Methodology for the estimation of expansive cement borehole pressure

Abstract

This work is part of a multi-phase project which aims to develop a sound methodology for rock fragmentation in underground mines using expansive cement. More specifically, it is the first phase of the project which focuses on laboratory tests to investigate the mechanical performance of expansive cement, also known as soundless chemical demolition agents (SCDA). This paper reports the results of laboratory tests conducted on instrumented thick-walled cylinders filled with expansive cement. Expansive pressure evolution and temperature variation with time are first examined for different borehole diameters. The classical analytical method for expansive pressure estimation is validated with direct pressure measurement using high-capacity pressure sensor, and an empirical model is obtained. A new methodology based on iterative procedure is developed using axisymmetric finite element modelling and test results to derive the modulus of elasticity of the expansive cement at peak pressure. The results of this study show that the expansive pressure increases with borehole diameter when the rigidity of the steel cylinder is constant reaching 83 MPa for a 38.1 mm borehole. It is also shown that the expansive pressure decreases significantly with increased cylinder rigidity for the same borehole diameter. The newly developed methodology revealed that the modulus of elasticity of expansive cement at peak pressure is estimated at 8.2 GPa. A discussion on the extension of the findings of this work to hard rock mining applications is presented.

Keywords

• Rock fragmentation
• Soundless chemical demolition agents
• Expansive cement