Abstract
ABSTRACT: Although it is generally accepted that the incorporation of extenders into concrete does reduce its material cost, there is little literature of work done to establish the cost-reducing extent by using extenders. This paper describes the effect of South African cement extenders on the cost of concrete without compromising the concrete strength, performance, and workability. The cost effect of cement extenders on concrete was evaluated by analyzing concrete mixtures of the same slump height and strength, and concretes of the same cost with different cementitious materials. In this study, concretes of 25, 35 and 50 MPa were prepared with or without 30% fly ash (FA) and 50% ground granulated blast furnace slag (GGBS), using normal (OPC) or rapid hardening cements (RHPC) CEM I 42.5 N, R. Existing market prices of the materials at the time of the study were used.
It was found that generally, for the same 28 - day compressive strength, the extenders reduced concrete material cost by 10 to 25% depending on the strength grade of the concrete and proportion of the extender incorporated. The cost of concrete reduces with increase in replacement level of the extender used. For equal cost of concrete, mixtures containing extenders gave relatively higher late age strengths than the control mixtures.