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Optimising concrete composition is a fairly complex problem. The cost and properties of fresh and hardened concrete depend on the aggregate mix, amounts of cement, water, superplasticisers, microsilica, retarders, air entrainment agents, etc. The problem can be split into two parts: optimisation of the aggregate mix for minimum voidage, and optimisation of the cement paste. Two articles published in Concrete Plant International (CPI 02-2008 and CPI 03-2009) described the first part of the problem and its solutions for three and four aggregates. This work focuses on the second part, with the aggregate mix fixed. This, of course, assumes that the aggregate mix does not significantly affect the workability or compressive strength, which is true to some extent.