Micromechanics of quartz sand breakage in a fractal context

Abstract

19From a Quaternary science perspective, sand-sized quartz as well as silt-sized quartz is often 20 acknowledged as final products of glacial abrasion through different evolution mechanisms. This view 21 challenges the existence of any universal comminution process, which may relate the formation of detrital 22 quartz sand and silt. The contribution of grain size, energy input, and crystalline integrity in the scale of 23 quartz crushability has long been matter of much debate. The present empirical work examines the 24 micromechanics of sand-to-silt size reduction in the quartz material. A series of grinding experiments was 25 performed on Leighton Buzzard Lower Greensand using a high-energy disc mill. Analogous conditions to 26 glacial abrasion are provided due to the combined abrasion between grains' asperity tips, and also 27 between grains and rotating smooth tungsten carbide pestle. Discontinuous breakage approach allowed 28 a control on grains' crystalline defects. To enable an objective assessment of micromechanics of size 29 reduction, measurements of particle and mode size distribution, fractal indexes and micro-morphological 30 signatures were made. The crushing approach was probed through varied grinding time at a constant 31 energy input, as well as varied energy input at constant grinding time. Breakage pathway was inspected 32 via laser diffraction spectroscopy and transmission light microscopy. Results suggested that the grain 33 breakdown is not necessarily an energy-dependent process. Non-crystallographically pure quartz sand 34 and silt are inherently breakable materials through a fractal breakdown process. Results also revealed 35 that the internal defects in quartz are independent from size and energy input. 36

Age and sedimentary record of inland eolian sediments in Lithuania, NE European Sand Belt

“…Recent empirical studies (Langroudi et al, 2014) have revealed that quartz grain fracturing is not necessarily the result of energy input, nor a function of duration and grain size at the start of the process, but is more controlled by internal defects in quartz. However, it has been suggested that quartz grains with characteristic outlines reflecting their origin become fragmented due to cryogenic cracking, as a result of a combination of thermal shock, ice crystal growths in fissures, and hydration shattering (Schwamborn et al, 2012).…”

Characterization of glacial silt and clay using automated mineralogy

“…If sediment is comminuted within till, then a complex history of grain loading and unloading (e.g. Rose and Hart, 2008; Langroudi and others, 2014) in a persistently wet environment might promote subcritical crack growth (e.g. Atkinson, 1984) that is not facilitated by EPD.…”

“…Observations from other workers indicate that there is no clear boundary between crushing and abrasion processes (e.g. Rogers et al, 1963; Chaolu, 1997; Langroudi and others, 2014). The observation of rounded sand-sized quartz grains (e.g.…”

“…The probability of fracture also depends on external factors such as the rate, direction and magnitude of applied stress (e.g. Sammis and Ben-Zion, 2008; Langroudi and others, 2014). Glaciological factors include the transport distance of till (e.g.…”

Effect of the Surface Roughness on the Shear Strength of Granular Materials in Ring Shear Tests

“…In general, the breakage potential of a soil particle increases with its size [22]. Using a large-sized ring shear apparatus, particle breakage can be measured by the grain size distribution curve before and after shearing [23,24]. However, the mechanical behavior due to particle breakage in different drained and shear velocity conditions is not fully understood.…”