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Why Are Expansion Joints Necessary With Concrete?

8 minutes read

Why Are Expansion Joints Necessary in Concrete Construction? -- Transition on Curved Walking Bridge

Buildings move more than you think.

In commercial construction, expansion joints tend to be the overlooked middle child, and designers are rarely experts on them in the first place. Combined, these two truths can result in the wrong joint going into a project, with the designer simply speccing what they’ve used before.

Think about it: The expansion joints are usually the last component someone installs on a precast garage or similar concrete build. The subcontractor just wants off the job by that point, and throws in the cheapest stuff possible (often a sealant instead of a mechanical joint).

Why are expansion joints necessary in concrete, masonry, and other material structures, yet being “value-de-engineered” out of projects? Beats us.

Why Are Expansion Joints Necessary? 7 Benefits

Expansion joints (also called movement joints) protect the structural integrity of concrete builds at transition and termination points. Let’s inspect how buildings shift and concrete cracks, and how the right protective systems can stop that (and add other benefits):

  1. Account for thermal movement
  2. Prevent moisture issues
  3. Mitigate dead-load impact
  4. Mitigate live-load impact
  5. Mitigate impact of seismic activity
  6. Seal cracks for added chemical resistance
  7. Add aesthetic appeal 

1. Account for Thermal Movement

Thermal movement refers to the natural fluctuation of a concrete object’s size in response to temperature changes. It’s inevitable science – the material swells as it gets warmer and shrinks when the temperature drops. 

This continuous movement can lead to cracks and other structural issues if you don’t properly manage it.

How Expansion Joints Help

In building construction, expansion joints are strategically placed gaps that allow concrete slabs to expand and contract without damaging the structure. They act as a buffer zone, absorbing thermal movement and preventing the formation of cracks and fissures. This ensures the long-term durability and appeal of the surrounding build.

2. Prevent Moisture Issues

Moisture is a silent enemy of concrete structures. When water penetrates the concrete, it creates a host of problems, including mold, corrosion of reinforcing steel, and even structural weakening. 

These issues are almost always expensive to fix, but leaving them alone can compromise the safety of the structure.

Depending on the job site, moisture ingress is potentially the #1 sign you need expansion joints in your concrete. Examples include:

  • Vertical applications 
  • Parking decks leaking on floors below
  • When there’s an occupied space below (i.e. plaza decks)

How Expansion Joints Help

Expansion joints serve as a moisture barrier, channeling water away from the concrete slabs and the structure's foundation. By doing so, they prevent the accumulation of moisture within the material, saving you the many challenges of concrete water damage. This is particularly important in climates with heavy rainfall or snow.

Note that expansion joints will leak if you don’t transition them properly. This can happen in many areas:

  • Between dissimilar joint systems 
  • Between similar systems at changes in plane & direction
  • Waterproofing & roofing membrane tie-ins
  • Vertical air barriers & coatings

Consulting with an experienced distributor and trainer can point you toward the appropriate expansion joint products for keeping them watertight and airtight. 

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3. Mitigate Dead-load Impact

“Dead load” refers to the static forces that a structure endures 24/7. This includes the weight of:

  • The building’s materials
  • Fixtures
  • Furniture
  • Other finished goods

This constant weight can have a huge impact on a building’s ability to move, exerting significant stress on the concrete. As you can guess, this may lead to cracks and structural instability down the road.

How Expansion Joints Help

Expansion joints distribute this constant weight more evenly across the concrete slabs. By doing so, they reduce the localized stress points that typically lead to cracking or buckling. 

This greatly improves the odds that the structure can withstand long-term pressures, extending its life span (and making you look good).

4. Mitigates Live-Load Impact on Movement

Less depressing-sounding but equally dangerous, “live load” refers to temporary or shifting forces on a structure. Examples include:

  • Pedestrians
  • Vehicles
  • Machinery & equipment
  • Even the wind!

These dynamic forces can swing wildly over time in terms of how much pressure they put on each area of your structure. This means they pose a unique set of challenges in maintaining structural integrity.

How Expansion Joints Help

Lucky you! Manufacturers can design expansion joints to adapt to these variable forces, allowing the necessary movement and flexibility within the concrete structure. By deflecting shifts in live loads, they prevent damage from sudden or uneven weight distribution.

Make sure you specify the right movement joint and supporting products for your specific application. If the joint allows too much contraction, the material can rise and sustain premature wear from traffic. The primary considerations in picking a system include:

  • Joint depth
  • Joint sizing
  • Cover plates

Fortunately, some suppliers carry an entire line of traffic-rated expansion joints for mitigating live-load impact.

5. Mitigate Impact of Seismic Activity

Seismic activity is a significant risk to concrete structures, most obviously in earthquake-prone regions. Smaller sources of seismic waves include explosions, volcanoes, landslides, avalanches, and even fast-moving rivers.

An intense event of seismic activity can cause catastrophic failure if you don’t prepare your structure accordingly.

How Expansion Joints Help

Expansion joints play a valuable part in earthquake resilience. They can absorb and distribute the forces of a seismic event, reducing the risk of structural failure. As with other threats, the joints manage this by allowing controlled movement between concrete slabs.

There are expansion joints created specifically for seismic applications; they’re similar in goals but different in application vs. standard systems. 

6. Seal Cracks for Added Chemical Resistance

In industrial settings and other areas where chemicals are at play, concrete is at risk of corrosion. Acids, alkalis, and other corrosives can weaken the concrete, creating slow-building structural issues that can wreak havoc later. 

How Expansion Joints Help

Movement joints in concrete applications inherently act as a sealant, keeping corrosive substances out of gaps. While it’s not their primary job, they do add an extra layer of protection against structural weakening.

From cover to filler, expansion joints often consist of materials with excellent chemical resistance. There are also specialized joint sealants available for extra chemical resistance. You’ll often find them in food processing applications where clean working areas are a must.

7. Adds Aesthetic Appeal

In most designs, you don’t want to draw the viewer’s eye to the joint. Transitions and terminations that are obvious or ugly can detract from the visual flair of a construction project.

And, of course, any cracking or crumbling due to unwanted concrete movement is a bad look for the structure.

How Expansion Joints Help

The primary function of expansion joints is structural, but they can also be a pretty effective Band-Aid for the “scars and scabs” of a build. A well-designed expansion joint can complement the architectural style of masonry, glass, and more, turning a bare necessity into a design feature.

Various materials and finishes are available to match the look of your structure. For example, a black or white joint might look off-putting on a school with brick masonry. By ordering a brick-colored joint, you could keep the harmony between structural integrity and visual appeal.

Finally, consider the other ways sections #1-6 keep your concrete intact. What’s going to be a better look for you and the property owner – a fractured, pitted mess, or a pristine structure?

When Should You Use Expansion Joints in Concrete?

Just about every job will have at least one expansion joint, whether it’s new or retrofit construction.

Transitions and terminations for building facades and horizontal concrete are great starts. Installing or repairing expansion joints is also a potential hurdle if you’re working on a parking garage, below-grade waterproofing, or similar project.

Common expansion joint repair and protection products include:

  • Sealants (including precompressed)
  • Caulks
  • Fillers
  • Covers
  • Barriers

Your application may need a purpose-designed joint system to secure a continuous seal. Don’t necessarily buy the first or cheapest one you see.

Materials & Education Are Necessary to the Cause, Too

Respect the benefits of an expansion joint. Just keep in mind it’s a tool – you’ll have to use it correctly to keep the value in “value engineering.”

If you don’t design your system properly for the application, failure can happen anywhere from sealant joints to actual structural elements. Pay close attention to material choices and environmental threats, and you’ll succeed in maintaining or restoring the function of the building envelope!

For more education on commercial concrete products, head to our blog, where we’ve got resources on both protection and repair: