Microcracking and Behavior of High Strength Concrete Subject to Short-Term Loading

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Title: Microcracking and Behavior of High Strength Concrete Subject to Short-Term Loading

Author(s): Ramon L. Carrasquillo, Arthur H. Nilson, and Floyd O. Slate

Publication: Journal Proceedings

Volume: 78

Issue: 3

Appears on pages(s): 179-186

Keywords: cracking (fracturing); failure; high strength concretes; loads(forces); microcracking; strength; stress-strain relationships; tests.

Date: 5/1/1981

Abstract:
The progressive microcracking of concretes with uniaxial compressive strengths from 4500 to 11, Ooo psi (31 to 76 MPa) was studied quantitatively and compared. Cracks were identified by types as related to unstable behavior and progressive failure. Differences in behavior between high strength concrete and normal concretes, including differences in stress-strain response and mode of failure, were related to and explained by differences in microcracking. The development of combined cracks, consisting of combinations of bond and mortar cracks, was found to be an essential step in progression toward impending failure. Such cracks must be identified and studied to understand the failure mechanism of concrete. Normal strength concretes start to develop combined cracks at about 70 percent of strain at maximum load, and thus are approaching instability and impending failure, while high strength concrete does not develop significant corn bined cracks until about 90 percent or more of strain at maximum load. High strength concrete has much less microcracking at all load levels than normal strength concrete, but fails more suddenly with fewer planes of failure.