A laboratory study on mix design to properly resemble brittle jointed rock

In this research attempts were made to create a mortar with relatively high uniaxial compressive strength (UCS), easy casting, high flexibility, instant hardening, low cost and easy availability. The main use of this material is to physically model the mechanical behavior of jointed rock-like blocks. The effect of four parameters such as joint roughness coefficient (JRC), bridge length (L), bridge angle (?) and joint inclination (?) on UCS of non-persistent jointed blocks were studied. For this purpose, 35 cylindrical specimens with a broad range of plaster content (P) and cement content (C) in different ages were tested. In order to increase the strength of blocky specimens, some amounts of retardant and lubricant agents were used. The results demonstrated that the utilization of 3 wt.% (weight percent) lubricant MGAR106 and 0.05 wt.% retardant decreases water content by 12.5% and increases plaster and cement content by 8.3% and 4.17% respectively. Consequently, UCS of blocky specimens increased by 284.33%. In order to formulate the effect of P/C content and also the age of cylindrical specimens (A) on compressive strength (UCS), Multivariate Non-linear Regression (MNR) and Bayesian Regularized Artificial Neural Network (BRANN) models were employed. The results showed that BRANN approach is able to provide more precise predictions of the specimen UCS compared to the results from MNR model. Moreover, P/C content had more impact on UCS than the specimen age had. Finally the UCS tests on blocky specimens indicated that an increasing in JRC, bridge length or bridge angle results in a rise in UCS; moreover UCS would be in its minimum when joint inclination was 60°. Furthermore, the capability of produced material to model cracking behavior of jointed blocks was verified.