SCALING OF AIR-ENTRAINED AND NON-AIR-ENTRAINED CONCRETE

CASE HISTORIES AND WEATHER DATA ARE PRESENTED FOR FOUR PAVEMENT SECTIONS CONSTRUCTED DURING DIFFERENT SEASONS WITH THE SAME CONCRETE MIXTURE POSSESSING THE SAME PROPERTIES OBTAINED FROM THE SAME READY-MIXED CONCRETE SUPPLIER. PHOTOGRAPHS WERE TAKEN OF AREAS OF THE PAVEMENTS AT DIFFERENT STAGES OF SCALING AND PETROGRAPHIC CORE EXAMINATIONS WERE MADE. AREA 80 CONSTITUTED WELL-AIR- ENTRAINED CONCRETE, BUT THE TOPMOST SECTION OF THE PAVEMENT WAS SUSCEPTIBLE TO DISRUPTION BY FREEZING AND THAWING BECAUSE OF HIGH ABSORPTIVITY, RESULTING FROM LACK OF ADEQUATE CURING, AND EARLY DRYING AND CARBONATION OF THE CEMENT PASTE MATRIX. THE ACTION OF FREEZING WAS AGGRAVATED BY THE PRESENCE OF DE-ICING SALTS. AREAS 92, 93, AND 98 COMPRISED NON-AIR-ENTRAINED CONCRETE THAT WAS NOT RESISTANT TO FREEZING AND THAWING WHILE WET, ESPECIALLY IN THE ESPECIALLY IN THE PRESENCE OF DE-ICING SALTS. WEATHER THE PAVEMENT COULD NOT EXPERIENCE ANY SUBSTANTIAL DRYING FOLLOWING PLACING AND WERE WELL SATURATED WITH WATER AT THE TIME OF FREEZING AND THAWING. THIS CONCRETE OF LOW-WATER CEMENT RATIO WAS SUSCEPTIBLE TO RAPID DISINTEGRATION DURING REPEATED FREEZING. INCIPIENT CEMENT-AGGREGATE REACTIONS INVOLVING DOLOMITES, CHALCEDONIC CHERTS, AND CHERTY PHASES OF DOLOMITES OCCURRED, BUT NO DELETERIOUS EFFECTS WERE INDICATED BY THE PETROGRAPHIC EXAMINATION. THESE TESTS INDICATE THAT AIR-ENTRAINMENT WILL NOT ENSURE ADEQUATE DURABILITY OF EXPOSED CONCRETE IN THE ABSENCE OF GOOD CONCRETING PRACTICES. THE DEFECT LEADING TO FAILURE OF THE CONCRETE IN AREA 80 WAS THE RESULT OF INATTENTION TO CURING AND PROTECTION OF THE CONCRETE FROM EARLY DRYING PRIOR TO DEVELOPMENT OF A SOUND CEMENT PASTE MATRIX OF LOW ABSORPTIVITY. THE DEFECT LEADING TO FAILURE OF THE PAVEMENT SURFACE IN THE OTHER AREAS WAS THE ABSENCE OF A PROPER ENTRAINED AIR VOID SYSTEM IN THE CONCRETE.