On the Accuracy of Fracture Toughness Test Results for Concrete Using Different Size and Geometry Specimens and Data Reduction Methods

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Title: On the Accuracy of Fracture Toughness Test Results for Concrete Using Different Size and Geometry Specimens and Data Reduction Methods

Author(s): J. H. Hanson and A. R. lngraffea

Publication: Special Publication

Volume: 201

Issue:

Appears on pages(s): 111-132

Keywords: fracture toughness testing; linear elastic fracture mechanics (LEFM); nonlinear fracture mechanics (NLFM); round dou-ble beam specimen; single edge specimen

Date: 7/1/2001

Abstract:
Much research has been performed on measuring the fracture toughness of concrete, but inconsistent toughness values tn the literature leave some questions yet unanswered. This paper provides results ol a broad-based experimental program designed to determine (/certain tests produce an accurmte measure of h-actute toughness for concrete. The results of this study can he used to help make rational dccistons when selecting a combination of specimen size. geometry and data reduction method to measure the fracture toughness of concrete. To be accurate, the fracture toughness value must he the same as would he obtained from an infinitely large test specimen. To show that a value of fracture toughness is accumte requires consistent values from tests using different size and geometry specimens and different data reduction methods. Therefore. this investigation uses three sizes of single edge, SE. and round double heam. RDB, specimens. More than one data reduction method was appltcd to the results of each sire and geometry combination. Four different data reduction methods wet-e used: Itnear elastic fractut-e mechanics. the two-parameter method. the size-effect method, and the Barker method. Results are presented from three hatches of concrete, which represent two dtstinctively different mixes. The fracture toughness values ohtatned were not consistent withtn each batch; therefore, the most aceurate value could not he shown conclustvely. Howevjer, several significant conclusions were formed. The most common laboratory specimen size. no more than 310 mm deep/tall, is UOI sufficiently large to ohtarn an accurate measure of fracture toughness for concrete using either specimen geometry. Even the lat-gest specimens. 1240 mm-tall RDB. experienced significant nonltnear fracture mechanics conditions for all of the concrete mixes. Combtntng the experimental results wtth numerical simulations could provide sufficient informatton to judge uhich of the fracture toughness values, if any, are close to the value that would be obtained from an tnftnitely large spectmcn.