chapter  2
Sem investigations of the contact zones between rock surfaces and cement paste
Pages 10

Abstract We have examined contact zones and traces of the fracture surfaces produced in specimens in which cement paste has been cast against previously fractured rock specimens and fractured again after appropriate curing. Fracturing of both the original rock and the composite specimens was by ISRM Method 1, using chevron-notched cylinders. Specimens were prepared with both dolomite and andesite rock, and cement paste with and without silica fume. Slices were cut normal to the original interface, and polished and coated for SEM investigation, using both secondary and backscatter electron modes. Failure cracks in some cases ran at the original interface; in others, presumably as the result of better bonding, the cracks left the interface at the notch, travelled 1 to 2 cm into the paste, and then turned and ran parallel to the interface. Silica fume bearing paste and andesite rock tended to favour the second mode. The fracture cracks, whether within the paste or at the interface, were found to show significant branching. Examination of the paste region near the original interface did not provide any particular indication of a transitional zone different in character from bulk paste away from the rock interface. Keywords: cement/rock interface; SEM; fracture surfaces; transition zone; dolomite; andesite.