Packing and film thickness theories for the mix design of high-performance concrete

Abstract

A high-performance concrete (HPC) is required to have superior performance in various aspects such as workability, strength, durability, dimensional stability, segregation stability, and passing ability. The mix design of HPC is rather complicated because the number of ingredients in HPC is usually more than those in conventional concrete and some of the required properties are conflicting with each other in the sense that improvement in one property would at the same time cause impairment of another property. However, there is still lack of understanding regarding how the various mix parameters should be optimised for achieving best overall performance. Most practitioners are still conducting mix design primarily through trial concrete mixing, which is laborious, ineffective, and often unable to timely respond to fluctuations in the properties of raw materials. To address these issues, the authors have been developing the packing and film thickness theories of concrete materials, in order to revamp the mix design philosophy of HPC in terms of the water film thickness (WFT), paste film thickness (PFT), and mortar film thickness (MFT) in the concrete. Based on the findings from an extensive experimental programme, suitable ranges of WFT, PFT, and MFT have been recommended.