Preliminary investigation on use of sewage sludge ash as partly cement replacement in lightweight aggregate concrete

  • L. M. Ottosen
  • R. J. Olsen
  • E. Ø. Hansen
Keywords: Ligthweight concrete, wood ash, sewage sludge ash, mechanical properties


This work is a preliminary investigation on major properties for lightweight aggregate (LWA) concrete where sewage sludge ash (SSA) partly replaces the cement. To use SSA in LWA concrete production could lower the CO2 footprint (due to use of less cement) and maybe also give better thermal insulating properties, as the SSA particles are porous and might result in a more porous LWA concrete, the thermal conductivity is however not investigated in this preliminary work. Blocks of LWA concrete were cast. The replacement percentage of cement with SSA was varied: 0, 15, 20, 25, 30, 35 or 45%. From each block, test specimens were drilled (75 mm in both diameter and height). Porosity and compressive strength were measured. It was found that up to 30% SSA did not reduce the compressive strength significantly compared to the reference. These replacement percentages without strength loss are high compared to mortar samples in a previous investigation with SSA from the same incineration plant. The compressive strength of the laboratory produced reference LWA concrete was 1.75 MPa, which was lower than an industrial produced LWA concrete (3 MPa) with the same aggregate, fly ash and cement mass ratio. The mass of water to obtain a LWA concrete mix ideal for casting increased with increasing SSA mass. This due to the porosity and irregular shape of the relatively coarse (d50 95 µm) SSA particles. The water demand for mortar with this SSA replacing 20% cement was increased by 16% compared to the reference without SSA. Thus, the increased need for water in the LWA concrete mixture was as expected. The porosity of the LWA concretes with SSA was higher than the reference, which partly might be due to the high porosity of the SSA particles, revealing that the thermal conductivity was lower. Thus all together the results from this investigation are encouraging in order to continue the research topic.

How to Cite
Ottosen, L. M., Olsen, R. J., & Hansen, E. Ø. (2017). Preliminary investigation on use of sewage sludge ash as partly cement replacement in lightweight aggregate concrete. Academic Journal of Civil Engineering, 35(2), 581-587.