Properties of concrete using high-lime pfa from a UK source

Recent changes in UK coal supply have resulted in the production of high-lime ash from a major UK power station. This paper offers results collected during a project to compare the key performance characteristics of concretes using an ASTM class C (high lime) and an ASTM class F (low lime) ash as a partial replacement for Portland cement. Mixes were produced using 40% replacement of Portland cement by weight, with pulverised fuel ash, and a water/cement (w/c) ratio of 0·4. Characteristics examined included workability, compressive strength, water permeability, water absorption, chloride permeability using the rapid chloride permeability test, resistance to sulfate attack, and freeze–thaw resistance. The results showed that the concrete containing the ASTM class C ash was superior in all of these areas except for sulfate resistance. Workability and compressive strength tests were also performed on mixes containing 60, 70, 80 and 90% replacement levels with the class C ash, all with 0·4 w/c ratio. Results showed a steady increase in the workability and a decrease in the compressive strength. Samples made at 90% replacement level showed extreme unsoundness and could not be tested for strength.