Lesson 1/Learning Event 2
TABLE 6.
DESIRABLE GRADATIONS OF AGGREGATE FOR DRYBOUND AND
WATERBOUND MACADAM BASE COURSES
Caliche. One of the fairly common characteristics of many caliches which make them valuable for
base courses is their quality of recementation upon being saturated by water, subjected to compaction,
and given a setting period. This is especially applicable to caliches which are cemented with lime, iron
oxide, or salt. Caliche is variable, however, in content (limestone, silt, and clay) and in the degree of
cementation; therefore, it is important that caliche of good uniform quality be obtained from deposits
and that it be compacted at optimum moisture. After caliches have been slaked for 72 hours the liquid
limit of the -40 fraction should not exceed 35, and the plasticity index should not exceed 10. For base
course material, caliches should be crushed to meet the following gradations:
Percent
Passing 2-inch square mesh...............
100
Passing No. 40 sieve .........................
15-35
Passing No. 200 sieve .......................
0-20
21
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