Adhesion Properties of Printable Polymer-Modified Concrete for Rock Tunnel Linings (2021-11)¶

Shotcrete used for rock tunnel linings calls for skilled technicians, which is the key aspect to control the rebound. Three-dimensional (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 (RDPs) and cellulose ethers (CE) 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 afterward. Also, a pulloff test was performed to measure the bond strength of the printed layers in the hardened stage. The results showed that the sag resistance of printable concrete is related to two aspects: 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: 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.