What does a CBR test primarily assess in road construction?

The California Bearing Ratio (CBR) test is a critical test in road construction that measures the load-bearing capacity of soil. The test evaluates the strength of the subgrade soil and provides a comparison of the soil's bearing capacity in relation to a standard material, typically crushed rock.

In road design, understanding the bearing capacity is essential because it informs engineers how much load the soil can support without undergoing significant deformation or failure. A higher CBR value indicates stronger subgrade material that can support heavier loads, which is vital for the long-term durability of the road.

The other choices do not align with the primary purpose of the CBR test. Durability of materials, while important, is assessed through different tests that look at the longevity and resilience of construction materials against environmental factors. Water absorption of asphalt does not relate to the CBR test, as it focuses on the permeability of asphalt rather than the soil's load-bearing properties. Finally, flexural strength of concrete assesses the ability of concrete to withstand bending forces, which is a separate aspect of materials engineering distinct from the CBR test's focus on soil capacity for road construction.