Development and characterization of strain-hardening cementitious composites with high volume fly ash

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Copyright: Lin, Chang
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Abstract
In contrast with the brittleness of concrete, strain-hardening cementitious composites (SHCC) have high ductility and toughness. However, SHCC mixtures generally contain a high cement content, which increases environmental and economic costs. The objective of this study is to use fly ash to replace a large portion of cement in SHCC and further improve their rheological and mechanical properties. The thesis approaches this objective from three aspects. First, composites reinforced with different types of fibres in high strength matrices containing high volume fly ash were investigated. Their mechanical properties were examined by compressive, direct tensile and flexural testings. The results showed that straight steel and micro-PVA fibres had the best reinforcing effect in the matrix under question. It was indicated that the dimension and material nature of the fibre are crucial in developing self-compacting high-strength SHCC with high-volume fly ash. Second, the mass ratios of fly ash to cement (FA/C) ranging from 1 to 4 were investigated. The results showed that high strength SHCC with a compressive strength of more than 80 MPa at 28 days were produced at the FA/C ratio of 1. With the further increase in FA/C ratio up to 4, the composites have a medium compressive strength value of more than 30 MPa at 28 days. The increase in the fly ash content resulted in reduction in the first-crack strength, which is favourable for achieving strain-hardening. The usage of high-volume fly ash also contributed to other benefits such as self-compactness and lightweightness. Third, the effect of high-volume fly ash on the bond between PVA fibre and the matrix was investigated. It was found that the majority of non-oil-coated PVA fibres pulled out without rupture in the matrices containing high-volume fly ash. The results indicated that the surface oil-coating on PVA fibres decreased the strength and ductility of high-volume fly ash SHCC. This implied that the high-volume fly ash effectively reduced the bonding of PVA fibre with the matrix and that the surface oil-coating on PVA fibres ought to be avoided. Furthermore, the theoretical analysis showed that the crack width largely depends upon the adhesional and frictional shear strengths of the interface. The crack width and the ultimate strain of SHCC can be controlled by adjusting the two strengths. This can be achieved by suitably designed usage of fly ash.
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Author(s)
Lin, Chang
Supervisor(s)
Kayali, Obada
Morozov, Evgeny
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Publication Year
2013
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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