Fly Ash Customization for Defined Performance Concretes

Abstract

This paper describes the approach for customization of fly ash, focused on the proportioning of concrete mixtures for applications where specific performance is needed such as strength, durability and workability. In order to tailor these specific concrete mixtures, bulk fly ashes can be selected and upgraded to fulfil the requirements with respect to for instance, grain size distribution and carbon content (LOI). By customization of fly ash its value will increase, which is beneficial in spite of the cost for upgrading. For customization, basic knowledge and relationships are needed about the decisive influential factors of the total system of concrete components and design. To this end, descriptive models have been evaluated and applied with the emphasis on models for fly ash fineness and packing. These models have been used as a background for classification and micronization of fly ash. In experimental work, a relation was found between the dry packing of the solid constituents of mortar and the workability after the addition of water. Then fine and ultra-fine fly ashes were processed through air-classification and grinding (micronization). These processed fly ashes were added to concrete and the strength development was compared to concrete with silica fume and with reference concrete. In full scale tests the suitability of micronized fly ash for the production of very workable concrete was confirmed.