Crack coalescence in molded gypsum and Carrara marble

This thesis investigates the fracturing and coalescence behavior in prismatic laboratory molded gypsum and Carrara marble specimens, which consist of either one or two preexisting open flaws, under uniaxial compression. In previous experimental studies, the determination of crack types (shear/tensile) was mainly based on the identification of fractographical features on the crack surfaces. In the present study, a high speed video system was used, which allowed one to precisely observe the cracking mechanisms.Seven crack types, which were characterized by different nature (shear/tensile) and orientations were identified to initiate from the pre-existing flaws in gypsum and marble in the present experimental study. Nine crack coalescence categories with different crack types and trajectories were also identified. The flaw inclination angle (beta), the ligament length (L), i.e. intact rock length between the flaws, and the bridging angle (a), i.e. the inclination of a line linking up the inner flaw tips, between two flaws, have all shown to have different effects on the coalescence patterns. Comparing the fracturing and coalescence behaviors in the two tested materials, tensile fracturing generally occurs more often in marble than in gypsum for the same flaw pair geometries.One of the pronounced differences observed between marble and gypsum during the compression loading test was the development of macroscopic white patches prior to the initiation of macroscopic cracks in marble, but not in gypsum. With the use of the scanning electron microprobe (SEM) and the environmental scanning electron microprobe (ESEM) techniques, the development of white patches and their evolution into macroscopic tensile cracks in marble, and the initiation of hair-line tensile cracks and their evolution into macroscopic cracks in gypsum were studied and compared.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Wong, Ngai Yuen

Advisor dc:contributor.advisor

• Herbert H. Einstein.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/42927

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/42927