14 Questions to Ask a Commercial Concrete Contractor Before Hiring
To help ensure you feel confident that you’ve chosen the right concrete contractor, we’ve compiled a list of important questions [...]
Concrete is known for its durability, but cracks are almost inevitable over time.
Whether it’s a driveway, foundation, patio, or sidewalk, cracks can form due to factors like settling soil, temperature changes, corrosion, improper installation, or heavy loads.
However, not all cracks are cause for concern. Some are purely cosmetic, while others indicate serious structural problems requiring immediate repair.
In this guide, we’ll cover 9 common types of concrete cracks, their causes, how to identify them, and — most importantly — whether they need to be fixed immediately.
Table of Contents
1. Structural Cracks
2. Settlement Cracks
3. Heaving Cracks
4. Overload Cracks
5. Expansion Cracks
6. Alkali-Silica Reaction (ASR) Cracks
7. D-Cracking
8. Plastic Shrinkage Cracks
9. Crazing Cracks
10. When to Call a Professional
Structural cracks are deep and wide and often run through the entire thickness of a concrete slab, foundation, or wall. They are a serious concern because they indicate movement or instability in the concrete structure.
Structural cracks typically result from poor foundation design or inadequate steel reinforcement, which make the concrete more susceptible to movement.
Expansive soils that shrink and swell with moisture changes can also put stress on the foundation, leading to cracks over time.
Additionally, excessive loads or sudden impact damage (such as from construction equipment or seismic activity) can contribute to structural cracking.
Water infiltration is another major factor, as it weakens the soil beneath the foundation, causing it to shift and crack under pressure.
Why Reinforced Concrete Is Such a Valuable Building Material
If left untreated, structural cracks can worsen, leading to foundation failure, uneven flooring, or costly structural repairs. They can also allow water to seep in, leading to moisture issues and mold growth.
Fix ASAP!
Call a professional immediately. Ignoring structural cracks can lead to serious safety issues and expensive foundation repairs.
Settlement cracks occur when the soil beneath a concrete slab shifts, causing one part of the slab to sink or tilt. These cracks often indicate an uneven foundation or poor soil compaction, which can lead to more severe structural issues if not addressed.
Settling cracks usually occur due to improper soil preparation before concrete pouring. If the soil is not compacted correctly, it can shift over time, causing the concrete above it to settle unevenly.
Erosion is another common culprit, as heavy rain, plumbing leaks, and improper drainage can wash away supporting soil beneath the slab.
Additionally, when fresh concrete is poured into new construction areas, it often experiences natural ground settling, which can lead to cracks in driveways, sidewalks, or foundations.
Settlement cracks can worsen over time, leading to trip hazards, water pooling, and foundation instability.
Fix ASAP!
Settlement cracks should be repaired quickly to prevent further damage. Depending on the severity, solutions like slab jacking, foundation underpinning, or proper drainage correction may be needed.
Heaving cracks occur when sections of concrete are pushed upward, creating uneven surfaces and significant fractures. This type of crack is common in colder climates where frost heaving is a concern, but it can also happen due to tree roots or soil expansion.
One of the main causes of heaving cracks is frost heaving, which occurs during a freeze-thaw cycle when water in the soil beneath the concrete freezes and expands, pushing the slab upward.
In warmer climates, expansive clay soils can also contribute to heaving as they absorb water and swell.
Additionally, large tree roots growing underneath concrete can exert pressure on the slab, causing it to lift and crack.
Poorly prepared subgrades and inadequate drainage can exacerbate these problems by allowing excessive moisture to build up beneath the concrete.
Heaving cracks create dangerous trip hazards and severely damage driveways, sidewalks, patios, and foundations. If left alone, the movement may continue, leading to further cracking and instability.
Fix ASAP!
Crack repair should be done as soon as possible. Heaving cracks require immediate attention, as they can worsen over time and pose safety risks. Solutions may include soil stabilization, improved drainage, root barriers, or concrete lifting techniques such as mudjacking.
Overload cracks develop when concrete is subjected to more weight than it was designed to handle. This can happen in driveways, parking areas, or industrial spaces where excessive loads exceed the slab’s capacity.
The most common cause of overload cracks is placing heavy objects or vehicles on a slab not designed for that kind of weight. This often happens with improperly reinforced concrete or when the slab’s thickness is insufficient for the applied load. Poor subgrade preparation and weak soil conditions can also contribute to overload cracking, reducing the slab’s ability to distribute weight evenly.
Overload cracks compromise the structural integrity of the concrete, making it prone to further damage. If the slab continues to bear excessive weight, it might fail completely, leading to costly repairs or concrete replacements.
Fix ASAP!
Overload cracks indicate the concrete is failing under stress and should be repaired immediately. To prevent further damage, reinforcement, slab replacement, or load redistribution may be necessary.
Concrete naturally expands and contracts with temperature fluctuations. Without adequately placed expansion joints, the concrete has nowhere to move, leading to expansion cracks caused by internal pressure and tensile stresses.
Expansion cracks form when concrete experiences significant temperature changes, causing it to expand in hot weather and contract in colder conditions.
If expansion joints are not properly placed or spaced, the concrete will crack under pressure. This issue is pervasive in regions with extreme seasonal temperature fluctuations.
Another contributing factor is when concrete slabs push against fixed structures such as walls, curbs, or other sections of pavement, leading to stress-induced cracking.
While not an immediate structural threat, expansion cracks can widen over time, allowing water infiltration that may lead to further damage or concrete buckling.
Fix soon.
These cracks should be filled with sealant to prevent moisture damage and worsening deterioration, especially in regions with high temperature fluctuations.
ASR cracking, also known as “concrete cancer,” occurs when certain reactive aggregates in the concrete mix react with alkalis in cement, forming a gel. This gel absorbs moisture, expands, and creates internal pressure, leading to widespread cracking and deterioration over time.
ASR cracking is caused by a chemical reaction between silica-rich aggregates and the alkaline cement paste, which produces an expansive gel. Moisture accelerates this reaction, making it more common in humid or wet environments.
Poor-quality aggregates, high-alkali cement, and insufficient drainage can all contribute to ASR-related damage. Over time, the reaction leads to progressive cracking and surface deterioration.
ASR cracks weaken the concrete structure, leading to long-term durability issues. While they may not cause immediate failure, the expansion from the reaction can worsen over time, leading to more severe cracking, spalling, and structural weakening.
Fix soon.
While ASR cracking does not always require urgent repair, it should not be ignored. Sealing the cracks and reducing moisture exposure can slow deterioration.
In severe cases, affected concrete may need to be replaced, and future projects should use ASR-resistant aggregates or low-alkali cement to prevent recurrence.
D-cracking is a specific type of concrete failure that occurs due to moisture-related damage at the edges or joints of concrete slabs.
It typically starts as fine cracks near expansion joints, control joints, or slab edges and progressively worsens as water infiltrates and weakens the concrete.
This type of cracking is most commonly found in older pavements and concrete surfaces exposed to freeze-thaw cycles.
D-cracking is primarily caused by using coarse aggregates that are susceptible to moisture absorption. When water penetrates these aggregates, it expands and contracts with temperature changes, leading to internal stress and cracking.
Poor drainage, excessive exposure to deicing salts, and repeated freeze-thaw cycles accelerate this process. Over time, D-cracking spreads from the edges inward, leading to more significant structural issues.
D-cracking weakens the concrete’s overall integrity, making it more vulnerable to further damage. If left untreated, it can lead to significant deterioration, requiring full slab replacement.
Fix soon.
While D-cracking doesn’t always require immediate repair, it should be addressed before it spreads further.
Solutions include improving drainage, sealing cracks to prevent water infiltration, and replacing affected sections with concrete that uses more durable, freeze-resistant aggregates.
Shrinkage cracks, also known as plastic or drying shrinkage cracks, are thin, hairline fractures that form as concrete dries and cures.
These cracks are typically shallow and do not extend through the entire slab. While they may be unsightly, they’re generally not a structural concern unless they continue to grow or allow water infiltration.
Shrinkage cracks occur when the water in the concrete mix evaporates too quickly during the curing process, causing the concrete to contract and crack.
This is often due to improper curing techniques, high temperatures, low humidity, or excessive water in the original mix.
Rapid drying can cause the surface to crack before the concrete has gained enough strength to resist the stress. Shrinkage cracking is more common in large slabs without adequate control joints to accommodate natural movement.
Shrinkage cracks are usually cosmetic, but if they widen over time, they can allow moisture to seep in, leading to long-term deterioration. In freeze-thaw climates, trapped water can expand in cold temperatures, causing further cracking and surface damage.
Monitor over time.
Plastic shrinkage cracks do not require immediate repair unless they grow wider or begin to cause moisture-related issues. Sealing them with a concrete sealer can help prevent water intrusion and extend the life of the surface.
Proper curing techniques, such as keeping the concrete moist and shaded during the initial drying phase, can reduce shrinkage cracking in future projects.
Crazing cracks, also known as surface cracks or pattern cracks, appear as a network of fine, shallow lines on the surface of concrete. They don’t typically compromise the structural integrity of the slab but can affect its appearance.
Crazing cracks form due to improper curing techniques, often when the surface dries too quickly after pouring.
This can happen in hot, dry, or windy conditions if the concrete isn’t properly covered or treated with curing compounds. Excess water in the mix can also lead to crazing, as it weakens the surface and makes it prone to shrinkage as it dries.
While crazing cracks are primarily a cosmetic issue, they can make concrete surfaces more susceptible to wear and moisture penetration over time. In extreme cases, they could lead to surface deterioration, especially in freeze-thaw climates.
Monitor over time.
Crazing cracks don’t require immediate repair, but sealing the surface of the concrete can help prevent further deterioration. To avoid this issue, proper curing techniques should be used in future concrete projects.
While some minor concrete cracks can be monitored or repaired with DIY methods, certain types require immediate attention from a professional. Ignoring serious cracks can lead to costly structural damage, safety hazards, and long-term stability issues.
No matter what, you should closely monitor all types of cracks and take immediate action when they’re serious. Of course, using the right construction practices to begin with can ensure the durability of the concrete for years.
Contact FMP Construction if you’re concerned or have any concrete repair or replacement needs.
