This work is part of a multi-phase project which aims to develop a sound methodology for rock fragmen-tation in underground mines using expansive cement.More specifically,it is the first phase of the project which foc...This work is part of a multi-phase project which aims to develop a sound methodology for rock fragmen-tation 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 evo-lution and temperature variation with time are first examined for different borehole diameters.The clas-sical 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 signif-icantly with increased cylinder rigidity for the same borehole diameter.The newly developed methodol-ogy 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.展开更多
The hydration characteristics and expansion impetus of three kinds of cement paste under free- and confined-curing conditions were investigated, which were respectively mixed with three different kinds of expansive ag...The hydration characteristics and expansion impetus of three kinds of cement paste under free- and confined-curing conditions were investigated, which were respectively mixed with three different kinds of expansive agent at low W/B ratio.The results show that the hydration products of pure cement paste and paste mixed with expansive agent are same,but the amount of hydration products,un-hydrated C 3S and C 2S are obviously different at the same hydration age.At 3d age,the amount of CH in pure cement paste is less than that of paste mixed with expansive agent,but it is reverse when at 28d age.The amount of AFt at 3d and 28d age in pure cement paste is less than those of paste mixed with expansive agent.Regardless of under free- or confined-curing condition,the amount of ettringite produced varies little since 3d age.The joint effect of the tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore caused by the crystalloid ettringite is the cause of the volume expansion of cement paste,and the former effect is much greater than the latter.展开更多
基金supported by a research grant from Natural Resources Canada,Clean Growth Program(No.CGP-17-1003)and industry partner Newmont Corporation.
文摘This work is part of a multi-phase project which aims to develop a sound methodology for rock fragmen-tation 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 evo-lution and temperature variation with time are first examined for different borehole diameters.The clas-sical 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 signif-icantly with increased cylinder rigidity for the same borehole diameter.The newly developed methodol-ogy 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.
文摘The hydration characteristics and expansion impetus of three kinds of cement paste under free- and confined-curing conditions were investigated, which were respectively mixed with three different kinds of expansive agent at low W/B ratio.The results show that the hydration products of pure cement paste and paste mixed with expansive agent are same,but the amount of hydration products,un-hydrated C 3S and C 2S are obviously different at the same hydration age.At 3d age,the amount of CH in pure cement paste is less than that of paste mixed with expansive agent,but it is reverse when at 28d age.The amount of AFt at 3d and 28d age in pure cement paste is less than those of paste mixed with expansive agent.Regardless of under free- or confined-curing condition,the amount of ettringite produced varies little since 3d age.The joint effect of the tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore caused by the crystalloid ettringite is the cause of the volume expansion of cement paste,and the former effect is much greater than the latter.
