Current status of research and application of curing technology for engineering soil and sludge
Article Introduction
engineering soil and sludge is China's urban construction and water environment management in the main solid waste, the annual output of nearly 3.5 billion tonnes, the traditional landfill and landfill not only take up a large amount of land resources, but also prone to lead to dust, leachate pollution and landslides and other environmental and safety issues. In recent years, with the ‘dual-carbon’ strategy and the promotion of the concept of green construction, engineering sludge and sludge disposal and resource utilisation has become the focus of industry attention. Among them, curing technology because of its high processing efficiency, adaptability, product availability and other advantages, has become the mainstream direction of sludge and sludge treatment. Current research is mainly focused on alkali stimulated curing, flocculation - dehydration - curing integration, ecological desilting and curing of synergistic treatment and other technologies, supplemented by the recycling of pressurised filtrate, curing agent optimisation ratio and other means to significantly improve the mechanical properties of the curing body and environmental stability. Some of the research directions are as follows:
01
Preparation of Fluid Cured Soil from Engineering Residue Soil
(Underground Backfill Material)
Taking engineering residue soil (including sand, clay, silt, all kinds of engineering slurry, etc.) as the main raw material, adjusting it with water to flowable slurry according to the performance of the residue soil, then mixing it with curing agent to stir well and finally forming the material with high fluidity. Its core advantage lies in the strong fluidity, can achieve self-levelling state, condensation and curing without external intervention.
Core indicators:
◆ Unconfined compressive strength: determine the material load-bearing capacity, need to be determined according to the backfill scene of the soil pressure, load, generally controlled at 0.6 MPa below to facilitate the second excavation;
◆ Wet density: ensure the shear strength by controlling the density, when there are more sand components, the wet density exceeds 1.6g/cm³ can rely on particle occlusion to enhance the shear resistance;
◆ Extensibility: measure the fluidity, too low (<140mm) will lead to pouring difficulties, too high is easy to segregate, need to be adjusted in conjunction with the construction needs;
◆ Water discharge rate: inhibit water analysis, to avoid surface cracking or uneven strength.
02
Industrial Waste Curing Engineering Slag Soil
Preparation of Roadbed Fill
Directly mix the slag soil with curing agent at natural water content in a wet way, and dehydrate and solidify the wet-mixed slag soil into a compactable granular material by tumbling and maintenance.
Zhejiang University Geotechnical Engineering Research Institute has studied the feasibility of industrial solid waste represented by casting slag for slag regeneration roadbed filler, the study shows that 4.5%~6.0% casting slag, 3% quicklime, 3% fly ash composition of the composite curing agent can be slag effective dewatering, and make the filler CBR value to reach the general hydrological and loading conditions (CBR greater than 8%) under the use of the roadbed each layer of the structural layer of the filling requirements.
Core indicators:
◆ Evaluate the effect of solid waste-based curing agent on dewatering and agglomeration of residual soil through water content and particle gradation;
◆ Explore the engineering performance of the fill through California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS).
03
Industrial Waste-Based Curing Agents for Dredged Silt Reinforcement
Preparation of Fill Materials
Using the mutual excitation and synergistic curing effect of different types of industrial wastes, curing materials suitable for dredged silt with high water content are developed to improve the physicochemical and mechanical properties of the silt and transform the silt into fill materials to meet the needs of the project. Among them, Southeast University, Hohai University, Fuzhou University and other universities and research institutions have studied the curing mechanism of cement-phosphogypsum double-mixed curing, blast furnace slag - calcium carbide slag-phosphogypsum synergistic curing, cement - slag - fly ash synergistic curing and other industrial wastes curing mechanism of the silt research. The results show that the mechanism of industrial waste sludge-based curing sludge is mainly through the alkali, sulfate joint excitation of blast furnace slag activity, to promote the generation of a large number of needle and rod AFt, and the use of AFt intertwining, filling effect, and intertwined with the foil, fibrous C-S-H gel climbing, the formation of structural dense three-dimensional spatial network of the soil structure, which in turn effectively improves the strength of the cured sludge.
In recent years, the country has systematically carried out a large number of basic research and projects, Hubei, Tianjin, Guangdong and other successive release of silt, sludge curing local standards (attached); ‘14th Five-Year’ National Key Research and Development Plan: ‘engineering residue, slurry resourceful disposal application’, ‘Yangtze River, Yellow River and other rivers’. The ‘14th Five-Year Plan’ National Key Research and Development Plan: ‘engineering sludge, slurry resource disposal application’, ‘the Yangtze River, Yellow River and other key river basin water resources and water environment integrated management - reservoirs and lakes dredging sludge low-carbon high-quality use of key technologies and equipment,’ is carried out in an orderly manner. It is believed that the curing of sludge and silt in the high water content of silt / sludge strength is low, chloride ions and heavy metals synergistic curing mechanism is unclear, industrial waste composition fluctuations lead to unstable performance and other challenges through a lot of research will eventually be resolved, sludge and silt will play an increasingly important role in the future of green construction.
Curing related standards:
◆JTG D30-2015 Highway Roadbed Design Specification
◆T/SDSZ8-2023 ‘Technical Standard for Application of Fluid Cured Soil’ (Shandong Province)
◆T/CECS1037-2022 ‘Technical Standard for Filling of Premixed Fluid-cured Soil’.
◆T/CECS 1480-2023 ‘Technical Specification for the Application of Cured Soil Prepared from Engineering Residue Sludge and Soil’.
◆DB42/T 2307-2024 ‘Technical Specification for Stabilisation of Grass-roots Level by Over-sulphurised Phosphogypsum Cementitious Materials for Urban Roads (for Trial Implementation)’ (Hubei Province, to be implemented on 4 March 2025)
◆DB12/T 1179-2023 Technical Specification for Road Filling with Mud-State Solidified Soil (Tianjin)
◆DB3207/T 2012-2023 Technical Regulations on Composite Curing and Utilisation of Silt and Industrial Waste Resources in Coastal Harbours (Lianyungang)
◆DB44/T 2171-2019 Technical Specification for Curing and Disposal of River Silt (Guangdong)
Source:https://mp.weixin.qq.com/s/CU7YDz9KOZbLTmwrHRqnpg