Bonding Of New Concrete to Old At Horizontal Construction Joints
Raymond E. Davis and Harmer E. Davis
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Presents results of tests to determine the rela-tive efficiency of various methods of bonding new concrete to old under conditions similar to those that exist along horizontal construction joints in dams. Authors discuss the effect of several methods of placement and several methods of ioint treat-ment on: permeability along plane of jioint, bond strength as indicated by the flexure test, and quality of concrete as indicated by unit weight and compressive strength. Methods of compaction were hand tamping, internal vibratory tamping and combined internal and surface vibratory tamping. Methods of surface cleanup were wirebrushing, scour in with air-water jet before final set cleaning wit high-pressure air after final set. In some cases, lifts were deposited directly on the surface of the previous lift; in other cases, of mortar was flushed on the old surface first. he T following variables were included: richness of mix type of cement, consistency of concrete, period of exposure of lower lift to drying in warm air time interval between lifts, and age of concrete at test.