Jappe, H.A. & Thomsen, C.R.
Grøn SCC til passive miljøklasser Undersøgelse af rheologiske egenskaber
BEng project (2016)
A way of reducing the CO2 footprints is to reduce the cement content in the concrete. Coal fly ash, limestone filler and calcined clay are materials that can replace part of the cement. Due to the current standards, none of these cement replacements can be included in the water to cement ratio. It will therefore result in a lower water to binder ratio, and subsequently also a more sticky and performance heavy concrete. This can be an obstacle for using these alternative and more sustainable concrete types.
This report deals with SCC-concrete in the passive environmental classes. Focus is on the rheological properties to enable design of new concrete types, which are both sustainable and performance wise easy to work with.
A number of mortar recipes where part of the cement was replaced by coal fly ash, limestone filler and calcined clay were investigated. To examine how the different elements in the concrete composition affect the fresh concrete’s workability, a number of variables were set, including the water to cement ratio, the content of fine aggregate, the content of superplasticiser (SP) and the content of cement replacement. All mortars were tested in a 4C-mini-rheometer, which measures slump flow and time, and from these the concrete’s yield stress and plastic viscosity can be measured.
The viscosity remains virtually constant when the content of fly ash increases. When the content of limestone filler increases, the viscosity increases slightly, while if the content of calcined clay is increased, the viscosity will increase significantly. Fly ash and limestone filler has a smaller impact on the viscosity than calcined clay.
For samples with variable content of fine aggregate, it is found that the viscosity increases with an increase in the aggregate volume. Similarly, the viscosity will increase if the water content is reduced. However, it is possible to lower both the yield stress and viscosity significantly, by using the proper dosage of superplasticizer.
Lars Nyholm Thrane and Thomas Svensson (Danish Technological Institute) co-supervised this project.
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