Use of sewage sludge ash in reinforced concrete. Risk of corrosion

The ash is obtained from the sludge ash deposit at Lynettefællesskabet and. The research is primarily focused on the risk of reinforcement corrosion caused by chloride ingress. Mortar specimens are cast both with and without ash (5% or 10% cement replacement). Compression strength tests of gave results that all meet the requirement for activity index when using fly ash in concrete. No difference in the porosity for reference mortar and mortar with ash is seen. The Cl content in all mortar specimens is beneath the limit for concrete. The diffusion of Cl into mortar is compared for 10% cement replacement, 5% sand replacement and reference mortar samples and no difference was found. Tests were conducted for 7, 14 and 21 weeks and neither showed a variation between the three mortar recipes. Experiments are carried out to investigate if Cl bind to either sewage sludge ash or mortar with SSA. After two weeks the results were encouraging in this sense. However after test periods of 16 weeks the ash overall released more chloride it adsorbed and mortar with unwashed ash does not adsorb as much Cl as the reference mortar. Mortar with washed ash has a better Cl binding than the reference mortar but the results are not as good after 16 weeks as after 2 weeks.

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