ABSTRACT
In order to determine the bond strength of shotcrete to rock surface, an instrumental setup has been devised. The different coal measure rocks like shale, sandstone (coarse, medium, and fine grained) were acquired from various mines. Using displacement transducer (LVDT) and potentiometer along with data acquisition system; an instrumental setup has been fabricated and corresponding software is developed to determine the rock surface roughness profiles and to quantify it. Three parameters Z2, SF and RL1, respectively root mean square of first derivative of the profile, Structural function, and Rock profile Length have been used to characterize numerically the roughness of rock surface. The joint roughness coefficients are estimated by using the equation given by Xianbin Yu and Vayssade (1990), considering the sampling interval of 1 mm. A thorough laboratory study of adhesion of shotcrete to same rock with different surfaces roughness shows that roughness of the rock surface play a more significant role in bond strength, for a particular range of JRC between 8 and 17. For a particular range of JRC, bond strength is strongly correlated to JRC. The result also showed that tensile strength of rock has no relationship with bond strength. For a perfect bonding minimum setting time of shotcrete mixture is found to be 21 days. It was further investigated that the use of some accelerating material becomes significant in order to achieve full bond strength at the earliest. A minimum of five days is required to get an early setting of the shotcrete.
