Solidified soil (SS) is widely applied for resource utilization of excavated soil (ES), however the waste solidified soil (WSS) may pose environmental hazards in future because of its high pH (>10). WSS is unsuitable for landfill but can be raw materials for preparing recycled solidified soil (RSS) with better mechanical properties than SS. This investigation used OPC and alkali-activated slag (AAS) as binders to solidify ES and WSS and prepare RSS. The mechanical properties of RSS were experimentally verified to be better than SS, increased by over 76 %. The mechanism is that the clay particles in WSS have been solidified to form sand-like particles or adhere to natural sand, resulting in increasing content of sand-sized particles, and the residual clay particles undergo cation exchange under the high pH and Ca2 + content, resulting in a decrease in zeta potential, reducing diffusion layer thickness. As a result, the flowability of RSS increases under the same liquid to solid ratio. The residual unreacted binder particles and high pH in WSS are beneficial for the early and final compressive strength increase of RSS, which allows preparing RSS with lower cost and carbon emission. Finally, the utilization of WSS has significant environmental benefits.

The treatment of excavated soil using the dry sieving method to produce recycled sand is an effective approach for resource utilization. Currently, the hot-air drying process used in this method exhibits high energy consumption. To address this issue, this study proposes a microwave drying technology to dry the excavated soil. Comparative experiments on microwave (1-6 kW) and hot-air (105-205 degrees C) drying of the excavated soil were conducted. The drying behavior and specific energy consumption of the excavated soil were investigated. The Weibull-Fick combined method was recommended for the segmental determination of the effective moisture diffusion coefficient, and the question of whether microwave drying adversely affects sand particles in the excavated soil was answered. The results revealed the following: Compared with hot-air drying, microwave drying demonstrated shorter drying time (3.5-38 min vs 75-1200 min), lower specific energy consumption (6.2-11.5 MJ/kg vs 22.3-55.4 MJ/kg), and a higher range of effective moisture diffusion coefficient (10-8-10-7 m2/s vs 10-9-10-8 m2/s). With increasing microwave power (3-6 kW), the time required for complete drying of the sample was reduced by up to 56 %. Under microwave drying, relaxing the termination moisture content criterion from 0 to 0.01 resulted in a 17 %-32 % reduction in specific energy consumption, accompanied by a 24 %-36 % decrease in drying time. Microwave drying did not damage sand particles within the excavated soil.

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.

Weathered residual soil of granite (WRSG) is the predominant type of excavated soil in southern China. This study explores the high-quality utilisation potential of WRSG by mixing it with a small amount of cement and preloading it within steel tubes to create preloaded-cement-soil filled steel tubular (PCSFST) columns. The research investigates the relaxation behaviour and axial compression performance of PCSFST columns through experiments, focusing on the influence of preloading indicator, cement content ratio, and water-to-solid rat io on their axial compression behaviour. The experimental results showed that an increase in the preloading indicator significantly enhanced the axial bearing capacity of the PCSFST column. Specifically, when the preloading indicator increased from 30 % to 90 %, the axial bearing capacity increased by 22.7 %. Although the increase from 6 % to 12 % in the cement content ratio significantly improved the unconfined compressive strength (UCS) of the cement-soil core, the corresponding reduction in the confining effect only resulted in a 3.2 % increase in the axial bearing capacity, indicating a limited benefit. A moderate increase in the water-to-solid ratio significantly boosted the UCS of the cement-soil core, which in turn, enhanced the axial bearing capacity of the PCSFST column. After the preloading load was released, the cement-soil core exhibited longitudinal rebound deformation, which significantly reduced the confining effect provided by the steel tube. Nevertheless, the contribution of the confining effect to the axial bearing capacity can reach as high as 37 %, partially compensating for the relatively low UCS of the cement-soil core. Finally, based on the experimental results, a formula was proposed to predict the axial bearing capacity of PCSFST columns, which demonstrated high prediction accuracy.

This work investigates the effects of substituting natural sand with excavated soil sand in the formulation of hydraulic mortar developed from a self-compacting concrete (SCC). Four excavated soil sand deposits were studied to assess their physicochemical properties. Subsequently, a reference mortar (RM) was designed using the concrete equivalent mortar method. Furthermore, the effect of incorporating 30% of excavation soil sand under different moisture conditions (natural storage conditions, dry and saturated surface dry state) on the properties of mortar is studied. Spreading tests were carried out to observe how the rheological properties evolve over time. The study includes compressive and flexural strength tests at 2, 7, 14 and 28 days. The results showed that some sands had densities similar to those of natural alluvial sand, while others had lower densities. Water absorption values varied considerably from one sand to another, with some showing values ranging from 1% to 6%, while other sands had values of up to 10%. The results of spreading tests indicate that mortar made with sand in a saturated dry-surface state is more fluid than mortar made with sand in a dry state. Under all conditions, all mortars lose their fluidity over time. The variation in compressive strength among all excavated soil sand mortars compared to the reference mortar remained below 10% at 2 and 28 days, except for one sand with a high clay content. The incorporation of excavated soil sand at this percentage as a substitute for river sand led to an enhancement in the flexural strength of the mortar, with improvements of 40% and 50% observed for certain types of excavated sand. The statistical study revealed a strong relationship between the properties of the sand (in particular, the fines content and their nature, as well as the sand skeleton) and its saturation state, the flowability and the compressive strength of the mortar.

In this study, the feasibility of sintering ceramsite from engineering excavated soil was studied from experimental verification perspective. The optimal preparation conditions for the sintered ceramsite were determined through multi-factor testing with the sintering temperature from 1100 degrees C to 1175 degrees C and Fe2O3 content from 23 % to 26 % and charcoal powder content from 1.5 % to 3.0 %. The cylindrical compressive strength of the ceramsite can reach 5.02 MPa. It is found that the synergistic effects of Fe2O3 and charcoal powder have a great influence on the expansion properties of ceramsite. The generation of gas and vitreous phase by charcoal powder burning and Fe2O3 reduction effectively can promote the expansion of ceramsite. The typical core-cortex structure of ceramsite is formed, and the compact structure of the external layer significantly reduces the water absorption of ceramsite. Experimental results indicate that under the conditions of adding 23-26 % Fe2O3 powder and 1.5-3.0 % charcoal powder, with a sintering temperature of 1100-1175 degrees C, the obtained ceramic material exhibits excellent strength properties.

This study comparatively investigated the performance of mortar prepared using excavated soil recycled fine aggregate (ESRFA), which mainly included fine aggregate obtained by sediment separation equipment and sieving. Scanning electron microscopy (SEM) was used to analyse the size and shape of ESRFA particles. The particle size distribution of ESRFA was uneven and its sphericality was lower than that of river sand. Two series of rendering mortar mixes were prepared using identical water/cement and aggregate/cement ratios of 0.55 and 3, respectively, using river sand as fine aggregate. ESRFA was used to replace 30%, 50%, 70%, and 100% of the river sand in each mixture. The experimental results showed that the flowability of the mortar prepared with ESRFA was lower than that of the aggregate-based mortar, but the porosity, water absorption, and mechanical properties (compressive strength, flexural strength, and drying shrinkage) increased and then decreased upon increasing the ESRFA content. In conclusion, ESRFA shows potential as a partial replacement for river sand in mortar, particularly at lower substitution rates. Further research is needed to optimize the processing and application of ESRFA in concrete to enhance its performance and sustainability.

This article investigates the hygrothermal properties of earth-based materials by analyzing experimental data from 88 articles spanning 32 countries worldwide. The focus is determining effective techniques for leveraging the use of excavated soil in construction, particularly emphasizing enhancement of hygrothermal comfort in specific climates. Based on statistical analysis, the study presents a comprehensive classification of earth production techniques, incorporating additives, and examines their impacts on hygrothermal properties of excavated soils. Additionally, it explores the intricate relationship between the climatic conditions of a region and the chosen earth-material production techniques. The analysis aims to propose standard parameters for earthen materials and identify gaps in both methods and experimental studies. Therefore, this study will provide valuable insights by proposing new design tools (ternary diagrams) to maximize the use of excavated soils in construction practices. The proposed diagrams illustrate the intricate relation linking either hygrothermal properties, the climate zone, and manufacturing techniques, or the relation between the most studied manufacturing techniques (compaction, fibered, and stabilization) and expected dry thermal conductivity. Thereby, results from this meta-analysis and critical review will contribute to advancing sustainable construction practices.