Series Of Tests Research Articles

Effect of Annealing Temperature on Microstructure and Mechanical Properties of 00Cr21CuTi Stainless Steel Cold-Rolled Sheets

To investigate the evolution of microstructure and mechanical properties in cold-rolled sheets of Ferritic Stainless Steel (FSS) during annealing, a series of annealing tests were performed on 00Cr21CuTi at different temperatures of 930, 990, and 1050 °C. The changes in microstructure at these annealing temperatures were characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron back-scattered diffraction (EBSD). The influence of annealing temperature on mechanical properties was assessed utilizing a universal tensile testing machine and a laser confocal microscope. The results indicated a gradual decrease in yield strength and tensile strength with increasing annealing temperature, whereas elongation exhibited an upward trend. At an annealing temperature of 930 °C, the yield strength, tensile strength, and elongation of the steel were 251 MPa, 409 MPa, and 30.9%, respectively, with a high product of strength plastic 12.64 GPa·%. This result represented an optimal balance between comprehensive strength and plasticity.

Evaluation of volumetric threshold shear strain of gravel-sand mixtures in centrifuge model tests

A series of dynamic centrifuge modeling tests were conducted to evaluate the volumetric threshold shear strain of loose gravel-sand mixtures composed of various ratios of gravel and sand by weight. The maximum and minimum void ratios of the mixtures were evaluated, and the optimum packing condition was determined when the mixture contained approximately 60–70 % gravel by weight. A total of six centrifuge modeling tests were performed at 50-g centrifuge gravitational acceleration. Each centrifuge model was subjected to six shaking events consisting of uniform sinusoidal motions with various amplitudes and numbers of cycles. During the entire duration of the test, the development of excess pore water pressure and settlement was monitored. Empirical relationships of pore water pressure ratio and shear strains were developed for these mixtures. The development of excess pore water pressure in the mixtures with greater than 60 % gravel exhibits transient behavior, while residual excess pore water pressure was observed in the mixtures with less than 60 % gravel. Based on the results, the volumetric threshold strain evaluated from the generation of pore water pressure and volume change during shaking is similar. The values were found to be in a range of 0.03–0.10 % and are influenced by soil composition. The threshold strain increases as the amount of gravel in the soil mixture increases.

Investigation of 3D Printed Self-Sensing UHPC Composites Using Graphite and Hybrid Carbon Microfibers

This paper explores the development of 3D-printed self-sensing Ultra-High Performance Concrete (UHPC) by incorporating graphite (G) powder, milled carbon microfiber (MCMF), and chopped carbon microfiber (CCMF) as additives into the UHPC matrix to enhance piezoresistive properties while maintaining workability for 3D printing. Percolation curves were established to identify optimal filler inclusion levels, and a series of compressive tests, including quasi-static cyclic, dynamic cyclic, and monotonic compressive loading, were conducted to evaluate the piezoresistive and mechanical performance of 29 different mix designs. It was found that incorporating G powder improved the conductivity of the UHPC but decreased compressive strength for both mold-cast and 3D-printed specimens. However, incorporating either MCMF or CCMF into the UHPC resulted in the maximum 9.8% and 19.2% increase in compressive strength and Young’s modulus, respectively, compared to the plain UHPC. The hybrid combination of MCMF and CCMF showed particularly effective in enhancing sensing performance, achieving strain linearity over 600 με. The best-preforming specimens (3G250M250CCMF) were fabricated using 3 wt% of G, 0.25 wt% of MCMF, and 0.25 wt% of CCMF, yielding a maximum strain gauge factor of 540, a resolution of 68 με, and an accuracy of 4.5 με under axial compression. The 3D-printed version of the best-performing specimens exhibited slightly diminished piezoresistive and mechanical behaviors compared to their mold-cast counterparts, yielding a maximum strain gauge factor of 410, a resolution of 99 με, and an accuracy of 8.6 με.

A Comprehensive Analysis of the Influencing Factors of Interharmonics on a Distributed PV Grid-Connected Power Generation System

In this paper, a detailed mathematical model for the interharmonic current in a distributed grid-connected photovoltaic (PV) system is proposed and the factors affecting its output characteristics are analyzed comprehensively. First of all, a transfer function approach is used to build a mathematical model for the interharmonic current in grid-connected PV systems. Then, the equation of the PV generator output characteristics is linearized. Furthermore, a real-time calculation method of the amplitude of interharmonic current is introduced based on the established mathematical model. Moreover, a series of comparative tests are conducted, and how various factors such as the MPPT parameters, the main circuit parameters and the environmental factors affect the interharmonic current are investigated. Finally, a series of simulation and experimental tests are conducted to verify the accuracy of the mathematical model for the interharmonic current and the real-time calculation method. The results show that the proposed model is useful for improving the performance of grid-connected PV systems in terms of the behavior of the interharmonic current. Moreover, the mathematical model and the analysis of the influencing factors provide valuable insights for improving system efficiency and reliability in practical applications.

Influence of the orientation of constructed blood vessels during the 3D printing on the measurement of the pseudo-oxygen saturation of an artificial blood substitute using conventional oxygen sensors: a test series

BackgroundThe development of phantoms to reduce animal testing or to validate new instruments or operation techniques is of increasing importance. For this reason, a blood circulation phantom was developed to test a newly designed retractor system with an integrated oxygen sensor. This phantom was used to evaluate the impact of the 3D printed blood vessel on the measurement of the oxygen saturation.MethodsA solution of nickel sulfate and copper sulfate was prepared as a substitute for real blood. The absorption spectra of these solutions were recorded and compared with those of blood. Subsequently, the oxygen sensor used was calibrated to the blood substitute. Additionally, blood vessels with a simplified geometry were designed and manufactured using inverted vat polymerization and an elastic material (Formlabs Elastic 50 A). To determine the orientation during the printing process, various vessels were printed. Measurements to assess the effects of disturbance (rotation of the vessels during measurements) on the sensor readouts were prepared.ResultsThe impact of disturbances was verified through the rotation of the 3D printed vessels. It was demonstrated that a direct measurement on the disturbances led to outliers and higher values. An optimal orientation was determined to be a lateral placement (90° or 270°) of the sensor. Regarding the orientation of the vessels within the printing space, an orientation of 45° yielded the best results, as the individual layers had the least impact on the light emitted and received by the oxygen sensor.ConclusionThe achieved results demonstrate the influence of the orientation of the vessel during 3D printing as well as the influence of the position of the vessel during the measurement using a conventional oxygen sensor.

Determining the Compaction Temperature of Warm-Mix Anti-Rutting Asphalt Mixture

In order to study the effect of a warm-mix agent on the compaction characteristics of an anti-rutting asphalt mixture, this study compared the compaction temperature of an anti-rutting asphalt mixture with different warm-mix-agent contents from two aspects: asphalt viscosity and asphalt mixture voids. Based on the rheological properties of asphalt, the optimal content of the anti-rutting agent was first determined as 6% by the weight of asphalt. Four warm-mix-agent contents of 0% (control group), 1%, 2%, and 3% were designed. The viscosity–temperature curve of the warm-mix anti-rutting modified asphalt was obtained by the Brookfield viscosity tests. After that, AC-20 standard Marshall specimens were prepared to conduct a series of consecutive temperature compaction tests. The voids were calculated based on the bulk density of the specimen measured by the saturated surface-dry method. Industrial Computerized Tomography (CT) was employed to further quantify the internal voids. Two voids–compaction temperature curves were constructed based on the saturated surface-dry and CT results, respectively. The comparative results show that significant differences exist between the compaction temperatures obtained from the three curves. The viscosity–temperature curve shows that when the warm-mix agent is increased from 0% to 3%, the compaction temperature only declines about 7.9%. However, the voids–compaction temperature curves from saturated surface-dry and CT, respectively, indicate a temperature decrease of 22.7% and 19.2%. This is because a warm-mix agent will interact with asphalt, resulting in a decrease in asphalt intermolecular adsorption, whereas an anti-rutting agent mixed with asphalt will increase the degree of cross-linking and aggregation between asphalt molecules. Both additions have a certain impact on the viscosity of the asphalt binder; thus the traditional method of using the asphalt viscosity–temperature curve to determine the compaction temperature of warm-mix anti-rutting asphalt mixture has become ineffective. It is suggested to use the equal voids method to determine the compaction temperature of warm-mix anti-rutting asphalt mixtures.

Pituitary stalk interruption syndrome complicated with liver cirrhosis: A case report

BACKGROUND Pituitary stalk interruption syndrome (PSIS) is a rare disorder, often characterized by delayed growth and development, short stature, and hypogonadism as the main clinical manifestations. It is not clear whether PSIS can lead to liver cirrhosis. CASE SUMMARY This paper reported a case of liver cirrhosis of unknown origin. The patient was admitted to Beijing Ditan Hospital Affiliated to Capital Medical University in November 2023. The diagnosis of PSIS complicated with liver cirrhosis was established after a series of blood tests and pituitary magnetic resonance imaging examination. CONCLUSION We also reviewed the literature from both domestic and international sources to deepen the clinical understanding of PSIS in conjunction with liver cirrhosis among medical practitioners.

A sequentially updated projection method for integrating the rate form of plasticity

AbstractWe propose a novel fully implicit algorithm named the Implicit Sequential Projection Method (ISPM) for integrating the rate form of plasticity. ISPM is inspired by the implicit construction of the Closest Point Projection Method (CPPM) and the Cutting Plane Method’s (CPM) treatment of state variables as functions of the plastic multiplier. Though all the state variables are treated as functions of the plastic multiplier, the evaluation of the derivatives of the state variables with respect to the plastic multiplier at the unknown solution makes ISPM a fully implicit algorithm similar to CPPM. ISPM iteratively updates the solution by projecting the state at the end of prior iteration to the yield surface, producing its characteristic sequential projection of the solution, hence the name. Furthermore, ISPM provides a straightforward to derive consistent tangent operator (CTO) with global convergence on par with CPPM. The mathematical formulation, main attributes, and geometric details of the return mapping are discussed in relation to CPPM and CPM, with an emphasis on showing the distinctness of the algorithm. Further, we establish the relationship between ISPM and CPPM. The versatility and accuracy of ISPM and its CTO are explored through a series of numerical tests conducted with three plasticity models. Tests that focus on material-level iterations show that the stress remapping of ISPM is as accurate as CPPM’s. Further, the mixed stress–strain loading history test conducted with non-linear elastic Drucker–Prager plastic material shows that ISPM can provide a runtime advantage over CPPM for some complex plasticity models involving all three stress invariants.

Potentiostatic electrolysis of fluoride melts with zirconium oxide additives

Currently, the demand for zirconium-based alloys and materials is growing significantly due to their high thermal and corrosion resistance combined with mechanical strength. Existing technologies for producing zirconium and its alloys are complicated by the high temperature of the process, or labor intensity and multi-stage nature, which significantly increases the cost of the target material up to the loss of profitability of the process. Electrochemical synthesis of zirconium and its alloys in fluoride-based melts, using zirconium oxides as the main metal-containing consumable component, seems more profitable. In this work, a series of electrolysis tests were carried out to deposit Al-Zr alloy at a potential of 1.6 V on graphite and molybdenum cathodes. According to the previously obtained results, in the presence of ZrO2 in the KF-AlF3-Al2O3 melt, a plateau and a discharge peak of electroactive ions appear on the cathode branch of the voltammograms at potentials of -1.4 and -1.7 V, ZrI and ZrII, respectively. Similar responses appear on tungsten at potentials of -1.3 and -1.6 V, respectively, and in the potential region of -1.9 V there is a clear peak (Al) of electroreduction of aluminum ions. As a result of electrolysis, it was found that the graphite anode was consumed, and a fairly well-bonded deposit was formed on the cathode. Part of the cathode deposit was mechanically separated from the cathode for analysis of its chemical and phase composition. Based on the results of X-ray phase analysis, it was found that the cathode deposit mainly consists of Al3Zr and aluminum compounds with molybdenum impurities, with the composition Al12Mo, which is consistent with known ideas about the formation of intermetallic compounds during the interaction of aluminum with other metals. Electrolysis of the melt on the graphite cathode was carried out under similar conditions. Based on a microphotograph of the cathode cross section, it was found that during electrolysis, a layer of deposit containing both zirconium and aluminum was formed at the electrode-electrolyte phase boundary.

Flexural behaviors of GFRP-wood sandwich beams with recycled wood formwork cores

The escalating consumption of wood products has inevitably led to a rapid accumulation of waste wood, of which a large amount has been landfilled. An innovative concept has been therefore proposed to repurposes waste wood formwork as the core material of Glass Fiber Reinforced Polymer (GFRP)-wood sandwich beams. A series of four-point bending tests were conducted on these sandwich beams, with the thicknesses and orientations of strengthening GFRP layers as the main test parameters examined. The test findings indicated that the GFRP-waste wood sandwich beams failed in either buckling of compression zone or rupture of GFRP covering. In addition, the increase in the number of GFRP layer resulted in a significant increase in the both bending stiffness and flexural strength, and the beams strengthened with three-layer GFRP sheets exhibited the bending stiffness and flexural strength up to respectively 4.7 and 6.5 times greater than those without such GFRP strengthening. The analytical and numerical predictions of flexural properties of sandwich beams are in a good agreement with the test results, thereby validating the accuracy of the models employed in the present study.

Bearing behaviors of rock-socketed piles in layered dynamically compacted soil-rock mixtures: A case study

After layered dynamic compaction (DC) treatment in a mountainous area with deep backfill in Chongqing, China, a series of pile tests and analyses were conducted to evaluate the vertical bearing capacity of rock-socketed piles and to investigate their mechanical characteristic and load-bearing behavior. Static pile load tests (SPLT) were carried out on three types of rock-socketed piles with different diameters (800 mm, 1000 mm, and 1200 mm). Based on the test data of pile reinforcement stress, the pile axial force, frictional resistance, and load-sharing ratio were calculated and analyzed. The results indicate that load-settlement curves of static load tests for all piles change progressively, and the S-lgt curves are relatively straight lines without obvious downward bending. The pile axial force exhibits the characteristics of “large at the top and small at the bottom”, resulting in stress concentration at the pile top, especially prominent in longer piles (lengths of 33.2–37.1 m). Additionally, the overall frictional resistance increases with the increase of pile top load. In shorter piles (lengths of 16.5–22.6 m), the frictional resistance presents a C-type curve with depth, while in longer piles, it presents an S-type curve distribution. Comparatively, the test pile bears the upper load mainly by the side friction resistance, which is more prominent in the longer pile. With the increase of pile top load, the load-sharing ratio of side friction decreases and the load-sharing ratio of pile tip resistance increases.

Chemo-mechanical benchmark for phase-field approaches

Abstract Phase-field approaches have gained increasing popularity as a consequence of their ability to model complex coupled multi-physical problems. The efficient modeling of migrating diffuse phase boundaries is a fundamental characteristic. A notable advantage of phase-field methods is their ability to account for diverse physical driving forces for interfacial motion due to diffusive, mechanical, electro-chemical, and other processes. As a result of this versatility, phase-field methods are frequently employed in the fields of materials science, mechanics, and physics, and are continually undergoing development. To test the accuracy of these developments, it is indispensable to establish standardized benchmark tests, to ensure the thermodynamic consistency of studies carried out. This work presents a series of such tests based on chemo-elastic equilibrium states for Fe-C binary alloys, benchmarking the performance of a phase-field model with chemo-elastic coupling based on the grand potential density. Use of parameters for the Fe-C system from a Calphad database allows for the determination of the Gibbs free energy, thereby enabling the quantification of chemical driving forces. For a circular inclusion, the capillary driving force is derived on a geometrically motivated basis using the lever rule and expressed as a function of the chemical potential. These simulations contribute to the development of standardized benchmark tests that validate chemical, capillary, and mechanical driving forces separately and in combination. The present study compares phase-field simulation results with results from the analytic solution of chemo-elastic boundary value problems and the generalized Gibbs–Thomson equation.

Technology for removing PM2.5 in clean coal processes

Most countries primarily utilize thermal power to meet their energy needs. However, thermal power generation generates a substantial amount of pollutants, such as particulate matter (PM), SOX, and NOX. These pollutants not only damage backend turbines and related equipment but also pollute the environment; thus, controlling their emissions is critical.This study developed a system operating under high temperature by integrating heating, pneumatic conveying, dust particulate supply, and filter material transport systems. This setup enables the simulation of the entry of syngas with PM at the output of a gasification unit. The developed composite filtration system was analyzed under various operational parameters, including different temperatures, inlet air velocities, and mass flow rates of filter material, to examine the changes in the dust particulate size distribution at its outlet and its PM2.5 collection efficiency. In a series of tests, the collection efficiency of this system reached at least 95% at operating temperatures between 20°C and 600°C. Each 100°C increase in the operating temperature resulted in a 0.63% decrease in the PM2.5 collection efficiency. The findings of this study lay the foundation for the future development of high-temperature gas purification systems.

Effects of air content on rheological behavior and segregation of self-compacting concrete

Self-compacting concrete (SCC) offers significant advantages due to its low yield stress and plastic viscosity, yet challenges such as bleeding and segregation can compromise its stability. Maintaining a uniform aggregate distribution is essential to prevent these issues. Air-entraining admixtures (AEA) are often used to introduce air bubbles that enhance SCC's resilience in freeze-thaw conditions and potentially improve stability. This study addresses contradictions in prior research regarding the impact of entrained air on SCC's rheological behavior, experimentally evaluates the effects of varying air content on SCC's workability and segregation resistance, and establishes correlations between rheological characteristics and segregation stability. A comprehensive series of rheological tests, including slump flow diameter, flow time, blocking rate, segregation stability, plastic viscosity, yield stress, and segregation index, was conducted on SCC mixes with different AEA dosages. Regression models revealed significant correlations between air content and both the stability and workability of SCC, with results indicating that optimal AEA levels improve flowability and reduce segregation risks. These findings provide valuable insights into designing stable, high-performance SCC formulations tailored for challenging structural applications.

An Extend Sliding Mode Disturbance Observer for Optical Inertial Platform Line-of–Sight Stabilized Control

As the imaging distance and focal length of photoelectric systems increase, the requirements for line-of–sight stabilization of optical inertial stabilized platforms (ISPs) become higher. Disturbance rejection directly determines the stability accuracy of optical inertial stabilized platforms. However, the accurate observation and suppression of wide-band and rapidly changing disturbances remains a challenge in current engineering applications. This paper proposes a robust extended sliding mode observer (ESMO) method to improve disturbance estimation performance. First, the linear extended state observer (LESO) is designed by taking the total disturbances as extended states. Then, a sliding mode observer (SMO) is incorporated in the extended states of the extended observer, forming a robust ESMO. Subsequently, the robustness and convergence characteristics of the proposed method are mathematically proved, revealing that it operates robustly without knowing the disturbance’s upper bound and offers faster dynamics and higher accuracy than the LESO. Finally, a series of simulation experimental tests are performed to demonstrate the effectiveness of the proposed method. The proposed method observes wide-band and rapidly changing disturbances utilizing the rapidly switching characteristic of the SMO and smooths the jitter of the SMO by cascading sliding mode estimation to the differentiation term of extended observation, achieving the integral effect of the reaching law. Meanwhile, this method only requires adjusting two parameters, making it suitable for engineering applications. It can be effectively used in optical inertial stabilized platform control systems for disturbance estimation and compensation.

How Does the Largest Cluster in the Strong Network Rule Granular Soil Mechanics? A DEM Study

ABSTRACTThe contact network of granular materials is often divided into strong and weak subnetworks, which play different roles in micromechanics. Within the strong contact network, there exists the largest connected component, that is, the largest cluster, which may connect system boundaries and could be the most important structure in force transmission of the whole system. This paper concerns the particular features of the largest cluster in the strong contact network of granular materials, by considering the combining effects of loading path and particle shape. A series of true triaxial tests with various intermediate principal stress ratios are conducted for granular assemblies of different shaped particles using the discrete element method (DEM). Both the macroscopic stress–strain responses and the microscopic topological changes of the contact network are investigated. It is found that both particle shape and loading path will influence the shear strength and the topological features of the strong network. The threshold (the ratio to the average force) is used to distinguish the strong and weak networks, and a critical threshold can be identified by comparing the network‐based metrics. The largest cluster within the strong network approaching the critical threshold can span the boundaries in each direction with minimum contacts, which occupies a small portion of particles and contacts but transmits a considerable portion of the applied stress. In addition, the similar contribution weight of the largest cluster to the deviatoric stress is identified for granular materials with different particle shapes.

Compound risks of floods and droughts over multi-hazard catchments: Revealing association through hydrodynamic-cum-statistical modelling and novel bivariate risk classifier

Floods and droughts are signature phases of the same hydrological cycle. Despite their profound impacts on the socio-economic structures and population globally, limited research efforts have encapsulated the resultant compound risks from them. Comprehending both water extremes presents a formidable challenge due to the relatively short-term occurrence of floods versus the prolonged impacts of droughts. The present study, for the first time in the context of global disaster risk reduction, develops a comprehensive framework driven by a novel concept of Bivariate Risk Classifier (BRC) that can readily integrate the marginal and compound impacts/hazards of floods and droughts. The study employs an exhaustive hydrodynamic-driven approach through LISFLOOD-FP and statistical modelling in terms of the Standardized Precipitation Evapotranspiration Index (SPEI), to derive compound flood and drought hazards. A series of extensive calibration and validation tests ensures minimal false alarms and inaccuracies in the simulated outputs. In the latter phase, populations and regions that are vulnerable to compound risks are identified. This study notices a high degree of synchronization of the exposed population to compound hazards that are otherwise associated with either floods or droughts. The efficient demonstration of the proposed framework over a highly disaster-sensitive catchment in India promises its further application to global multi-hazard catchments. The findings from this study call for an integrated approach directed towards targeted, adaptive disaster risk management and resilient infrastructure planning for regions facing concurrent flood and drought impacts.

Experimental analysis and gene expression programming optimization of sustainable concrete containing mineral fillers.

Rapid urbanization has led to a high demand for concrete, causing a significant depletion of vital natural resources, notably river sand, which is crucial in the manufacturing process of concrete. As a result, there is a growing need for environmentally sustainable alternatives to fine aggregate in concrete. Quarry dust (QD) has evolved as a viable and ecologically friendly substitute in response to this demand. In the past, limited experimental investigations and only conventional modeling techniques were used to promote sustainable mineral fillers in concrete. This study proposed a robust soft computing technique using gene-expression programming (GEP) to enhance the usability of sustainable alternatives in concrete. Initially, an experimental study was carried out to examine the feasibility and mechanical characteristics of concrete made from materials including quarry dust and superplasticizer as a partial replacement for fine aggregate. Ten mixed proportions with various proportions (0%, 20%, 40%, and 60%) of quarry dust were used to make M15 and M20 grades of concrete. A series of experimental tests, such as workability, compressive strength (CS), and tensile strength (TS), were conducted to examine the fresh and hardened properties of modified concrete. The established database from the experimental investigations was then used to develop machine learning (ML) models using GEP. The outcomes of the GEP models were validated by comparing them with multi-linear regression (MLR) models and using various statistical metrics such as root mean squared error (RMSE), performance index (PI), correlation coefficient (R), and external validation methods. Finally, sensitivity analysis was performed to investigate the influence of ingredients such as mineral fillers, superplasticizers, and others on the mechanical properties of concrete. To enhance the practical usage of the study, a graphical user interface (GUI) was also created. The study revealed that 40% of the replacement of fine aggregates with mineral filler and superplasticizer shows the optimum properties. GEP models outperformed MLR, achieving R² values of 0.96 in CS and 0.92 in TS, compared to MLR's lower values of 0.85 in CS and 0.81 in TS. The proposed GEP equations and user-friendly GUI can be used to develop the pre-mix design of concrete using quarry dust and superplasticizers.

Balancing act: D&O liability insurance and ESG disclosure in the Chinese corporate landscape

ABSTRACT Environmental, social, and governance (ESG) information disclosure refers to a corporation’s voluntary disclosure of information regarding specific practices. This study empirically tests the effects of Directors’ and Officers’ (D&O) liability insurance on corporate ESG disclosure levels in Chinese listed firms. The findings show that compared to firms without D&O liability insurance, firms with coverage exhibit significantly higher levels of ESG disclosure overall and in the individual dimensions. Furthermore, the conclusions hold after a series of robustness tests, suggesting that D&O liability insurance plays an incentive supervisory role. Moreover, the mechanism analysis reveals that D&O liability insurance promotes corporate ESG disclosure by improving a firm’s internal control quality. Further analysis finds that the promotion effects of D&O liability insurance on the level of ESG disclosure are more pronounced in firms that are state-owned, have a higher proportion of institutional shareholding, use ‘BIG4’ auditing, and have higher analyst coverage. This study enriches the literature on the economic consequences of D&O liability insurance and provides practical insights into the promotion of corporate ESG disclosure.

Experimental study on the durability of cement-stabilized soil for post-grouted piles in calcareous sand under marine environment

To address the durability of post-grouted piles in calcareous sand within marine environments, a series of tests including micro-cone penetration, unconfined compressive strength (UCS), scanning electron microscope, energy dispersive spectrometry, and X-ray diffraction was conducted to study the strength changes of cement-stabilized calcareous sand under different curing times and cement ratios. The relationship between UCS and penetration resistance was established and compared with similar tests on cement-stabilized siliceous sand, revealing the micro-erosion mechanisms specific to cement-stabilized calcareous sand. The results show that based on the distribution of penetration resistance, the cement-stabilized soil in a seawater environment can be divided into eroded and non-eroded layers, with erosion depth increasing as curing time extends and cement ratio decreases. After 90 days of curing, the eroded layer exhibited increased porosity, a 34.4% reduction in peak heights of hydration products, and a 16.4% decrease in Ca2+ content compared to the non-eroded layer. These findings highlight that strength changes under seawater erosion result from a balance between enhanced strength due to hydration and weakened strength due to erosion. The study provides insights into evaluating the durability and long-term stability of post-grouted piles in calcareous sand.