Spring Cube Crushing
- Design of Apparatus
- After studying the tensile strength of silica polymers, and silica gel growth in the vicinity of stressed silica contacts, the next step in the research is to study how the growth of silica gel affects bonding between sand grains. Based on our hypothesis, the growth of silica gel between stressed silica cube contacts contributes a significant bonding forces between silica grains to make soil exhibits aging phenomena such as increased compressibility over time. The Spring Cube Crusher is designed for this purpose.
- Two silica cubes were secured between the bottom and the middle metal plates. One cube sat on the bottom plate with an edge pointing upward. The other cube was fastened by screws on to the middle plate with a flat face facing downward. Four springs were placed between the middle and the top metal plates. Four long screws went through all three metal plates, securing them together with wing nuts on top. As the wing nuts were tightened, the springs were compressed, therefore exerting a constant downward force on the middle plate which held the two silica cubes together under constant pressure. The amount of force exerted by the springs can be calculated by multiplying the distance of compression (converted from the number of turns applied to the wing nuts) and the spring constant. The metal plates were made of aluminum to minimize weight and prevent rusting. All screws were made of stainless steel.
- To start a spring crushing experiment, assemble the apparatus and place two amorphous silica cubes with dimensions 3 mm x 3 mm x 3 mm on the bottom and middle plates. After a desired amount of pressure is applied to the cubes by tightening the wing nuts, the device is placed in a plastic container with solution containing a certain level of silica ions. After two to three weeks of aging, the device is removed from the box and attached to a load frame (benchtop universal testing machine by Tinius Olsen, S-H50KS). Operate the load frame to make the apparatus sits firmly on an analytic scale placed beneath the load frame. Remove the top plate and springs from the apparatus so that the silica cubes are no longer pressed together by the springs. Instead, the long threaded rod attached to the load frame pushes the apparatus firmly on the scale. Then slowly raise the middle plate up from the bottom plate so to separate the two cubes.
- Two silica cubes were secured between the bottom and the middle metal plates. One cube sat on the bottom plate with an edge pointing upward. The other cube was fastened by screws on to the middle plate with a flat face facing downward. Four springs were placed between the middle and the top metal plates. Four long screws went through all three metal plates, securing them together with wing nuts on top. As the wing nuts were tightened, the springs were compressed, therefore exerting a constant downward force on the middle plate which held the two silica cubes together under constant pressure. The amount of force exerted by the springs can be calculated by multiplying the distance of compression (converted from the number of turns applied to the wing nuts) and the spring constant. The metal plates were made of aluminum to minimize weight and prevent rusting. All screws were made of stainless steel.
- Intergranular Force Measurements
- Two force-extension curves obtained from Spring Cube Crushing experiments are shown above. Both tests were conducted in 500 ppm solution, the left curve shows a 3-week aging period whereas the right curve shows a 4-week aging period. Research is ongoing regarding interpreting the results and collecting more data.
- Effect of Mica on Intergranular Force
- A different force-extension curve is obtained when a piece of mica sheet 30 microns thick is inserted between silica cubes prior to compression. Research is ongoing in this area.
Complete data pack of Spring Cube Crushing experiments in different silica ion concentration solution for different test time and effect of mica can be downloaded here.