CEE Seminar (ZOOM): Fracture and Size Effect in Quasibrittle Cementitious Composites - Experiments and Theory

ZOOM Link will be distributed by the CEE Department
Christian Hoover, Ph.D.

Assistant Professor
School of Sustainable Engineering and the Built Environment
Ira A. Fulton Schools of Engineering
Arizona State University

Abstract: Although hundreds of concrete fracture tests exist, their evaluation is ambiguous because they have limited ranges of specimen size, initial notch depth and post peak response, and refer to different concretes, different batches of concrete, different ages, different environmental conditions, different loading rates and test procedures, and different specimen types. Presented is an experimental investigation of unprecedented comprehensiveness and low scatter, using specimens made from one batch of concrete. It includes: (1) notched and unnotched beams tested at virtually the same age; (2) crack depths ranging from 0% to 30% of beam depth; (3) a broad size range (1: 12.5); (4) tests in transition between type 1and type 2 size effects; (5) virtually complete post peak softening data; (6) properly correlated loading rates; and (7) complete standard characterization of the concrete used. The fracture tests are evaluated to clarify the size effects and fracture energy dissipation. The test results for beams with notches of various lengths agree closely with Bazant’s Type 2 size effect law and yield the value of the initial fracture energy Gf. Since nearly complete post-peak softening load–displacement curves have been obtained, the total energy dissipation by fracture can be accurately evaluated and used to determine the RILEM total fracture energy GF. The transition between the Type 1 and 2 size effects are determined and a universal size-shape effect law (USEL) that describes the dependence of nominal strength of specimen or structure on both its size and the crack (or notch) length is derived. The USEL exhibits the correct small-size and large-size asymptotic properties as required by the cohesive crack model (or crack band model). The new USEL is shown to fit the comprehensive data quite well, with a coefficient of variation of only 2.3%.

Bio: Christian Hoover received his bachelor's and master's degrees in civil\structural engineering from the New Jersey Institute of Technology. He earned his doctorate in applied mechanics from Northwestern University in 2012 with a focus on theoretical and experimental cohesive fracture mechanics. He then joined the Massachusetts Institute of Technology where his research focused on experimental fracture mechanics on the micro and nano scales. Hoover joined the faculty of Arizona State University as an assistant professor of civil engineering in the School of Sustainable Engineering and the Built Environment where he is continuing his work on micro and nano scale mechanics of materials. His current projects include elucidating the compositional dependence of favored inelastic energy dissipation mechanisms in glass and enhancing fracture resistance of concrete beams with chemically treated waste plastics.