This research explores the use of cup lump rubber (CLR), an agricultural by-product, as a component in controlled low-strength material (CLSM) for pavement applications in road construction. Two distinct CLSM mixtures were developed: one based on cement and the other on alkali activation. The study evaluated the workability, mechanical properties, and microstructures of both CLSM formulations. Key fresh properties, including slump flow, setting time, and bleeding, were analysed to assess their impact on the self-compaction process. Mechanical characteristics such as unconfined compressive strength, resilient modulus, and wave velocities were also measured. Some CLSM mixtures, both cement-based and alkali-activated, were found to meet the requirements for soil cement bases and subbases. Notably, the resilient modulus values showed significant improvement after 28 days, with certain mixtures achieving subbase-quality gravel standards. The study concludes by recommending the use of both cement-based and alkali-activated CLSMs in pavement design, highlighting their potential to enhance the field of pavement engineering.

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.

Controlled low-strength material (CLSM) is a flowable, self-leveling backfill material used as an alternative to compacted soil for backfilling trenches, retaining walls, underground cavities, and in pavement construction. This study aims to investigate the permanent deformation of CLSM reinforced with basalt fibers. Basalt fibers with lengths of 6 and 24 mm are incorporated into CLSM mixtures to assess their impact on flowability, setting times, and mechanical properties. Mechanical testing indicates that longer fibers improve tensile strength through a bridging effect. Repeated load triaxial tests are conducted to evaluate the permanent strain behavior under repeated loading. The results show that permanent strain increases with the deviator stress and number of loading cycles. A regression model accounting for the number of loading cycles and deviator stress provides accurate permanent-strain predictions, and the permanent strain behaviors are classified based on the refined shakedown theory. Therefore, the basalt-fiber-reinforced CLSM suggested in this study may be suitable for pavement base material due to its relatively low permanent strain under typical stress conditions.

Red-bed mudstone from civil excavation is often treated as waste due to its poor water stability and tendency to disintegrate. This study proposes a sustainable approach for its utilization in controlled low-strength material (CLSM) by blending it with cement and water. Laboratory tests evaluated the fresh properties (i.e., flowability, bleeding rate, setting time, and subsidence rate) and hardened properties (i.e., compressive strength, drying shrinkage, and wet-dry durability) of the CLSM. The analysis focused on two main parameters: cement-to-soil ratio (C/S) and water-to-solid ratio (W/S). The results show that increasing W/S significantly improves flowability, while increasing C/S also contributes positively. Flowability decreased exponentially over time, with an approximately 30% loss recorded after 3 h. Bleeding and subsidence rates rose sharply with higher W/S but were only marginally affected by C/S. To meet performance requirements, W/S should be kept below 52%. In addition, the setting times remained within 24 h for all mixtures tested. Compressive strength showed a negative correlation with W/S and a positive correlation with C/S. When C/S ranged from 8% to 16% and W/S from 44% to 56%, the compressive strengths ranged from 0.3 MPa to 1.22 MPa, meeting typical backfilling needs. Drying shrinkage was correlated positively with water loss, and it decreased with greater C/S. Notably, cement's addition significantly enhanced water stability. At a C/S of 12%, the specimens remained intact after 13 wet-dry cycles, retaining over 80% of their initial strength. Based on these findings, predictive models for strength and flowability were developed, and a mix design procedure was proposed. This resulted in two optimized proportions suitable for confined backfilling. This study provides a scientific basis for the resource-oriented reuse of red-bed mudstone in civil engineering projects.

Controlled low-strength materials (CLSM) have been used for conventional backfilling and structural filling owing to their flowability, self-consolidating, and self-leveling features. This study investigates the rheological, mechanical, and dynamic characteristics of lignosulfonate-modified CLSM. The elemental analysis of lignosulfonate reveals the presence of various elements and an irregular morphology, as observed using a scanning electron microscope. A series of tests, including flow tests, Vicat needle tests, uniaxial compression tests, and shear wave monitoring, are conducted to evaluate the flowability, setting time, strength, and shear wave velocity of lignosulfonate-modified CLSM. The experimental results show that the flowability and initial and final setting times of the CLSM mixtures increase with increasing lignosulfonate content (LC), which improves workability in the field but results in a slight strength loss. Regarding the uniaxial compressive strength, CLSM mixtures with lower LC exhibit a rapid increase in strength during the early stages, while those with higher LC show higher performance on the 14th day of curing. In contrast, an LC of 0.21% led to a slight reduction in the strength on the 28th day. The current study also shows an exponential correlation between the uniaxial compressive strength and shear wave velocity.

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.

In order to reduce heat loss and diffusion of underground heating pipelines, this research incorporated phase change material (PCM) into the controlled low-strength material (CLSM) to prepare a pipeline backfill material with temperature control performance. In response to the problem that PCM leaks easily, a new type of paraffin-rice husk ash composite PCM (PR-PCM) was obtained by adsorbing melted paraffin into rice husk ash. Through mixing PR-PCM with dredged sediment (DS) and ordinary Portland cement (OPC), a controlled low-strength material (CLSM) with temperature control performance was prepared. The flowability, mechanical properties, microscopic characteristics, thermal characteristics, and durability of CLSM were analyzed through flowability, unconfined compressive strength (UCS), X-ray diffraction (XRD), scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), and phase change cycle tests. The results show that when water consumption is constant, as the PR-PCM content increases, the flowability of CLSM increases, and the strength decreases. The CLSM has an obvious paraffin diffraction peak in the XRD pattern, and its microstructure is dense with few pores. The melting point of CLSM is 50.65 degrees C and the latent heat is 4.10 J/g. Compared with CLSM without PR-PCM, the maximum temperature difference during the heating process can reach 3.40 degrees C, and the heat storage performance is improved by 4.1%. The strength of CLSM increases and the melting point decreases after phase change cycles. CLSM containing PR-PCM has the characteristics of phase change temperature control, which plays a positive role in reducing heat loss by heating pipelines and temperature change in backfill areas.

In urban areas, backfilling voids with complex and narrow shapes necessitates alternative backfill methods and materials, such as controlled low-strength materials (CLSMs), to minimize ground subsidence caused by improper compaction of backfill soils. This study aims to propose a predictive methodology for the mechanical properties of CLSMs using regression analysis and a deep neural network (DNN). CLSM mixtures are prepared with various mixing ratios of calcium sulfoaluminate (CSA) expansive admixture, water, Portland cement, fly ash, sand, silt, and alkali-free accelerator. The flow consistency and compressive strength at 12 hrs and 7 days post-mixing are estimated. The relationships between CLSM mixing ratios and the estimated mechanical properties are established through multiple regression analysis and DNN. The DNN's performance is evaluated, with coefficients of determination being 0.0874, 0.8432, and 0.6826 for flowability, and compressive strength at 12 hrs and 7 days, respectively. To address the low performance, oversampling algorithms like the synthetic minority oversampling technique (SMOTE) and the conditional tabular generative adversarial network (CTGAN) are utilized. Analysis of the oversampled data using SMOTE indicates improved performance, with the coefficients of determination rising to 0.6818, 0.9856, and 0.983 for flowability, and compressive strength at 12 hrs and 7 days, respectively. This study illustrates that the identified correlations may be effectively used to predict flowability and compressive strength based on the mixing ratio.

Gasification slag (GS) is rich in SiO2, Al2O3, and Fe2O3, and has excellent particle size gradation, which has the potential to be employed as an aggregate in the field of controlled low-strength material (CLSM). Nevertheless, the large-scale application of GS as the fine aggregate for the preparation of CLSM has been scarcely investigated. In the present work, the applicability of replacing part of coal gangue (CG) with gasification coarse slag (GCS) as fine aggregate for the preparation of CLSM was investigated. The results revealed that using GCS as a fine aggregate improved the flowability of CLSM, and increasing the GCS content from 0 to 50 wt% improved the flowability from 250.0 to 280.0 mm. The 28-day compressive strength of all CLSM conformed to the requirements of ACI Committee 229. Compared to the Blank group, the 7- and 28-day compressive strength of the CLSM increased by 23.07% and 26.80%, respectively, at a GCS content of 50 wt%. The increase in compressive strength was mainly due to the pore-filling and hydration-promoting effect of the GCS, which made the structure denser. The dense structure reduced the expansion rate, absorption, and porosity rate of CLSM and increased the wet density. The optimal process parameter was the addition of 10 wt% of GCS. The results of heavy metal ion leaching showed that the optimal sample GS10 leached all heavy metal ions in much less than the limit values of GB 8978-1996 and GB 5085.3-2007. The results will provide new ideas and technical approaches for the large-scale application of GCS as the fine aggregate in CLSM.