REPORT OF COMMITTEE ON WARPING OF CONCRETE PAVEMENT SLABS

STUDIES WERE MADE TO FIND THE CAUSE, MEANS OF PREVENTION, AND CORRECTION OF WARPING OF CONCRETE PAVEMENT. THE DATA WERE OBTAINED FROM OBSERVATIONS OF PAVEMENTS AND FROM FIELD AND LABORATORY TESTS IN CALIFORNIA, KANSAS, MISSOURI, MINNESOTA AND TEXAS. THE DATA INDICATE THAT WARPING IS CAUSED BY AN EXTERNAL FORCE PRODUCED BY THE DIFFERENTIAL SWELL, OR SHRINKAGE AND SUBSEQUENT SWELL, OF SUBGRADE SOIL. SOIL EXPANSION RESULTS FROM ABSORPTION OF WATER ENTERING THROUGH LEAKY JOINTS, CRACKS AND AT PAVEMENT EDGES. IN MINNESOTA, THE SWELL USUALLY DEVELOPS FROM THE FORMATION OF ICE LENSES BUT IN CALIFORNIA, KANSAS, MISSOURI AND TEXAS, FROST ACTION HAS ONLY A MINOR EFFECT AND THE VOLUME CHANGE OCCURS LARGELY BECAUSE OF THE EXPANSIVE CHARACTERISTICS OF THE SOIL ITSELF. THE AMOUNT OF SWELL IS DEPENDENT ON THE CHARACTERISTICS OF THE SOIL, ON ITS MOISTURE CONTENT AND DENSITY AT THE TIME THE PAVEMENT IS PLACED, AND ON THE SUBSEQUENT ABSORPTION OF MOISTURE. THAT WARPING CAN BE PREVENTED BY AVOIDING EXPANSIVE SUBGRADE SOILS IS INDICATED BY THE DATA. OBJECTIONABLE WARPING CAN BE PREVENTED BY CONTROLLING MOISTURE DIFFERENTIAL AND RESULTANT VOLUME CHANGE OF THE SOIL. BASES AND JOINT DRAINS WERE ONLY PARTIALLY EFFECTIVE IN PREVENTING WARPING. THE RECURRENCE OF SEASONAL WARPING WAS PREVENTED BY EFFICIENT JOINT AND CRACK MAINTENANCE. THE MOST PRACTICAL AND ECONOMICAL MEANS OF CORRECTING OBJECTIONABLE ROUGHNESS DUE TO WARPING IS BY MEANS OF THE MUD-JACK. /AUTHOR/