Mercury Intrusion Porosimetry Tests Research Articles

Durability performance of superabsorbent polymer incorporated concrete modified by nano-silica addition in seasonal frozen regions

In seasonal frozen regions, ion erosion and freeze-thaw (F-T) cycles threaten pavement concrete durability. This study evaluates the suitability of superabsorbent polymer (SAP) concrete modified by nano silica (NS) for enhancing durability. Tests were conducted to analyze chloride impermeability and frost resistance effects on modified SAP concrete. The coupling impact of ion erosion and freeze-thawing was also evaluated. Mercury intrusion porosimetry (MIP), scanning electron microscopy, and energy dispersive spectrometry were employed to investigate microstructure characteristics. Results demonstrated that NS-modified SAP concrete exhibited high resistance to ion erosion and F-T cycles. Adding 3% NS reduced the relative dynamic elastic modulus (RDEM) loss by 23.21% after 300 F-T cycles. The enhancement was more pronounced under the coupled action of ion erosion and freeze-thawing, and the RDEM loss and scaling quantity per unit area of NS-3% decreased by 13.21% and 41.48% respectively, and compressive strength was 28.33% higher than that of SAP concrete after 135 salt-frost cycles. MIP testing indicated that 3% NS significantly improved pore structure, reducing deterioration in much harmful pores by 12.82%. SAP promoted the efficient pozzolanic reaction of NS, generating high-density C-S-H. Additionally, second-hydration products were adsorbed by the ionization of SAP microgel, densifying its shrinkage voids and delaying ITZ width and micro-crack propagation, thereby enhancing concrete durability.

Effects of Remolding Water Content and Compaction Degree on the Dynamic Behavior of Compacted Clay Soils

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade.

Enhancing Sustainability in Construction: An Evaluation of Lightweight Concrete with Sintered Fly Ash and Waste Marble Sand

Abstract Marble waste and fly ash are industrial waste, and disposal of these wastes is a big challenge for environmental sustainability. In this study, we explore an innovative approach to sustainable construction by utilizing industrial by-products: sintered fly ash aggregate (SFA) and waste marble sand in lightweight aggregate concrete (LWAC). This study used SFA as a coarse aggregate, whereas river sand was partially replaced by waste marble sand (10–50 %). The waste marble sand modified LWAC has been investigated for mechanical and durability properties. The test related to permeability like water absorption, sorptivity, permeability, and drying shrinkage has been performed. Mercury intrusion porosimetry test was performed to validate durability results. The results indicate that 30 % of river sand can be replaced with waste marble sand as it improves the overall performance of LWAC. Our research contributes to global sustainability efforts by providing a method to reduce industrial waste through its incorporation in building materials. This study not only addresses the urgent need for environmental preservation but also offers potential enhancements in the mechanical properties of LWAC, making it a viable and eco-friendly option in the construction industry worldwide.

Bacterial activity and cementation pattern in biostimulated MICP-treated sand-bentonite mixtures

The application of microbially induced carbonate precipitation (MICP) in clayey soils has attracted much attention, and many studies used clay as an additive to enhance microbial mineralization efficiency in sandy soils. Within the sand-clay-bacteria-calcite system, the property and content of clay play crucial roles in affecting bacterial growth and calcite formation. More important, bentonite is particularly sensitive to changes in the geochemical environment. In this study, the sand-bentonite mixtures were treated by biostimulated MICP, aiming to provide insights into the behavior of this system. The bacterial activity and cementation pattern at different bentonite contents were evaluated through a series of tests such as enrichment tests, unconfined compressive strength (UCS) tests, cementation content measurements, mercury intrusion porosimetry (MIP) tests, scanning electron microscopy (SEM) observations, and energy dispersive X-ray spectroscopy (EDS) analyses. The findings showed that the bentonite presence promoted the enrichment of indigenous ureolytic bacteria, with lower bentonite levels enhancing ureolytic activity. Macroscopic and microscopic characterization indicated that the bentonite-coating sand structure was more conducive to the formation of large-sized calcite crystals capable of cementing soil particles compared to sand-supported and bentonite-supported structures. Additionally, excessive calcium ions (Ca2+) concentrations in the cementitious solution would lead to predominant calcite deposition on soil particle surfaces, contributing minimally to strength improvement.

Freeze-thaw effects on pore structure of clay by 3D X-ray computed tomography and mercury intrusion porosimetry

Thaw settlement of soils is a comprehensive reflection of multiscale pore changes induced by freeze-thaw (F-T). In this study, three-dimensional (3D) X-ray computed tomography (CT) tests were utilized to investigate alterations in the macropore and mesopore structures, while mercury intrusion porosimetry (MIP) tests were used to examine the micropore structure in clay due to F-T influenced by different freezing temperatures without water supply. The maximum increase in CT transverse-sectional porosity after F-T can be used to identify where ice lenses formed most abundantly in the clay after thawing, and the diameter and horizontal orientation of the macropores exhibit the most significant increase after thawing. As the freezing temperature decreases, the location becomes farther from the cold end. Macropores are significantly more affected by F-T compared to mesopores, and changes in macropore porosity and diameter can be attributed to moisture migration and freezing shrinkage, with lower freezing temperatures amplifying the influence of freezing shrinkage and weakening the impact of moisture migration. Considering the small size of samples, the MIP porosity was defined to analyze the effects of F-T on the micropores. Compared to the CT volumeratic porosity, the influence of F-T on micropore porosity is less significant. As the freezing temperature decreases, the changes in micropore diameter become smaller. Overall, the lower the freezing temperature, the smaller the changes in macropores, mesopores and micropores. Lastly, a method is proposed for predicting the mass porosity based on the CT volumetric porosity and MIP porosity. This study demonstrates that changes in soil mass porosity reflect a comprehensive representation of multiscale pore variations and provides important theoretical support for thaw settlement control in artificial freezing engineering.

Medieval and Restoration Bricks: Water Transport (Hygric) and Microstructural Properties – A Compatibility Study

ABSTRACT The aim of this work was to analyze and ascertain the physical, hygric and mechanical properties of historical bricks, in order to deepen knowledge about the properties of existing historical building brick structures. Laboratory tests, such as density, water absorption and compressive strength, were conducted. In order to assess the microstructural characteristics of the tested bricks, mercury intrusion porosimetry (MIP) tests were performed. These tests were conducted on clay bricks from four medieval buildings (14th Century) of great historical significance, as well as on those currently produced, in order to identify the similarities and differences between specific groups of material properties. The results of this study and previous research will form a basis for creating a database of complete information in terms of physic, hygric and mechanical properties of historical bricks from different time periods, from the Middle Ages to modern times. The results will supplement modeling programmes utilizing materials specific to Polish construction periods, which can help simulate, as closely as possible, humidity transfer in real conditions. Moreover, the results will lead to the development of a useful tool for selecting materials in restoration processes, that will correspond with those used historically.

Numerical and experimental study of Yellow River sand in engineered cementitious composite

Engineered cementitious composites (ECCs) represent a significant advancement in concrete technology, addressing the issues and limitations of conventional concrete and environmental challenges related to sedimentation in rivers such as the Yellow River in China. This study investigates the integration of Yellow River sand (YRS) into ECC mix designs for sustainable development. YRS replacement rates (0, 25, 50, 75 and 100%) with quartz sand are systematically analysed through flexural, compressive, uniaxial tensile and four-point bending tests. In addition, scanning electron microscopy and mercury intrusion porosimetry tests are conducted to investigate the micro-mechanical properties. The results reveal that the optimal mechanical performance with 100% YRS substitution improves the compressive and flexural strengths to 26.4 and 11.5 MPa, respectively. These values are 6.20% lower than the those of the 0% substitution rate. Notably, a 100% replacement maintains an ultimate tensile strain of 3.71%, improving the crack width and spacing compared with those at 0%. The average crack width and spacing decrease by 4.87 and 11.2%, respectively, compared with those of 0% substitution. The four-point bending test results show the highest ductility at a 75% substitution rate. Furthermore, a finite-element method model of ECC beams with YRS is developed and validated under the same loading conditions as the experimental data. This study recommends an analytical method for predicting flexural strength compared with the experimental data, enhancing its suitability for sustainable engineering applications.

Preparation of self-consolidating cemented backfill with tailings and alkali activated slurry: Performance evaluation and environmental impact

Development of low-cost and eco-friendly mine backfills is essential for the sustainable mining technology. This study focuses on the design and performance assessment of self-consolidating cemented backfills consisting of iron tailings and alkali-activated slurry (SCBTA). The effects of alkali content, activator modulus, and precursor constituents on SCBTA were clarified by means of investigations including workability and stability at fresh state, mechanical properties, drying shrinkage, and environmental benefits. Moreover, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were employed to understand the mechanism behind phenomena. The research findings indicate that the alkali activator modulus, alkaline content, and fly ash promote the flowability and stability of fresh SCBTA slurry. When the water-cement ratio is 0.6 and the alkali activator modulus increases from 0 to 1.0, the flow diameter of the fresh SCBTA slurry increases by 40 %. When the alkali activator modulus was 1.0 and the alkali content was 8 %, the addition of fly ash significantly improved the resistance to bleeding and segregation of the slurry. Compared to the alkaline-activated pure slag slurry, the inclusion of fly ash increases these properties by 60 % and 20 %, respectively. However, higher alkaline content and modulus result in a decrease in the resistance to shrinkage strain of hardened slurry. Hardened SCBTA slurry with an alkali activator modulus of 1 and alkaline content of 6 % and 8 % experiences severe shrinkage cracking within 7 days. MIP tests demonstrate that a higher alkali activator modulus promotes structural densification, with gel pores being the primary pore types distributed below 100 nm. Considering the mechanical properties, fluidity, workability, shrinkage, and environmental indicators, the recommended backfill slurry for mining operations is a slag/fly ash mixture with an alkaline content of 6 %, an alkali activator modulus of 0.5, and a water-cement ratio of 0.6.

Durability Assessment of Eco-Friendly Bricks Containing Lime Kiln Dust and Tire Rubber Waste Using Mercury Intrusion Porosimetry

The global challenge faced due to the impact of the construction industry on climate change, along with the issues surrounding sustainable waste disposal, has necessitated various research on using waste products as eco-friendly alternatives in construction. In this study, the avoidance of waste disposal through landfills in Australia was encouraged by incorporating lime kiln dust (LKD) and tire rubber waste (TRW) into masonry mixes to manufacture green bricks. Furthermore, the investigations in this article highlight the use of mercury intrusion porosimetry (MIP) to determine the durability of the LKD-TRW bricks when exposed to freeze–thaw (F-T) cycles by examining the pore size distribution within the bricks. The LKD waste was blended with ground granulated blast furnace slag (GGBFS) at a 70:30 blending ratio and combined with the TRW in stepped increments of 5% from 0 to 20% to produce these eco-friendly bricks. The compressive strength (CS), flexural strength (FS), frost resistance (FR), pore size distribution according to mercury intrusion porosimetry (MIP), and the water absorption (WA) properties of the bricks were assessed. The CS and FS values at 28 days of curing were recorded as 6.17, 5.25, and 3.09 MPa and 2.52, 2, and 1.55 MPa for 0, 5, and 10% TRW contents, respectively. Durability assessments using the F-T test showed that the bricks produced with 0% TRW passed as frost-resistant bricks. Furthermore, the results from the MIP test showed a total pore volume of 0.033 mL/g at 3 µm pore size for the 0% TRW content, further confirming its durability. Hence, the 0% LKD-TRW bricks can be utilized in cold regions where temperatures can be as low as −43 °C without deteriorating. Lastly, WA values of 7.25, 11.76, and 14.96% were recorded for the bricks with 0, 5, and 10% TRW, respectively, after the 28-day curing period. From all of the results obtained from the laboratory investigations, the LKD-TRW bricks produced with up to 10% TRW were within the satisfactory engineering requirements for masonry units.

Structure evolution law of coalbed methane reservoirs under different initial pressure CO2 phase change fracturing conditions

As a new coal bed fracturing technology, CO2 phase transition fracturing (CPTF) has received much attention due to its advantages of safety and high efficiency. However, little research has been conducted to investigate the fracture behavior of CPTF in coal seams under different CO2 release pressure conditions. To address this research gap, we performed fracture tests on coal rock under different initial pressure conditions using the developed CPTF experimental system. Then, scanning electron microscopy, low-pressure nitrogen adsorption, and mercury intrusion porosimetry testing techniques were used to investigate the fracture characteristics and microstructural evolution of coal rocks under different initial pressures of CPTF. The results show that with increasing initial pressure, the number of macroscopic fractures and the degree of fragmentation of the coal after CPTF fracturing increased significantly, the number of microscopic fractures and pores in the fractured coal samples increased, the N2 adsorption capacity and the amount of mercury intrusion of the coal samples increased to a greater extent, and the visible porosity increased from 52.47% of the raw coal to 63.88%, 64.31%, 68.48%, 63.64%, and 62.83%, and the proportion of macroporosity increased from 24.31% to 28.48%, 31.73%, 26.55%, and 34.38%. This research will contribute to a fuller understanding of the potential of CPTF as a technique for improving the pore and fracture structure of coalbed methane reservoirs.

Experimental study of compression behavior and its correlation with the microstructure of a deep-water sediment

Understanding the volume change behavior of deep-water sediments is essential for the safety design of deep-water engineering structures. In this study, the volume change behaviors of marine sediments from the South China Sea were studied through oedometer and isotropic compression tests. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests have been conducted to investigate the microstructure evolution of two types of sediments under loads. The experimental results showed that the structural anisotropy of intact specimens is more pronounced in oedometer tests with the increase of stress, however, depolarization occurs in the isotropic consolidation test. The volume change after yield in the oedometer and isotropic consolidation tests comes from inter-aggregate pore variations associated with the adjustment of the soil fabric. The reconstituted specimen presents a more uniform distribution of pores than that of the intact specimen, and the macropores are more easily compressed for the reconstituted specimen than those of the intact specimen. With increasing stress, the oedometer compression and isotropic consolidation curves of intact specimens gradually approach those of the reconstituted specimen. The deformation mechanism under high stresses is that soil particles are reoriented and the variation of micropores.

Estimation of unfrozen water content of saturated sandstones using nuclear magnetic resonance, mercury intrusion porosimetry, and ultrasonic tests

The unfrozen water content (UWC) is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions. In this study, three different methods were employed to test and estimate the UWC of saturated sandstones, including nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and ultrasonic methods. The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay (FID). The MIP method was used to analyze the pore structures of sandstones, with the UWC subsequently calculated based on pore ice crystallization. Therefore, the MIP test constituted an indirect measurement method. Furthermore, a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory, which could be employed to estimate the UWC as an empirical method. All methods demonstrated that the UWC initially exhibited a rapid decrease from 0 °C to −5 °C and then generally became constant beyond −20 °C. However, these test methods had different characteristics. The NMR method was used to directly and accurately calculate the UWC in the laboratory. However, the cost and complexity of NMR equipment have precluded its use in the field. The UWC can be effectively estimated by the MIP test, but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution. The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory. This method may be more suitable in the field. All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process. The average hysteresis coefficient was approximately 0.538, thus validating the Gibbs–Thomson equation. This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.

Exploring an eco-friendly approach to improve soil tensile behavior and cracking resistance

Soil tensile strength is a critical parameter governing the initiation and propagation of tensile cracking. This study proposes an eco-friendly approach to improve the tensile behavior and crack resistance of clayey soils. To validate the feasibility and efficacy of the proposed approach, direct tensile tests were employed to determine the tensile strength of the compacted soil with different W-OH treatment concentrations and water contents. Desiccation tests were also performed to evaluate the effectiveness of W-OH treatment in enhancing soil tensile cracking resistance. During this period, the effects of W-OH treatment concentration and water content on tensile properties, soil suction and microstructure were investigated. The tensile tests reveal that W-OH treatment has a significant impact on the tensile strength and failure mode of the soil, which not only effectively enhances the tensile strength and failure displacement, but also changes the brittle failure behavior into a more ductile quasi-brittle failure behavior. The suction measurements and mercury intrusion porosimetry (MIP) tests show that W-OH treatment can slightly reduce soil suction by affecting skeleton structure and increasing macropores. Combined with the microstructural analysis, it becomes evident that the significant improvement in soil tensile behavior through W-OH treatment is mainly attributed to the W-OH gel's ability to provide additional binding force for bridging and encapsulating the soil particles. Moreover, desiccation tests demonstrate that W-OH treatment can significantly reduce or even inhibit the formation of soil tensile cracking. With the increase of W-OH treatment concentration, the surface crack ratio and total crack length are significantly reduced. This study enhances a fundamental understanding of eco-polymer impacts on soil mechanical properties and provides valuable insight into their potential application for improving soil crack resistance.

Macro and microscopic characteristics of soft soil stabilized by Portland cement-soda residue under dry-wet cycling

The durability of soft soil stabilized by Portland cement-soda residue (PC-SR) subjected to dry-wet cycles remains relatively unclear now despite previous studies have extensively examined the engineering attributes of soft soil stabilized by PC-SR. Therefore, this study delineates the impacts of dry-wet cycles on the macro and micro features of soft soil stabilized by PC-SR. Based on the orthogonal test design, the unconfined compressive tests, X-ray diffraction test, scanning electron microscopy, and mercury intrusion porosimetry tests were conducted to analyze the impact of dry-wet cycles on the strength, mineral components and microstructural characteristics of stabilized soil cured for 28 days. The experimental findings revealed that the strength of soil stabilized by PC-SR initially ascends and subsequently declines after dry-wet cycles. At the microscale, the tests showed that the dry-wet cycles transform the microstructure of stabilized soil by damaging the cementation among soil particles, expanding the pore diameter, and forming macropores and fissures. Combined with macro and micro results, it is shown that in the initial stage of the dry-wet cycle, the continuous hydration reaction promotes the increase of the microstructure density of solidified soil. However, under the continuous influence of the dry-wet cycle, the dissolution and expansion of mineral components lead to the degradation of the microstructure, which leads to the decline of the macro strength of the stabilized soil, further revealing the mechanism of the macro strength of the stabilized soil rising first and then decreasing. This study showed that Portland cement-soda residue treatment was efficient to prevent the deterioration from the dry-wet cycles.

Influences of alumina type and sulfate content on hydration and physicochemical changes in Portland–limestone cement

This study explored the influence of alumina type and gypsum content on the hydration, mechanical properties, and chemical changes of Portland–limestone cement (PLC) using isothermal calorimetry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), ionic chromatography (IC), compressive strength testing, X-ray diffraction (XRD), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR) spectroscopy, and mercury intrusion porosimetry (MIP) testing. The addition of alumina shortened the induction period, accelerated the acceleration period, and increased the mechanical strength of the PLC pastes with 3 and 7 wt% gypsum. The acceleration effect and strength enhancement were not distinct in the PLC pastes with less gypsum (0.1 wt%). The addition of γ-alumina led to the greatest accelerating effect and strength improvement in the PLC pastes with 3 and 7 wt% gypsum, and the compressive strength achieved was comparable to those of pure Ordinary Portland cement (OPC) pastes without limestone. The addition of γ-alumina induced the rapid dissolution of gypsum and consumption of sulfate ions. The chemical change affected by the addition of alumina varied greatly depending on the gypsum content, and trends in AFt and AFm formation in the PLC pastes with different gypsum contents were confirmed. Finally, pore size refinement was observed through the addition of alumina to PLC pastes with 3 and 7 wt% gypsum.

Mechanics and deformation behavior of lithium-ion battery electrode during calendering process

The calendering process in lithium-ion battery electrode manufacturing is pivotal and significantly affects battery performance and longevity. However, current research on the mechanical and deformation characteristics of lithium-ion battery electrodes during calendering is limited, and a systematic theoretical foundation for informing practical production is lacking. This study investigated the mechanics and deformation behavior of lithium-ion battery electrodes during calendering through experimental methods. Data on the calendering pressure for electrodes at varying compression rates were gathered, revealing a correlation between the calendering pressure and compression rate that aligns well with the Kawakita equation commonly used in powder forming. Furthermore, the study examined the effects of the roller diameter and roller surface temperature on the calendering pressure. Within the typical compression rate range, a linear relationship was observed between the compression rate and the percentage elongation of the battery electrode. The study also explored how the roller diameter, roller surface temperature, and number of calendering passes influence the percentage of elongation. A quantitative formula linking the roller diameter to the percentage elongation of the battery electrode was proposed considering the effect of the roller diameter. Additionally, through electrode cleaning experiments, the study identified the coordination relationship between the extension of the electrode coating and the current collector. Mercury intrusion porosimetry (MIP) tests were conducted to elucidate the influence of calendering on the porosity, pore size distribution and specific surface area of the electrode coating. This research offers valuable insights and a theoretical basis for optimizing the calendering process in lithium-ion battery electrode production.

Effect of SF and GGBS on Pore Structure and Transport Properties of Concrete.

Ground Granulated Blast-Furnace Slag (GGBS) and silica fume (SF) are frequently utilized in gel materials to produce environmentally sustainable concrete. The blend of the two components contributes to an enhancement in the pore structure, which, in turn, increases the mechanical strength of the material and the compactness of the pore structure and decreases the permeability, thereby improving the durability of the concrete. In this study, the pore structures of GGBS and SF blends are assessed using Nuclear Magnetic Resonance (NMR) and Mercury Intrusion Porosimetry (MIP) tests. These methodologies provide a comprehensive evaluation of the effect of GGBS and SF on the pore structure of cementitious materials. Results showed that the addition of SF and GGBS reduces the amount of micro-capillary pores (10 < d < 100 nm) and the total pore volume. The results indicate that the transport properties are related to the pore structure. The incorporation of SF reduced the permeability of the concrete by an order of magnitude. The pore distribution and pore composition had a significant effect on the gas permeability. The difference in porosity obtained using the MIP and NMR tests was large due to differences in testing techniques.

Strength and microscopic pore structure characterization of cement-fly ash stabilized organic soil under freeze-thaw cycles

In seasonal frost areas, an organic soil stratum is often encountered during engineering construction due to the widespread existence of organic soils. The soil stratum will experience frost heave in winter and thaw settlement in summer, resulting in a significant variation in its engineering behaviour, especially for organic soil stratum. In this study, with the help of cement, fly ash, and fulvic acid, cement-fly ash stabilized organic soil (CFOS) specimens were prepared and the unconfined compressive (UC) and mercury intrusion porosimetry (MIP) tests were carried out on CFOS specimens. The effects of fly ash content, number of freeze-thaw cycles (FT-N), and curing period on the strength, resilient modulus, and porosity were investigated. Test results revealed that the fly ash content increased from 0% to the optimum content of 5%, the unconfined compressive strength (UCS) and resilient modulus of CFOS with FT-12 increased by 50.30% and 118.92%, respectively. The pore size distribution (PSD) curve and fractal dimension (Dn) of specimens were obtained from the MIP test. The proportion of macropores was the main factor affecting the UCS of CFOS. With the increasing FT-N, the macropore proportion of CFOS with 5% fly ash content increased by 333.33%, and the UCS decreased by 28.25%. Based on a freeze-thaw damage model, the damage parameters of the CFOS specimens were extracted with the Dn as an independent variable. The microscopic pore characteristics and the relationship between the strength, Dn and damage parameter were analyzed. The microscopic pore structure of specimens with different fly ash contents experienced a change subjected to freeze-thaw cycles. The lower the strength, the lower the Dn of CFOS. The damage parameters quantitatively reflected the damage degree of specimens after freeze-thaw cycles on the micro scale. The damage parameter of CFOS with 5% fly ash content increased by 341.57% with the increase of FT-N. The introduction of fly ash was able to reduce freeze-thaw damage to the specimens. The damage parameter and CFOS strength exhibited a significant correlation. The relationships of the strength and microscopic pore structure of CFOS subjected to freeze-thaw cycles were conducive to a better understanding of the freeze-thaw damage mechanism of CFOS on the micro scale. These findings are beneficial for engineering construction design in seasonal frost areas.

Research on the Fracture Behavior of Ultra-fine Dredged Sand Concrete Based on the Microstructure Characteristics

Abstract The dredged sand generated by the dredging projects has been abandoned and reclaimed from designated areas. It meets the requirements of environmental construction and resource utilization, if the dredging sand can be used as building material in construction. In order to investigate the fracture behavior of dredged sand concrete, five kinds of concrete with different dredged sand replacements (0 %, 12.5 %, 25 %, 37.5 %, 50 %) were designed in this article. Three-point bending fracture tests were carried out on the concrete. The test results show that with the increase of dredged sand replacement, the initiation load, peak load, fracture toughness, and fracture energy first decrease and then increase. Computerized tomography scan and mercury intrusion porosimetry tests show that with the increase of dredged sand replacements, the porosity, pore volume, and pore surface area increase first and then decrease. Dredged sand can improve the pore structure, increase the compactness of concrete, and improve the fracture behavior of concrete. Scanning electron microscopy and X-ray diffraction tests show that dredged sand mainly plays the role of physical filling, and proper dredged sand can improve the compactness of concrete.

Effect of Initial Conditions on the Pore Structure and Bimodal Soil–Water Characteristic Curve of Compacted Granite Residual Soil

Granite residual soil typically forms complex pore structures and exhibits high water sensitivity due to physical and chemical weathering processes. Changes in initial compaction conditions significantly affect the mechanical and hydraulic properties of in situ granite residual soil subgrades, with these variations fundamentally related to changes in pore structure and soil–water characteristics. This study investigates the pore structure and bimodal soil–water characteristic curve (SWCC) of a compacted granite residual soil through laboratory tests and mercury intrusion porosimetry tests. Nine initial conditions were selected based on potential in situ compaction conditions of subgrades, and their effects on the pore size distribution (PSD) and SWCC were thoroughly analyzed. The results show strong correlations between bimodal pore structure and SWCC. The size and volume of inter-aggregate pores exhibit noticeable changes with initial conditions, affecting SWCC within the low and middle suction range. Conversely, the intra-aggregate pores, which constitute over 60% of the pore structures, remain nearly intact across different initial conditions, resulting in similar SWCCs within the high suction range. As the compaction energy increases, the inter-aggregate pores are compressed and lead to a higher water retention capacity. In addition, as the compaction water content increases, the SWCC becomes less sensitive to compaction energy after the aggregates in the pore structure are fully saturated. Additionally, a three-dimensional bimodal SWCC equation is proposed and validated using test data with an R2 value above 0.98. These findings offer valuable insights for the design and quality control of granite residual soil subgrades.