MITIGATING CONCRETE CRACKING
By Jose Arcila, Senior Geostructural Engineer, and Garrett Overcash, Senior Structural Engineer
Concrete is the most widely used construction material in the world. The durability, strength, and versatility are unmatched. The simplest form of concrete comprises cement, aggregate (large and small), and water. Modern concrete mixes often contain chemical admixtures that can greatly enhance the properties of the mix and/or the final cured material. With all the technological advances since the concrete was first used thousands of years ago, one fact still holds true……concrete cracks. Sometimes, the cracks are on a microscopic level, and other times, they impact the functionality of the intended structure. As contractors and engineers, we cannot “cure” concrete cracking but treat the “symptoms” and mitigate cracking to provide a useful product.
What Are Common Causes of Cracking?
Shrinkage
The most common cause of excessive concrete cracking is related to the volume change of concrete when it cures. Traditional concrete loses moisture when it cures, and the resulting shrinkage exceeds the concrete’s ability to resist tension, resulting in areas where the concrete stress is relieved in the form of cracks. Shrinkage cracking can be minimized by allowing concrete to shrink in a controlled manner.
Wayne Brothers Shrinkage Mitigation Procedures:
- Relief Joint Placement to Reduce the Volume of Concrete Undergoing Volume Change
- Curing Techniques to Reduce and Slow the Amount of Moisture Loss
- Scheduling of Concrete Placement to Reduce the Effects of Temperature, Humidity, and Wind
- Added Reinforcing at Areas of Geometric Change that are Subject to Tension Concentrations
Settlement
When concrete members are supported on a stable foundation, they can function as designed and adequately resist the known applied loading. When exterior forces from unaccounted-for sources are introduced into the concrete structure, cracking can occur to relieve these additional stresses. A common source of additional forces on a structure results from dimensional changes due to settlement, lateral or vertical. Preventing settlement begins long before the first concrete truck arrives.
Wayne Brothers Settlement Mitigation Procedures:
- Compaction of the underlying soil and the addition of a stiffened base layer, if necessary
- Excavation protection in the form of mud mats, coverings, and proper drainage to preserve the prepared base for concrete addition
- Shoring and earth stabilization to prevent lateral movement during and after concrete placement
Thermal
Concrete exposed to large variations in temperature can develop cracks, both at the time of placement and throughout the life of a cured structure. Immediately after placement, controlling the temperature difference between an exposed surface and the internal core of a large concrete pour ensures that the volume of concrete cures properly does not develop excessive stress due to internal restraint, and achieves the designed compressive strength. To address the effects of ambient temperature differences on cured concrete, adding contraction/control joints or eliminating restraint to large concrete volumes can reduce the development of cracks.
Wayne Brothers Thermal Mitigation Procedures:
- Developing a Thermal Control Plan to Maintain Allowable Thermal Range Across a Large Volume Concrete Member Placement
- Scheduling and Dividing Pours Based on Geometry and Volume to Reduce Thermal Delta Between Sections of the Structure
- Working with Ready-Mix Partners to Select a Concrete Mix Design that Minimizes Thermal Output During Curing Stage
- Deploying Thermal Sensors to Validate the Thermal Control Plan and Provide Real-Time Data
- Adding Relief Joints to Allow Thermal Expansion/Contraction without Restraining Concrete
Structural
Stress concentrations, loads, movement, and strength of the concrete are all concerns when designing concrete structures. Experience and careful planning can augment the code-prescribed concrete design to lessen the negative effects of all the factors listed above on the finished concrete design. A holistic approach to concrete design can eliminate or, at a minimum, reduce the severity of strength-related cracking.
Wayne Brothers Structural Mitigation Procedures:
- Careful Analysis of Loading as it Relates to the Final Intended Structure
- Addition of Reinforcement based on Experience Gained in Past Design and Construction Projects
- Detailed Conversations with Owners and End Users to Understand the Perceived Use of the Structure
- Designing the Structure with Placement of Volume Relief Joints and Construction Joints in Mind
- Providing Design Alternatives to Better Suit the End User’s Needs
- Providing Detailed Specifications to Aid Construction
Concrete cracking is a common issue. Wayne Brothers has developed a range of mitigation procedures to address these causes. By taking a holistic approach to concrete design and construction, Wayne Brothers aims to provide a satisfactory product.
