Paper by SATO HAYASHI from ISCR 5th 1986 Aachen Germany
Even though a bonded overlay has the advanta~es such as lower cose and fewer problems in matching adjacent facilities, ic has not been used widely in Japan. The reason is that bond characteristics in concrete overlays have not been revealed and insufficient bond in con~entional techniques has caused some problems such as separation of corner and/or edge. The purposes of this research are to investigate the factors that affect bonding and to propose some effective means to ensure higher bonding. The following main conclusions have been obtained. (I) Shot blasting on existing concrete pavements for one of surface preparation techniques in a concrete bonded overlay has a quite effectiveness in improving bond bending and tensile strengths, but its improvement in bond shear strength is insufficient. This insufficient bond shear strength causes the separation of the corner and/or the edge of overlay slabs. (2) The proposed new bonding technique which is to groove on the surface of existing concrete slabs has shown a good efficiency to improve the ~ond shear strength. If this technique is applied at the corner and the edge of the slabs, the reliability of a bonded overlay will become higher. (3) Bond shear strength is an important factor among the bond characteristics of concrete overlays as shown in (I). We have developed a new method which can evaluate the bond shear strength easily. (4) It has been found chat the anxiety of cracking by drying shrinkage of overlay concrete slabs can be reduced by the addition of expansion ~ agents into overlay concrete.