Mode I fracture strength based on pullout force and equivalent age
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abstract
Fracture mechanics theory can account for the influence of a specimen or structure size on the fracturing strength of concrete materials. Reviewed fracture mechanics and the pullout test literature indicated that the geometry of a pullout test apparatus could be modified to produce a Mode I type fracture when extracting an embedded insert from hardened concrete. Based on reviewed literature, a pullout apparatus was designed and fabricated with a geometry for measuring Mode I fracture strength. This apparatus was applied in an experimental investigation of early age Mode I concrete fracture strength. The fracture toughness of mixtures tested for pullout fracture strength was determined by applying the size effect law to the fracturing strength of three-point bend specimens. At ages generally corresponding to one day, the results show that Mode I pullout fracture force provides an accurate estimate of fracture toughness. This Mode I pullout apparatus provides a simple, quick, and effective method of estimating in-place fracture strength for applying fracture mechanics theory during construction. For the early age curing temperatures encountered, the equivalent age function is shown to provide factors that quantitatively account for the effect of time and temperature of cure on Mode I pullout fracture strength development. The equivalent age function used in conjunction with the Mode I pullout testing apparatus can provide the construction industry with a method of monitoring in-place fracture strength development for applying fracture mechanics theory.
