Olsen R.J.

An expanding building industry all over the world combined with an increasing demand for green solutions, lead to a relevant investigation of partial replacements of Portland cement in concrete. The use of sewage sludge ash (SSA) in standard concrete has been investigated before with positive results. This work investigate whether positive results can be obtained for using SSA as a partial replacement for cement in lightweight aggregate concrete (LWAC) as well.

Part one investigates environmental impacts of using SSA in LWAC. A life cycle assessment (LCA) is performed for a standard wall constructed with LWAC blocks and it is concluded that if 45 % of the cement is replaced with SSA, the CO2 emissions caused by production, transportation, use, and end of life for that wall, could decrease with a total of 13 %. The environmental impacts of using SSA in LWAC was also
investigated by modifying an environmental product declaration (EPD) for 1 ton of LWAC blocks. It was concluded that if 45 % of the cement is replaced with SSA, the CO2 emissions caused by production and transportation, could decrease with a total of 22 %.

Part two investigates the practical possibility of replacing a partial amount of cement in LWAC with SSA.
The sewage sludge ash is obtained from the waste water treatment plant Avedøre. Investigations of the
water requirement of SSA concluded that the activity factor increases with the percentage amount of sewage sludge ash in a mortar or concrete mix. This means that when casting LWAC containing SSA it was necessary to add more water.

Lightweight aggregate concrete was produced using a block machine consisting of a mould with a separate lid and an external vibrator. After filling the mould with the LWAC mix the vibration was turned on while the compressing force was gradually increased until reaching 300 kg. After hardening for at least seven days, the blocks were cut into cylinders with a diameter and height of 75 mm. A total of seven blocks with a partial replacement of cement with SSA (10-45%) were cast. Ref-blocks and SSA-blocks were compared with LWAC blocks produced in an industrial setting supplied by Weber Saint Gobain.

From replacements of 15-30% the average compressive strengths are at the same level. When reaching a replacement of 35 % and 45 % of cement with SSA the strength decreases and it was observed that these blocks were very fragile. It is concluded that there is no correlation between the replacement of cement with SSA and the compressive strength, but there is a pronounced limit to how much SSA can be added.

Report comming soon