Saif R

The purpose of this work is to investigate how the addition of wood ash will affect the compressive strength development. Focus is on the activity factor for the used wood ash from Køge CHP (Combined Heat & Power Station).

The wood ash was tested as a 10% sand replacement and 2.5%, 5%, 7.5% and 10% cement replacement.
The ash is characterized. The slump flow, setting time, porosity, density, capillary suction and compressive strength are measured on mortar.

Results show that the ash composition limits its use, but it can still be used within certain limits. For example, the chloride content limits the use to low percentages. The capillary suction decreased in a mortar specimen compared to the reference sample. The overall porosity increases with the addition of wood ash. For larger amounts of ash in the mixtures the slump flow was smaller and the setting time shorter. In addition, a reduced compressive strength was seen due to increasing porosity and decreasing density.

From the measured compressive strengths, activity factors for the different mixtures are determined. The activity factor depends on the hardening time, substitution rate and substitution type. Thus a single activity factor cannot be stated for this ash.

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