Investigation of Fatigue Crack Growth Mechanisms in Mortars Containing Fly Ash

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Title: Investigation of Fatigue Crack Growth Mechanisms in Mortars Containing Fly Ash

Author(s): P. C. Taylor and R. B. Tait

Publication: Special Publication

Volume: 189

Issue:

Appears on pages(s): 203-222

Keywords: crack growth; fatigue; fly ash; fracture toughness; mortar

Date: 1/1/2000

Abstract:
Mortar mixes were prepared with similar compressive strengths using a range of three fly ash contents from 0% to 25% replacement by mass of cement. Samples prepared suing these mixes were tested in double torsion under cyclic loading; and the rates of crack growth measured, recorded and compared in crack velocity versus applied stress intensity (V-K) diagrams. It was apparent that the influence of the presence of fly ash was dependent on the age of the mortar. At early ages (seven days) the fly ash was found to increase fatigue resistance and toughness which was thought to be due to the spherical shape of the fly ash particles resulting in a blunting effect on cracks. At greater ages the mixes containing fly ash were slightly less resistant to fatigue crack growth, probably because the poor bond between some fly ash particles and the matrix resulted in significantly large flaws. The results of tests carried out in a variety of environments and over a range of load cases also pointed to an environmentally assisted cracking mechanism dominating, yet there was also a slight non-linear plasticity-type influence apparent.