| After duct segments are demoulded,quite a few circumferential bubbles tend to occur on both sides of them,which affect not only their appearance quality but also their compressive strength and impervious performance to a certain extent.Therefore,it is highly advisable that the bubbles be completely prevented,or,at least,they be minimized.With production practice of the pre-cast duct segments for the shield section of the 1st-term project of Line Two of the rail transit in Taiyuan as a practical example, the causes of the circumferential bubbles on both sides of the duct segments are analyzed,as a result of which it is found that the structure of the mould,the slump of the concrete,the ways of distributing materials and some others all may result in bubbles.Aiming at solving the specific problems,some targeted control measures are put forward in the paper,which result in very good effects.The paper may serve as a certain reference for the control of the appearance quality in pre-casting concrete duct segments for lining in the future. |
