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What Is Concrete Shrinkage and How Can It Be Reduced?
Concrete is one of the strongest and most durable construction materials available, but even the highest-quality concrete changes as it cures. One of the most common issues contractors and property owners encounter is concrete shrinkage. While shrinkage is a natural part of the curing process, excessive shrinkage can lead to cracking, curling, joint separation, and long-term durability concerns.
Whether you’re building a commercial slab, warehouse floor, parking lot, driveway, or foundation in Denver, Colorado, understanding concrete shrinkage is essential for achieving long-lasting results.
At 28 Concrete, we provide reliable concrete supply and placement solutions throughout Denver, Colorado, Aurora, Commerce City, Westminster, and surrounding communities. Understanding how shrinkage works allows contractors to make better decisions and avoid costly repairs later.
What Is Concrete Shrinkage?
Concrete shrinkage refers to the reduction in volume that occurs as concrete loses moisture and continues to cure over time.
When concrete is first mixed, it contains water that allows the cement particles to hydrate and bind the aggregates together. As hydration progresses and excess water evaporates, the concrete gradually contracts.
This reduction in volume is known as shrinkage.
Shrinkage is unavoidable to some degree, but problems occur when concrete shrinks unevenly or excessively. Because concrete has relatively low tensile strength, shrinkage stresses can result in cracks if they exceed the material’s ability to resist tension.
Why Does Concrete Shrink?
Several factors contribute to concrete shrinkage:
1. Drying Shrinkage
Drying shrinkage is the most common type.
As water evaporates from hardened concrete, the cement paste contracts. The greater the moisture loss, the greater the shrinkage.
This process can continue for months or even years after placement.
2. Plastic Shrinkage
Plastic shrinkage occurs before concrete hardens.
When moisture evaporates from the surface faster than bleed water can replace it, the surface contracts and cracks may develop.
This is especially common during:
- Hot weather
- Low humidity
- Windy conditions
- Direct sunlight
These conditions are common throughout Denver, Colorado, during the summer months.
3. Autogenous Shrinkage
Autogenous shrinkage occurs during hydration as cement consumes water internally.
High-strength concrete mixes with low water-cement ratios are particularly susceptible to this type of shrinkage.
4. Thermal Shrinkage
Concrete expands when warm and contracts when temperatures drop.
Significant temperature swings can contribute to cracking and shrinkage-related stress.
In Colorado, where daytime and nighttime temperatures can vary dramatically, thermal movement is an important consideration.
Why Is Concrete Shrinkage a Problem?
Some shrinkage is expected and manageable.
However, excessive shrinkage can create several issues:
Cracking
The most visible consequence is cracking.
Shrinkage cracks can:
- Reduce appearance
- Allow moisture penetration
- Accelerate freeze-thaw damage
- Increase maintenance costs
Curling
Concrete slabs may curl upward at edges or corners due to uneven moisture loss.
Curling can create:
- Trip hazards
- Equipment vibration
- Joint deterioration
Joint Separation
Shrinkage can pull slabs away from joints, reducing their effectiveness and creating gaps.
Reduced Durability
Cracks caused by shrinkage can allow:
- Water infiltration
- Salt penetration
- Chemical attack
- Reinforcement corrosion
This becomes especially important for parking lots, sidewalks, and industrial facilities exposed to Colorado’s harsh weather conditions.
How Much Does Concrete Shrink?
Typical concrete experiences drying shrinkage ranging from approximately:
- 400 to 800 millionths of strain
- Roughly 1/8 inch per 20 feet of slab
Actual shrinkage depends on:
- Mix design
- Aggregate type
- Water content
- Environmental conditions
- Curing practices
While these numbers may seem small, even minor movement can generate significant stress in large slabs.
Factors That Increase Concrete Shrinkage
Excess Water in the Mix
One of the biggest contributors to shrinkage is excessive water.
Many contractors are tempted to add water on-site to improve workability.
Unfortunately, this often leads to:
- Increased shrinkage
- Lower strength
- More cracking
A properly designed mix should achieve workability without excessive water.
High Cement Content
Cement paste shrinks more than aggregate.
Mixes with unnecessarily high cement content often experience greater shrinkage.
Poor Aggregate Selection
Aggregates help restrain shrinkage.
Concrete containing larger, well-graded aggregates generally shrinks less than mixes with smaller aggregate sizes.
Improper Curing
Rapid moisture loss during curing significantly increases shrinkage.
Without proper curing, concrete may lose water before hydration is complete.
Environmental Conditions
Colorado’s climate presents unique challenges:
- Low humidity
- Strong sunlight
- High winds
- Rapid temperature changes
These factors can accelerate moisture loss and increase the potential for shrinkage.
How Can Concrete Shrinkage Be Reduced?
Fortunately, several proven methods can significantly reduce shrinkage.
Use the Correct Water-Cement Ratio
One of the most effective strategies is maintaining a low water-cement ratio.
Less water means:
- Lower shrinkage
- Higher strength
- Better durability
Rather than adding water, contractors can use admixtures that improve workability while maintaining mix performance.
Use Quality Aggregates
Aggregates occupy most of the volume of concrete.
High-quality aggregate reduces the amount of cement paste required and helps limit shrinkage.
Well-graded aggregate blends are particularly effective.
Incorporate Shrinkage-Reducing Admixtures
Modern concrete technology offers admixtures specifically designed to reduce shrinkage.
These products help:
- Reduce moisture-related contraction
- Minimize cracking
- Improve long-term performance
Many commercial projects in Denver, Colorado, now incorporate these admixtures into their specifications.
Proper Joint Placement
Control joints help manage shrinkage by encouraging cracks to occur in predetermined locations.
Proper joint spacing is essential.
As a general rule:
- Joint spacing should not exceed 24 to 30 times the slab thickness.
Properly installed joints can dramatically improve slab appearance and performance.
Cure Concrete Correctly
Curing is one of the most overlooked steps in concrete construction.
Proper curing:
- Retains moisture
- Supports hydration
- Reduces shrinkage stress
- Improves strength development
Common curing methods include:
- Water curing
- Curing blankets
- Curing compounds
- Plastic sheeting
The longer moisture is maintained, the better the final results.
Use Fibers
Synthetic or steel fibers can help reduce shrinkage-related cracking.
Fibers distribute stresses more evenly throughout the slab and improve crack resistance.
Many industrial and commercial projects now routinely incorporate fiber reinforcement.
Plan for Weather Conditions
Weather monitoring is critical during placement.
Avoid pouring during:
- Extreme heat
- High winds
- Very low humidity
When challenging conditions cannot be avoided, contractors should use protective measures such as:
- Windbreaks
- Sunshades
- Evaporation retardants
These precautions are especially important for projects requiring Aurora concrete delivery during the summer months.
Concrete Shrinkage in Colorado
Colorado presents unique challenges for concrete contractors.
Projects throughout:
- Denver Colorado
- Aurora
- Commerce City
- Westminster
must contend with environmental factors that can accelerate shrinkage.
These include:
High Elevation
Higher elevations increase evaporation rates and exposure to ultraviolet radiation.
Low Humidity
Dry air rapidly draws moisture from fresh concrete.
Freeze-Thaw Cycles
Cracks created by shrinkage can worsen when moisture enters and freezes.
Large Temperature Swings
Daily temperature changes place additional stress on concrete surfaces.
Because of these conditions, proper mix design and curing procedures are particularly important throughout Colorado.
The Importance of Working With an Experienced Concrete Supplier
Shrinkage control begins long before concrete arrives on-site.
An experienced supplier can help contractors choose:
- Proper mix designs
- Appropriate admixtures
- Aggregate blends
- Air entrainment levels
- Strength requirements
At 28 Concrete, we work closely with contractors to provide mixes designed for Colorado conditions and project-specific performance requirements.
Whether you’re pouring a commercial slab, foundation, parking lot, or industrial floor, selecting the right mix can significantly reduce shrinkage-related issues.
Learn more about our concrete solutions on our service page:
When Should You Be Concerned About Shrinkage?
Not every crack indicates a serious structural problem.
However, professional evaluation may be warranted when:
- Cracks continue to widen.
- Edges begin curling significantly.
- Water intrusion occurs
- Joint separation becomes excessive.
- Surface scaling develops
Early intervention often prevents more expensive repairs later.
Final Thoughts
Concrete shrinkage is a natural part of the curing process, but excessive shrinkage can create costly problems, including cracking, curling, joint separation, and reduced durability.
Fortunately, shrinkage can be significantly reduced through proper mix design, quality aggregates, controlled water content, appropriate curing methods, shrinkage-reducing admixtures, and careful placement practices.
For contractors and property owners throughout Denver, Colorado; Aurora; Commerce City; and Westminster, understanding shrinkage is an important step toward achieving durable, long-lasting concrete installations.
If you’re planning an upcoming project and want expert guidance on mix selection and concrete delivery, contact the team at 28 Concrete today.
Contact us here:
Our experienced team is ready to help ensure your next concrete project performs as intended for years to come.
FAQ:
Q.: Does all concrete shrink as it cures?
A.: Yes. Concrete naturally shrinks as excess moisture evaporates and the cement hydrates. Some shrinkage is expected, but proper mix design, curing, and joint placement help prevent excessive cracking and movement.
Q.: What causes shrinkage cracks in concrete?
A.: Shrinkage cracks typically occur when concrete loses moisture too quickly or when the slab is restrained from moving naturally. Excess water in the mix, hot weather, wind, and poor curing practices are common causes.
Q.: Why is shrinkage control especially important in Colorado?
A.:Colorado’s low humidity, high elevation, strong sunlight, and temperature swings can accelerate moisture loss from fresh concrete. Without proper curing and mix design, these conditions can increase the risk of shrinkage cracking and long-term durability issues.
