Why Does Concrete Sink & What You Can Do About It
Concrete sinks because the soil or ground beneath it gradually erodes or settles over time. Let’s take a look at the primary reasons behind this phenomenon:
- Soil Erosion
- Soil Compaction
- Soil Shrinkage
- Freeze-Thaw Cycles
Soil Erosion
Water from rain, flooding, or leaks can wash away the soil under the concrete, creating voids into which the concrete slab settles. This is often seen when downspouts are pointed directly at the concrete slab, gutters overflow onto the concrete, or there is a lot of water runoff in the area.
If cracks are not properly sealed, water can seep underneath the slab and gradually wash away the soil.
- Solution: Concrete replacement is the easiest option as the damaged concrete is removed, the soil is repaired, and new concrete is poured. Another option is slabjacking (also known as mudjacking). This is a common repair technique where a foam or grout mixture is pumped under the sunken concrete to raise it back to its original level.
- Prevention: Ensure proper landscaping and drainage around the concrete areas to prevent water from pooling. Using gutters and downspouts effectively can redirect water away from concrete slabs.
Soil Compaction
When the soil beneath the concrete isn’t compacted well before pouring concrete, it may sink over time. During construction, the soil gets disturbed and becomes loose. It can take 5 to 10 years for the disturbed soil to naturally settle down.
In the case of new construction, a significant amount of soil is displaced and rearranged. As soon as the concrete is poured onto that disturbed soil, it’s only a matter of time before the soil and the concrete sink due to natural compaction. Unfortunately, due to high demand and the rapid process of constructing homes, proper soil compaction is becoming less common in residential home builds.
Even with soil compaction procedures, it is challenging to get the soil 100% compacted, which can lead to some settling.
- Solution: Remove the damaged concrete, properly compact the soil, and repour new concrete. Another option is slabjacking which can be used to lift the concrete back into place.
- Prevention: Before pouring concrete, ensure the soil is properly compacted and prepared. Hiring a professional to assess and prepare the site can help avoid future issues.
Soil Shrinkage
In areas with lots of clay, a long period of dry conditions can cause the soil to shrink.
As the soil dries out, it contracts or shrinks, reducing the volume and support it provides to the concrete above. Concrete can begin to sink unevenly without sufficient support, creating tripping hazards, cracks, and other structural issues. This sinking not only compromises the aesthetic and functional aspects of the concrete but also leads to costly repairs.
- Solution: Polyurethane Foam Injection is a common repair technique that involves injecting a high-density foam under the concrete.
- Prevention: Regular soil watering and proper landscaping around your concrete slabs can help maintain consistent moisture levels, especially during dry seasons. This can prevent the soil from drying out and shrinking.
Freeze-Thaw Cycles
In colder climates, the freeze-thaw cycle can cause the ground to heave and then settle, which can displace the concrete slabs.
Over time, as the cycles repeat, these pressures can cause cracks and breakage, compromising the integrity of the concrete. During thaw periods, the ice melts, and the water can erode the base or subgrade beneath the concrete, leading to uneven settling or sinking. This repeated process gradually undermines the stability of the concrete, causing it to sink and often resulting in the need for repairs or replacement to maintain safety and functionality.
- Solution: Polyurethane foam injection is an effective method to lift and stabilize sunken concrete caused by freeze-thaw cycles. It’s less invasive and has a quick curing time.
- Prevention: Use sealants to protect the concrete from absorbing water, which can expand when frozen and cause cracking and heaving.
Should You Fix Your Sinking Concrete?
Fixing sinking concrete is important to protect visitors and keep your property looking great. Plus, it can save money on longer-term repairs.
Aurora Asphalt & Concrete can help you understand the cause behind sinking concrete and get it back in the right position.
Inevitably, concrete will crack in its lifetime. Therefore, it is important to have concrete reinforced with rebar so that when it does crack, the rebar prevents uneven lips.
If you’d like to see what we can do for your concrete, request a free estimate and a member of our team will visit your property; or visit the Pricing Calculator for an ‘unofficial’ estimate.