Reuse of Sintered Sludge from Municipal Sewage Treatment Plants for the Production of Lightweight Aggregate Building Mortar

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.

Experimental Study on Preparation and Performance of Concrete With Large Content of Fly Ash

“…This indicates that the flow friction of cement grains was decreased by the fly ash with a smooth surface of spherical particles, and the hydration process of cement was reduced by the dilution of fly ash with lesser cement. In fact, the hydration process of cement controls the setting time of binder paste; the reaction of fly ash with cement hydration product Ca(OH) 2 is a little bit in the early age (Li et al, 2013;Li et al, 2021). This indicates that the replacement of cement by excessive content of fly ash is applicable to maintain the workability of fresh cement fly-ash mortar with content over 40% of fly ash.…”

Development of Lightweight Mortars Using Sustainable Low-Density Glass Aggregates from Secondary Raw Materials

“…In the manufacture of lightweight mortars, the use of different low-density aggregates, such as natural aggregates (pumice, perlite, or vermiculite) [ 29 , 30 , 31 ] and expanded clay [ 32 ], has been documented. Furthermore, within the framework of the circular economy, in recent years various research projects have been carried out to manufacture lightweight mortars with incorporations of different types of waste, such as fly ash aggregates [ 31 , 33 , 34 ], biochar [ 35 , 36 ], sludge from municipal sewage treatment plants [ 37 ], poly(terephtalate ethylene) (PET) flakes from recycled packages [ 38 ], and wood processing by-products [ 39 ].…”

Onsite treatment of wastes in municipal waste incinerator: Co-sintering of fly ash and leachate sludge into value-added ceramic granule

“…The heavy metals leaching concentration of sintered products met the requirement of standard by sintering in the previous study [ [31] , [32] , [33] ]. Some researchers have measured the properties of ceramic produced from the co-sintering of FA and sludge, the products meet the requirement of ceramistes [ [34] , [35] , [36] , [37] , [38] ]. Changyong Li demonstrated that the compressive strength of lightweight aggregate was no less than 3 MPa produced from sintered sludge [ 34 ].…”

“…Some researchers have measured the properties of ceramic produced from the co-sintering of FA and sludge, the products meet the requirement of ceramistes [ [34] , [35] , [36] , [37] , [38] ]. Changyong Li demonstrated that the compressive strength of lightweight aggregate was no less than 3 MPa produced from sintered sludge [ 34 ]. Fanlu Min demonstrated that the compressive strength of the sintered products reached higher than 8 MPa by co-sintering of FA and municipal sludge 1223K–1423K [ 36 ].…”