Title: Utilisation of a Non-complying Fly Ash in Blended Cement Concrete

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Publication: CIA

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Date: 2/28/2011

Abstract:
Power Station ZWD produces fly ash from burning of lignite (brown coal), which has much larger calcium, magnesium, and sulfate contents, but much lower silica content compared to pozzolanic fly ash produced from black coal. This fly ash (ZWD) is not allowed for use in concrete due to its unfavourable composition, as compared to the requirements of AS 3582.1 and ASTM C618-05. However, it was thought that its high salt content could be used as activator for the slag in blended slag cement. In this work, investigations were carried out on mortar and concrete incorporating replacement levels of 20, 30 and 40% for blended slag cement that consisted of 60% GP cement and 40% slag. Test results show that the 20% and 30% replacement levels produced acceptable strength (40 MPa) and expansion values, and resulted in improvement of some durability properties. The 40% replacement produced lower strength and unacceptable expansion. Microstructural examinations using SEM showed that the latter was caused by excessive ettringite formation within the binder matrix. MgO hydration may also have contributed to the expansion. It has been concluded that up to 20–30% of fly ash ZWD could be used as replacement for the blended slag cement in concrete mixtures of 30–40 MPa strength grades, with some advantageous effects.