PRELIMINARY INVESTIGATION ON USE OF SEWAGE SLUDGE ASH AS PARTLY CEMENT REPLACEMENT IN LIGHTWEIGHT AGGREGATE CONCRETE

Author(s): Lisbeth M. Ottosen, Randi J. Olsen, Esben Ø. Hansen
Paper category: Proceedings
Book title: Proceedings of the 2nd International Conference
on Bio-Based Building Materials
Editor(s): Sofiane AMZIANE, Mohammed SONEBI and Karine CHARLET
ISBN:
e-ISBN: 978-2-35158-192-6
Publisher: RILEM Publications SARL
Publication year: 2017
Pages: 601-607
Total Pages: 7
Language : English

Abstract: 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.

Online publication :2017
Publication type :full_text
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