Packing density: a key concept for mix design of high performance concrete

High performance concrete (HPC) has become more and more popular in recent years. However, the various required performance attributes of HPC, including strength, workability, dimensional stability and durability, often impose contradictory requirements on the mix parameters to be adopted, thereby rendering the concrete mix design a very difficult task. The conventional mix design methods are no longer capable of meeting the stringent multiple requirements of HPC. This paper introduces the concept of packing density as a fundamental principle for designing HPC mixes. The concept is based on the belief that the performance of a concrete mix can be optimised by maximising the packing densities of the aggregate particles and the cementitious materials. A preliminary HPC design method, called three-tier system design, is also presented in this paper.