The PLASTICITY INDEX (PI) of a soil is the numerical difference between its liquid limit and its plastic limit; that is, PI = LL PL. The PI that appears in figure 15-37 means plasticity index.

Before delving into the remainder of this chapter, you may find it helpful to return to chapter 7 and review the topics concerning concrete. As you recall, in that chapter you studied concrete in terms of its use as a construction material, and you learned of the properties and requirements that comprise a good concrete. You also know that when concrete is placed in the field on a construction project, the concrete used must satisfy certain specified requirements. It is towards those properties and various requirements that concrete testing is directed.

In concrete testing, as in soils testing, no single test will provide all of the information required. Rather, there is an array of tests that must be per-formed. The following describes those tests with which an EA is most commonly concerned.