High Performance Grade 75–80 Concrete for In-Situ Construction in Hong Kong

Abstract

Currently, the highest strength concrete being used for in-situ construction in Hong Kong is only of grade 65. In order to develop higher strength concrete, a number of trial concrete mixes made of locally available material were tested. For minimizing the heat of hydration and the creep and shrinkage strains, lire trial mixes were designed to have paste contents as low as possible. During the tests, the effects of fine to local aggregates ratio and the usage. of superplasticizer, pulverized fuel ash and condensed silica fume were investigated. The results show that it is quite possible to produce high performance grade 75 - 80 concrete locally with a paste content of only 30% by volume. It is also found that fairly high dosages of superplasticizer will generally be needed and therefore it is important to select a superplasticizer which can be used at high dosages without producing excessive retardation. Lastly, three alternative mixes for making grade 75 - 80 concrete are recommended.