Effect of Crushing and Strain Rate on Mechanical Behavior of Type-F Fly Ash

  • Kanika Gupta
  • Ajanta Sachan
Technical Paper


Fly ash is a by-product of coal combustion from thermal power plant. It comprises of hollow spherical silt size particles with low specific gravity. The increased use of fly ash in highway/railway embankment construction as a structural fill material raises the need to study its mechanical behavior in detail. Although it has been reported that fly ash particles are susceptible to breakage, the effect of crushing on mechanical behavior of fly ash is yet to be explored. The current experimental research was conducted on type-F fly ash to study the following: (a) effect of crushing of fly ash particles on its macroscopic and microscopic behavior and (b) effect of strain rate on pore pressure evolution and stress-strain response of fly ash (uncrushed). Macroscopic (shear strength, compressibility, compaction behavior) and microscopic (particle’s shape and size using SEM images) tests were performed on fly ash to study the crushing effect. Strain rate effect on pore pressure and stress-strain response of uncrushed fly ash was studied by performing CU triaxial tests at different loading rates (0.005–9% per min). Macroscopic response of fly ash exhibited that higher crushing reduced shear strength and compressibility of fly ash and improved its compaction behavior. Microscopic response indicated deformation and breakage of fly ash particles due to crushing. Strain rate study showed large negative pore pressure generation along with brittle stress-strain response of uncrushed fly ash at 9% per min as compared to lower strain rates.


Fly ash Cenospheres Plerospheres Crushing Strain rate Pore pressure 



The financial support from IIT Gandhinagar is gratefully acknowledged. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of IIT Gandhinagar.


BSkempton’s pore pressure parameter

B 10breakage factor w.r.t. diameter at which 10% of particles are finer

B 75breakage factor w.r.t. diameter at which 75% of particles are finer

C c compression index

C c coefficient of curvature

C r recompression index

C u coefficient of uniformity


c′effective cohesion

D 10diameter at which 10% of particles are finer

GSDgrain size distribution

G s specific gravity

LLliquid limit

OMCoptimum moisture content

MDDmaximum dry density

SEMscanning electron microscopy

XRDX-ray diffraction

uexcess pore pressure

β maxangle of maximum obliquity

ε aaxial strain

ϕangle of internal friction

ϕ′effective angle of internal friction

σ d maxpeak deviatoric stress

σ 1′/σ 3′effective stress ratio


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Authors and Affiliations

  1. 1.IIT GandhinagarGandhinagarIndia

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