ORIGIN, EVOLUTION, AND EFFECT OF THE AIR VOID SYSTEM IN CONCRETE

AIR IN CONCRETE ORIGINATES IN FOUR GENERAL WAYS, PRODUCING 'ENTRAPPED' AND 'ENTRAINED' VOIDS WHICH ARE DIFFERENTIATED BY THEIR SPATIAL AND PRESSURE RELATIONSHIPS TO THE SURROUNDING WATER AND SOILDS...THE AIR VOID SYSTEM DETERIORATES IN CHARACTERISTIC WAYS, MAINLY BY INTERCHANGE OF AIR BETWEEN SMALL BUBBLES AND LARGE, AND BY LOSS OF A PORTION OF THE AIR DURING COMPACTION OF THE CONCRETE. SEVERAL FACTORS DETERMINE THE RATE AND EXTENT OF DETERIORATION EFFECTED BEFORE HARDENING OF THE CONCRETE ARE DESCRIBED. AIR ENTRAINING AGENTS OF DIFFERING CHEMICAL COMPOSITION PRODUCE AIR VOIDS OF DIFFERENT SIZE, DISTRIBUTION, AND SPACING. THE AMOUNT OF AGENT ALSO HAS AN EFFECT ON THESE PARAMETERS, IN GENERAL, REDUCING THE AIR VOID SIZE AND SPACING WHEN USED IN INCREASING AMOUNTS. IN GENERAL, THE FACTORS WHICH TEND TO REDUCE SPACING ALSO TEND TO INCREASE FREEZING-THAWING RESISTANCE OF CONCRETE. INCREASED FREEZING AND THAWING RESISTANCE GENERALLY REFLECTS A REDUCTION IN VOID SIZE AND SPACING FACTOR. SUCH REDUCTIONS ARE OBTAINED, OTHER FACTORS BEING EQUAL, THROUGH REDUCED WATER-CEMENT RATIO, INCREASED AMOUNT OF AIR-ENTRAINING AGENT, AND IN THE CASE OF VOID SIZE THROUGH INCREASED PERIODS OF VIBRATION. THE AIR VOID SYSTEM OBSERVED IN CONCRETE FROM ENGINEERING STRUCTURES IS COMPARABLE TO THAT OBSERVED IN CONCRETE SPECIMENS PREPARED IN THE LABORATORY. METHODS FOR MICROSCOPICAL MEASUREMENT OF THE AIR VOID SYSTEM IN HARDENED CONCRETE ARE DESCRIBED IN AN APPENDIX TO PART IV.

  • Supplemental Notes:
    • Vol 55, No 1-4, PP 95-121, 261-272, 359-375, 507-517
  • Authors:
    • Mielenz, R C
    • Wolkodoff, V E
    • Backstrom, J E
    • Flack, H L
    • Burrows, R W
  • Publication Date: 1958-7

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  • Accession Number: 00212678
  • Record Type: Publication
  • Source Agency: Highway Research Board Bibliography
  • Files: TRIS
  • Created Date: May 21 1994 12:00AM