7.2 : Behavior of Concrete Under Compressive Load

Concrete exhibits specific behaviors under different compressive loads. Understanding this is crucial for understanding its structural integrity. When concrete undergoes uniaxial compression, it tends to develop cracks that run parallel to the direction of the force. These parallel cracks stem from localized tensile stresses that occur perpendicular to the compression direction. Additionally, angled cracks may appear due to the formation of shear planes.

As the concrete specimen fractures under this uniaxial load, it typically separates along two planes aligned with the force, breaking into elongated, columnar fragments that mirror the stress direction. Under biaxial compression, the failure usually happens along a plane parallel to the loads, producing slab-like fragments. In contrast, triaxial compression leads to a crushing behavior, indicating a distinct failure mechanism compared to fracturing.

The observed fracture patterns and behaviors are indicative of the concrete's response under direct stress conditions only. To ensure accuracy in testing, specimens should have a length-to-width ratio of two, which helps avoid additional lateral forces that might otherwise be introduced by the testing machine's platens. This specific setup aids in isolating the concrete's inherent response to compressive stress, essential for evaluating its performance and durability in various construction applications.