Unconfined Compressive Strength Tests Research Articles

Mechanical properties of discarded shield residue improved by calcium carbide slag and fly ash as subgrade filling.

To utilize discarded shield residue and alleviate the shortage of subgrade filling, industrial wastes such as calcium carbide slag (CCS) and fly ash (FA) were considered to enhance the mechanical properties of the shield residue. A series of laboratory tests, including California Bearing Ratio (CBR) tests, unconfined compressive strength (UCS) tests, moisture content tests, pH tests, water stability tests, and dry-wet cycles tests were performed on discarded shield residue with additive contents. The results show that the UCS and CBR values enhanced significantly with the increase in curing time. However, the moisture content and pH of the stabilized soil exhibited a decreasing trend. The early UCS of CCS-FA stabilized soil is slightly lower than that of QL-FA stabilized soil. After 60 curing days, all stabilized soil exhibited a UCS value exceeding 1.9 MPa. In addition, the CBR values of CCS-FA stabilized soil were more than 8 times higher than those of the original shield residue. Furthermore, the water stability of CCS-FA stabilized soil is slightly better than QL-FA stabilized soil, especially at 7 days and 14 days. As for dry-wet cycles test, after the fifth cycle, the CCS-FA stabilized soil maintained overall integrity. The CCS can effectively replace QL to enhance the mechanical properties of shield residue as subgrade filling.

Evaluating the Strength and Durability Properties of Geopolymer-Stabilized Soft Soil for Deep Mixing Applications

Soft soil poses serious challenges and is unsuitable for engineering projects because of its insufficient bearing capacity, low shear strength, and high compressibility. Deep soil mixing (DSM) is one of the most popular methods of enhancing soft soil qualities, such as increased bearing capacity and reduced settling, which are critical for building any structure. The environmental effects of creating binders such as cement and lime make it crucial to identify alternative materials for geotechnical applications. This study employed fly ash (class C) --based geopolymer to investigate its effectiveness as an environmentally friendly substitute for cement for DSM applications. The experimental program included unconfined compressive strength, flexure strength, and durability tests. The parameters in the study are binder content (10, 15, and 20%) and activator/binder ratio (0.4, 0.6). Results revealed that UCS and flexural strength, GP-treated soil were in the range of 0.9–5.3 and 0.8–1.5 MPa, respectively (depending on the ratio of fly ash and activator). These strengths were even higher than those of cement-stabilized soil. The geopolymer-treated specimens exhibited excellent endurance over the wetting-drying cycle, with a modest weight loss of less than 4.5%. A binder dosage of more than 10% and an AC ratio of 0.6 were recommended to meet DSM application guidelines. The current study concludes that employing a fly ash-geopolymer binder to stabilize soft soil is an effective alternative to cement in DSM applications.

Study on the leaching behavior of cemented paste backfill containing arsenic trioxide roaster waste

After decades of mining at Giant Mine in Yellowknife, Northwest Territories, a significant amount of arsenic trioxide roaster waste (ATRW), containing around 60% arsenic, was stored underground, posing serious health hazards. This study explored solidification and stabilization of ATRW through its incorporation into cemented paste backfill (CPB). It evaluated the stability of arsenic-bearing compounds and the mechanisms of arsenic trioxide stabilization within CPB. Based on the results of unconfined compressive strength (UCS) tests on CPB samples, certain samples were selected for monolithic tank leaching tests (TLT) and a range of microstructural analyses, including thermogravimetry, X-ray absorption spectroscopy, Fourier-transform infrared spectroscopy, and computed tomography. These tests aimed to examine the leaching behavior of arsenic and the microstructure of the selected CPB samples, and to investigate the relationship between their strength, leaching behavior, and pore characteristics. Findings indicated significant arsenic release from CPB surfaces. Up to 41% of arsenic was leached from the CPB samples, and the leaching of arsenic, calcium, and sulfate showed no signs of stabilizing, suggesting potential long-term leaching risks. The pH levels ranged between 9.2 and 10.0, with the dissolution of ATRW contributing to a decrease in pH. This lower pH inhibited the formation of portlandite, while calcium-silicate-hydrate (C-S-H) gels were identified as the primary hydration product, albeit in limited quantities. Thermogravimetric analysis showed weight losses primarily due to calcite decomposition, while X-ray absorption spectroscopy revealed arsenic was present predominantly in its + 3 oxidation state, with no significant As-Ca bonding observed in high-strength samples. CT scans highlighted a relationship between higher strength and larger pore volumes. The study concluded that while ATRW incorporation in CPB can provide mechanical stability, modifications are necessary to reduce arsenic solubility and mitigate environmental risks.

Eco-friendly stabilization of clayey soil with waste glass powder-based geopolymer

ABSTRACT This research studied the feasibility of using waste glass powder, Portland cement, and sodium chloride to stabilise and geopolymerization clayey soil. The chemical composition and microstructure of the materials were determined by X-ray fluorescence and scanning electron microscopy, respectively. Cement and waste glass powder contents were determined through previous laboratory tests and literature reviews. Unconfined compressive strength tests were performed to determine the optimal sodium chloride content, which was used in this research as an alkaline precursor in geopolymer formation. The effects of cement, waste glass powder, and geopolymer (composed of soil+(5 and 15% waste glass powder)+1% sodium chloride) were investigated through unconfined compressive strength and splitting tensile strength tests. The results revealed that the specimens stabilised with geopolymer presented higher strengths, finding strengths approximately 24 times higher than the pure soil and 1.6 times higher than the soil stabilised with 8% cement. Adding waste glass powder and geopolymer allowed some blends to become suitable for use as a subbase in pavement applications. Microstructure analyses confirmed the formation of geopolymer through a more homogeneous structure. Finally, it was concluded that stabilising with geopolymer based on waste glass powder is an ecological and effective technique for increasing soil strength.

Optimal Utilization of Biochar, Polyacrylamide, and Straw Fiber for Subgrade Stabilization of Forest Roads

Subgrade stabilization is crucial for forest road construction, especially in Northeast China and the Russian Far East, with great economic growth potential. This study explored a novel and green solution of integrating biochar (BC), polyacrylamide (PAM), and straw fiber (SF) in the form of a ternary composite for stabilizing forest subgrade soil in cold regions. Using central composite design-based response surface methodology, the optimal mix ratio design was obtained, and the composite stabilizer was designated as BPS. Afterward, the stabilizing performance of BPS was studied by conducting an unconfined compression strength (UCS) test. The results showed that the optimum composition of BC:PAM:SF stood at 81:9:10. The UCS and deformation modulus with 3% BPS at 28 days reached 565.42 kPa and 17.24 MPa, respectively, which were 3.36 and 6.05 times higher than those of the untreated samples. The BPS-treated soil also possessed better resistance to freeze–thaw cycles. The freezing–thawing-induced loss ratio of strength was 49.3% lower than that of natural soil. Moreover, empirical models for the UCS of BPS-stabilized soil, as well as its relationships with the modulus, were established and validated by data in the literature. Finally, the “filling, cementing, and reinforcing” stabilization mechanism of BPS was elucidated by scanning electron microscopy analysis.

Performance evaluation of lime-improved lateritic soil with the addition of pulverised snail shell and sawdust ash for sustainable highway infrastructure

This research investigated the effects of lime, Pulverized snail shell (PSS), and sawdust ash on the mechanical properties of lateritic soil for soil stabilization in construction. The use of this waste materials aligns with the United Nations’ Sustainable Development Goals (SDGs), particularly Goal 12 on responsible consumption and production and Goal 9 on sustainable infrastructure development. Reusing waste materials for soil stabilization supports a circular economy approach, diverting these materials from landfills and promoting their sustainable use as valuable resources. Various tests, including maximum dry density, moisture content, unconfined compressive strength (UCS), triaxial, permeability, compressibility, and California Bearing Ratio (CBR) tests, were conducted on soil samples with different proportions of additives. The results show that the addition of additives reduced maximum dry density and increased moisture content. The sample with 6% lime and 7.5% PSS exhibited the highest UCS of 302 kPa after 28 days of curing, while the untreated sample had a UCS of 121 kPa. Triaxial tests revealed reduced cohesion and increased angle of internal friction with higher additive content. The 6% lime and 7.5% PSS sample displayed the highest shear strength of 60.6 kPa and elastic modulus of 181.8 MPa. Permeability tests demonstrated that the 6% lime and 6% sawdust ash sample had the lowest permeability (6.67 × 10–7 m/s) among the stabilized samples. The untreated soil exhibited high compressibility, whereas the 6% lime and 7.5% PSS sample exhibited the highest resistance to compression and deformation. The untreated soil had a soaked CBR value of 8%, while the 6% lime and 7.5% PSS sample achieved the highest soaked CBR value of 38%, making it suitable as a sub-base material. These findings highlight the effectiveness of lime, PSS, and sawdust ash in enhancing the mechanical properties of lateritic soil and offer valuable insights for soil stabilization in construction of Sustainable Highway Infrastructure.

Field investigation on the performance of low-carbon MgO-carbonated composite piles for ground treatments

Carbonation technology using MgO and CO2 has been considered a rapid, effective, and environmentally friendly method for improving weak soils, mainly applied in shallow foundation treatments. This study introduced a novel MgO-carbonated composite pile (MCP) technique developed by injecting CO2 through a gas-permeable pipe pile into a MgO-mixing column for carbonation and solidification and its applications in weak subgrade treatments. Several field tests were carried out to study the characteristics of MCP as well as the performance of the MCP-reinforced foundations, including carbonation reaction temperature monitoring, pore-water pressure monitoring, standard penetration tests (SPT), unconfined compressive strength (UCS) tests, static load tests, and subgrade deformation monitoring. Results showed vigorous and uniform carbonation within the MgO-mixing column, confirming the feasibility of constructing large-diameter MgO-mixing columns. The distribution, evolution, and affected zone of excess pore-water pressure induced by MCP installation were determined. The MCP exhibited good pile quality, with average SPT-N and UCS values of 39 and 1021 kPa, respectively. MCP’s bearing capacity was superior to pre-stressed high-strength concrete pipe piles, with ultimate vertical and lateral bearing capacities of 1920 kN and 119 kN, respectively. The MCP-reinforced foundation exhibited a small settlement of 54.5 mm under embankment loads. Life cycle assessment indicated significant carbon reduction benefits for MCP, with 44.7% lower carbon emissions compared to traditional composite piles.

Strength Characteristics of DMJ Piles Based on Indoor Tests

The Deep Cement Mixing Integrated Drilling, Mixing and Jetting (DMJ) method represents a novel approach to the construction of slurry piles in the Yellow River Floodplain, offering the potential to enhance the quality of these structures. In order to investigate the pile strength and its distribution characteristics under different conditions, an unconfined compressive strength test was conducted on DMJ pile core samples. The Kolmogorov-Smirnov (K-S) test was employed to evaluate the normal distribution characteristics of the strength, and the fluctuation of the pile strength was evaluated by the autocorrelation function method to elucidate the distribution characteristics. Moreover, a resistivity non-destructive test was conducted to ascertain the correlation between strength and resistivity and to perform supplementary strength testing. The distribution of the pile body strength is normal at the 5% level of significance. A clear correlation was observed between the strength of the pile core and depth, while the correlation between the strength of the pile outer side and depth was less pronounced. Additionally, a positive linear correlation was observed between resistivity and strength, which can be used to evaluate the strength of DMJ piles.

Utilization of cement deep mixing pile for soft soil foundation: a malaysian case study

Cement deep mixing piles, as representatives of deep mixing technology, are mature and widely applied. However, effective application cases of cement deep mixing piles are relatively scarce in countries like Malaysia in Southeast Asia. In this paper, the application of cement deep mixing pile reinforcement in Malaysia is presented. Solidifying material was selected for deep mixing piles based on the soil conditions using unconfined compressive strength (UCS) tests. The relationship between the strength of deep mixing piles on-site and soil properties (type, organic matter content, and ion content) was analyzed. And a quality evaluation of the deep mixing piles in the project is conducted based on Kolmogorov-Smirnov (K-S) tests and relevant standards. Results show that fly ash cement is suitable as a solidifying agent for acidic soil layers containing organic matter in the local area. The strength of piles is significantly related to the soil condition. The UCS of cement mixing piles in silty clay and peat soils is smaller than clay. The overall correlation between organic matter content in the soil and UCS is negative, particularly when the organic matter content ranges from 10% to 14%, resulting in a significant drop in UCS. The bilateral significance probability is greater than 0.05 in K-S test, indicating that the UCS results in the projectconform to a normal distribution. Additionally, the evaluation of the overall quality of the mixing piles aligns with the requirements in the Japanese standard “Manual of Deep Mixing Construction Technology for Harbors and Airports” and the Chinese standard “Technical Code for Building Foundation Detection”.

Green-reinforced clay sandy soil with natural fibers

Several studies focus on enhancing soil strength through the incorporation of natural or synthetic fibers. However, there is limited published data on the effectiveness of rice husk in soil reinforcement. The use of rice husk as a reinforcing material is supported by the fact that rice is one of the most produced and consumed cereals globally. In this article, we analyze the behavior of a clayey soil from southern Brazil with the addition of 0.5, 0.75, and 1% rice husk (RH), comparing it to coconut coir (CC) and curauá fibers (CU). In unconfined compressive strength tests (UCS), increases in soil strength of 20, 40, and 140% were observed for RH, CC, and CU, respectively, compared to pure soil. From consolidated undrained triaxial compression tests, both unreinforced soil and soil reinforced with 1% RH, CC, and CU were examined. The triaxial tests revealed an increase in the internal friction angle of 72 and 98%, alongside a decrease in cohesion of 57 and 94% due to the addition of CC and CU, respectively, in terms of effective stress. In contrast, RH did not significantly enhance the soil’s behavior, likely due to its shorter fiber length.

Utilization of recycled rubber crumbs and tile powder as additives to enhance clayey soil performance

Clayey soils present challenges in engineering applications due to their inherent properties, such as low shear strength, which usually limits their use in engineering applications. Stabilization of clayey soils is crucial to enhance their performance and suitability for various purposes. Utilizing waste materials like discarded tyres and tile powder as soil stabilizers presents a sustainable solution to mitigate environmental concerns while enhancing soil properties. While previous studies have explored using either crumbled rubber or tile powder independently for soil improvement, their combined effect remained largely unexplored. This study addresses this gap by investigating the synergistic potential of blending crumbled rubber and tile powder to enhance the strength and ductility of clayey soils. A series of laboratory tests were conducted to investigate the combined effect of crumbled rubber and tile powder. First, varying percentages of crumbled rubber (2.5%, 5.0%, 7.5%, and 10%) were mixed with the soil, and standard proctor tests, California bearing ratio (CBR) tests, and unconfined compressive strength (UCS) tests were performed. Results showed optimal performance at 5.0% crumbled rubber, exhibiting the highest values for maximum dry density, CBR, and UCS. Subsequently, different percentages of tile powder (5%, 10%, 15%, and 20%) were added to the soil-rubber mixture (with 5% crumbled rubber). The addition of 15% tile powder to the 5% crumbled rubber mixture yielded the most significant improvements as maximum dry density (MDD) increased from 1.842 g/cm3 (raw soil) to 1.963 g/cm3, UCS increased from 0.5176 kg/cm2 (raw soil) to 2.606 kg/cm2, and CBR increased from 1.757% (raw soil) to 7.84%. The addition of crumbled rubber was found to shift the failure behaviour of the clayey soil from brittle to more ductile, indicating an enhanced ability to undergo deformation before failure. This study’s findings highlight the potential of combining crumbled rubber and tile powder as a sustainable solution for enhancing clayey soil properties, paving the way for further research into optimized mixture designs and expanded applications in geotechnical engineering.

Study on the Microscopic Pore Characteristics and Mechanisms of Disturbance Damage in Zhanjiang Formation Structural Clay

To investigate the microscopic pore evolution characteristics of Zhanjiang Formation structural clay during the disturbance process, unconfined compressive strength tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were conducted on disturbed samples subjected to various disturbance conditions after vibrational disturbance. Based on the evolution characteristics of the microstructure, the microscopic pore characteristics of the disturbance damage of Zhanjiang Formation structural clay were examined. The results indicate the following. (1) The porosity in three-dimensional visualization images of the microstructure reconstructed by ArcGIS 10.1 increases with the disturbance degree, showing a linear growth trend. (2) The correlation analysis between macroscopic mechanics and microscopic pores shows that the unconfined compressive strength of Zhanjiang Formation structural clay is mainly affected by its porosity, with a significant linear negative correlation. Based on this, a reasonable regression model between the microscopic porosity and the unconfined compressive strength has been established. The model can rapidly estimate the unconfined compressive strength from porosity data, facilitating the assessment engineering properties of the soil. (3) The microscopic pore structure of Zhanjiang Formation structural clay exhibits prominent Menger fractal characteristics. The three-dimensional pore fractal dimension has a certain positive correlation with the disturbance degree, and can be utilized to characterize the pore structure and complexity, serving as a significant parameter for the quantitative evaluation of the pore structure characteristics of Zhanjiang Formation structural clay. Consequently, the complexity of the pore structure of the engineering soil can be evaluated by the pore fractal dimension. (4) The impact of disturbance on soil is primarily manifested in the structural changes in secondary clay minerals, transitioning from a relatively intact to a fully adjusted state. During this process, interparticle pores continuously increase, pore structure complexity increases, and interparticle cementation weakens, resulting in the continuous degradation of unconfined compressive strength. This study contributes to a deeper understanding of the disturbance damage characteristics of Zhanjiang Formation structured clays from a microscopic pore perspective, providing a theoretical basis for the engineering construction and operational maintenance in regions with Zhanjiang Formation structural clay.

Mechanical characterization of calcareous sand reinforced by EICP multivariate tests and synergistic biochar reinforcement

The foundation bearing capacity in island reef infrastructure construction is often inadequate due to the poor engineering properties of calcareous sand. Enzyme-induced carbonate precipitation (EICP) has emerged as an efficient and environmentally friendly method to improve these properties, significantly enhancing the mechanical behavior of calcareous sand. However, the effectiveness of EICP is constrained by environmental factors that affect free urease activity and the limited availability of nucleation sites. To further improve the mechanical properties of EICP-reinforced calcareous sand, this study explores the addition of biochar to the sand. The characteristics of the samples were evaluated using unconfined compressive strength tests, calcium carbonate content measurements, and scanning electron microscopy. The results indicate that incorporating biochar into EICP significantly increases calcium carbonate production, strengthens the reinforced sand, and reduces surface porosity. This improvement is attributed to biochar’s surface properties, which provide additional nucleation sites for calcium carbonate formation, enhancing calcium carbonate content and sand strength. However, controlling the biochar content at approximately 5% is crucial to avoid excessive porosity, which could weaken the material. These findings offer a theoretical foundation for applying EICP-biochar-reinforced calcareous sand in engineering projects.

Studying the Constitutive Model of Damage for a Stainless Steel Argon–Oxygen Decarburization Slag Mixture

The purpose of this study was to fully explore the mechanical properties of five different doses of an Argon–Oxygen Decarburization slag mixture in an unconfined compressive strength test. The peak stress, elastic modulus, and stress–strain curve of the mixture were studied for 90 days. Based on the experimental data and according to the theory of damage mechanics, the concept of damage threshold (t) was introduced to construct a damage constitutive model. Referring to the damage threshold of concrete, that of the mixture was determined to be 0.7 times higher than the peak strain, and the correlation coefficient between the established model and the test curve was above 0.85. These results indicate that the addition of AOD slag and fly ash can cause hydration reactions, increase the quantity of hydration products, and enhance the peak stress and elastic modulus of the mixture. The maximum increases were 94.9% and 43.1%, respectively. Parameters a and b reflect the peak stress and brittleness of the mixture, respectively. The incorporation of Argon–Oxygen Decarburization slag can make the mixture less brittle and improve its properties. The incorporation of Argon–Oxygen Decarburization slag can protect the mixture from damage. The maximum decrease is 40.2%.

Polymer-assisted soybean crude urease carbonate precipitation technique for soil improvement

This study presents a sustainable approach to soil improvement by integrating polyvinyl alcohol (PVA) into the Soybean Crude Urease Carbonate Precipitation (SCU-CP) technique. The research aims to enhance SCU-CP, which utilizes soybean-derived urease to precipitate calcium carbonate, binding soil particles and increasing strength. Challenges such as low solution viscosity and inconsistent carbonate precipitation are addressed by incorporating PVA, a biodegradable polymer that improves viscosity and retention. Comprehensive evaluations reveal significant findings: increasing PVA concentration enhances solution viscosity and results in higher calcium carbonate precipitation. Water retention assessments show that the PCP-1% treatment increases saturation water content (ws) to 0.263 compared to 0.217 for untreated soil, while also reducing the air-entry value (α). Unconfined Compressive Strength (UCS) tests indicate substantial improvement for PCP-1%, achieving approximately 140 kPa, with values reaching 179 kPa after 28 days. Calcium carbonate content measurements reveal that SCU-CP exhibits a variable distribution (standard deviation of 1.13), while PCP-1% demonstrates a more uniform distribution (standard deviation of 0.60), indicating improved effectiveness. Durability assessments through wet-dry cycling show that SCU-CP experiences a mass loss of 36.5%, while PCP-1% retains only 5% mass loss and maintains a UCS values. SEM images indicate that SCU-CP forms spherical structures, whereas PCP-1% produces a more diverse and crystalline morphology, suggesting better nucleation and distribution. Overall, the polymer-assisted SCU-CP technique (PCP) demonstrates significant potential for effective soil improvement.

Use of seawater as an accelerator in 3D printed concrete (3DPC)

Seawater (SW) is one of the viable alternatives to replace freshwater (FW) for producing concrete in regions facing extremely severe water stress. Seawater has high potential to be used as a set-on-demand accelerator among the other expensive materials being widely researched in additive manufacturing. The current study evaluated the progress of heat of hydration in 3DPC-FW and 3DPC-SW mixes using isothermal calorimetry. Furthermore, fresh and early-age properties of these mixes were studied using a flow table, manual shear vane, uniaxial unconfined compressive strength tests, and dynamic elastic modulus development. Strength development and shrinkage progress up to 28 days were evaluated. A detailed investigation reveals that an increase in compressive strength from the very first hours of hydration, a reduction in workability which could be compensated by modifying SP, and higher shrinkage were observed in SW-mixed 3DPC compared to the FW-mixed counterpart. Furthermore, the potential improvement in the speed of printing is highlighted in this study with 3DPC-SW mix demonstrating acceleration in early strength.

Experimental Research on the Performance of Recycled Waste Concrete Powder (RWCP) on Concrete.

Waste concrete is a large amount of solid waste produced in the process of urban construction and renewal in China. Its resource utilization is of great significance for saving mineral resources and improving urban environmental quality. The present study was designed to investigate the effects of mechanical grinding time on the particle size distribution and activity of recycled waste concrete powder (RWCP). Combined with unconfined compressive strength, slump, electric flux and chloride ion penetration resistance tests, the effects of RWCP on the mechanical properties, working performance and impermeability of concrete were analyzed, and the phase and microstructure of concrete containing RWCP were analyzed by XRD and SEM. The results showed that the RWCP is mainly composed of quartz, gismondine, C2S, cancrinite and portlandite. The optimum activity of RWCP obtained by ball milling for 45 min was 44.41%. RWCP can improve the fluidity of concrete and shorten the initial setting time of concrete. When the blast furnace slag in the concrete was replaced by the RWCP, the early strength and impermeability of the concrete decreased. When RWCP replaced blast furnace slag by 69.1%, the UCS of the concrete at 1, 3, 7, and 14 d decreased from 9.56, 22.1, 34.1, and 41.2 MPa to 5.9, 14.5, 22.7, and 33.2 MPa, respectively. While RWCP replaced fly ash, the normal strength of concrete increased with the increase in fly ash replacement amount. When RWCP completely replaced FA in concrete, the 28-day strength of the concrete increased from 45.2 MPa to 50.8 MPa. The impermeability results showed that the appropriate substitution of RWCP for fly ash was beneficial to increase the impermeability of concrete while excessive substitution reduced. Based on these results, the RWCP has the potential for large-scale application in the preparation of concrete.

Reaction mechanism study of calcium carbide residue with graphene oxide in aqueous environment: Adsorption properties and mechanical potentials

Graphene Oxide (GO) is widely used, but its hydrophilic properties make it difficult to remove once it enters water and soil environments. In this paper, the adsorption effect of calcium carbide residue (CCR) as adsorbent on GO was investigated through a series of adsorption tests. Adsorption thermodynamics, kinetics, isotherm models, and various characterization techniques were employed to explore the adsorption mechanism. Additionally, the study assessed CCR’s ability to stabilize GO-contaminated soils through unconfined compressive strength tests. The results showed that (1) at T = 303 K, with a pH of 11 and an initial GO concentration of 80 mg/L, CCR demonstrated excellent adsorption performance. (2) The adsorption process followed the Langmuir isotherm and a quasi-second-order kinetic model, indicating chemical adsorption with spontaneous heat adsorption. (3) CCR not only acts as an effective adsorbent for removing GO from wastewater but also has the potential to strengthen GO-contaminated soils. In addition, due to its favorable environmental benefits, this study has a wide range of potential applications in industrial fields such as wastewater treatment, air purification, and energy storage and conversion. This study not only proposes an effective method for removing graphene oxide from aqueous environments, but also provides a new idea for waste resource utilization, which helps to achieve the dual goals of environmental protection and resource reuse.

Study on the strength characteristics and microscopic mechanism of sewage sludge ash modified lime soil

The large amount of sewage sludge ash (SSA) generated by incineration treatment of sewage sludge each year can seriously pollute the environment, and there is an urgent need to seek an effective resource utilization method for SSA treatment. SSA has the significant pozzolanic activity, and can be used as an auxiliary cementitious material. For that, SSA was adopted to modify lime soil in this work. The strength characteristics of SSA modified lime soil (SLS) were investigated by conducting unconfined compressive strength test and unconsolidated-undrained triaxial compression test, and X-ray diffraction (XRD) test and scanning electron microscopy (SEM) test were conducted to investigate the mineral composition, microstructure and porosity of SLS. It is observed that the unconfined compressive strength (UCS) increases first and then decreases with increasing SSA content in the range of 0–20 %, and reaches the maximum value while SSA content is 15 %, which increases by 25 % at the curing age of 28 days comparing to the specimen without SSA. Additionally, the triaxial strength and cohesive force both have the same change law as UCS with SSA increasing, and 15 % can be used as the optimal content of SSA to modify lime soil. The added SSA can promote the pozzolanic reaction, and more hydration products fill the specimen porosity so that the specimen strength can be improved. Furthermore, the porosity of SLS decreases first and then increases with SSA content increasing, and there is a linear relationship between the porosity and strength of SLS. Finally, a simple function is proposed, which can simulate the quantitative relationship between UCS and the triaxial strength with satisfying accuracy. Generally, the research results can be used as a reference for the application of SSA in soft soil foundation treatment.

Low-dose cement stabilized large particle size graded crushed stone: Laboratory and field investigations

Compared with traditional graded crushed stone (GCS), the maximum aggregate size of large particle size GCS (LPS-GCS) is larger and the content of large-size aggregates is more, which can form an interlocking skeletal structure with a stronger bearing capacity. Nevertheless, LPS-GCS occasionally exhibits unstable performance, and one effective way to enhance LPS-GCS's mechanical and physical properties is to stabilize it with low-dose cement. In this study, four cement contents (1.5 %, 2.0 %, 2.5 %, and 3.0 %, by mass) were selected to form low-dose cement stabilized LPS-GCS (LCS-LPS-GCS) mixtures with a maximum aggregate particle size of 53 mm. Unconfined compressive strength (UCS) and compressive resilient modulus (CRM) tests were performed on LCS-LPS-GCS samples for different cement contents and curing times. Moreover, prediction models and correlations for the UCS and CRM at different curing times were established. Furthermore, a test road was used to evaluate the LCS-LPS-GCS's field compaction level and deflection. Laboratory test results indicated that while the California bearing ratio was significantly higher than that of conventional GCS, the maximum dry density of LPS-GCS designed in this study was close to that of conventional GCS. With the same cement content, LCS-LPS-GCS outperformed conventional GCS in terms of UCS and CRM. Based on the variation law of the mechanical properties, the ideal cement content should be around 2.5 %. There was a strong positive correlation between UCS and CRM scores from LCS-LPS-GCS. The UCS and CRM were appropriate to be predicted by exponential and growth functions models, respectively. The field investigations indicated that asphalt pavements reconstructed with LCS-LPS-GCS had high compaction and low deflection, resulting in better bearing capacity and durability. The results of this investigation can serve as a reference for the design and application of LCS-LPS-GCS base for long-lasting and resilient pavements.