COLORADO CONCRETE PAVEMENT AND SUBBASE EXPERIMENTAL PROJECT

IN 1952, THE FIRST TWO LANES OF A PLANNED FOUR-LANE CONCRETE HIGHWAY BETWEEN DENVER AND CASTLE ROCK, COLO. WERE PLACED. THE ALIGNMENT FOR THE HIGHWAY TRAVERSED AREAS HAVING SOIL OF HIGH SWELL CHARACTERISTICS. WITHIN A SHORT TIME AFTER PLACEMENT, THE PAVEMENT WARPED AND CRACKED IN CERTAIN AREAS. IN 1956 THE ADDITIONAL TWO LANES WERE PLACED. IN THIS CONSTRUCTION, THE SUBGRADE WAS ADJUSTED ON THE WET SIDE OF OPTIMUM MOISTURE FOR THE SPECIFIED COMPACTIVE EFFORT. FIVE PAVEMENT STRUCTURES WERE INCORPORATED IN THE JOB: AN 8-INCH PLAIN CONCRETE SLAB BUILT ON A 4-INCH GRANULAR SUBBASE TREATED WITH 2 PERCENT PORTLAND CEMENT, A 10-INCH PLAIN PAVEMENT ON A 4-INCH SUBBASE, AN 8-INCH PLAIN PAVEMENT ON A 20-INCH SUBBASE, AND TWO MESH-REINFORCED 8-INCH PAVEMENTS ON A 4-INCH SUBBASE. THE JOINT SPACING WAS 106 FT IN ONE REINFORCED SECTION AND 61 FT IN THE OTHER. DURING THE SPRING OF 1959, THE FIVE EXPERIMENTAL DESIGNS WERE TESTED UNDER DYNAMIC AND STATIC WHEEL LOADS. DEFLECTIONS AND STRAINS DUE TO DYNAMIC LOADS AND DELECTIONS UNDER STATIC LOADS WERE MEASURED. THE MODULUS OF SUBGRADE REACTION WAS DETERMINED FROM PLATE BEARING TESTS. DATA FROM THE TESTS SHOW THAT THE REINFORCED PAVEMENT DESIGNS HAVING A RELATIVELY LONG JOINT SPACING UNDERGO GREATER CORNER DEFLECTIONS UNDER LOAD, AND ATTAIN HIGHER CURL THAN THE PLAIN CONCRETE PAVEMENT HAVING RELATIVELY SHORT JOINT SPACING. AN EXPERIMENTAL SECTION HAVING A 20-INCH CEMENT-TREATED SUBBASE GAVE LOWEST CORNER DEFLECTION. ONLY LIMITED CONCLUSIONS ARE DRAWN PENDING FURTHER VISUAL OBSERVATIONS AND TESTING AFTER A LONGER PERIOD OF SERVICE. /AUTHOR/