Concrete Cracks, What Causes Them & How to Fix Them

1. Shrinkage Cracks

• What Causes Them: Concrete shrinks as it cures - the chemical hydration process that hardens the concrete consumes water and reduces the material's volume slightly. This volumetric change is normal and expected, but when it's uneven - because the surface is drying faster than the interior, because the mix had too much water, or because curing conditions were too warm or too dry - the differential shrinkage produces surface cracking.

  Shrinkage cracks typically appear as fine, shallow, somewhat random hairline patterns across the concrete surface within the first days or weeks after placement.

• How to Fix Them: Shrinkage cracks that are narrow - hairline to approximately one-eighth inch wide - and haven't displaced vertically are cosmetic rather than structural. They can be filled with a concrete crack filler or penetrating sealant that closes the crack against moisture infiltration without requiring structural intervention. The repair's goal is preventing water entry, which in Michigan's climate prevents freeze-thaw cycling from widening the crack through subsequent winters.

  Cracks that have widened beyond hairline width or that show any vertical displacement warrant closer inspection before assuming shrinkage is the cause.

2. Temperature Changes and Freeze-Thaw Cycles

• What Causes Them: Concrete expands with heat and contracts with cold - the thermal cycling across Michigan's seasonal temperature range introduces low-frequency stress on the slab that accumulates over years.

  Freeze-thaw cycling operates on the more damaging mechanism: water absorbed into surface pores or existing micro-cracks freezes and expands by approximately nine percent, exerting internal pressure that fractures the surrounding material.

  The crack widens, admits more water in the next wet event, experiences more expansion in the next freeze, and widens further.

  Southeast Michigan produces dozens of freeze-thaw events between November and March - the damage is cumulative and accelerates as the crack opens.

• How to Fix Them: Narrow cracks from thermal cycling without significant displacement are filled with flexible concrete sealant - the flexibility allows the repaired crack to accommodate the thermal movement that caused it without reopening at the repair joint.

  Larger or deeper cracks that have developed from repeated freeze-thaw cycling are filled with epoxy injection for structural cracks or polyurethane foam injection for cracks that need flexibility rather than rigidity.

  Where freeze-thaw damage has produced surface spalling alongside cracking, resurfacing the affected area after crack repair addresses the surface deterioration that complements the crack repair.

3. Settlement and Soil Movement

• What Causes Them: The slab rests on the soil beneath it, and when that soil changes - through erosion that creates voids, through consolidation under load, through Michigan's clay-rich soils expanding and contracting with seasonal moisture variation, or through frost heave displacing the base in winter - the slab expresses that movement as cracking and displacement.

  Settlement cracks typically appear as diagonal or staircase patterns, with visible vertical displacement between the two sides of the crack - one side higher than the other. That displacement is the diagnostic feature that distinguishes settlement cracks from shrinkage or thermal cracks.

• How to Fix Them: Settlement cracks require addressing the soil condition before the crack repair will hold - filling a settlement crack while the soil movement that caused it continues produces a repair that reopens on approximately the same timeline as the original crack.

  For minor settled sections where the base is otherwise sound and the movement has stabilized, mudjacking or polyurethane foam injection fills the void beneath the slab and raises it back toward level, after which the crack is patched.

  For significant ongoing settlement or base conditions that foam injection can't adequately address, slab replacement with properly compacted base material and corrected drainage is the appropriate scope.

4. Overloading and Heavy Traffic

• What Causes Them: Concrete slabs are designed for specific load capacities based on their thickness, mix specification, and reinforcement. Residential driveways are typically designed for passenger vehicle loads - not the repeated heavy loads of delivery trucks, construction equipment, or loaded commercial vehicles.

  When loads exceed the slab's design capacity, the concrete flexes more than its tensile strength can accommodate, and structural cracks propagate from the bottom of the slab upward.

  These cracks typically run perpendicular to the direction of travel in driveways, and they often have visible displacement between the two sides.
• How to Fix Them: Cracks from overloading that have displaced vertically can't be adequately addressed with surface crack filler - the structural integrity of the slab at that location has been compromised, and the crack will continue to displace under repeated loads regardless of what fills it at the surface.

  Small structural cracks without significant displacement can be stabilized with epoxy injection, which bonds the two crack faces and restores some tensile capacity across the repair.

  Larger cracks or areas with multiple structural cracks typically require removal and replacement of the affected slab sections with a thickness and specification appropriate for the actual loading conditions.

5. Corrosion of Reinforcement Steel

• What Causes Them: Reinforced concrete uses steel rebar embedded within the slab to provide tensile strength that concrete alone doesn't have. When water and chloride compounds - from de-icing salt applications, from chloride-bearing soils, or from sustained moisture infiltration - reach the rebar, they initiate and accelerate steel corrosion.

  Corroding steel expands as iron oxide forms on the bar surface, exerting outward pressure on the surrounding concrete that eventually exceeds the concrete's tensile capacity. The result is cracking and spalling along the rebar line - typically appearing as longitudinal cracks running parallel to the rebar path, often with rust staining at the crack faces.

• How to Fix Them: Rebar corrosion repair is more involved than surface crack repair because it requires addressing the corroded steel rather than just the crack the corrosion produced.

  The concrete over the corroded bar is removed to expose the steel, the rust is treated or the bar replaced if section loss is significant, a corrosion-inhibiting coating is applied, and the cavity is filled with compatible repair mortar or concrete.

  The crack at the surface is the visible expression of the problem; the corroded steel is the actual problem. Repairs that fill the surface crack without addressing the steel continue to spall as the corrosion progresses.

6. Plastic Shrinkage Cracks

• What Causes Them: Plastic shrinkage cracks develop during the very early phase of concrete placement - when the concrete is still plastic (workable) rather than hardened.

  The crack mechanism is differential evaporation: surface moisture evaporates faster than bleed water from the interior can replenish it, creating tensile stress in the surface layer that the unhardened concrete can't resist.

  Hot temperatures, low humidity, and wind all accelerate surface evaporation and increase plastic shrinkage crack risk. These cracks are typically shallow, relatively parallel, and spaced a few inches to a foot apart - the characteristic pattern distinguishes them from later-forming crack types.

• How to Fix Them: Plastic shrinkage cracks that are shallow and closed can be sealed with concrete crack filler or penetrating sealant that closes them against moisture infiltration without requiring structural intervention.

  Wider plastic shrinkage cracks are patched with polymer-modified concrete patching compound applied to clean, sound crack faces.

  The prevention side is more important than the repair side for plastic shrinkage. On pour days with high evaporation potential, contractors apply evaporation retarder to the fresh surface, cover the placement with plastic sheeting during finishing delays, and begin curing immediately after finishing to limit the surface drying that drives crack formation.

How to Prevent Concrete Cracks

Prevention is partially within control and partially a function of service conditions that can't be fully managed. The controllable factors at installation are the most impactful:

• Correct water-to-cement ratio in the mix - the single most common installation error that reduces concrete quality is excess water added at the site to improve workability - produces concrete with the design strength and lower porosity that resists cracking and freeze-thaw damage.
• Control joints placed at appropriate intervals - typically every 8 to 12 feet in residential flatwork - create planned weak points that direct shrinkage and thermal cracks to the joint rather than allowing them to propagate randomly across the slab. For a detailed look at how joint design and maintenance affect concrete performance over the long term, our guide on Everything You Need to Know About Concrete Joint Repair and Maintenanceeverything you need to know about concrete joint repair and maintenance covers the full picture.
• Proper curing - keeping the surface moist and covered for the minimum recommended curing period - allows the concrete to gain strength before it's exposed to drying and stress.
• Sealant applied to cured concrete surfaces reduces moisture infiltration, limits freeze-thaw damage, and protects against chloride penetration that drives rebar corrosion.
• Proper soil preparation and compaction beneath the slab establishes the stable base that prevents the settlement cracks that compromised base conditions produce.

Bethel Custom Brick – Your Concrete Repair Experts in the Detroit Metro Area

Concrete cracks don't fix themselves - and the longer they're left, the more water enters, the more freeze-thaw cycling widens them, and the more expensive the repair becomes. At Bethel Custom Brick, we provide Professional Concrete Crack Repair and Restoration Servicesprofessional concrete crack repair and restoration services throughout the Detroit Metro area - identifying the root cause of each crack type and delivering lasting solutions that restore the strength, safety, and appearance of your concrete surfaces. Contact Bethel Custom BrickContact us today for a free inspection and let us help you stop the damage before it spreads.