Test study on retarted bond prestressed concrete

Retarded bond prestressed concrete is a new prestressing type. It absorbs the advantages and abandons the disadvantages of bonded and unbonded tendons in posttensioned prestressing concrete. Its primary features are similar to the unbonded tendons during the construction phase and to the bonded ones in actual use. The currently used method in the retarded bonding tendon basically follows that in unbonded tendon. Undoubtedly the bond force between the tendon and the surrounding concrete is reduced partly after the final setting of retarded cement mortar. In this study the objective is to develop a new type of retarded material and a new technology for retarded bond tendons. By lots of comparative tests, it is found that the retarded bonding tendon with the gradient coating can provide better bond with the surrounding concrete. This study is helpful to the designs of retarded bond prestressed concrete.