There has been a growing interest in controlled low strength material CLSM due to its engineering features, such as self-leveling and early strength development, as well as it potential for utilizing industrial waste. Still, the dynamic properties on CLSM are rarely studied. This study evaluates the feasibility of red mud as a partial aggregate replacement in foamed-lightweight CLSM, incorporating high-carbon fly ash and preformed foam. We varied both the red mud contents RMc and foam volume ratio FVR within the mixtures and examined their impact on unconfined compressive strength and dynamic properties including shear modulus G and damping ratio D. The results reveal that the red mud enhances foam stability, leading to more uniform pore structures and increased porosity, which reduces bulk densities. Despite higher porosity, red mud serves as a strong alkaline activator, enhancing geopolymer reactions of high-carbon fly ash and thereby increasing both compressive strength and initial shear modulus G0. Interestingly, increasing FVR had minimal impact on the D, while higher RMcnotably increased D, highlighting its distinct role in energy dissipation. The red mud-incorporated foamed CLSM exhibits strain-dependent normalized shear modulus G/G0 comparable to that of gravel, while its D is 40-100 % higher than gravel or gravelly soil at shear strain of 1.10-5, which corresponds to typical traffic-induced vibration levels. Moreover, theoretical volumetric-gravimetric relationships are introduced to account for the combined effects of FVR and RMcon CLSM behavior. These findings demonstrate that the red mud included foamed CLSM can be utilized as advanced structural backfill material capable of effectively mitigating the vibrations induced by traffic, low-amplitude seismic events, and mechanical sources.

Deep foundation pits, pipe gallery troughs, culverts, and other infrastructure often require backfilling operations. Soil-based controlled low-strength material (soil-based CLSM), with its advantages of self-compaction, self-leveling, and self-hardening, has garnered significant attention in recent years and shows potential as a replacement for traditional rolling compaction backfill materials. Based on the backfill project of the pipe gallery at the Xihong Bridge in Ningbo, this study investigates the unconfined compressive strength, permeability coefficient, compression characteristics, and flow behavior of soil-based CLSM with varying curing agent ratios, assessing its engineering feasibility through field testing. The results demonstrate that soil-based CLSM, particularly with polycarboxylate superplasticizer agent, exhibits substantially improved strength, permeability, construction workability, and other service performance. Additionally, a detailed simulation of the entire pipe gallery foundation pit construction process-including pipe gallery construction, trench backfilling, support removal, and road construction-was performed using the Hardening soil with small strain stiffness model of the soil. The deformation characteristics were analyzed under different backfill conditions to assess the suitability of soil-based CLSM for trench backfilling. The analysis also considered soil deformation under varying curing ages and upper load conditions. The optimized backfilling solution for soil-based CLSM was obtained and validated with field test data. The findings suggest that using soil-based CLSM for foundation trench backfilling can effectively mitigate settlement issues.

With the rapid growth of shield-discharged soil (SDS), there is an increasing demand for effective recycling and transformation methods. This study aims to develop an alkali-activated controlled low-strength material (CLSM) by utilizing ground granulated blast furnace slag (GGBFS) and fly ash (FA) as precursors, SDS as fine aggregate, and sodium hydroxide (NaOH) solution as an activator. The Box-Behnken design (BBD) within the response surface methodology (RSM) framework was employed, considering liquid-to-solid ratio, alkali equivalent, aggregate-to-binder ratio, and foam agent content (FC) in SDS as key factors. Regression models were constructed to analyze the effects of these factors on flowability, bleeding rate, setting time, compressive strength, elastic modulus, and water absorption. The results confirmed the effectiveness of RSM in determining optimal conditions for material performance. In addition, microscopic analyses were conducted to explore hydration products, microstructural characteristics, and pore distribution. The findings revealed that the fresh density of the CLSM ranged from 1460 to 1740 kg/m(3), classifying it as a low-density material. The 28-day compressive strength varied from 1.837 to 7.884 MPa, while the setting time ranged between 1.2 and 5.6 hours. These properties comply with the ACI 229 standard and are suitable for practical applications. Interestingly, when the aggregate-to-binder (A/B) ratio was between 0.2 and 0.4, increasing the ratio did not lead to a consistent reduction in mechanical properties. Instead, the properties initially decreased and then improved. Moreover, an increase in foam agent content (FC) extended the setting time and reduced mechanical strength. The correlation coefficients of all models exceeded 0.98, with a coefficient of variation below 10 % and a signal-to-noise ratio greater than 4, demonstrating strong reliability and accuracy of the models. Additionally, the average relative error between predicted and experimental values in six scenarios was under 6 %, validating the feasibility of optimizing the design of alkali-activated CLSM using RSM. The formation of Ca(OH)(2) crystals facilitates early strength development, resulting in final cementitious materials reticular, fibrous C-S-H, C-A-H, and other gel-like hydration products. Calcium promotes the formation of gels such as C-S-H, shortening the setting time and enhancing microstructural density. This study provides valuable insights for optimizing the design of alkali-activated CLSM containing SDS, thereby expanding methods for utilizing construction and demolition waste.

The storage of mining waste not only consumes a vast tract of land, but it also poses environmental problems due to the leaching of heavy metals, dusting, and occasional slope failure. A coal mine overburden (hereafter referred to as black shale) is one of the mining wastes produced during the coal mining activity, dumping of which causes an environmental problem. By considering the issue associated with waste storage and the requirement for alternate civil engineering material, an attempt has been made to develop cementless controlled low strength material (CLSM) from black shale. For this purpose, black shale is mixed with a varying percentage of alkali activated ground granulated blast furnace slag (GGBS) and fly ash. The fresh CLSM is investigated for flowability, bleeding, and density, whereas the hardened CLSM is examined for unconfined compressive strength (UCS), hardened density, water absorption, ultrasonic pulse velocity, and durability. The CLSM developed in the present research is found to have self-flowing and self-leveling consistency, with flowability higher than 200 mm and a relative flow area between 2.06 and 7.70. The CLSM is found easily excavatable with a removability modulus less than 1. The 28-day UCS of CLSM is found between 0.48 MPa and 2.1 MPa, whereas it is found low to medium durable with a durability index between 84.44 % and 87.39 %. Further, the shear modulus of the hardened CLSM is evaluated using ultrasonic pule velocity. Finally, the CLSM is found non-toxic based on the result of the leaching analysis.

The volume of shield tunnel spoil (STS) is very large, its effective management is difficult, and it even causes environmental pollution. In this study, to achieve its recycling, a novel controlled low strength material (CLSM) was prepared by utilizing high fine-grained STS as partial aggregates instead of sand, and its engineering performance was thoroughly evaluated. In the process of mix proportion design, key parameters such as the STS-tototal aggregate ratio (TS/TA), foam agent content (F), water-to-binder ratio (W/B), binder-to-total aggregate ratio (B/TA), and fly ash-to-cement ratio (FA/C) were employed. Workability aspects (i.e., flowability, bleeding rate, and setting time) and physical and mechanical properties (i.e., unconfined compressive strength and density) were evaluated. Additionally, the pH of bleeding and leachate, as well as the impact of foam agent content on CLSM properties, were examined. The findings revealed that an increase in the TS/TA ratio was associated with a decrease in flowability, density, and compressive strength, as well as an extension in setting time. The CLSM, with a flowability range of 150-300 mm, exhibited a bleeding rate below 2%, setting times between 3.6 and 6.1 hours, 28-day strength ranging from 1.06 to 3.24 MPa, and fresh density ranging from 1810 to 2060 kg/m3. Generally, these results met the required specifications, although the fresh density was slightly lower. The pH results indicated that the CLSM is non-corrosive. Furthermore, our investigation highlighted the substantial influence of foam agent content on flowability and setting time. An increase of 0.1 parts per thousand in the proportion of foam agent within the total aggregates resulted in a flowability increase of 2.1-2.6 mm and a setting time increase of 4.25-4.99 minutes. Therefore, it is feasible to utilize high fine-grained STS in the production of CLSM.

针对现有岛状冻土地区冻胀路基的维护技术存在的突出问题,为最大限度地降低利用传统换填材料处治对道路通行能力的影响,研究提出了两种具备良好隔温性能,且能够快速硬化、施工便捷的新型填料。基于可控性低强度材料(CLSM)的高流动性、自填充、自密实特性,对其掺入泡沫颗粒,并通过对两种配合比进行无侧限抗压强度试验、导热系数试验和抗冻融循环试验,确定换填材料的泡沫颗粒的最佳体积比为1%。从技术经济角度出发,提出治理方案为:对沉陷面积不大的区域,采用全厚度换填修复;对沉陷面积较大的区域,采用XPS板+CLSM换填修复。最后通过现场试验段的实施,分析结果表明,本文提出专用于现有岛状冻土地区路基换填的新型材料,能够达到实际的工程应用要求。