| Summary: | The study of previous classifications of pulverised fuel ash (pfa) has led the author to believe that a new approach is required to look Into the physical properties of pfa. In this study a large number of tests have been carried out In an attempt to establish a criterion which is related to the performance of, fresh and hardened pfa concrete. A classification for pfa Is proposed, based on Its particle size distribution, followed by , determination of the grading modulus (Gf). The results of the research show a close correlation between workability as measured by the VB time and. grading modulus with a marginally lower correlation between compressive strength and grading modulus. - The correlation values with Gf being higher than with the percentage mass retained on 45 m sieve. Taking Gf as the physical criterion which influences the behaviour of pfa concrete, the author proceeded to develop a mix design based upon Gf, whereby the required strength and workability can be achieved accurately by replacing a portion of the opc with pfa. Furthermore, the new design method is capable of achieving a wide range of workability and strength with different cement contents, and covers a variety of pfa finenesses (Gf). The cement and pfa content being adjusted in accordance with the properties and content of the aggregates. A newly developed technique, using the Scanning Electron Microscope, which investigated the hydration and porosity of hardened cementitious paste was implemented. The results showed that fog curing Is essential for the development of hydration products. The Interlock between the pfa particles and the matrix showed an influence on the strength of opc/pfa paste which was more pronounced than the porosity of the hydration products. Porosity was also measured, using an alcohol exchange method, which was found to give a higher porosity than the method using the Scanning Electron Microscope. The former measuring total porosity whilst the latter only measures pores in the matrix and does not take Into consideration cracks, capillaries or air voids.
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