ABSTRACT
This paper reports on the use of Ultra-Fine Fly Ash (UFFA) used as up to 50% partial replacement for cement in concrete. UFFA is a new generation fine coal fly ash, which is double-classified to obtain the finer particles from the classified bulk. The influence of UFFA on fresh properties (flow, setting time and air content), porosity of mid to high strength, medium workability concrete mixes (designed for equal 28-day strength) are reported and compared with concrete mixes made with OPC, Micro-Silica (MS) and seven BS 3892 Part 1 fly ashes (PEA).
The study shows that UFFA has significantly higher pozzolanicity than all UK fly ashes tested and significantly reduces the water demand and air content of concrete. The compressive strength results indicate that a partial replacement of OPC with UFFA can not only reduce the total binder content required to obtain target strength at specific ages irrespective of curing, but also increases the efficiency of the combination binder by up to 50% at later ages.
The porosity of concrete made with UFFA all showed improvement compared to equal strength concrete made with OPC and UK PFA, irrespective of curing. A high strength of 130 N/mm2 was attained at 28 days for a blend of UFFA/MS/OPC concrete with a combination of selected aggregates sizes proportions.
