Characterisation of Microstructure as a Systematic Approach to High Strength Cements

Scrivener, Karen; Baldie, K. D.; Halse, YH; Pratt, P. L.

doi:10.1557/proc-42-39

Cited by 3 publications

(1 citation statement)

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“…While fracture surfaces are ideal for examining morphology, it must be remembered that when produced by slow fracture, the surfaces show the weakest path, and other measurements [degree of hydration, quantitative X-ray analysis, porosimetry] which characterise the bulk microstucture give no information about the distribution of components. On the other hand polished surfaces are representative of the structure, and image analysis (Scrivener et al, 1985) allows quantitative assessment of the amounts and distribution of anhydrous material and calcium hydroxide, and by implication C-S-H. Extension of the examination of polished surfaces to include introduced cracks can provide a quantitative measure of the microstructural components involved in fracture, and by comparison with the uncracked microstructure should provide an insight into the possible methods of improving the strength of HCP.…”

Section: A Microstructure Of and Crack Paths In Hcpmentioning

confidence: 99%

Crack Growth in Hardened Cement Paste

Baldie

Pratt

1985

MRS Proc.

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This thesis describes the examination of the microstructure of hardened cement paste [HCP], in particular, cracking in HCP, and the measurement of subcritical crack growth in HCP.A scanning electron microscope has been used to examine, fracture surfaces, complementary fracture surfaces, polished surfaces, and polished surfaces containing introduced cracks. This examination has provided information about fracture paths in HCP, which shows that the main hydration products [C-S-H gel and calcium hydroxide] form the majority of crack path elements. The interpenetration of these products during hydration, and the expected variations in strength of these hydration products suggest that both must be recognised as significant contributors to the mechanical properties of HCP. The examination of cracks in polished surfaces appears to be a very useful way of determining the microstructural aspects of cracking, and its possible future applications are discussed.Two methods of determining the subcritical crack growth parameter [n] were performed, the first, load-relaxation in double torsion plates yielded a value of 64, while the second, the variation in the critical stress intensity of single edge notched beams with loading rate yielded a value of 27. The much higher value determined by load relaxation is thought to be due to both, the effect of crack resistant inhcmogeneities in the microstructure which have a more marked effect on load relaxation measurements, and a susceptibility to creep in the double torsion plates which reduced the amount of crack growth. The susceptibility to creep was identified by a shift of the crack velocity-stress intensity [V-K] curves to higher stress intensities with repeated loading. The value of subcritical crack growth parameter of 27, determined by the variation of critical stress intensity with loading rate, is therefore regarded as the more valid.

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Section: A Microstructure Of and Crack Paths In Hcpmentioning

confidence: 99%