FALLACIES IN THE CURRENT PER CENT OF TOTAL ABSORPTION METHOD FOR DETERMINING AND LIMITING THE MOISTURE CONTENT OF CONCRETE BLOCK

CRACKING IN CONCRETE MASONRY WALLS CAN BE REDUCED BY MINIMIZING MOISTURE SHRINKAGE IN THE WALL. IT IS NECESSARY TO PRESHRINK THE UNITS BY ADEQUATE DRYING BEFORE THEY ARE PLACED IN THE WALL. THE DEGREE OF DRYNESS NEEDED VARIES, BUT FOR ANY GIVEN LOCALITY, THE CONCRETE SHOULD BE IN AN AIR-DRY CONDITION CORRESPONDING TO THE AVERAGE ANNUAL RELATIVE HUMIDITY OF THE OUTSIDE AIR FOR THAT LOCALITY. THE LONG-STANDING TEST FOR MOISTURE CONTENT WAS INTENDED TO LIMIT THE PERMISSIBLE MOISTURE CONTENT OF CONCRETE BLOCK. HOWEVER, IT IS INADEQUATE SINCE IT FAILS TO GIVE A REALISTIC INDICATION OF THE MOISTURE CONDITION OF THE CONCRETE NEEDED TO SHOW WHETHER OR NOT BLOCK IS AT THE DESIRED DEGREE OF DRYNESS TO REDUCE DRYING SHRINKAGE AND CRACKING IN THE WALL. DATA IS PRESENTED SHOWING THAT THE MOISTURE HELD BY AIR-DRY CONCRETE AT EQUILIBRIUM WITH A GIVEN RELATIVE HUMIDITY IS INFLUENCED BY MANY FACTORS AND IS NOT SIGNIFICANTLY RELATED TO THE TOTAL ABSORBED WATER IN A SATURATED BLOCK. HENCE, THE CURRENT PER CENT OF TOTAL ABSORPTION METHOD SHOULD BE REPLACED BY THE RELATIVE HUMIDITY METHOD WHICH PROVIDES A RELIABLE INDICATION IN ABOUT 20 OF 60 MIN OF THE STATE OF DRYNESS AND POTENTIALITY FOR DRYING SHRINKAGE OF CONCRETE BLOCK IN SUBSEQUENT EXPOSURE TO ATMOSPHERIC CONDITIONS. THIS IS LESS THAN 2 PERCENT OF THE 48 TO 72 HR NEEDED TO SATURATE AND THEN OVEN-DRY BLOCK TO CONSTANT WEIGHT AS REQUIRED BY THE CURRENT ASTM METHOD. /AUTHOR/

• Supplemental Notes:
  • Vol 57, pp 1057-1076, 7 FIG, 1 TAB, 8 REF, 1 APP
• Corporate Authors:

  American Society for Testing and Materials (ASTM)

  100 Barr Harbor Drive, P.O. Box C700
  West Conshohocken, PA  United States  19428-2957
• Authors:
  • Menzel, C A
• Publication Date: 1957

Media Info

• Serial:
  • ASTM Proceedings
  • Publisher: American Society for Testing and Materials (ASTM)

Subject/Index Terms

• TRT Terms: Concrete; Drying; Fracture mechanics; Humidity; Moisture content; Reduction (Chemistry); Shrinkage
• Uncontrolled Terms: Data
• Old TRIS Terms: Reduction
• Subject Areas: Highways; Materials;

Filing Info

• Accession Number: 00213887
• Record Type: Publication
• Files: TRIS
• Created Date: Jun 1 1971 12:00AM