This study aims to enhance the sustainable utilization of electrolytic manganese residue (EMR), an industrial solid waste rich in sulfates and pollutants, by modifying it with appropriate proportions of granulated blast furnace slag (GBFS) and carbide slag (CS) and evaluating its potential as a cement retarder. The influence of both the GBFS/CS ratio and the dosage of modified EMR on the performance of cement mortar was systematically investigated, focusing on workability, mechanical properties, hydration behavior, leaching toxicity, and carbon emissions. Results showed that GBFS and CS significantly reduced pollutant concentrations in EMR while improving gypsum crystallinity. Modified EMR exhibited retarding properties, extending the initial and final setting times of cement mortar from 98 min and 226 min to 169 min and 298 min. With an 8 wt.% dosage, the 28-day compressive strength reached 58.76 MPa, a 1.3-fold increase compared to cement mortar (45.21 MPa). The content of reactive SiO₂, Al₂O₃, Ca(OH)₂, and CaSO₄·2H₂O promoted secondary hydration of cement and generated significant ettringite (AFt) and calcium silicate hydrate (C-S-H) gels, forming a dense microstructure. Pollutants in the modified EMR-cement mortar were reduced through precipitation, substitution, and encapsulation, meeting leaching toxicity standards. This study highlights the feasibility and environmental benefits of employing modified EMR as a cement retarder, demonstrating its potential in sustainable building materials.

To investigate the dynamic evolution of macro- and fine-scale characteristics during the compaction process of Stone Mastic Asphalt (SMA-13), the following methodology was employed. First, the compaction characteristics were analyzed based on the Marshall compaction test, and an exponential regression model for compaction was established. A compaction coefficient was proposed to evaluate the ease of compaction of SMA-13. Second, Marshall specimens subjected to different number of blows (5, 15, 25, 50, 75, 100, and 125 times per face) were scanned using a Computed Tomography (CT) scanner, and image processing techniques were applied to precisely extract void characteristics (void number, void area, and equivalent void diameter) under various compaction states. Third, the evolution of void characteristics in SMA-13 during the compaction process was analyzed, and correlations with macroscopic compaction properties were established. The experimental results demonstrated that SMA-13 achieved optimal compaction at an asphalt content of 5.9% and an initial compaction temperature of 170 °C. The established compaction numerical regression model can effectively characterize the compaction characteristics of SMA-13. A higher compaction coefficient indicated easier compaction and better compaction performance. During compaction of SMA-13, the void number and void area exhibited exponential decay, and voids with equivalent diameters of 1–7 mm gradually decreased, showing a non-proportional linear decay in their distribution. In contrast, voids with equivalent diameters of 0–1 mm increased during compaction, and they are the dominant component of the void structure in SMA-13. During compaction, the void ratio of SMA-13 gradually decreased along the direction of height, and the distribution of void ratio was “great at both ends and small in the middle”. The void ratio at 5–55 mm decreased from about 10% to about 0%, and the void ratio distribution was relatively uniform. The void ratio at the bottom 0–5 mm and top > 50 mm was large and unevenly distributed, mostly between 10% and 40%.