FIELD AND LABORATORY STUDIES OF THE EFFECT OF SUBBASE TYPE ON THE DEVELOPMENT OF D-CRACKING

FIELD AND LABORATORY OBSERVATIONS OF PAVEMENTS INDICATED THAT THE DEVELOPMENT OF D-CRACKING DEPENDS ON THE NATURE OF THE COARSE AGGREGATE USED IN THE CONCRETE AND THE FACILITY WITH WHICH MOISTURE CAN BE TRANSPORTED AWAY FROM THE SUBBASE AND PAVEMENT SLAB. IT WAS FOUND NECESSARY TO INSTALL LONGITUDINAL TILE SUBDRAINS IN THE SHOULDER AREAS TO PREVENT D-CRACKING ASSOCIATED WITH COARSE AGGREGATES. VARYING THE TYPE OF SUBBASE MATERIAL ALSO AFFECTS THE RATE OF DETERIORATION DEVELOPMENT. BASED ON THESE OBSERVATIONS, A SERIES OF SIMULATED PAVEMENT SLABS WAS CAST IN THE PCA OUTDOOR TEST PLOT TO STUDY THE EFFECT OF GRANULAR, CLAY, CEMENT-TREATED, AND GRANULAR + VAPOR BARRIER SUBBASES ON MOISTURE MOVEMENTS AND THE DEVELOPMENT OF DISTRESS IN THE CONCRETE SLABS. THREE COARSE AGGREGATES KNOWN TO CAUSE D-CRACKING WERE USED. MOISTURE CHANGES WERE BASED ON WEIGHT MEASUREMENTS OF 1-IN. THICK BY 5 1/2-IN. DIAMETER CONCRETE DISCS TIGHTLY SECURED AND INSERTED INTO PRECAST CYLINDRICAL HOLES OF SIMILAR SIZE IN EACH SLAB. RESULTS AFTER TWO FREEZE-THAW SEASONS SHOWED THAT THE LEVEL OF SATURATION IN ALL SLABS HAD INCREASED AND, FROM EXAMINATION OF CRACK PATTERNS IN CORES TAKEN FROM THE SLAB, SOME COARSE AGGREGATE PARTICLES HAD BECOME CRITICALLY SATURATED PRIOR TO FREEZING. /AUTHOR/