Sewage sludge ash in concrete. Risk of reinforcement corrosion

The sewage sludge ash used in this project is from Avedøre Spildevandscenter. Compressive strength of mortar samples with 5% cement replacement with milled ash shows slight increased compressive strength and similar sompressive strength as the reference sample, respectively. The chloride content of the ash is low (28 mg/kg). Cl-penetration tests are reported without (diffusion) and with electric current (migration), the latter accelerating the chloride penetration into the mortar samples and a new setup developed in this work is used. By diffusion Cl did not reach further than 1-2 cm into the mortar samples during the 60 days of experiments and no difference between mortar with and without ash was seen. By migration Cl reached up to 8 cm into the each mortar sample. Here a slight tendency for a lower Cl concentration in the first centimeter in the samples with ash is seen. No sign of corrosion of reinforcement steel is seen in samples with or without ash.

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