预应力孔道注浆脱黏缺陷的冲击回波响应特征

为区分预应力孔道因注浆体收缩导致的界面脱黏和因注浆欠密实导致的脱空两种缺陷的冲击回波响应特征,分别通过波纹管内壁界面剂的使用、浆体中膨胀剂的存在、注浆后试件的养护方式3个控制条件制取不同界面脱黏状态试件,采用波纹管内壁预埋泡沫板的方式形成注浆脱空缺陷.对4组注浆密实试件与1组注浆脱空试件的冲击回波响应进行了连续5天测试.测试结果表明:对于注浆密实试件,注浆后前2天的频谱特征与无空洞实心试件类似,第2天后因注浆体收缩导致的界面脱黏现象开始萌生,并导致试件的厚度主频显著降低及频谱结果趋于复杂,据此可较易分辨脱黏发生与否;对于注浆体中有预置空洞但界面无脱黏试件,虽然其厚度主频一直较密实无脱黏试件的低,但随注浆龄期的发展规律与后者相似,且每一测试时刻二者的频率比基本维持在0.85不变.注浆饱满试件发生脱黏后,其厚度主频发展曲线逐渐降低并与预置空洞试件的相交,此时,相互间的厚度主频相近.因此,仅凭某一时刻厚度主频的单次冲击回波测试结果难以分辨注浆空洞和界面脱黏两种缺陷,而通过注浆后4天左右的连续测试,基于厚度主频和频谱的变化规律则可较易分辨.

Impact-echo Response Characteristics of Grouting Defects with Interface Debonding in Prestressed Concrete Ducts

In order to identify the impact echo response characteristics of two kinds of void-existed defects induced by the interface debonding between the grouting medium and duct''s inner surface due to the shrinkage of grouting material and initial void in grouting medium within the duct of post-tensioned concrete members, four grouted specimens with different interface debonding state were fabricated by using interfacial bonding agent, expansive agent and curing ways after grouting, and another specimen with void defect in grouting medium was formed by presetting a foam in the duct. The spectrum response was continuously measured by impact echo system within five days after grouting. The results show that the spectrum within first 2 days after grouting of well grouted specimens without any preset void in the grouting medium were almost identical and similar to that of solid specimens without duct, and obvious interface debonding in specimens without expanding agent in the grouting material was observed, resulting in the lower thickness frequency and more complicated spectrum at the third and following days after grouting, which can be considered the principle to ascertain the occurrence of interface debonding for specimens with well grouted duct. In the specimen with a preset void in the grouting medium but without any interface debonding, although its thickness frequency was always lower than that of well grouted specimens without interface debonding, its spectrum form was very similar to that of the latter and its thickness frequency ratio almost kept unchanged as about 0.85. The thickness frequency development curves with the grouting age between the specimens with a preset void and interface debonding intersected, and both had the same frequency at about the third day, which indicates that the two different defects of interface debonding and existing void cannot be identified uniquely only by the thickness frequency at some moment. To distinguish these two defects mentioned previously through the response characteristics and the development curves of thickness frequency during about 4 days after grouting is necessary.