The large-scale development of urban underground spaces has resulted in hundreds of millions of cubic meters of accumulated shield soil dreg waste, occupying huge amounts of land resources and potentially causing groundwater pollution and soil salinization. In this study, shield soil dreg waste is recycled and activated to substitute cement in ultra-high performance concrete, aiming to promote solid waste management and sustainable construction. The slump, mechanical performance, and autogenous shrinkage of the concrete are investigated through macro-scale tests, and the underlying mechanism is revealed via micro-scale experiments. The incorporation of calcined shield soil dreg reduces flowability and leads to a 10.2 % deterioration in compressive strength of the ultra-high performance concrete while mitigating autogenous shrinkage. The primary reason is due to the low CaO content of shield soil dreg, which limits the formation of calcium silicate hydrate, and its high SiO2/Al2O3 content slows hydration kinetics. The environmental and economic benefits of the concrete are determined via life cycle analysis. Recycling shield soil dreg waste into concrete results in about 35 % reduction in carbon emission and 22 % reduction in energy consumption. According to multi-criteria assessment, the overall performance of the concrete considering economic cost, environmental benefit, as well as physical and mechanical properties increases compared to the pristine concrete, achieving well-balanced economic feasibility, environmental sustainability, and engineering performance. The findings of this study provide an effective approach for recycling shield soil dreg and preparing low-carbon concrete, thus promoting solid waste management and sustainable construction.

This study explores the influence of the water-cement ratio and fiber content in engineered cementitious composite (ECC) on the mechanical characteristics of foamed lightweight soil (FLS) through experimental analysis. Two types of cementitious materials-ECC and ordinary Portland cement (OPC)-were utilized to create FLS specimens under identical parameters to examine their mechanical performance. Results indicate that ECC-FLS exhibits superior toughness, plasticity, and ductility compared to OPC-FLS, validating the potential of ECC as a high-performance material for FLS. To assess the influence of the ECC water-cement ratio, specimens were constructed with varying ratios at 0.2, 0.25, and 0.3, while maintaining other parameters as constant. The experimental results indicate that as the water-cement ratio of ECC increases, the flexural strength, compressive strength, flexural toughness, and compressive elastic modulus of the lightweight ECC-FLS gradually increase, exhibiting a better mechanical performance. Moreover, this study investigates the effect of basalt fiber content in ECC on the mechanical properties of FLS. While keeping other parameters constant, the volume content of basalt fibers varied at 0.1%, 0.3%, and 0.5%, respectively. The experimental results demonstrate that within the range of 0 to 0.5%, the mechanical properties of FLS improved with increasing fiber content. The fibers in ECC effectively enhanced the strength of FLS. In conclusion, the adoption of ECC and appropriate fiber content can significantly optimize the mechanical performance of FLS, endowing it with broader application prospects in engineering practices. ECC-FLS, characterized by excellent ductility and crack resistance, demonstrates versatile engineering applications. It is particularly suitable for soft soil foundations or regions prone to frequent geological activities, where it enhances the seismic resilience of subgrade structures. This material also serves as an ideal construction solution for underground utility tunnels, as well as for the repair and reconstruction of pavement and bridge decks. Notably, ECC-FLS enables the resource utilization of industrial solid wastes such as fly ash and slag, thereby contributing to carbon emission reduction and the realization of a circular economy. These attributes collectively position HDFLS as a sustainable and high-performance construction material with significant potential for promoting environmentally friendly infrastructure development.

Engineered cementitious composites (ECC), which are a kind of novel composite building material with high ductility and high toughness, can be utilized in areas susceptible to salt-freezing damage, such as that caused by snowmelt agents, seawater, and saline soils. In this paper, engineered cementitious composites reinforced with polyethylene fibers (PE) are analyzed to study the changes in the flexural static load properties, and flexural fatigue life of PE-ECC specimens after four different freeze-thaw cycles (0, 50, 100 and 150) in fresh water and a 3.5 % mass fraction NaCl solution. The results show that upon reaching 150 freeze-thaw cycles, there was a notable disparity in the relative equivalent flexural strength between specimens subjected to chloride salt freeze-thaw and freshwater freeze-thaw environments, with the former exhibiting a 1.07-fold increase in damage compared to the latter specimens. Using the relative dynamic elastic modulus as the damage variable, a relationship model was made between the relative equivalent flexural strength and the freeze-thaw damage degree of PE-ECC in two freeze-thaw environments. The flexural fatigue life of PE-ECC after freeze-thaw obeyed a two-parameter Weibull distribution, and the P-S-N curves at various reliability probabilities correlated well with the test results. The safety coefficient of PE-ECC varied with changes in freeze-thaw conditions, necessitating an increase in the safety coefficient to assure structural safety in locations with more severe freeze-thaw damage. The results of this study can serve as a reference for the development of freeze-thaw-resistant designs for PE-ECC structures in future applications.

The dumping of titanium slag (TS) and fly ash (FA) could lead to the occupancy of abundant land resources and the pollution of air, soil and underground water. The meso-regulatory function of the lightweight and thermally stable porous TS makes it a feasible material as the fire-resistive cementitious composites (FRCCs). This paper proposed a novel low-carbon FRCC with favorable high-temperature resistance by using TS and FA. Then, the mechanical properties and mechanism improving the heat resistance were systematically studied. The results revealed that the addition of TS with proper quantity decreases the mass loss by 19.6% and degradation degree of mechanical strength by 31.8% after 800 degrees C heating. The thermally stable perovskite and akermanite phases in TS are conducive to improving the stability of mineral phases during high-temperature heating. Meanwhile, the porous structure of TS enhances the thermal insulation of FRCC, which postponed the mineral phase decomposition. In addition, the secondary hydration effect of FA consumes a large amount of Ca(OH)2, which effectively weakens the deterioration caused by the decomposition of Ca(OH)2 after 600 degrees C heating. Based on the CT results, the variations of internal pore structure including pore distribution, porosity, and fractal dimensions, were systematically analyzed. It is found that the TS particles can effectively optimize the internal pore distribution and limit the generation and deterioration of macro-pores. Moreover, the thermal damage model of the prepared FRCC was established by combining the pore structure deterioration degree and residual mechanical strength. Finally, compared with traditional fire-resistive fillers, the low carbon emission of the prepared FRCC was verified.

The conservation of the environment and the protection of natural resources are urgent and current challenges. The objective of this experimental investigation was to evaluate the potential use of aggregates derived from recycled glass waste, blast furnace slag, recycled brick waste aggregates and recycled electronic waste aggregates (textolite) as replacements for natural aggregates in cement -based composites. The experimental tests aimed to investigate how the replacement of natural aggregates with recycled waste aggregates affects various physico-mechanical parameters, including density, compressive strength, flexural strength, abrasion resistance and capillary water absorption. This investigation also included detailed microstructural analysis using optical microscopy, SEM, EDX and XRD techniques. The aim of the research was to explore the potential for soil conservation by reducing the amount of waste to be disposed of, and at the same time to conserve natural resources by identifying alternatives using recycled materials, thereby contributing to the implementation of the circular economy concept. The results of the research confirmed this potential; however, depending on the nature of the recycled aggregates, there are influences on the physico-mechanical performance of the cement composite that can be seen at the microstructural level.