Assessment of ultra-high tensile-strength polyurea for underground roof fall support: Insights from work of adhesion

Abstract

Underground mining often faces the threat of roof fall disaster. As a new type of supporting technology, thin spray-on liner (TSL) has gained an increasing attention in underground mining due to its notable tensile strength, elongation capability, and bond strength with rock surfaces. To evaluate the roof fall support performance of TSL based on a novel ultra-high tensile-strength polyurea, tensile adhesive strength between polyurea and rock substrates were tested under different thicknesses, curing conditions, substrate strength, primer and coating method. Meanwhile, this study proposed a new testing method for dynamic tensile adhesive strength between TSL material and rock. The results indicate that the adhesive strength is inversely proportional to the square root of the coating thickness. When the curing time exceeds 7 days, the adhesive strength remains relatively constant. As the curing temperature/humidity increases, the adhesive strength gradually increases. But when the humidity exceeds 70%, the adhesive strength significantly decreases. Since the soft rock has the tensile strength that even lower than the adhesive strength, polyurea-based TSL is more suitable for harder rock from the perspective of adhesive strength. The application of a primer significantly improves the tensile adhesive strength more than 10 ​MPa. When the coating thickness is less than 2 ​mm, the adhesive strength of sprayed polyurea is significantly higher than that of brushed polyurea. Dynamic adhesive strength exhibits an insignificant loading rate effect with DIF ranging from 1.05 to 1.34. Based on the adhesion results, a supporting model was established, assessing the capability of supporting roof loose rock mass by polyurea-based TSL.