Class C Concrete (ODOT Specification)

Class C concrete is a structural concrete classification commonly referenced in Ohio construction specifications, particularly in standards published by the Ohio Department of Transportation (ODOT). The designation refers to a required performance level for the concrete rather than a single fixed mix recipe.

Performance Requirements

Under ODOT Item 499 – Concrete (General), Class C concrete typically includes the following criteria:

• Minimum compressive strength: 4,000 PSI at 28 days

• Minimum cement content: 600 pounds per cubic yard

• Maximum water-cement ratio: 0.48

• Air entrainment: Typically 5–8% for durability in freeze-thaw climates

Concrete mixes must be proportioned so they can consistently achieve the specified 28-day compressive strength while maintaining proper workability and durability for the intended application.

Typical Applications

Class C concrete is widely used for structural and civil construction projects throughout Ohio, including:

• Foundations and footings

• Structural slabs

• Retaining walls

• Curbs and sidewalks

• Pavement repairs

• Bridge and infrastructure components

Because it provides a balance of strength and durability, Class C concrete is considered a standard structural mix in many municipal and transportation projects.

Mix Design Considerations

While the specification establishes performance requirements, the exact mix design may vary depending on factors such as:

• Aggregate source and size

• Environmental exposure conditions

• Placement method and workability needs

• Admixtures used to improve performance

Concrete producers develop a Job Mix Formula (JMF) to ensure the mix meets the required strength, water-cement ratio, and air-entrainment specifications.

Durability in Ohio’s Climate

Air entrainment is an important component of Class C concrete. The inclusion of microscopic air bubbles helps protect the concrete from damage caused by freeze-thaw cycles, a common concern in northern climates such as Ohio.