Construction Craft Research Of Bond-Retarded Prestressed System

As a new pre-stressed system,the bond-retarded prestressed system has the advantage of both bonded prestressed and unbonded prestressed concrete,but has not the shortcoming of both two.During the construction stage,it is flexible and convenient as unbonded prestressed concrete;during the using stage,it is secure and reliable as bonded prestressed concrete.At present,domestic study about bond-retarded prestressed system is in exploring stage. For example,the adhesive formula has not matured, variety is few, large-scale production line has not been established,etc.All of them greatly restrict the development of the bond-retarded prestressed system. Specially in construction craft aspect, there also has not summarized a suit of practical and feasible technique for few typical project.This article mainly summarizes the characteristic of bond-retarded prestressed system in construction craft ,according to the application in Changzhou Fudu Hotel and the achievements of experiments about frictional resistance and anti-pull.The frictional resistance experiment selects prestressed tendons(no waves) with 6-months solidification time.According to stretching in different periods, summarizes a series of rules,such as the influences of time,stress level,disturding,and temperature,etc,and discusses the reason of the change. At the same time,through the anti-pulled experiment,we abtain the bond strength of the bond-retarded prestressed tendon.According to the conclusions of experiments,combining the application in Changzhou Fudu Hotel,this article summarizes a full suit of construction crafts, especially discusses how to protect tendons in construction,the effective and best stretching time,how to select the frictional resistance coefficient,and how to reduce prestressing loss,etc,and accumulates experience for the spread of bond-retarded prestressed system.Finally combining these studies, this article points out a series of problems that restricted its development,such as too small diameter of steel wire strand,too good rheology of the adhesive,not perfect craft of pressing ripples and too high price of bond-retarded tendon,etc,and provids the direction for the next research.