Which two types of poor grading are identified?

The correct choice identifies "uniformly graded" and "gap graded" as the two types of poor grading. Understanding these terms in the context of grading is essential for evaluating the quality of the graded materials or aggregate.

"Uniformly graded" means that the material consists of particles that are mostly similar in size. This lack of variety in the particle sizes can lead to inadequate void spaces, which may hinder proper drainage, reduce strength, and lead to other structural issues in applications such as construction or road building. A well-graded material, on the other hand, includes a variety of particle sizes that can maximize packing density and minimize voids, improving the material's overall properties.

"Gap graded" refers to a situation where certain particle sizes are missing from the grading spectrum. This can create weak points within the material structure, where the absence of these sizes leads to inefficiencies in load distribution and strength. In construction, gap-graded materials do not perform as well compared to well-graded materials because the resulting voids cannot be effectively filled, again impacting the overall performance.

Understanding these types of grading is crucial for applications where material performance is critical, as both uniformly graded and gap graded systems can lead to adverse outcomes in terms of stability and strength.