Introduction

The original work relied on the investigations of Powers (1966 and earlier) for introducing the benefits of voids ratio diagrams for demonstrating the behaviour of mixtures. By analysis of such diagrams for aggregates and the development of suitable models, the author was able to develop a tentative Theory of Particle Mixtures and to apply it to aggregates, mortars and concretes. Experience since 1983 identified potential areas for modifications and further development. From 1994 to 1997 extensive research was undertaken by the author as part of a PhD thesis at City University, London designed to achieve the following

• Confirm or modify the basic concepts of the theory, and the empirical constants used in the formulae from more detailed experimental work by the author and others

• Develop the theory and formulae to cover more accurately size ratios between 0.15 and 1

• Appraise published and unpublished research and other technical information, in particular that since 1983

• Investigate and where appropriate take account of the influences of • different energy levels of compaction • cement properties • inclusion of plasticising admixtures and air-entraining agents • inclusion of additions such as fly-ash, ground granulated slag and

silica fume • Develop empirical formulae for including entrained air content and

strength of concrete within the prediction system. • Compare the results of using the theory with data and experience from

practice

• Develop a method for optimising multi-component mixtures for minimum voids ratio

Each of these aims has been achieved to a greater or lesser extent. Where uncertainties remain they have been identified for future workers. A copy of the thesis is lodged with the library of City University.