Assessment of high volume replacement fly ash concrete – Concept of performance index

This paper examines the practicality and suitability of high proportion replacement of cement by class F fly ash. Binary and ternary blends of fly ash/Portland cement and fly ash/silica fume/Portland cement, were tested. The investigation focussed on the realistic conditions of concrete making on site and the effects on the mechanical aspects as well as the consequences on corrosion of reinforcement.It has been found that class F fly ash may replace 50% of the Portland cement and at the same time result in improving resistance to chloride initiated corrosion. Such replacement however, may significantly reduce the values of the mechanical properties. Nevertheless, such concrete is considered a high performance concrete. The authors therefore suggest that the mechanical and durability characteristics of concretes may be assigned numerical Performance Index values. These values may provide the means for making informed decisions on the extent of cement replacement by other cementitious materials.

► 50% fly ash replacement may significantly reduce strength and E-modulus.
► Total chloride and RCPT values in 50% fly ash concrete are larger than their values in OPC concrete.
► 38 MPa 50% fly ash concrete may be obtained with industry practices using 225 kg Portland cement.
► 50% fly ash concrete was superior to 450 kg OPC concrete in resistance to chloride caused corrosion.
► Performance index concept is suggested assigning numerical values for strength and durability.