of moisture that concrete normally contains.  When this occurs, you have set up what amounts to a differential cell that over time can accelerate defects to form in the formally existing older concrete that surrounds the repair.  This process is known as the Halo effect.  

Many procedures can be utilized to prevent the Halo effects from causing additional corrosion and problems.  Some projects use sacrificial Anodes these Anodes are made by many different manufacturers and normally come with good clear instructions as to their use.  ICRI also has a standard that governs such Anodes.  These devices are sold by Sika, Vector and many others.

Additionally, there are compounds that can be used with the patching concrete and as a patching concrete that contain anti-corrosive material so that when they are used they set up a protective cocoon around the rebar and prevent corrosion that may form due to the Halo effect.