plactic index below 22

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Flexible pavement:

Are those pavements which reflect the deformation of subgrade and the subsequent layers to the surface.

Rigid pavement:

The rigid characteristic of the pavement are associated with rigidity or flexural strength or slab action so the load is distributed over a wide area of subgrade soil.

"Subgrade" is typically written as one word when referring to the layer of soil or aggregate material beneath a road or structure.

It's a grading term.

EF (or XF) stands for Extremely Fine, and 40 is a numeric subgrade within that broader class. It's just below AU - Almost Uncirculated - and means that the coin has been in circulation but has only very slight visible wear.