Sewagesludge ash in concrete. Risk of corrosion

Sewage sludge ash from Lynettefællesskabet is used in this project. It is investigated how the replacement of 5 and 10% cement with this ash affects: transportation of chloride by diffusion, capillary suction, porosity and density. Mortar samples with embedded reinforcement bars are placed in an air-saltwater cycle to follow the corrosion. In the Cl-diffusion test it is found that the chlorides diffuse 1.5–2.0 cm into the samples during 28 days. Even though the concentration of chlorides was increased in these first centimeters after 53 and 78 days, the chlorides did not diffuse further into the samples. No differences in diffusion between the reference samples and the samples with milled sludge ash are observed. Visual inspection of the reinforcement steel shows no sign of corrosion, neither in the reference mortar samples nor in the samples with sewage sludge ash. The mortar samples were probably too dense for the chlorides to reach the reinforcement in the weekly cycles over the two month of experiments. A tendency for the mortar specimens with sewage sludge ash to have lower porosity than the reference sample is seen, and a slight increased capillary suction in the mortar with sewage sludge ash is also found.

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