Work

Coupled effects of treated wastewater and sewage sludge biochar on performance and resource efficiency of low-carbon cement mortar

Year: 2026

Type: article

Abstract: This work studied the properties of low-carbon cement mortars with biochar from sewage sludge replacing 5–15 wt% of ordinary Portland cement and treated wastewater instead of drinking water for mixing. The flowability, compressive and flexural strength, ultrasonic pulse velocity (UPV), and water absorption were measured to evaluate the effect of the two waste-derived components on fresh, mechanical, and transport properties. Workability and strength decreased with an increase in biochar dosage, particularly at 15% replacement, mainly due to a reduction in reactive binder availability and an increase in pore volume. Mortar mixed with treated wastewater, by comparison, approached the control strength and UPV at later ages despite a small early-age reduction. At 5%–10% biochar, the combined mixtures retained more of their performance than the 15% mixture, reflecting the competing effects of water retention and pore development. A Performance-Sustainability Coupled Index (PSCI) was therefore formulated from normalized engineering and resource-efficiency terms. Within the mixtures tested, OPC-SW had the most favorable overall PSCI, whereas 5% biochar produced the best balance among the biochar-containing mortars; this balance deteriorated as replacement increased to 10%–15%. Thus, the wastewater investigated here can serve as an alternative mixing source, but the biochar dosage must be controlled. The PSCI offers a comparative means of screening waste-integrated mortars when performance retention and resource savings must be considered together.

Source: AIMS Geosciences

DOI: 10.3934/geosci.2026036