Alternative ashes in concrete. Investigation of sewage sludge ash from Lundtofte Waste Water Treatment Plant as puzzolan in concrete

The experiments of this work are conducted with sewage sludge ash from Lundtofte Renseanlæg. The ash contained about 5 wt% soluble sulphate and thus the ash was washed in order to improve the quality. The Strength Activity Index (SAI) for mortar with 20% cement replacement with washed ash was 77%, which is just above the SAI indicating puzzolanic effect (75%). For comparison SAI was 61% for the unwashed ash. Mortar with washed ash had up to 28 percent increased compressive strength compared to Mortar with ash as received.

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