Abstract
In recent years, the sludge produced by municipal sewage treatment plants has become an important recyclable resource for producing green building materials. After the systematic processing of incineration and particle formation, the sintered sludge can be processed into fine lightweight aggregate to produce building mortar with the controlled leaching of heavy metals and radioactivity. In this paper, to increase its economic and environmental benefits, mortar with sintered sludge aggregate was made by cement admixing of fly ash or limestone powder. The water-to-binder ratio was set at three levels—0.82, 0.68, and 0.62—and either flay ash or limestone powder was used to replace equal masses of cement at 10%, 20%, or 30%. Eighteen groups of mortar were studied to evaluate their workability, air content, compressive strength, tensile adhesive strength, dry density, and thermal conductivity. The results indicate that with a proper water-to-binder ratio, and the replacement ratio of fly ash or limestone powder, the mortar can be produced with good workability, consistency, water-retention rate, layering degree, and setting time. The mortar made with sintered sludge lightweight aggregate, designated by the mix-proportion method for conventional lightweight aggregate mortar, did not meet the target strength, although the compressive strength of mortar was no less than 3.0 MPa, which meets the strength grade M2.5. The tensile adhesive strength reached 0.18 MPa. The mortar was super lightweight with a dry density less than 400 kg/m3, and a thermal conductivity within 0.30~0.32 W/(m⋅K). The effects of water-to-binder ratio and replacement ratio of fly ash or limestone powder on the above properties are discussed with test results. The study provides a basis for using sintered sludge lightweight aggregate for building mortar.
Highlights
Sludge is a product of sewage treatment, which is a complex composition of extremely heterogeneous organic fragments, bacteria, inorganic particles, and colloids
All mortars satisfied the target consistency of 60–80 mm and the water-retention rate of no less than 84% [34,35]. This indicates that the workability of the test mortars was less affected by the sintered sludge aggregate with features such as an irregular shape, multiple edges, and greater water absorption compared to the targets designated by methods for producing conventional and lightweight masonry mortar with common lightweight
The workability of the test mortar was less affected by the sintered sludge aggregate with features such as irregular shape, multi-edges, and greater water absorption
Summary
Sludge is a product of sewage treatment, which is a complex composition of extremely heterogeneous organic fragments, bacteria, inorganic particles, and colloids. The disposal trends of sewage sludge are its incineration and its utilization in building materials [3,4,5,6]. Raw sewage sludge can be used to directly replace clay and shale when producing bricks [7,8,9,10,11,12,13]. In this aspect, some of the expensive and energy-intensive stages of sludge disposal can be eliminated, and environmentally harmful waste can be transformed into safe and stable products [4,5,14]. Given the porosity and light weight of sintered sludge slag, the concrete products formed from it have better thermal and acoustic insulation properties so can be used for lightweight building walls [23,24,25]
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