The failure behaviour of a plaster beam when coated with a thin layer of polymeric liner was studied both experimentally and numerically. Plaster beams without any liner coating were tested to failure in a four-point bend test scenario and were found to fail in tension at the mid span of the beam. To assess the support mechanisms of thin spray-on liners when adhered to a rock surface, the plaster beams were coated with a 5 mm thick fibreglass reinforced polymer liner. These beams were tested to study the effect the polymer liner has on restricting tensile failure of the beam. Results of flexural tests on plaster beams with a reinforced polymer liner showed failure originating near the support points and extending to the loading points with some delamination of the polymer liner at higher loads. This ability of a thin polymeric liner to resist crack propagation at the interface of the liner was simulated numerically using a cohesive zone model. The model developed predicted the failure behaviour accurately and the numerical results obtained were comparable to the experimental results.
Thin spray-on liners (TSL) form a composite skin layer and support the rock after application (Stacey, 2001). It has performance characteristics that lie between those of shotcrete and mesh. Liners like TSL and shotcrete, which are well adhered to the rock surface can restrict small movements of already fractured and loosened rock mass. However, the TSL being more flexible than shotcrete can generate more support resistance over a full range of rock deformations (Tannant, 2001). Laboratory tests were undertaken to quantify the strata skin reinforcement using a polymer based TSL. The polymer liner was adhered to plaster beams and then flexural tests were conducted on the polymer-plaster composites. Similar tests were also done on plaster only samples. The support resistance provided by TSLs was demonstrated by comparing the flexural strength of the polymer-plaster composite with that of plaster only beams.
The results of flexural tests on plaster only and a TSL coated plaster composite were simulated numerically using finite element modelling (FEM) and the failure behaviour was compared with experimental results. Cohesive zone interaction, available in Abaqus library (Abaqus, 2014), was used to model the interface between the plaster and polymer layers. The interface properties required for defining the cohesive zone interaction were from the work carried out by earlier researchers (Qiao et al., 2015, Shan, 2017) at the University of Wollongong.
To simplify sample preparation, hydrostone, gypsum plaster and 5% Portland cement, was used to simulate the substrate instead of rock. Plaster beams having dimensions 160 mm by 40 mm by 40 mm were cast and textured to mimic rock beams. All hydrostone samples were prepared by mixing in a ratio of 3.5:1 by weight of plaster to water. The samples were then allowed to cure at 40° C in an oven for two weeks.
