Experimental Studies on Adhesives for Joins of Shield Segments

Abstract

Shield construction is employed on a large scale for the subway construction project of Osaka Municipality in which water leakage from the joints of shield segments is a serious problem during the construction as well as maintenance after completion.For this reason, an adhesive mainly composed of tar modified epoxy resin is coated onto the contact surfaces of the segments by which adhesion of the segments is reinforced, the segment being then clamped by means of bolts. However, there are many points unclarified regarding the primer, the coating method of the adhesive, the curing method and the setting time required.Experiments were conducted by varying the method applying the adhesive, and the respective effects produced on the adhesion effectiveness were studied. The results obtained are as follows.(1) Pre-coating with primer is considerably effective in improving the adhesion effectiveness of the adhesive in case of using tar-epoxy resin adhesive to adhere segment joints. This fact is quite favourable for the job at sites where the segments are liable to be wetted due to underground water such as found in shield construction.(2) In the above case, coating with tar-epoxy adhesive must be performed after the primer is hardened, so as to make it possible to use a rapid curing type of primer.(3) Adhesion effectiveness can be increased by inserting a sheet of glass cloth as reinforcement between the two coats of tar-epoxy adhesive.(4) In case of adhesion being made in water with the use of tar-epoxy adhesive, the following method is considered to be practical after primer pre-coated onto the concrete surface is cured.The surface of one concrete will be coated with tar-epoxy adhesive, and glass cloth will be applied to it. Then it will be coated again with tar-epoxy adhesive, and then it will be pressed against the other surface which is submerged in water.(5) The two-component type of primer consisting of epoxy and polyamide, which is low in viscosity and with curing time of around 24 hours as well as long in pot life and oderless, is considered to be suitable for use as the primer for segment joints.