When non-reinforced concrete breaks, how does it typically fail?

Non-reinforced concrete typically fails in a brittle manner, which means that it breaks suddenly without significant deformation or warning. This characteristic of brittleness is a result of the material's inability to absorb and redistribute stress effectively when subjected to loads beyond its capacity. Once the compressive strength is exceeded, cracks form quickly and the material fractures, leading to a complete failure rather than a gradual breakdown. This is in stark contrast to more ductile materials, which would exhibit noticeable deformation before breaking.

The other terms do not accurately describe the failure mode of non-reinforced concrete. For instance, gradual failure suggests a slow process, which is not typical for non-reinforced concrete as it tends to break quickly under stress. Crazed failure refers to fine cracking often seen on the surface, which might occur due to drying or shrinkage but does not characterize the overall failure mode. Lastly, flexible suggests the ability to bend or deform without breaking, which does not apply to non-reinforced concrete, as it lacks the capacity for flexibility under tensile stress.