What Does Concrete Spalling Mean?
Concrete spalling is a defect that appears in a hardened concrete structure or blocks situated in colder climates, where the concrete is slowly broken down into small flakes known as spalls from a larger solidified concrete body. Spalling is normally seen in a concrete slab or a layer of concrete in locations that have colder climates and experience the constant destructive forces of cyclic freezing and thawing (freeze-thaw cycle). The situation is exacerbated when salt or deicing chemicals are used on the concrete surface.
Concrete spalling is also known as concrete scaling.
Corrosion reinforcing steel in concrete is a problem that has the capacity to cause a wide range of issues ranging from economic to aesthetic. However, many of these issues can be reduced - or even eliminated - if corrosion effects are considered in the design phase and adjustments are made prior to construction. Steel corrosion in concrete can be greatly accelerated in harsh environments, such as coastal, tropical, or desert regions where high salt levels and extreme temperatures accelerate the rate of its decay. In most cases, the more exposed elements tend to deteriorate first; however, in steel corrosion, most of the corroded reinforcement is not visible and it may take up to five or more years of active corrosion before cracks initiate in the concrete, at which point the damage becomes visible.
Corrosionpedia Explains Concrete Spalling
When a concrete structure is exposed to freezing temperatures, the water stored in the capillaries of the concrete solidifies and expands, creating an internal pressure on the top solidified layer. Over time, due to the force applied by freezing and thawing cycles along with the internal pressure of expanded water, the top layer of the concrete tends to chip away leaving pit marks, concrete fragments or spalls.
The threat of concrete spalling can be minimized by preparing the concrete with the appropriate water-cement ratio, air content and a minimum specified compressive strength, and by proper finishing. Corrosion is known to be something that affects all concrete buildings and structures around the world to at least some degree, with huge amounts being allocated to fixing these issues. These cost implications are of great importance, as the effects of ignoring the problems caused by corrosion in concrete buildings and structure poses a safety risk.
Fortunately, most cases of concrete spalling can be prevented by sealing to ensure moisture penetration is prevented. In certain cases where the concrete is new, a waterproofing sealer should be applied a month after concrete placement as well as every few years after that.
Correct measuring and mixing of the concrete mix can also help in spalling prevention. Concrete spalling can be caused by a lot of things, these include;
- Incorrect placement or reinforcement
- Electrochemical reactions that occur between embedded metals in the concrete
- The corrosion of embedded reinforcing steel due to water and chemical exposure
- An alkali silica reaction, where the alkalis present in cement react with the strained quartz present in aggregates
- Exposure to fire can turn the moisture particles present in concrete to steam, placing internal pressure on the construction, which results in the subsequent spalling of the concrete surface
- Steel reinforcements installed in concrete applications are not covered by an adequate volume (depth) of concrete