Low Strength Material Research Articles

An innovative sustainable solution: Recycling shield-discharge waste soil as fine aggregate to produce eco-friendly geopolymer-based flowable backfill materials

The disposal of Shield-Discharge Waste Soil (SDWS) is substantial, yet their recycling rate remains low, necessitating the exploration of new recycling methods for effective waste management. This study examines the potential use of SDWS as a fine aggregate in the production of Controlled Low-Strength Material (CLSM), incorporating slag and fly ash as precursors. Key properties such as strength, flowability, setting time, microstructure, chemical composition, CO2 emissions, energy consumption, and cost were assessed and analyzed. Additionally, the environmental impact and material-related strategies were discussed. The results reveal that the developed CLSM exhibits competitive performance, with compressive strengths ranging from 2.830 MPa to 4.121 MPa, achieving over 1.0 MPa strength within 24 hours. The material demonstrates high flowability, exceeding 200 mm within 30 minutes, and has a setting time between 2.10 and 4.23 hours, offering advantages in both setting time and early strength. SDWS contributes to extending the coagulation process and enhancing the flowability. Optimal strength is observed when SDWS constitutes approximately 30 % of the binders or when the alkali equivalent is around 7 %. Compared to traditional cement-based CLSMs, incorporating SDWS results in reduced CO2 emissions and lower energy consumption. When considering savings from reduced waste disposal costs, the overall material cost remains competitive. Furthermore, higher SDWS content leads to enhanced environmental benefits, and it is recommended to keep the alkali equivalent below 7 % for optimal performance. In conclusion, the developed CLSM presents significant potential for wide-scale applications and offers a sustainable solution for recycling SDWS.

Cement-based and alkali-activated controlled low-strength materials made from cup lump rubber for use as road materials

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.

Optimization and characterization of GGBFS-FA based alkali-activated CLSM containing Shield-discharged soil using Box-Behnken response surface design method

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/m³, 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.

Development of a Controlled Low-Strength Material Containing Paraffin–Rice Husk Ash Composite Phase Change Material

Development of a Controlled Low-Strength Material Containing Paraffin–Rice Husk Ash Composite Phase Change Material

Harnessing hazardous wastes: the production, characterization, and performance of controlled low strength materials using common effluent treatment plant sludge

India's rapid industrialization has led to an increase in waste generation, necessitating efficient disposal methods. This research addresses this challenge by exploring the use of Common Effluent Treatment Plant (CETP) sludge, a hazardous waste, in the production of Controlled Low-Strength Materials (CLSM). The study aims to mitigate the environmental impacts associated with CETP sludge disposal while providing a sustainable solution. To assess the feasibility of this approach, an experimental program was conducted with variations in the mix ratio of CETP sludge and slag sand, a byproduct of steel production. The properties of the produced CLSM, such as flowability and unconfined compressive strength (UCS), were thoroughly examined using Scanning Electron Microscopy, X-ray Diffraction, and X-ray Fluorescence analyses. The results reveal that the CLSM produced with CETP sludge and slag sand exhibits promising performance, with excellent flowability and UCS values ranging from 1.8 to 5.5 MPa. This research underscores the potential of waste materials in creating sustainable and environmentally friendly construction materials, contributing to effective waste management practices and sustainable industrial growth.

Impact of polycarboxylate superplasticizer dosage on controlled low strength material flowability and bleeding: Insights from water film thickness

Civil excavation projects frequently yield substantial excess spoil, posing challenges to sustainable construction. This study explores repurposing such spoil for creating controlled low strength material (CLSM), emphasizing the novel use of polycarboxylate superplasticizer (PCE) to reduce the water requirement. The work also distinctively utilizes water film thickness (WFT) theory to elucidate the effects of PCE dosage and WFT on material properties, thereby advancing CLSM mix design. First, using an experimental approach, a series of fresh CLSM samples are prepared, with varying the water-to-solid ratio (W/S) and PCE dosage, to evaluate their packing density, WFT, flowability, and bleeding rate. It is demonstrated that both packing density and WFT experienced a non-linear increase with rising PCE dosage. Regression analysis of the experimental data reveals that the flowability and bleeding rate linearly increase with the rising WFT, and the enhancements are more pronounced at higher PCE dosage. Notably, at a given WFT, the impact of PCE dosage on flowability and bleeding rate reduce as WFT decreases. Additionally, the research identifies specific WFT thresholds correlating with maximum flowability and a 5% bleeding rate. These thresholds mark the critical point at which WFT ceases to influence flowability and delineate the maximum WFT that satisfies the bleeding rate requirements, respectively. These insights are important for optimizing the design of CLSM with PCE in terms of flowability and bleeding rate.

Behavior of controlled low-strength material incorporating industrial by-products fly ash, quarry waste and concrete waste

The widespread generation of concrete waste from demolished structures presents a significant challenge in construction waste management. However, its integration into Controlled Low Strength Material (CLSM) presents a promising avenue for sustainable construction for utility fill or backfilling applications when suitable granular fills are not available. A low strength flowable fill mix necessitates a mix design that achieves a compressive strength below 0.7 MPa after 28 days for easy excavatability using hand tools. This study delves into the feasibility of replacing fly ash by incorporating concrete waste and quarry waste into CLSM formulations with minimal amounts of cement through laboratory investigations to engineer CLSM blends optimized for easy excavation, particularly for utility fills. Results indicate that the inclusion of concrete waste reduces the water demand and mitigates bleeding in CLSM, thereby enhancing the overall stability of the mix. Moreover, CLSM compositions exhibit densities akin to the density of sand. The addition of 10 % and 20 % of concrete waste led to substantial increases in unconfined compressive strength (UCS). The impact was more pronounced at lower cement contents, with significant early strength development observed when concrete waste was included.The split tensile strength was found to have a linear correlation with the UCS and the dry density of the mix. The formation of pozzolanic hydration products, particularly in mixes with higher fly ash content, was identified as a key factor contributing to strength development, while increased friction between particles of quarry waste further increased the strength and the same has been confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The findings also revealed that a CLSM blend composed of, 30 % fly ash, 50 % quarry waste and 20 % concrete waste supplemented with an extra 3 % cement at 250 mm flowability could be used for backfilling applications where sufficient strength and excavatablity with hand tools is required.

Development of insulating backfill materials produced from the ternary mixtures of red mud, fly ash and preformed foam

Many public utility lines to transport power, water, natural gas, water, sewer, and communication are placed beneath trafficable areas. However, insufficient or inadequate backfill induces sudden subsidence, damage, or pothole on the road. This study aims to develop lightweight controlled low-strength materials (CLSM) with low thermal conductivity using the ternary mixtures of red mud to replace aggregate sand, high carbon fly ash, and preformed foam. Changes in flow consistency, air void characteristics, bulk unit weight, unconfined compressive strength (UCS), and thermal conductivity (k) of the tested materials with varying red mud contents were investigated as a function of the foam volume ratio (FVR). The results demonstrate that the UCS and k of tested materials decreased with increasing FVR due the decrease in unit weight, and a greater UCS but smaller k was observed at a given FVR with increasing red mud content because the inclusion of red mud in the lightweight CLSM mix design helps improve the stability of air bubbles and achieve uniform distribution of air voids. In addition, the red mud can act as a NaOH supplier, leading to the developed material had additional strength gain from the alkali activation. Thus, the developed insulating backfill material showed 43 % decrease in k while maintaining UCS similar to non-foam CLSM without red mud.

Microstructure formation mechanism and mechanical properties of super-thickness TC11 titanium alloy joint by electron beam welding and laser additive manufacturing hybrid connection technology

Advanced connection technology for extra-large/super-thickness titanium wrought components is urgent demand in aerospace manufacturing industries. For achieving high-performance titanium alloy super-thickness joint with a high connecting efficiency, a novelty concept of hybrid connection technology with electron-beam welding and subsequent laser additive connection is proposed. A super-thickness (200 mm) TC11 titanium alloy joint has been successfully prepared, and microstructure, tensile properties and fracture behavior of different regions in which are investigated. The results suggest that in stress-relieve heat treatment (SRT) condition, deformation and fracture of the joint are prone to occur in its low-strength wrought base material zone; after double annealing heat treatment (DAT), lamellar α phases in different zones of the joint become similar, associating with a higher fraction of fine secondary α phases in wrought base material zone. Therefore, the tensile properties of the joint are comparable to wrought properties. Although strength in different zones of hybrid connection joint is similar, ductility is not uniform and apparently lower in middle fusion zone due to grain heterogeneity. Overall, these findings indicate that hybrid connection can be one potential technology for fabricating high performance super-thickness titanium alloy joint with a high connection efficiency in engineering application fields.

Utilization of waste silty soil as fine aggregate in controlled low-strength material

Utilization of waste silty soil as fine aggregate in controlled low-strength material

Dynamic failure behaviour of sandstone with filling joints using the Brazilian disc method

Rock masses contain joints often filled with low-strength materials such as mud and gum. The instability mechanism of a filled jointed rock mass under dynamic loads is complex, posing challenges for disaster control. Splitting tests were conducted using a split Hopkinson pressure bar device and a high-speed camera to investigate the effects of weak-filling joints at various angles on the failure mechanism and mechanical properties of sandstone. The typical failure processes, splitting mechanical properties and fracture morphologies were analysed. The results indicated that as the joint angle increased from 0 to 90°, the crack coalescence pattern of the jointed sample under static and dynamic splitting loads evolved from complete separation along the bonding surfaces to shear–slippage failure along the direction of the joint angle and tensile–shear failure with a dominant zigzag track, ultimately leading to typical tensile failure. Under dynamic loads, filled joints reduced the brittleness of the samples, contrary to the behaviour observed under static loads. The peak load and displacement were proportional to the joint angle and impact gas pressure, respectively. The fracture surface morphology precisely reflected the macroscopic fracture mechanism at the microscopic scale.

Valorization of Industrial and Agro By-products into a Biobased Sustainable Controlled Low Strength Material

Valorization of Industrial and Agro By-products into a Biobased Sustainable Controlled Low Strength Material

Effect of nano-SiO2 on flow-ability, setting time and strength properties of controlled low-strength materials using native silt soil

Effect of nano-SiO2 on flow-ability, setting time and strength properties of controlled low-strength materials using native silt soil

IMPACT OF FREEZE-THAW CYCLES ON BACTERIAL VIABILITY IN CONCRETE

Calcium carbonate precipitating bacteria can improve mechanical and physical properties of building materials. Most commonly, bacteria are used for the crack repair, production of self-healing concrete, or as a cementitious agent for low-strength materials. The favorable effect of bacterial metabolism can only be achieved if the sufficient number of cells remain viable in the structural material. Besides the limited amount of oxygen, extremely high pH level and mechanical pressure on cell walls, bacteria must survive the repetitive freezing and thawing in concrete-type materials. Freezing water may generate additional internal pressure damaging the bacterial cells and suppressing the bacterial activity. In present study, the viability two of bacteria strains (Bacillus pseudofirmus and Bacillus cohnii), was studied under repeated freezing and thawing conditions. It was shown that concrete-embedded bacteria may survive fluctuations of low temperatures and freeze-thaw cycles, compromising approximately 50% of viable spores. This survivability may only be achieved if bacterial spores are protected from the concrete environment itself, for example, spores could be injected to the expanded clay particles and coated with the styrene-acrylate emulsion. These findings confirm that Bacillus pseudofirmus and Bacillus cohnii bacteria could be used in cold climatic regions, retaining viable bacteria spores within the concrete.

IMPACT OF FREEZE-THAW CYCLES ON BACTERIAL VIABILITY IN CONCRETE

Calcium carbonate precipitating bacteria can improve mechanical and physical properties of building materials. Most commonly, bacteria are used for the crack repair, production of self-healing concrete, or as a cementitious agent for low-strength materials. The favorable effect of bacterial metabolism can only be achieved if the sufficient number of cells remain viable in the structural material. Besides the limited amount of oxygen, extremely high pH level and mechanical pressure on cell walls, bacteria must survive the repetitive freezing and thawing in concrete-type materials. Freezing water may generate additional internal pressure damaging the bacterial cells and suppressing the bacterial activity. In present study, the viability two of bacteria strains (Bacillus pseudofirmus and Bacillus cohnii), was studied under repeated freezing and thawing conditions. It was shown that concrete-embedded bacteria may survive fluctuations of low temperatures and freeze-thaw cycles, compromising approximately 50% of viable spores. This survivability may only be achieved if bacterial spores are protected from the concrete environment itself, for example, spores could be injected to the expanded clay particles and coated with the styrene-acrylate emulsion. These findings confirm that Bacillus pseudofirmus and Bacillus cohnii bacteria could be used in cold climatic regions, retaining viable bacteria spores within the concrete.

Pond ash as a fine aggregate for controlled low-strength materials (CLSM): a study of its geotechnical and geoenvironmental aspects

Pond ash as a fine aggregate for controlled low-strength materials (CLSM): a study of its geotechnical and geoenvironmental aspects

Prediction of flowability and strength in controlled low-strength material through regression and oversampling algorithm with deep neural network

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.

A two-point fatigue strength assessment for surface-hardened notched components under consideration of residual stresses based on the local strain approach

The “Guideline non-linear” of the German Research Association for Mechanical Engineering provides a fatigue strength assessment for machine components based on the local strain approach. Currently, this assessment is limited to homogeneous components and without the possibility to consider residual stresses. The methods are thus inadequate for surface-hardened components, where the presence of material inhomogeneity and the introduced residual stresses significantly impacts fatigue life and the potential failure origin. In the following paper, an adaptation of the proof of structural durability of the guideline is shown, that firstly includes a two-point assessment and the estimation of load cycles to crack initiation at two failure-relevant points simultaneously. This enables the consideration of inhomogeneous material states, since the failure of surface-hardened components may initiate from the notch root as well as from the transition area between the low-strength core material and the high-strength surface layer. Secondly, the consideration of the residual stress state for both failure-relevant points is also introduced as part of the adapted fatigue strength assessment.

Utilization of high fine-grained shield tunnel spoil in CLSM and effect of foam agent content on properties

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-to-total 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‰ 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.

Damage evolution and failure mechanism of masonry walls under in-plane cyclic loading

Masonry structures often exhibit poor seismic performance during earthquakes owing to their low material strength, structural integrity, and ductility. To address the mechanism of in-plane damage and collapse of masonry walls subjected to earthquake ground motion, three full-size brick walls, one with structural columns and two without structural columns, were designed and constructed in this experimental study to quantitatively investigate the effect of structural columns on the seismic performance of masonry walls. Quasi-static tests of masonry walls subjected to cyclic lateral loading were conducted using electrohydraulic servo actuators. The in-plane damage evolution and failure mode of the masonry walls under lateral loading were investigated. A numerical model with a novel plastic damage constitutive model of masonry was established. The accuracy of this model and the calculation results were verified by comparing them with the crack development and mechanical property curves obtained from the experiments. Based on the numerical model, a parametric analysis was conducted to investigate the influence of critical factors, such as mortar strength, vertical load, and height-to-width ratio, on the seismic performance of masonry structures. The test results showed that structural columns can effectively improve the performance of masonry structures. Properly installed structural columns can improve the peak load-bearing capacity, ductility, and energy dissipation of masonry structures. The masonry damage constitutive model used in this study could simulate the damage to masonry wall specimens well and reflect the hysteretic curves of the specimens within an acceptable range of accuracy. Thus, it provides a valuable reference for physical experiments. An appropriate mortar strength and vertical compressive stress can effectively enhance the load-bearing capacity of masonry structures within a certain range. For structural column walls. Walls with mortar strengths (average compressive strength) of 12.5 MPa, 10 MPa, 7.5 MPa, and 5 MPa showed an increase in peak bearing capacity of 26.2 %, 23.9 %, 18.5 %, and 9.4 %, respectively, compared to walls with mortar strengths (average compressive strength) of 2.5 Mpa. The aspect ratio had a significant impact on the shear load-bearing capacity of the masonry walls. An increase in the aspect ratio led to a transition from shear failure to flexural failure and a subsequent decrease in shear load-bearing capacity. For masonry walls with structural columns, increasing the diameter of the longitudinal steel in the structural columns can enhance the load-bearing capacity of the masonry wall, resulting in a significant improvement in its overall performance.