The research presented hereinafter was carried out with the aim of evaluating the effects of high volume Class C fly ash on the strength and sulphate resistance of construction materials. To this end, physical, mechanical, and sulphate resistance tests were conducted on ?50 mm/100 mm specimens. The physical tests in the focus of this research were apparent specific gravity, water absorption and dry unit weight whereas the mechanical properties examined were compressive and flexural strength. Finally, the durability property considered was that of sulphate resistance. Generally speaking, it can be said that strength and sulphate resistance of high volume fly ash (HVFA) concretes were considerably affected by the amount of fly ash used. Also, the strength properties for the 20% fly ash concrete mixes were either comparable or superior to the ones not containing any fly ash. The sulphate resistance of HVFA composites was either comparable to, or even better than, the no-fly ash composites. However, all the mixes, with and without fly ash, tested in this investigation did conform to the strength and durability requirements for excellent quality structural grade concretes. Based on the sulphate test results of this study, there are indications that the engineering performance of the final product can be adequate for use in the manufacture of construction materials such as brick, ceramic tile, paving stone and briquette, and also for use in various civil engineering applications like structural fills, embankments, grouting injections, road bases and sub-bases.