Adhesion Properties of Printable Polymer-Modified Concrete for Rock Tunnel Linings

Abstract

Shotcrete used for rock tunnel linings calls for skilled technicians, which is the key aspect to control the rebound. 3D concrete printing of tunnel linings has the potential to reduce manual labor for construction workers and to eliminate rebound, especially at overhead positions. In this study, the sag resistance and bond properties of printable concrete for overhead applications were explored. Mixtures with the addition of redispersible polymer powders and cellulose ethers were formulated. Roughened concrete slabs were used to replace the tunnel wall rock. A tack test with a loading control mode and a stress growth test were performed. To verify the results of the tack test and the stress growth test, a 3D concrete printing test, involving upside-down printing against the lower face of a supported concrete slab, was performed afterwards. Also, a pull-off test was performed to measure the bond strength of the printed layers in the hardened stage. The results showed that sag resistance of printable concrete is related to two aspects including the adhesion at the interface and the shear resistance of the fresh material itself. The adhesion and shear resistance properties determined two different failure modes (i.e. adhesion failure and cohesion failure). The results also demonstrated that the tack test results were more consistent with the upside-down printing test results, compared to the stress growth test.

Application-Driven Material Design of Printable Strain Hardening Cementitious Composites (SHCC)

“…To assess the adhesiveness of the SHCC mixtures, several tests were performed first one, the tack test (TT), is a typical test used to evaluate the adhesion between har soft materials [38]. In the field of 3D concrete printing, this test was used to evalua adhesion properties of printable material for rock tunnel lining [39]. In the present i tigation, the TT was performed as follows: In a metal mold with internal dimensio 160 mm × 140 mm and a height of 40 mm, SHCC was placed at the top, and the u surface was leveled.…”