EFFECT OF PLASTIC SHRINKAGE ON SUBSEQUENT SHRINKAGE AND SWELLING OF THE HARDENED CONCRETE

CONCRETE PRISMS VARYING IN MIX-DESIGN WERE SUBJECTED TO INTENSE EVAPORATION INSIDE A WIND TUNNEL, IN WHICH THE WIND SPEED, HUMIDITY AND TEMPERATURE COULD BE CONTROLLED, FOR A PERIOD OF 1 TO 22 HOURS, AFTER WHICH THEY WERE COVERED. CHECK SAMPLES WERE COVERED AT THE BEGINNING OF THE TEST. MEASUREMENTS WERE CARRIED OUT OF THE TEMPERATURE, EVAPORATION AND SHRINKAGE. AFTER BEING REMOVED FROM THE TUNNEL ALL SAMPLES WERE IMMERSED IN WATER FOR 28 DAYS AND TRANSFERRED TO A CURING CHAMBER WITH CONSTANT TEMPERATURE (20 DEGREES C) AND HUMDITY (50 PER CENT H.R.) VARIATIONS IN LENGTH AND WEIGHT WERE REGULARLY RECORDED: (1) VARIATIONS IN WEIGHT FOR A PERIOD UP TO 425 DAYS UNDER CONSTANT ENVIRONMENTAL CONDITIONS, (2) CHANGES IN LENGTH UNDER CONDITIONS DEFINED IN PARAGRAPH 1, AT THREE DIFFERENT DEPTH LEVELS INSIDE THE SAMPLE, (3) CHANGES IN LENGTH IN A GROUP OF 300 DAYS OLD SAMPLES SUBJECTED TO FOUR DRYING-WETTING CYCLES, AND (4) THE BULK DENSITY AND ABSORPTION OF SOME SAMPLES WERE ALSO MEASURED. RESULTS SHOWED TWO TYPES OF HARDENED MATERIAL: THE MATERIAL SUBJECTED TO SHORT OF NO EXPOSURE (E.G. ONLY INSIGNIFICANT SHRINKAGE OCCURRING IN ITS EARLY AGE) SHOWED MARKED SHRINKAGE AND LOSS OF WEIGHT IN LATER STAGES, A CONSIDERABLE CHANGE IN LENGTH DURING THE CYCLES, LOW BULK DENSITY, AND HIGH ABSORPTION ABILITY. THE MATERIAL SUBJECTED TO LONG EXPOSURE (E.G. EXTENSIVE SHRINKAGE OCCURRING IN ITS EARLY AGE) SHOWED IMPROVED CHARACTERISTICS. THE BENEFICIAL EFFECT OF EVAPORATION SEEMS LIMITED BY THE FORMATION OF CRACKS APPEARING AFTER A CERTAIN PERIOD OF EVAPORATION. /LCPC(A)/RRL/