This study aims to address the challenge of backfill compaction in the confined spaces of municipal utility tunnel trenches and to develop an environmentally friendly, zero-cement-based backfill material. The research focuses on the excavation slag soil from a utility tunnel project in Handan. An alkali-activated industrial-solid-waste-excavated slag-soil-based controllable low-strength material (CLSM) was developed, using NaOH as the activator, a slag-fly ash composite system as the binder, and steel slag-excavated slag as the fine aggregate. The effects of the water-to-solid ratio (0.40-0.45) and the binder-to-sand ratio (0.20-0.40) on CLSM fluidity were studied to determine optimal values for these parameters. Additionally, the influence of excavated soil content (45-65%), slag content (30-70%), and NaOH content (1-5%) on fluidity (flowability and bleeding rate) and mechanical properties (3-day, 7-day, and 28-day unconfined compressive strength (UCS)) was investigated. The results showed that when the water-to-solid ratio is 0.445 and the binder-to-sand ratio is 0.30, the material meets both experimental and practical requirements. CLSM fluidity was mainly influenced by the excavated soil and slag contents, while NaOH content had minimal effect. The unconfined compressive strength at different curing ages was negatively correlated with the excavated soil content, while it was positively correlated with slag and NaOH content. Based on these findings, the preparation of zero-cement CLSM using industrial solid waste and excavation slag is feasible. For trench backfill projects, a mix of 50-60% excavated soil, 40-60% slag, and 3-5% NaOH is recommended for optimal engineering performance. CLSM is a new type of green backfill material that uses excavated soil and industrial solid waste to prepare alkali-activated materials. It can effectively increase the amount of excavated soil and alleviate energy consumption. This is conducive to the reuse of resources, environmental protection, and sustainable development.

Salt-frost heaving of canal foundation saline soils is the primary cause of damage to the lining structures of water conveyance channels in the Hetao Irrigation District, China. Chemical solidification of saline soils can mitigate frost heave; however, application studies exploring the salt-frost heave resistance of saline soils solidified through the synergistic use of multiple industrial solid wastes in the Hetao remain limited. This study employs a sustainable solidifying material composed of slag, fly ash, coal gangue, coal-based metakaolin, carbide slag, and potassium silicate activator. The optimal mix ratio was determined using Response Surface Methodology (RSM). Unidirectional freezing tests evaluated the effects of solidification material content, curing period, and salt content on salt-frost heave development. Unconfined compressive strength tests assessed salt-frost heave durability of high-salinity solidified saline soils. Microstructural characteristics were analyzed using Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TG) to investigate resistance mechanisms. Results indicated that the industrial waste materials exhibited synergistic effects in an alkaline environment, with the optimal mix ratio of slag, fly ash, coal gangue, coal-based metakaolin, carbide slag, and potassium silicate at 21:25:33:8:7:6. Increasing solidified material content and curing time significantly enhanced salt-frost heave resistance, as evidenced by improved freezing temperature stability, deeper freezing front migration, and reduced salt-frost heave rate. The optimal group (35 % solidifier, 7 days curing) showed a 5.53 degrees C increase in stable freezing temperature, a 3.78 cm upward migration of the freezing front, and a 3.94 % reduction in salt-frost heave rate. Salt-frost heave durability of highsalinity soils improved post-solidification, with a gradual decrease in the degradation of unconfined compressive strength, achieving a minimum weakening of 21.13 %. Hydration products C-S-H, C-A-H, and AFt filled voids between soil particles, restricting water and salt migration. Hydration of industrial wastes reduced free water and SO24 content, decreasing water-salt crystallization and mitigating salt-frost heave. The findings provide an engineering reference for in-situ treatment of salt-frost heaving in saline soils of water conveyance channels in the Hetao Irrigation District.

Calcium carbide slag (CCS), phosphogypsum (PG), and red mud (RM), three types of industrial solid wastes, were employed to improve tunnel muck for assessing the feasibility of their reuse. A series of indoor tests were conducted to investigate the effects of their contents on the physical and mechanical properties of the improved tunnel muck. Microscopic tests were also conducted to reveal the improvement and interaction mechanisms involved. Results indicate that the incorporation of CCS, PG, and RM can significantly improve and enhance the physical and mechanical properties of tunnel muck. The improved tunnel muck containing 2% PG and 6% RM shows higher early strengths as CCS content exceeds 4%. However, after curing for more than 14 days, the unconfined compressive strength (UCS) of the tunnel muck with 4% PG and 4% RM is the maximum regardless of the CCS content. Microscopic analysis shows that reactive substances in industrial solid waste react chemically with soil components, exchanging ions and forming cementitious products such as calcium hydroxide, calcium silicate hydrate (C-S-H), calcium aluminosilicate hydrate (C-A-S-H), and ettringite (AFt). They bind, fill, and encapsulate soil particles, compacting the soil and significantly enhancing the physical and mechanical properties of tunnel muck. Moreover, there is a notable mutual synergy between PG and RM, primarily attributed to their acid-base neutralization and the complementary action of reactive ions. The improved tunnel muck containing 4% CCS, 4% PG, and 4% RM demonstrates the highest enhancement efficiency.

Large-scale engineering projects frequently involve pit excavation and wetland landfill operations, resulting in significant silt accumulation that occupies land and adversely affects the environment. Curing technology offers a solution for reusing this waste silt. In this study, straw ash and calcium carbide slag are proposed as effective curing agents for silt soil. Various indoor tests were conducted to evaluate the mechanical properties of the cured silt soil, while X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze its mineral composition and micro-morphology. The results showed that increasing the curing agent dosage significantly improved soil strength. Specifically, at a 10% dosage, the California bearing ratio (CBR) value increased to 18.7%, which is 13.4 times higher than untreated silt soil and exceeds road specifications by 8%. At a 20% dosage, the unconfined compressive strength (UCS) value reached 1.38 MPa, meeting the >= 0.8 MPa requirement for roadbeds. Based on economic considerations, a 20% dosage of straw ash-calcium carbide slag was selected as optimal. Microscopic analysis revealed that the addition of these agents promoted the formation of hydrated calcium silicate, filling pores and enhancing the mechanical properties of the cured soil, resulting in a more dense and stable structure.

To improve the mechanical and durability properties of low liquid limit soil, an eco-friendly, all-solid, waste-based stabilizer (GSCFC) was proposed using five different industrial solid wastes: ground granulated blast-furnace slag (GGBS), steel slag (SS), coal fly ash (CFA), flue-gas desulfurization (FGD) gypsum, and carbide slag (CS). The mechanical and durability performance of GSCFC-stabilized soil were evaluated using unconfined compressive strength (UCS), California bearing ratio (CBR), and freeze-thaw and wet-dry cycles. The Rietveld method was employed to analyze the mineral phases in the GSCFC-stabilized soil. The optimal composition of the GSCFC stabilizer was determined as 15% SS, 12% GGBS, 16% FGD gypsum, 36% CS, and 12% CFA. The GSCFC-stabilized soil exhibited higher CBR values, with results of 31.38%, 77.13%, and 94.58% for 30, 50, and 98 blows, respectively, compared to 27.23%, 68.34%, and 85.03% for OPC. Additionally, GSCFC-stabilized soil demonstrated superior durability under dry-wet and freeze-thaw cycles, maintaining a 50% higher UCS (1.5 MPa) and a 58.6% lower expansion rate (3.16%) after 15 dry-wet cycles and achieving a BDR of 86.86% after 5 freeze-thaw cycles, compared to 65% for OPC. Rietveld analysis showed increased hydration products (ettringite by 2.63 times, C-S-H by 2.51 times), significantly enhancing soil strength. These findings highlight the potential of GSCFC-stabilized soil for durable road sub-base applications. This research provides theoretical and technical support for the development of sustainable, cost-effective, and eco-friendly soil stabilizers as alternatives to traditional cement-based stabilizers while also promoting the synergistic utilization of multiple solid wastes.

To reuse industrial solid wastes and waste clay with low liquid limit, a kind of soil solidification material by using cement, quicklime and industrial solid wastes such as ground granulated blast -furnace slag (GGBS), silica fume (SF) was developed in this study. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiment and optimize the mix ratio of GGBS, quicklime and SF under certain cement content conditions (i.e., the content ratio of cement, GGBS, quicklime, and SF was 5: 9.14: 1.7: 2.13). A soil solidification agent named O-QGS was developed to solidify waste clay with low liquid limit. To clarify the solidification mechanism of solidified soil, a series of laboratory experiments such as UCS test, water stability test, and scanning electron microscopy (SEM) test were carried out to capture the mechanical properties, water stability, and microstructure of O-QGS solidified soil and cement solidified soil. For practical purpose of O-QGS, a method for forming prefabricated pile by using O-QGS solidified soil was developed, and a method for strengthening soft foundations with prefabricated O-QGS solidified soil pile was proposed. Based on the results of load tests, the bearing capacity of prefabricated O-QGS solidified soil pile and cement high-pressure rotary jet grouting pile, as well as the composite foundations bearing capacity of prefabricated O-QGS solidified soil pile and cement high-pressure rotary jet grouting pile used for strengthening soft foundations, were analyzed. The feasibility of prefabricated O-QGS solidified soil pile used for strengthening soft foundations was verified in practice. The present study shows that the UCS of O-QGS solidified soil is 7.25 MPa at 28 days, and the water stability coefficient of O-QGS solidified soil is larger than 0.8. Compared with the method of cement highpressure rotary jet grouting pile to reinforce soft foundation, the bearing capacity of prefabricated O-QGS solidified soil pile to reinforce soft foundation is higher, and the cost can be saved by 22.4 %.

This review systematically introduces the current status and development trend of inorganic industrial solid waste (IISW)-based materials. IISWs have the characteristics of wide sources, large land occupation, low utilization rate, and high environmental risk. In this paper, IISWs from different sources are introduced firstly, including coal (coal fly ash, coal gangue, flue gas desulfurization gypsum), metallurgy (steel slag, blast furnace slag, electrolytic manganese residue, red mud, etc.), chemistry (phosphogypsum, lithium slag), construction (waste glass, ceramic waste), mining (tailings) and other industries. Then the main research progress of IISWs in building material preparation (cement, aggregate, glass, ceramic, road, brick), water/air treatment (catalyst and adsorbent), and soil improvement (fertilizer and remediation agent) is discussed in detail. At the same time, the role of IISWs in material systems and the solidification/stabilization (S/S) mechanisms of heavy metals in IISWbased materials are emphasized. Finally, the challenges of IISWs material utilization are discussed, and prospects for the development of this field are proposed. Overall, the construction industry is expected to achieve largescale and comprehensive utilization of IISWs, while the research in other fields requires more value-oriented and industrialized exploration. More importantly, the migration and transformation of heavy metals in IISWs during material utilization need full attention.

There is a huge stock of industrial solid waste piles such as phosphogypsum (PG), desulfurization ash (DA), and waste soil (WS) in China, and their utilization rate is insufficient. These have potential risk for environmental safety due to pollutants contained in them. In this study, after proportioning design, raw material pretreatment, bubble regulation and multi -temperature maintenance process, successfully prepared a high blending solid waste based functional prefabricated autoclaved aerated concrete slabs (FPAS) with excellent functional performance, and the optimal ratio of each raw material is PG: WS: DA: cement: lime = 8:50:20:10:12, and the dry mass ratio is up to 75%, the compressive strength of the slabs is up to 5.2 MPa, the standard dry density is 606 kg/m 3 , the dry shrinkage value is 0.36 mm/m, and the post -freezing strength is 4.0 MPa, which is in line with the basic requirements in the standard Autoclaved aerated concrete slabs (GB/T15762) , and at the same time, its fire-resistant integrity is qualified for 240 min, and the coefficient of thermal conductivity is 0.15w(m. k), airborne sound -weighted sound insulation is 46 dB, also can show different functional characteristics. In order to investigate the environmental safety of heavy metals (HMs) in the slabs, the simulation experiment of HMs leaching from outdoor stacking of slabs was carried out. The results show that the HMs in the slabs do not pose obvious risks to the natural environment and human body, but three of the characteristic HMs, Cr, Cd and Hg, have significant leaching patterns, which can be expressed by a second -order kinetic model. Finally, the life cycle assessment and cost analysis of the high blending PG -DA -WS based FPAS and the conventional aerated slabs were carried out. The main environmental damage category of the high blending PG -DA -WS based FPAS is land ecological risk, and it has obvious environmental and economic benefits compared with the conventional aerated slabs.