Title: Fracture Properties and Brittleness of High-Strength Concrete

Author(s): Ravindra Gettu, Zdenek P. Bazant, and Martha E. Karr

Publication: Materials Journal

Volume: 87

Issue: 6

Appears on pages(s): 608-618

Keywords: brittleness; cracking (fracturing); crack propagation; energy; fracture properties; high-strength concretes; load-deflection curve; models; Materials Research

DOI: 10.14359/2513

Date: 11/1/1990

Abstract:
The size-effect method to determine material fracture characteristics, as previously proposed by Bazant and extensively verified for normal strength concrete, is applied to typical high-strength concrete. Geometrically similar three-point bending specimens are tested and the measured peak load values are used to obtain fracture energy, fracture toughness, effective length of fracture process zone, and effective critical crack-tip opening displacement. The brittleness of the material is shown to be quantified objectively through the size-effect method. Comparing the material fracture properties obtained with those of normal strength concrete shows that an increase of 160 percent in compressive strength causes 1) an increase of only about 25 percent in fracture toughness; 2) a decrease of effective fracture process zone length by about 60 percent; and 3) more than doubling of the brittleness number, which may cause adverse effects that must be dealt with in design. The brittleness number, however, is still not high enough to permit the use of linear elastic fracture mechanics. The R-curves are demonstrated to derive according to the size-effect law exclusively from the maximum loads of specimens of various sizes and yield remarkably good predictions of the load-deflection curves.