A frequently asked question in the concrete business is why does my concrete crack or pop? The easy answer is due to the freeze-thaw cycle, here is a quick explanation of what happens.
- Concrete is NOT waterproof. In fact, there is a large network of pores and capillaries running throughout the paste portion the concrete that is created as the concrete sets and bleed water migrates out of the concrete.
- When water freezes, it generally expands up to 9% in volume. This is no problem when the water is free to expand but when it is contained or trapped in a container it can exert a considerable amount of force of the walls of the container. Most people are familiar with how frozen water can split pipes or break a glass bottle when it freezes. Concrete, with its low tensile strength, cannot hold up to the force of the freezing water from within.
- Most exterior concrete will become saturated to some depth whenever there is rain or melting snow. The more porous (lower quality) the concrete, the faster and deeper this water penetrates into the network of pores and capillaries. During warm weather this isn’t a problem and even allows the cement to continue to hydrate. If there is only a small amount of water in the pores and capillaries, then freezing water does no damage.
- However, if in freezing conditions the water fills the pores and capillaries to critical saturation (approximately 91.7% full) the freezing water can lead to damage. Because the freezing water is pushing in all directions with a lot of tensile force and concrete has a low tensile strength, tiny cracks can form. These cracks will then fill with water themselves and freeze, leading to more cracks and eventually we get concrete damage and surface spalling.
- So what is the solution? Using a high quality sealer. Sealing the your concrete will prevent much of the water from entering the pores and capillaries reducing the amount of water and the forces created when it freezes.