Abstract:
THE CONSTRUCTION OF GRADED MIX ROADS DURING 1937-1938 WAS LIMITED TO PROVIDING BASES FOR THEIR BITUMINOUS WEARING COURSE TREATMENTS. THE MATERIALS USED, SUCH AS CRUSHED LIMESTONE, CHERT GRAVEL, AND CHERT MINE TAILINGS, ARE DETERMINED BY THE LOCALITY. SINCE 1937 THE DEPTH OF STABILIZED COMPACTED MATERIAL WAS INCREASED TO 6 IN. MIXED IN ONE COURSE AND COMPACTED IN THIN INCREMENTS BY SHEEPS- FOOT TAMPERS. OTHER CHANGES THAT DEVELOPED IN THE CONSTRUCTION METHOD AFTER NOTING INCREASED RAVELING AND PITTING, CONSISTED OF TWO COURSE CONSTRUCTION THAT SHORTENED MIXING TIME, PRODUCED A FINISHED MIX AND COMPACTED THE MATERIAL TO A DENSE AND STABLE CONDITION WHILE CLAY- AGGREGATE STABILIZATION WAS BEING DEVELOPED, THE PRIMARY CONSIDERATION HAS BEEN TO OBTAIN A PLASTIC INDEX OF ABOUT 10. HOWEVER, REGARDLESS OF THE PLASTIC INDEX, LITTLE OR NO RAVELING OCCURS WHEN A THIN BITUMINOUS ARMOR COAT IS APPLIED AFTER THE BASE HAS BEEN PRIMED AND COMPACTED. SOMETIMES A WATER-BOUND MACADAM BASE WILL SUFFICE.
Supplemental Notes:
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