The Utilization of Recycled Sewage Sludge Ash as a Supplementary Cementitious Material in Mortar: A Review

Abstract

The output of sewage sludge has been increasing in recent years in China. Traditional treatment methods, such as incineration and landfilling, cannot meet the requirement of sustainability in various industries. As one of the efficient recycling methods for sewage sludge, previous studies have proven that sewage sludge ash (SSA) can be used as a supplementary cementitious material to partly replace cement in mortar or concrete. To understand the performance of SSA comprehensively, which contributes to its better utilization, this study reviews the basic properties of SSA and the effect of SSA on the performance of mortar. Firstly, the basic properties of SSA, such as chemical composition, heavy metal content, activity, and microstructure, are investigated. Then, the effects of SSA on the workability, setting time, and mechanical properties of mortar are reviewed. The results show that the particle size distribution of SSA is in the range of 2.5–250 μm. SSA contains active oxides such as SiO2, Al2O3, Fe2O3, and CaO, which are similar to fly ash, indicating that SSA has potential pozzolanic properties. The leaching concentration of SSA is much lower than the required values in the relevant specifications, leading to an allowable environment influence. The incorporation of SSA has a negative impact on the workability, setting time, water absorption, compressive strength, and flexural strength of the mortar. The 90-day compressive strength of the SSA mortar is 71.72–98.6% of the cement mortar, when the replacement ratio of SSA is in the range of 10–30%. However, performance can be improved by increasing the grinding time or adding an admixture. The drying shrinkage and capillary water absorption of SSA mortar are higher than those of normal mortar, which is mainly related to an increase of porosity. In conclusion, it is proven that SSA can be used to partly replace cement in mortar with appropriate properties. Source and production process have a great influence on the basic properties of SSA, leading to varied, even opposite, effects on the mechanical properties and durability of mortar. In the future, the selected raw materials and a standard preparation method should be proposed for promoting the application of SSA.

Performance of Mortar Incorporating Heat-Treated Drinking Water Treatment Sludge as a Silica-Sand Replacement

“…Furthermore, according to the research conducted by Donatello et al [31] compressive strength of mortar increases as the particle size of the added sludge decreases. Also, the chemical reaction between cement and silica sand could be improved due to the high fineness of sludge particles, thus resulting in a noticeable improvement in strength [32,33]. This explanation agrees with Pan et al [34], who concluded that the compressive strength of mortar made with fine sludge particles is greater than that of mortar made with coarse particles, where the fine particles provide sites for cement hydration reaction and the grinding process can enhance the pozzolanic activity of sludge.…”

Identifying Potential Household Waste as Secondary Raw Materials in the Construction Industry: A Case Study of Sri Lanka

“…For instance, the utilization of plastic waste as a binder in construction materials or using organic waste to produce biodiesel for construction machinery exemplifies innovative approaches that align with circular economy principles. These findings resonate with studies that highlight the potential of waste materials to enhance the properties of construction materials (Lamba et al, 2021;Liang et al, 2022).…”

Evaluation of Solidified Wastewater Treatment Sludge as a Potential SCM in Pervious Concrete Pavements

“…Prior research suggested that WWTS addition leads to an increase in water demand influencing the consistency of the fresh mix [ 30 , 31 ], whereas the SWWTS addition decreases mechanical properties of ordinary concrete [ 27 ]. For every 5% increase on average in WWTS ash content in mortars, the fluidity decreases by 4.07% [ 32 ]. It was also found that porosity of mortar increases by 3.73% on average, for every 20% increase of WWTS ash content in cement mortars [ 32 ].…”

“…For every 5% increase on average in WWTS ash content in mortars, the fluidity decreases by 4.07% [ 32 ]. It was also found that porosity of mortar increases by 3.73% on average, for every 20% increase of WWTS ash content in cement mortars [ 32 ]. Therefore, considering previous findings, LWPCP was selected as a product where the SWWTS was incorporated in the cement matrix.…”