EARLY (PLASTIC) CRACKING OF BRIDGE DECKS

THE PROBLEM OF RANDOM CRACKING OF CONCRETE BRIDGE DECKS WAS INVESTIGATED IN VIRGINIA. PROJECTS STUDIED SHOWS THAT CRACKING RESULTED FROM PLASTIC CRACKING OF THE CONCRETE. THE TERM 'PLASTIC SHRINKAGE CRACKING' IS USED TO DENOTE THE CRACKING WHICH OCCURS IN THE SURFACE OF CONCRETE WHICH IS FRESH AND HAS NOT ATTAINED ANY SIGNIFICANT STRENGTH. THE MORE IMPORTANT CAUSES OF PLASTIC SHRINKING CRACKING ARE: (1) RAPID EVAPORATION OF WATER FROM THE CONCRETE SURFACE, (2) THE OBSTRUCTION OF SETTLING OF THE SOLIDS IN CONCRETE BY REINFORCEMENT, COARSE AGGREGATE, ETC., (3) DIFFERENCES IN WATER ABSORBING ABILITY OF SUBGRADE MATERIALS, (4) CEMENT CHARACTERISTICS WHICH CAUSE FALSE SET, AND (5) STRESSES SET UP IN THE SURFACE DURING HARDENING. RAPID EVAPORATION OF WATER IS THE CHIEF CAUSE. THE RATE OF EVAPORATION OF WATER FROM THE SURFACE OF CONCRETE IS INFLUENCED BY THE TEMPERATURE, RELATIVE HUMIDITY, WIND VELOCITY, CONCRETE TEMPERATURE AND THE DIFFERENTIAL BETWEEN THE CONCRETE AND AIR TEMPERATURES. A LITERATURE REVIEW WAS CONDUCTED ON THE METHODS OF PREVENTION OF PLASTIC SHRINKAGE CRACKING. MOST OF THESE ARE GOOD CONCRETING PROCEDURES WHICH SHOULD ALWAYS BE EMPLOYED: (1) SCHEDULE CONCRETING TO AVOID WORST HOURS, (2) DAMPEN THE SUBGRADE AND FORMS, (3) DAMPEN THE AGGREGATES IF THEY ARE DRY AND ABSORPTIVE, (4) LOWER THE CONCRETE TEMPERATURE IN HOT WEATHER, (5) AVOID OVERHEATING THE CONCRETE IN COLD WEATHER, (6) REDUCE TIME BETWEEN PLACING AND THE START OF CURING BY IMPROVED CONSTRUCTION PROCEDURES, (7) START CURING THE CONCRETE AS SOON AS POSSIBLE AFTER PLACING AND FINISHING, (8) PROTECT THE CONCRETE WITH TEMPORARY COVERINGS, OR APPLY A FOG SPRAY DURING ANY APPRECIABLE DELAY BETWEEN PLACING AND FINISHING, (9) ERECT WIND BREAKS TO REDUCE THE WIND VELOCITY ON THE CONCRETE, AND (10) PROVIDE SUNSHADES TO CONTROL THE TEMPERATURE AT THE SURFACE OF THE CONCRETE. THE SOLUTION OF THE PROBLEM SEEMS TO LIE IN (1) RECOGNITION OF THE PROBLEM, AND (2) APPLYING GOOD CONCRETING PRINCIPLES.

• Supplemental Notes:
  • Bull No 34, PP 105-121, 15 FIG, 4 TAB, 8 REF
• Authors:
  • Newlon, H
• Conference:
  • Tennessee Highway Conference Proc
• Publication Date: 1968-1-1

Subject/Index Terms

• TRT Terms: Bridge decks; Concrete; Concrete curing; Concrete placing; Cracking; Evaporation; Humidity; Polymer concrete; Reviews; Settlement (Structures); Shrinkage; Temperature; Velocity; Water; Wind
• Uncontrolled Terms: Concrete cracking
• Old TRIS Terms: Shrinkage cracks; Wind velocity
• Subject Areas: Bridges and other structures; Highways;

Filing Info

• Accession Number: 00208955
• Record Type: Publication
• Files: TRIS
• Created Date: Apr 21 1994 12:00AM