PERFORMANCE OF TREATED AND UNTREATED AGGREGATE BASES

THERE WERE THREE MAJOR EXPERIMENTS INCLUDED IN THE STUDY OF FLEXIBLE PAVEMENT PERFORMANCE AT THE AASHO ROAD TEST, THE FACTORIAL, THE SPECIAL BASE, AND THE PAVED SHOULDER EXPERIMENT. IN THE SPECIAL BASE STUDY FOUR DIFFERENT TYPES OF BASE COURSE WERE INCLUDED: CRUSHED STONE, A WELL-GRADED UNCRUSHED GRAVEL, A CEMENT-TREATED MATERIAL, AND A BITUMINOUS TREATED MATERIAL. THE DESIGN OF THE BASE TYPE EXPERIMENT WAS SUCH THAT NO MATHEMATICAL ANALYSIS WAS ATTEMPTED. THE ANALYSIS WAS ESSENTIALLY GRAPHICAL. FROM THE GRAPHS PRESENTED THE THICKNESS OF THE STONE, CEMENT-TREATED, AND BITUMINOUS TREATED BASES NECESSARY TO MAINTANIN A LEVEL OF SERVICEABILITY OF 2.5 AT ANY NUMBER OF AXLE-LOAD APPLICATIONS CAN BE OBTAINED. RESULTS SUGGEST THAT THERE WAS CONSIDERABLE DIFFERENCE IN THE TREATED AND NON-TREATED BASES; ALSO A LESSER DIFFERENCE OF THE CEMENT- AND BITUMINOUS-TREATED BASES. THE LOSS OF SERVICEABILITY OF THE CEMENT-TREATED BASE SECTIONS WAS DUE LARGELY TO HIGH SLOPE VARIANT; THAT OF THE BITUMINOUS-TREATED BASE SECTIONS WAS DUE MORE TO A RELATIVELY HIGH LEVEL OF DEPTH OF RUTTING. THE SECTIONS CONTAINING THE UNTREATED GRAVEL BASE FAILED EARLY IN THE TEST, TO THIS DEGREE THEIR PERFORMANCE WAS VASTLY INFERIOR TO THE STONE, BITUMINOUS- AND CEMENT-TREATED BASES. IN SUBSECTIONS CONTAINING THE STONE, CEMENT-TREATED AND BITUMINOUS-TREATED BASES THAT SURVIVED THE TEST, THE RATE OF PROGRESSION OF RUTTING WAS LOWER DURING THE SECOND YEAR OF TRAFFIC THAN DURING THE FIRST. THERE WAS A LEVEL OF THICKNESS OF THE STONE, CEMENT TREATED AND BITUMINOUS-TREATED BASES ABOVE WHICH THE DEPTH OF RUT ON THE SURFACE REMAINED CONSTANT WITH AN INCREASE IN BASE THICKNESS, AND BELOW WHICH IT INCREASED RAPIDLY WITH DECREASED IN THICKNESS. THE BITUMINOUS-TREATED BASE AND BITUMINOUS CONCRETE SURFACE OFFERED CONSIDERABLY MORE STANCE TO CONSOLIDATION AND DISPLACEMENT AT LOW THAN AT HIGH TEMPERATURES. RESULTS OF THE SPECIAL BASE STUDY SHOULD HAVE CONSIDERABLE INFLUENCE ON THE DESIGN AND CONSTRUCTION OF FLEXIBLE PAVEMENTS. THE FACT THAT RELATIVELY LOW COST AGGREGATES CAN BE USED FOR STABILIZATION SHOULD MAKE THIS TYPE OF CONSTRUCTION PRACTICAL AND ECONOMICALLY FEASIBLE. LOCAL CONDITIONS, AVAILABILITY AND COST SHOULD BE THE MEANS OF DETERMINING WHICH TYPE OF STABILIZATION, CEMENT BITUMINOUS OR OTHER, WILL BEST SERVE EXISTING REQUIREMENTS.