KANSAS EXPERIMENTAL CONCRETE PAVEMENTS

IN AN EFFORT TO DETERMINE THE CAUSES OF THE WARPING OF CONCRETE PAYEMENTS AND TO DEVELOP PRACTICAL AND ECONOMICAL MEANS OF AVOIDING ITS OCCURRENCE ON NEW CONSTRUCTION, THE KANSAS HIGHWAY COMMISSION BUILT AN EXPERIMENTAL PAVING PROJECT, 5 MI. IN LENGTH, ON HIGHWAY NO. 10, EAST OF THE CITY LIMITS OF LAWRENCE, KANSAS. THE PROJECT WAS BUILT IN 1935 AND WAS DIVIDED INTO 20 SECTIONS AND IN EACH OF 13 OF THE TWENTY SECTIONS SOME SPECIAL TYPE OF SUBGRADE TREATMENT WAS USED. EXPANSION JOINTS WERE PLACED AT INTERVALS OF 100 FT. AND INTERMEDIATE CONTRACTION JOINTS WERE USED IN SOME SECTIONS. THE SUBGRADE TREATMENTS CONSISTED OF: (1) DRYING SOIL TO AN EXTREMELY LOW MOISTURE CONTENT FOR DEPTHS OF 6, 12, AND 24 IN.; (2) PLACING SOIL AT PLASTIC LIMITS FOR DEPTHS OF 6, 12, AND 24 IN.; (3) PONDING SUBGRADE UNTIL SOIL MOISTURE EXCEEDS THE PLASTIC LIMIT; (4) USE OF GRANULAR BLANKETS OVER WET AND DRY SOIL; 75) USE OF BITUMINOUS MEMBRANE OVER DRY SOIL; (6) SPRINKLING DRY SOIL CONTINUOUSLY FOR 48 HOURS. THE OBSERVATIONS MADE ON THE PROJECT HAVE RESULTED IN THE FOLLOWING CONCLUSIONS: (1) WARPING OF PAVEMENT SLABS IS PRODUCED BY VOLUME CHANGE OF EXPANSIVE SOILS CAUSED BY A DIFFERENTIAL IN MOISTURE CONTENT BROUGHT ABOUT BY SURFACE WATER ENTERING SUBGRADE THROUGH JOINTS OR CRACKS; (2) WARPING OF PAVEMENT SLABS WAS AVOIDED BY PLACING THE SUBGRADE SOIL AT A MOISTURE AND DENSITY SUCH THAT NO SUBSEQUENT DIFFERENTIAL MOISTURE CONTENT RESULTED FROM THE ENTRANCE OF WATER THROUGH JOINTS OR CRACKS; (3) WARPING DID NOT OCCUR ON EXPANSIVE SOILS WHEN THE SUBGRADE MOISTURE WAS EQUAL TO OR GREATER THAN THE PLASTIC LIMIT; (4) A BLANKET COURSE OF NONEXPANSIVE SUBSOIL HAVING MOISTURE CONTENTS ABOUT TEN PER CENT BELOW THE PLASTIC LIMIT; AND (5) WARPING CAUSED BY EXPANSION OF SOIL DUE TO DIFFERENTIAL MOISTURE CONTENTS WAS REDUCED IN TIME AS THE MOISTURE IN THE SUBGRADE BECAME EVENLY DISTRIBUTED. /AUTHOR/