WHAT IS CONCRETE SPALLING AND WHY DOES IT OCCUR?

Concrete Spalling is a common concern in older concrete structures. Alkalinity, a normal corrosion mechanism, causes the steel bar inserted in the concrete to corrode over time.

The steel bars rust and increases in thickness as carbon dioxide corrodes the concrete and mixes with water. As a result of this, the concrete surface peels, fractures, and ultimately breaks off, a phenomenon known as spalling or concrete spalling.

This is a general concern in high-moisture/coastal areas, hence why many South Florida structures have this problem. However, the good news is if handled promptly, it can have little to no effect on the structural stability of a building. If not treated quickly, it may spread and degrade the foundation of the structure, resulting in serious and potentially detrimental damage. It is important to be vigilant and look out for the warning signs and triggers of concrete spalling.

Main Causes of Concrete Spalling

As mentioned earlier, corrosion and excessive humidity are the main causes of concrete spalling. But why exactly does this happen? Let’s dig a little deeper. Here are some cases:

• A Silica-Alkali Response

This occurs as reactive silica in concrete aggregates and reacts with alkaline cement pastes, causing elevated strain in the concrete, swelling, and ultimately spalling.

• Steel Bar Oxidation

Water permeates the concrete base, causing the steel bar to rust and take up more room than the initial rebar, resulting in pressure accumulation and spalling.

• Period of Freeze-Thaw

This is a type of weathering erosion that occurs in colder climates where ice can grow. When the temperature decreases and water soaks into the concrete, it will freeze into ice. The expansion of the ice can create fissures. As the temperature increases, the ice melts into water, causing further damages to the interior. This process continues until spalling in the concrete slab occurs.

What makes concrete spalling so hazardous?

Concrete spalling not only degrades the building’s visual quality but also has a long-term effect on the structure’s efficiency and integrity. Concrete is a hardened combination of cement, aggregates, and water that is high in compression but poor in tension. This means that under tension strain (pulling apart motion), concrete breaks apart relatively quickly, roughly at a magnitude of 10% of its power. This deficiency in concrete is solved by using rebar in structural concrete structures that have a high tensile strength to soak up the tensile force in the component.

The rebar under spalled concrete is exposed to ambient moisture as well as direct contact with water. This allows for the rebar to rust resulting in a decrease in rebar diameter and hence tensile capacity over time. Eventually, the rebar becomes severely affected, making it structurally weak. This structural breakdown is a time bomb waiting to happen in this case. Fortunately, we have specialized structural/concrete engineers, like G. Batista to help you with this problem.

Need help with concrete spalling? Call G. Batista today (954) 434-2053

Since corrosion is a slow process, the property owner or management company should not underestimate the seriousness of concrete spalling and neglect the issue for an extended period of time. The problem of structural failure caused by rebar corrosion is not recent in the industry. Concrete that has been spalled must be rectified not only by fixing but by identifying and correcting the root cause. Regular Inspections by a licensed engineer like G. Batista should be performed.

Over time, It’s important to keep an eye on whether the restored concrete spalling is rusting again as well as to recognize any other new design flaws in the building that needs corrective action.

Can Concrete Be Protected Against Spalling?

The short response to this question is “No”. There is no sure-fire way to prevent concrete spalling. Unfortunately, there are far too many factors to control in both the installation and treatment of concrete and of course the environmental conditions. The amount of cement, the ambient temperature as it is poured, the water content, how it is worked, and how quickly it dries are only a couple of the factors to consider when applying concrete. You will reduce the amount of spalling of your concrete by sealing it once a year. Although sealing it would not entirely prevent spalling, it will help to lessen the chances of it happening.

The basic rule to note is that concrete will most likely crack and spall over time. Pouring it in ideal weather, using high-quality concrete, controlling the environmental factors as much as possible, and sealing it periodically can help avoid cracking and spalling and keep the concrete in the best condition for as long as possible.

Concrete Spalling Repair

The use of a highly skilled concrete engineer is recommended when you need concrete repair. This is one of G. Batista’s specialties. Check out this video to better explain how concrete spalling was addressed in a building.