Fundamental Study on the Effectiveness of Resin Emulsion in Improving the Bond Strength at Horizontal Joints of Concrete

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Experimental study was conducted to examine both the reliability of widely-spread easy joining method of spraying resin emulsions on the finished surface of fresh concrete and its applicabity as an emergency measure for preventing the occurrence of cold-joints in concrete structures. Main conclusions are as follows.1. Even in the portions of sections where consolidation of concrete is made only by the propagated vibration from internal vibrators, cold-joint may not occur when the joining of concrete is made while the penetration resistance of lower concrete is less than 0.1 N/mm^2.2. When the spraying of resin emulsions is made without removing the excess breeding water on the joining surface, the bonding strength at joints is badly damaged.3. When the spraying of resin emulsions is made after the removal of bleeding water, the joining strength of concretes is improved compared with the case where no treatment is made. However, the improved strength is not higher than the strength at joints treated properly by conventional procedures.4. The bonding strength at horizontal construction joints can be improved when the mixture of resin emulsion and cement is spreaded at the rate of about 1 kg/m^3 over the surface of lower concrete, which has been strengthened by spraying resin emulsions.5. Spraying resin emulsions is not a reliable method for the prevention of cold-joints.