What Causes Sidewalks to Buckle? (3 Considerations)

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Have you ever been walking on a sidewalk only to get interrupted by a buckle, crack, or split on your way?

These bumps may look like a big deal, and they are. They require immediate and extensive repair to prevent accidents and further damage to the concrete.

But what causes sidewalks to buckle in the first place?

The main reason for concrete buckling is thermal expansion, which occurs when concrete heats up at high temperatures.

When concrete absorbs heat, it expands and pushes against itself, resulting in buckling. Though, there are other factors that might cause sidewalk buckling.

In this article, we’ll answer what causes sidewalks to buckle. We’ll go through everything from causes to how to prevent concrete buckling.

Why Do Sidewalks Buckle?

Sidewalks are made of concrete; one of the most commonly used construction materials. However, concrete has its fair share of flaws despite maximum hardness, stability, and durability.

Buckling mainly occurs when the temperature rises in and around the concrete’s structure. Heat forces the concrete to expand and push against itself, causing cracking and buckling.

Ever heard of the terms thermal expansion and contraction? It’s when materials expand due to heat and shrink when they cool down. That’s pretty much what happens to concrete.

Concrete retains heat from the sun, surrounding objects, and water. As the concrete absorbs heat, it expands, leading to buckles or cracks along joints, weak spots, and edges.

The same issue occurs during temperature fluctuations. While the concrete expands and cools unevenly, it creates tension, forming buckles in weak spots.

What Causes Concrete Expansion and Contraction?

While heat and temperature changes are the main reasons for concrete buckling, there are other factors that cause concrete expansion and contraction.

1 – Water to Cement Ratio

Concrete is typically made of water and cement. These components have varying coefficients of thermal expansion. In other words, they expand and contract at different rates during temperature changes.

For example, if there’s more water, it’ll dry in high summer temperatures, leading to concrete shrinkage. Conversely, the extremely low temperature in winter leads to water expansion, increasing the concrete volume.

2 – Cementitious Material

Concrete is rarely used alone. Instead, cementitious materials are often added to provide more durability, stability, and aesthetics.

These materials have different coefficients of thermal expansion, so they expand and contract at different rates, impacting the volume of the concrete.

For instance, limestone and marble are two common concrete additives. Limestone has a higher coefficient of thermal expansion compared to marble.

So if the concrete is mixed with limestone, it’ll expand much faster than concrete mixed with marble.

3 – Humidity

Humidity means more moisture content, and weather humidity highly affects the degree of concrete expansion and contraction. How?

If the sidewalk is exposed, it’ll absorb moisture from the atmosphere and swell, causing expansion. When humidity is low, water within the concrete evaporates, leading to shrinkage.

As a result of continuous expansion and contraction, the sidewalk will eventually buckle or crack.

How to Prevent Concrete Buckling (Before Construction)

Concrete buckling is common in areas where there are extreme temperature fluctuations. However, you can prevent sidewalk buckling with proper design and smart engineering.

1 – Adding Expansion Joints

One common method to avoid concrete buckling is to add relief joints. If you look closely at sidewalks, you’ll notice a soft material where open spaces are expected.

These are expansion joints made of flexible butter material like cork or plastic. Expansion joints allow the concrete to expand freely without pressuring other slabs or nearby objects.

Including expansion joints in concrete structures ensure the concrete responds well to external and internal temperature changes without buckling or cracking.

2 – Monitoring Weather Changes Before Building

Weather is a crucial factor to consider when building a concrete structure. A general rule of thumb is to place your structure in a way that doesn’t get much sunlight (if applicable). Why?

Because direct sunlight rapidly evaporates the water content in the concrete during the curing process. This weakens the structure, making it prone to buckling and cracking in the long run.

Since the curing process usually takes up to 30 days, predicting the weather changes may not be possible. In these cases, it would be best to water the concrete frequently and cover it with nylon sheets or tarps to prevent premature water evaporation.

3 – Concrete Reinforcement

Reinforcing concrete with metal can help resist cracking and buckling.

That’s because buckling is mainly caused by weak spots. By strengthening the concrete with metal, you can reduce these weak points.

A wire mesh and rebar layer would be ideal for maximizing the concrete’s strength and durability.

How to Protect Concrete From Thermal Expansion

Sidewalks are prone to buckling and cracking, especially if constructed with inferior materials or improperly installed.

However, there are some measures to take to prevent the concrete from buckling and keep it sturdy.

1. Try to minimize temperature fluctuations if possible. For example, keep your garage warm during summer and cooler in winter
2. Add thermally insulating materials around the concrete structure to tackle temperature changes
3. Control moisture by sealing any cracks and ensuring proper drainage around the structure
4. Add wood or steel buttresses to your structure to lighten the pressure exerted by higher slabs on the lower ones

How to Fix Buckled Sidewalks

While it might seem minor, a buckled sidewalk can have serious consequences. It can be dangerous for pedestrians as well as nearby vehicles.

Despite taking preventive measures during construction, concrete is still susceptible to buckling.

One common way to repair buckled sidewalks is to remove the damaged sections and then repour with adhesive caulk to fill any gaps or cracks.

If the buckling is in a driveway, it would be best to use rebar, tie the new and old sections, and then pour new concrete. The rebar will hold the two sections together, providing more strength and sturdiness.

Unfortunately, removing the damaged concrete part and filling in the gaps will only solve the problem aesthetically. That’s because the resulting concrete is usually not that strong.

Furthermore, the expansion pressure is still there, so buckling is still a threat. Adding more relief joints might help reduce buckling, but it’s not guaranteed.

Final Thoughts

So what causes sidewalks to buckle?

Thermal expansion is the main reason for concrete buckling and cracking.

In hot weather, the concrete absorbs heat around and inside the structure, which leads to concrete expansion. Meanwhile, in winter, the concrete cools faster, leading to contraction.

This consistent expansion and contraction eventually results in buckling.

Moreover, excess water also plays a significant role in concrete buckling.

Water from sprinklers, buildings, rain, and snow often gets into pores in the concrete, leading to insulated hydration and concrete expansion.

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