Effects of Concrete Aggregate Crushing on Rheological Properties of Concrete and Matrix

Abstract

The global aggregate demand in society is increasing while the distribution of the glaciofluvial and fluvial sources traditionally used for concrete is uneven with scarcity in some regions. This has led to a situation where the natural sand resources, that previously were taken for granted, are now depleted around many populated areas in Norway, Sweden, Japan, Australia and several other countries/ regions in the world. The need to develop technology for 100% use of manufactured aggregate in concrete is then obvious.In this Master’s thesis the performance of manufactured fine aggregate produced by different crushing processes and containing normalized amount of fines is analysed with respect to fresh concrete and filler modified paste (matrix) rheology. In addition characterization of all the fine aggregates with different methods was performed with a goal to investigate which of the fundamental rheological parameters of concrete correlate with crushed aggregate properties.

The main results indicate that it’s possible to measure changes in concrete rheological properties if manufactured fine 0/2 mm aggregate produced by different crushing processes and containing normalized amount of fines is analysed in concrete. Workability increase due to replacement of a cone crusher with a VSI for the last step seems to be of a higher order than changes due to VSI tip speed. Those factors were found to have no effect on rheological properties of the corresponding matrix. It was found that most of the convenient fine aggregate characterization parameters can give an indication of the 0/2 mm crushed sand performance in concrete with respect to rheology. The order of relation is rather limited and none of them can be used as a fundamental parameter. Loose and compacted packing measurements tend to show a lot better correlation. However the correlation is not perfect and based on the results acquired within the thesis two other parameters by combining packing and specific surface concepts have been proposed.