Moderate strength concrete from lightweight sludge ash aggregates

A range of artificial aggregates has been developed from incinerated municipal sludge ash and tested in concrete. The ash is either pelletised or slabbed, and subsequently fired until it sinters and expands to form lightweight products. From the tests conducted on size, grading, bulk density, absorption and compressive strength, it appears that both the pellets and slabs have potential as lightweight aggregates. Their use in producing moderate strength concrete of up to 2000 psi and unit weight 50 lb/cu ft (800 kg/m³) via steam curing has specifically been investigated. Although concrete prepared from the pellet form of aggregates are somewhat heavier, they exhibit superior strength than those prepared from the slabs and commercial aggregates derived from expanded clays. It is anticipated that because of their spherical shape and uniform size distribution, the pellets could provide better workability and compaction; and their lower moisture absorption may also render them as potentially better thermal insulators.