Every winter, salt and the freeze-thaw cycle test the resilience of masonry materials. Here we explain the science behind winter’s damaging effects on brick, concrete, and stone, with tips to help protect your masonry assemblies.
What is the freeze-thaw cycle?
The freeze-thaw cycle occurs as temperatures change from mild to below freezing and back again. Porous materials such as concrete, stone, and brick capture pockets of water, which freeze when temperatures drop. Because the volume of ice is greater than water, the freezing process exerts extra pressure on the material, causing cracks. Every time the freeze-thaw cycle occurs, cracks and voids become larger, allowing more water to find its way into the surface. The next freeze exerts even more pressure, creating an endless cycle of damage.
Climate change and the freeze-thaw cycle
In Ontario, freezing and thawing begin in the fall, taper off as temperatures drop below zero, and begin again in the spring. The freeze-thaw cycle also occurs when there is a mid-winter thaw. Consistent temperatures reduce the damaging effects of freezing and thawing. As a result, winters that remain below freezing see less destruction than milder winters. Unfortunately, as milder Ontario winters become more common, there is a higher risk for the freeze-thaw cycle to occur throughout the winter months.
Freeze-thaw cycle: surface spalling
Constant water and snow accumulation expose masonry surfaces to extended moisture. When temperatures drop, “spalling” cracks and fractures the external layer, causing chunks of the material to fall away.
Spalling exposes underlying concrete aggregates, increasing deterioration and eventually exposing the reinforcing bars. Spalling also causes flaking on the outer layer of bricks, exposing the softer, more porous inner layers, leading to internal cracking and collapse of the entire brick.
Freeze-thaw cycle: internal cracking
As mentioned, internal voids in masonry materials become larger during the freeze-thaw cycle, increasing internal cracks and gaps. Internal cracking is more insidious, as it is not visible until the damage makes its way to the surface.
Using weather-appropriate materials for masonry
Weather-appropriate materials address the freeze-thaw cycle prior to installation. For example, bricks are graded based on their weather resistance. Grade SW is designed for severe weathering, ideal for climates with a higher risk for cyclic freezing.
For concrete materials, using low water-to-cement ratios and smaller aggregates minimizes freeze-thaw damage. Also, air-entrained concrete uses microscopic bubbles to improve flexibility as the concrete expands and contracts to reduce the risk of cracking.
Science of salt damage on masonry
When de-icing salt comes into contact with water, it creates a corrosive saline solution containing chloride ions. Concrete contains a network of capillaries and pores that facilitate water and ion movement. As the saline is absorbed, it reacts with the cement compounds, increasing expansion and contraction. Every time salt is applied, it melts the ice, exposing the underlying concrete or paving stones to the saline. Ice melt triggers the chemical reaction and worsens the damage.
Proactive masonry maintenance
Because freeze-thaw damage is progressive, the following seasonal maintenance is essential to prevent harm:
- Spring and fall inspections: Regular inspections spot the early stages of damage to ensure repairs are made to slow progression.
- Waterproofing: Breathable sealers prevent moisture penetration while ensuring moisture can escape. For example, liquid membranes fill concrete pores and gaps creating a seamless seal.
- Avoid rock salt: Using sand or calcium magnesium acetate instead of rock salt prevents saline damage.
Taking a proactive approach helps mitigate damage, prolong masonry life, and avoid the cost of early replacement. WellDone Inc. offers qualified masonry inspections to protect your assets, maintain property value, and enhance building performance during its lifetime.
If you would like more information about building masonry and inspections, speak to the experts at WellDone Inc., a building restoration company specializing in building improvements for commercial and multi-unit residential buildings throughout the GTA.