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Research Papers

Subcritical Crack Growth in Cementitious Materials Subject to Chemomechanical Deterioration—Experimental Test Using Specimens of Negative Geometry

[+] Author and Article Information
Weijin Wang

Department of Civil and
Environmental Engineering,
University of Pittsburgh,
Pittsburgh, PA 15261
e-mail: wew41@pitt.edu

Teng Tong

Department of Civil and
Environmental Engineering,
University of Pittsburgh,
Pittsburgh, PA 15261
e-mail: tet16@pitt.edu

Susheng Tan

Department of Electrical and
Computer Engineering,
University of Pittsburgh,
Pittsburgh, PA 15261
e-mail: sut6@pitt.edu

Qiang Yu

Department of Civil and
Environmental Engineering,
University of Pittsburgh,
3700 O'Hara Street,
730 Benedum Hall,
Pittsburgh, PA 15261
e-mail: qiy15@pitt.edu

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received September 8, 2016; final manuscript received December 14, 2016; published online February 22, 2017. Assoc. Editor: Daining Fang.

J. Appl. Mech 84(4), 041004 (Feb 22, 2017) (11 pages) Paper No: JAM-16-1437; doi: 10.1115/1.4035523 History: Received September 08, 2016; Revised December 14, 2016

Knowledge of the subcritical crack growth (SCG) in cement-based materials subject to concurrent physical and chemical attacks is of great importance for understanding and mitigating the chemomechanical deterioration in concrete structural members. In this study, the SCG in hardened cement pastes is investigated experimentally by a novel test approach aided with microcharacterization. In the test, specimens of negative geometry are designed, which enable the use of load control to trigger stable crack propagation in hardened cement pastes. Multiple specimens, cast from the same batch of mixture, are exposed to the same chemical condition and loaded at the same age. With the aid of a high-resolution microscopy system, which is used to trace the crack tip, the average trend and the associated variation of the dependence of crack velocity v on the stress intensity factor K at the crack tip are obtained. Different from static fatigue, three distinctive regions are captured in the K–v curves of specimens experiencing chemomechanical deterioration. With the help of advanced techniques including scanning electron microscopy (SEM), atomic-force microscopy (AFM), and Raman spectroscopy, the microstructure destruction and chemical composition change induced by the imposed chemomechanical attack are characterized at different stages. In addition to the physical insights for deeper understanding of the coupled effect of chemomechanical attack, these experimental results provide important macro- and microscopic benchmarks for the theoretical modeling and numerical investigation in the future studies.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

(a) Typical setup of DT test, (b) schematic illustration of a K–v curve under stress corrosion, and (c) schematic illustration of a K–v curve under static fatigue

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Fig. 2

(a) An infinite trapezoidal strip based on Tada's handbook [15] and (b) the dependence of K on α for different slopesm

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Fig. 3

Illustration of the specimen geometry and loading configuration

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Fig. 4

The numerically obtained K–α curves for different w/b ratios under unit load

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Fig. 5

Dimensions of specimens used in the test

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Fig. 6

(a) Top view of the experimental setup for stress corrosion and static fatigue tests and (b) a subcritical crack captured in the microscopy system

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Fig. 7

The crack tip identified in a 3D CT scan system

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Fig. 8

Advance of crack tip with time and the corresponding K–v curves for the specimens under static fatigue: (left) w/b = 0.35 and (right) w/b = 0.40

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Fig. 9

Advance of crack tip with time and the corresponding K–v curves for the specimens under stress corrosion: (left) w/b = 0.35 and (right) w/b = 0.40

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Fig. 10

Decalcification development observed in the trapezoidal plates and prisms at different stages: (a) w/b = 0.35 and (b) w/b = 0.40

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Fig. 11

(a) The selected representative regions in the trapezoidal plate; the measured apparent porosity at (b) stage A, (c) stage B, and (d) stage C

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Fig. 12

Raman spectra of regions V, F and T at stage A for samples of (a) w/b = 0.35 and (b) w/b = 0.40

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Fig. 13

SEI images with 500 (left) and 2500 (right) magnification obtained in (a) region V, (b) region T, and (c) region N of the trapezoidal plate (w/b = 0.35) at stage C

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Fig. 14

AFM images under contact mode obtained in (a) region V, (b) region T, and (c) region N of the trapezoidal plate (w/b = 0.35) at stage C

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Fig. 15

Fitted Gaussian distributions representing virgin cement paste of (a) w/b = 0.35 and (b) w/b = 0.40

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Fig. 16

Fitted Gaussian distributions representing the cement paste (w/b = 0.35) in region T at (a) stage A, (b) stage B, and (c) stage C

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