Wet-dry Cycles Research Articles

Experimental Study on Strength and Microstructure of Loess Improved by CG-2 Curing Agent and Cement

In order to study the improvement effect of the CG-2 curing agent and cement on loess, a series of physical and mechanical property tests and microstructure tests were carried out on loess improved with different dosages of curing agent and cement to study the physical and mechanical properties, durability and microscopic pore characteristics of the CG-2 curing agent and cement-improved loess. The results show that the unconfined compressive strength of improved loess increases gradually with the increase in curing agent and cement dosage, and the higher the compaction degree and the longer the curing age, the higher the unconfined compressive strength. In the case of the same cement content, the higher the dosage of curing agent, the more the unconfined compressive strength of improved loess increases. Under the condition of reaching the same unconfined compressive strength, the addition of curing agent can significantly reduce the amount of cement. The more the content of cement and curing agent, the less the unconfined compressive strength decreases after a certain number of freeze–thaw cycles, and the higher the dry-wet cycles index after a certain number of dry-wet cycles, indicating that the addition of curing agent can significantly improve the ability of the sample to resist freeze–thaw cycles and dry–wet cycles. According to the microscopic test results, it is found that the addition of curing agent can reduce the porosity of soil particles, change the contact and arrangement mode between soil particles, and enhance the agglomeration and cementation characteristics between soil particles, and obviously improve the physical and mechanical properties of soil. The research results can provide new ideas and methods for the improvement technology of loess.

Valorisation of municipal solid waste incinerator bottom ash for the production of compressed stabilised earth blocks

This research centres its attention on the valorisation of incinerator bottom ash derived from municipal solid waste with the aim of producing compressed stabilised earth blocks. Compressed stabilised earth blocks is prepared with 6–12% cement and 10–40% MSWIBA, whose performance is assessed in terms of strength and durability. This includes several properties of compressed stabilised earth blocks, including dry compressive strength, flexural strength, tensile strength, water absorption, wetting-drying cycle, ultrasonic pulse velocity and acid attack. The findings indicate that the inclusion of municipal solid waste incinerator bottom ash as a 20% replacement of soil enhances the compressive strength and ultrasonic pulse velocity of the blocks. Nevertheless, the excessive use of municipal solid waste incinerator bottom ash (beyond 20%) results in an augment of void content and a reduction in compressive strength. The results of the study suggest that the usage of municipal solid waste incinerator bottom ash in the blocks leads to the enhancement of their aesthetic qualities. The study employing scanning electron microscopy indicates an excessive quantity of ettringite crystals in the samples derived from ash of quantity beyond 20%. This is because these samples have higher porosity, which enables the acidic medium to penetrate samples easily and react with the cement hydration products. Hence, though showing less discolouration on the surface, these samples show a significant reduction of compressive strength at the end of the testing regime. Similar results were obtained for the wetting and drying test as well. Therefore, this study recommends a maximum usage of 20% municipal solid waste incinerator bottom ash as a replacement for soil.

Disintegration characteristics of sodic–saline loessial soil after freeze–thaw and wet–dry cycles

AbstractGeological hazards such as gully erosion, collapse and slope failure occur frequently in loess areas, which are closely related to the soil disintegration characteristics. Understanding the impact of freeze–thaw and wet–dry action on soil disintegration in the context of climate change is essential to establish effective soil and water conservation strategies and prevent engineering geological hazards in loess areas. In this study, sodic–saline loessial soils with different clay content were subjected to freeze–thaw and wet–dry cycles, followed by aggregate durability tests, direct shear tests and disintegration tests to investigate the effects of the two natural processes on soil disintegration characteristics. The results showed that the samples subjected to freeze–thaw cycles primarily exhibited rapid and stable disintegration, followed by slow disintegration, whereas the samples subjected to wet–dry cycles revealed weight gain, continuous slow disintegration and eventual sudden disintegration. Freeze–thaw action continuously deteriorated the disintegration resistance of soil, while wet–dry action improved the disintegration resistance of soil after the first cycle, and gradually weakened it in subsequent cycles. Statistical analysis showed that, for samples undergoing freeze–thaw cycles, the number of cycles and clay content were positively correlated with the disintegration rate, while the aggregate durability was negatively correlated with the disintegration rate. For samples undergoing wet–dry cycles, the number of cycles had a positive effect on the disintegration rate, while the clay content, shear strength and cohesion had a negative correlation with the disintegration rate. At a certain clay content, there was a positive correlation observed between the surface crack ratio, crack length and width with the disintegration rate of the wet–dry samples, while shear strength and cohesion had a negative correlation with the disintegration rate of both freeze–thaw and wet–dry samples. Furthermore, the study outlined the disintegration mechanism of loessial soils based on internal factors, driving factors, resistance factors and evolutionary factors. This study contributes to the in‐depth understanding of the catastrophic mechanism of geological hazards in cold and arid areas and provides experimental evidence for its control and management.

Expansive soil improvement using industrial bagasse and low-alkali ecological cement

Cement is the primary material used for mitigating expansive soil hazards due to its easy availability and relatively low cost. However, the most commonly used ordinary Portland cement renders the soil strongly alkaline after treatment, and the development of cracks in the soil is not effectively controlled under the influence of wet-dry cycles following cement stabilization. These two drawbacks significantly impact both the ecological environment and the strength of the cement-stabilized expansive soil. This study innovatively proposes an improvement to the method of cement stabilization of expansive soil by incorporating low-alkali ecological cement and industrial sugarcane bagasse (a byproduct of sugar production). After assessing the basic physical properties of the expansive soil, it was improved by mixing with industrial bagasse and low-alkali ecological cement. Through experiments on dry-wet cycles, soil-water characteristic curve tests, direct shear tests, and electron microscopy scans, we explored the enhancement of the expansive soil. Our focus was on the development of cracks, soil moisture migration patterns, changes in shear strength, and microstructural alterations. The following conclusions were drawn from the experiments: i. Compared to the method of ordinary Portland cement stabilization, the pH of expansive soil improved by low-alkali ecological cement combined with industrial sugarcane bagasse is more suitable for plant growth. ii. The unique tubular structure of industrial sugarcane bagasse provides elastic space for soil deformation, inhibiting the development of soil cracks. iii. The water retention capacity of expansive soil significantly increases after improvement with low-alkali ecological cement and industrial sugarcane bagasse. Within the range of matrix suction for plant growth, soil moisture changes more slowly, providing a more stable water supply for plants. iv. The combination of 1.2% industrial sugarcane bagasse and 7% low-alkali ecological cement exhibits the highest shear resistance, maintaining strength exceeding that of untreated expansive soil after five wet-dry cycles. v. SEM analysis confirms the effectiveness of industrial sugarcane bagasse and low-alkali ecological cement in improving expansive soil. This study improved the widely used cement stabilization method for expansive soil in practical engineering applications. Additionally, it introduced an additional utilization pathway for industrial bagasse residue waste. This research provides a new direction and reference for the combination of waste utilization and natural disaster management in the treatment of expansive soil hazards.

An eco-friendly and low-cost superhydrophobic alkali-activated Portland slag cement mortar

Alkali-activated slag cement (AASC) has shown immense potential for application as a low-carbon and eco-friendly cementitious material. It’s crucial to modify the AASC with superhydrophobic property to obtain excellent durability performance. In this paper, low-cost and non-toxic stearic acid (SA) is selected as a hydrophobic agent to impart integral hydrophobic property to the alkali-activated Portland slag cement mortar (AAPSCM). The SA-modified AAPSCM (M-AAPSCM) shows superhydrophobicity with a contact angle of 150.6° and a sliding angle of 9.5°, even when hammered to reveal its broken inner structure. The characterization analysis indicates that stearic acid not only successfully grafts onto the mortar surface but also forms calcium stearate, which successfully reduces the surface energy of the material. Combined with the porous rough structure constructed by medium sand and ethanol volatilization, the originally hydrophilic material achieves hydrophobic modification under the dual synergistic effect. The M-AAPSCM reached a compressive strength of 20.8 MPa after 28 days of curing, satisfying the requirements for hydraulic engineering applications. And the M-AAPSCM not only exhibits an excellent self-cleaning ability against contaminants like sand particles and chalk powder, but also demonstrates remarkable mechanical robustness, even after being subjected to blade scratching or mechanical fracture. Concurrently, the initial and final setting times of M-AAPSCM were determined to be 32 minutes and 41 minutes respectively, demonstrating its rapid-setting characteristic. Additionally, following the hydrophobic modification, AAPSCM effectively overcomes its inherent issues of severe autogenous shrinkage and poor carbonation resistance. Furthermore, when compared with the ordinary AAPSCM (O-AAPSCM), the durability of the M-AAPSCM against dry-wet cycles, icing, and freeze-thaw cycles is significantly enhanced.

Compressive strength resistance coefficient of sustainable concrete in sulfate environments: Hybrid machine learning model and experimental verification

The compressive strength corrosion resistance coefficient of sustainable concrete (SC-SCRC) is a crucial indicator for evaluating the mechanical performance degradation of SC after erosion. Therefore, this study collected 326 sets of SC-SCRC data from 20 literature sources and established an optimized machine learning algorithm-based SC-SCRC prediction model, evaluating its performance. To validate the model's accuracy, thirteen different SC mix ratios were prepared for SC-SCRC testing. The results demonstrate that the grey wolf optimization supported vector regression (GWO-SVR) model provides predictions that better align with the actual values. The model exhibits lower standard deviation and mean of model residuals. The performance evaluation indicators of the GWO-SVR model (R=0.972; MSE=1.46e-3; MAE=2.9e-2; MAPE=3.1e-2; RMSE=3.9e-2) are also outstanding. Furthermore, Shapley Additive Explanations reveal that the dry-wet cycle count and the water-binder ratio are the two most critical influencing factors on SC-SCRC, with both showing negative correlations. A graphical user interface (GUI) based on the GWO-SVR model has been developed to enable efficient predictions of SC-SCRC. Test results indicate that the error between the experimental values and the predicted values is less than 6%, demonstrating the model's high accuracy and generalizability. This work lays the foundation for optimizing the performance of SC and predicting SC-SCRC. The findings provide valuable guidance for engineering projects in areas with high concentrations of sulfate ions.

Macro-microscopic study on the crack resistance of polyester fiber asphalt mixture under dry-wet cycling and neural network prediction

Asphalt mixture is a composite material with a complex multiphase dispersed system, and its macroscopic mechanical behavior is inherently related to the microstructure characteristics. To investigate the low-temperature crack resistance degradation law of polyester fiber asphalt mixture under different dry-wet cycling conditions, six polyester fiber contents (0%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%) were dry-blended into SMA-13 asphalt mixture to prepare fiber-reinforced SCB specimens with pre-notches. Semi-circular bending tests were conducted to test the crack resistance performance of the fiber asphalt mixture after 0, 2, 4, 6, and 8 dry-wet cycles. The experimental results show that the crack resistance performance of specimens with different fiber contents decreases with the increase of dry-wet cycling times, and the influence of salt-dry-wet coupling is greater than that of water-dry-wet coupling. Under the same conditions, the crack resistance index (CRI) increases first and then decreases with the increase of polyester fiber content, reaching its maximum at a polyester fiber content of 0.4%. When the fiber is added at 0.5%, the agglomeration of polyester fibers restricts the low-temperature performance of the specimen. In addition, the DIC technology is used to analyze the trend of horizontal strain variation of specimens after different dry-wet cycles. The results indicate that with the increase of the cycle period, the strain concentration area becomes more apparent, and in the destruction stage, the full-field horizontal strain Exx in the crack concentration zone gradually increases, while the crack resistance decreases. Finally, addressing the limitations of traditional BP neural networks in solving nonlinear problems, a particle swarm optimization algorithm is proposed to optimize the BP neural network, and a PSO-BP neural network model is constructed. Through the analysis of evaluation indicators, it is found that the PSO-BP neural network has improved generalization ability compared to the traditional BP neural network model, and overfitting is reduced, making it an effective tool for predicting the low-temperature performance of polyester fiber asphalt mixtures.

Stability of Expansive Soil Slopes under Wetting–Drying Cycles Based on the Discrete Element Method

The swelling-shrinkage behavior of expansive soils under climate changes will cause the crack development, which can be destructive of expansive soil slopes. This study investigated the effect of drying/wetting cycles on the stability of an expansive soil slope using the discrete element method (DEM), in consideration of the crack development induced by climate changes. The strength reduction method was adopted in the DEM calculations, which was coupled with the unsaturated seepage analysis given by the finite element method. The slope stability and the failure model of the slope after different times of wetting–drying cycles were analyzed, and the results were compared with those calculated by the limit equilibrium method and the finite element method. The results indicated that the failure pattern of the expansive soil slope was strongly influenced by the wetting–drying cycles. A shallow sliding surface of the expansive soil slope occurred after several wetting–drying cycles. Similarly, the safety factor of the expansive soil slope decreased gradually with the wetting–drying cycles. Considering the cracks’ evolution inside the expansive soil slope from the drying/wetting cycles, a shallower sliding surface with a smaller safety factor was obtained from the strength reduction method of the DEM, in comparison with the two conventional methods of the Limit equilibrium method and finite element method. Therefore, cracks play an essential role in the expansive soil slope stability. The strength reduction method of the DEM, which considers the cracks’ evolution during drying/wetting cycles, is more reliable.

Hysteretic water-retention behaviour of unsaturated hydrophobised soils

Hydrophobised soils found in the superficial region of earthen infrastructure can affect the hydrological processes of these structures. The hysteretic water-retention curve (WRC), which governs these processes, for hydrophobised soils has rarely been reported. Existing apparatus is unable to measure the WRC of unsaturated soils as it could not control the condition of pore water pressure (uw) in excess of pore air pressure (ua) when the contact angle was larger than 90°. In this study, a new apparatus was created, which sandwiches a soil sample between a high water-entry value (WEV) membrane and a high air-entry value (AEV) ceramic disc, to control the uw < ua and uw > ua conditions. Contact angle hysteresis and menisci evolution in the test materials during wet–dry cycles were measured to interpret the WRC. The WEV of soil increased with decreasing chemical heterogeneity and particle size. When drying the hydrophobised soils, they could retain water before reaching a certain negative uw. The WEV identified from the second wetting cycle was lower than that from the first cycle, whereas the AEV remained largely unchanged. The WEV and AEV decreased when the particle size of the hydrophobised materials was increased, resulting in a smaller hysteresis size.

Unraveling the Mystery of Water-Induced Loess Disintegration: A Comprehensive Review of Experimental Research

Loess disintegration is a significant physicochemical and mechanical dissolution process that occurs when loess comes into contact with water. This phenomenon contributes to geological disasters such as loess cave erosion, landslides, and debris flows. The disintegration of loess can be influenced by both internal and external factors. Research on internal factors of loess disintegration has been widely recorded, but the research progress on external environmental factors that affect loess disintegration is not well summarized. This review summarizes the impacts of external water environmental factors on loess disintegration and reveals that six external water environmental factors, namely the temperature of the aqueous solution, hydrodynamic conditions, solution pH, salt concentration and type in the solution, freeze–thaw cycles, and dry–wet cycles, can significantly impact loess disintegration. Furthermore, this review delves into three key research areas in loess disintegration under the influence of these water environmental factors: experimental research on loess disintegration, the disintegration parameters used in such research and their variations, and the water–soil chemical reactions and microstructural changes during loess disintegration. It concludes that current experimental research on loess disintegration suffers from inadequate studies, with existing research associated with poor comparability and weak representativeness, and a lack of comprehensive, systematic analysis of its regularities of influence and response mechanisms from both microscopic and macroscopic perspectives. This paper can provide valuable insights for the prevention of loess geological disasters and engineering safety construction.

Role of hygroscopic chloride salts on corrosion performance and hydrogen absorption of steel under cyclic wet-dry conditions

The corrosion morphology of steel under aqueous NaCl, MgCl2, and ZnCl2 droplets and the corresponding hydrogen permeation behaviour were investigated using surface characterization techniques and electrochemical methods. Under cyclic wet-dry conditions, Mg2+ and Zn2+-containing surface layers were formed on steel and the latter presented a high corrosion resistance. The most active hydrogen entry occurred under ZnCl2 during drying, while it happened under MgCl2 at low humidity. The effects of chloride salts on the formation of rust layers and hydrogen entry into steel during wet-dry cycles were discussed based on the hardness of metal cations and the deliquescence properties of salts.

Effect of glass fibre on the strength and durability of artificially cemented alluvial clay

ABSTRACT Using cement with fibers is a cost-effective way to improve soft clays’ engineering properties. This study investigates the strength, stiffness, and durability of artificially cemented alluvial clay stabilized with glass fiber. Unconfined compressive strength and shear wave velocity tests were used, along with microstructural analysis via scanning electron microscopy and energy-dispersive spectroscopy. Durability and resistance to harsh weather were evaluated using wet-dry cycles. The combination of cement and glass fiber improved the mechanical response, with 0.4% glass fiber being the most effective. A blend of 0.4% glass fiber with 13% cement showed the highest strength and stiffness improvement and reduced mass loss. This mixture, supported by unique power functions forecasting its properties, is suitable for various civil engineering projects, such as unbounded sub-layers, highway barriers, stone columns, and ground improvement.

The Effect of Wetting–Drying Cycles on the Deterioration of the Physical and Mechanical Properties of Cemented Paste Backfill in Open-Pit Coal Mines

To promote the sustainable exploitation of open-pit coal resources, waste is used as backfill material to realize the comprehensive utilization of solid waste mine resources. We proposed a mining method that is a combination of the highwall mining and filling mining methods. Cemented paste backfill (CPB) samples were prepared with high-clay-mineral-content marl particles as aggregate and normal Portland cement, sulfoaluminate cement and gypsum as cementing materials. The physical and mechanical properties and microstructural evolution of CPB with different binder ratios under wetting–drying cycles were measured. The results showed that the CPB with 0–3 wetting–drying cycles underwent shear and tensile coalescence, and that with 4–10 cycles underwent shear coalescence. The unconfined compressive strength (UCS) and elastic modulus (EM) decreased exponentially with increasing number of wetting–drying cycles but decreased exponentially and cubically with increasing porosity, respectively. The EM is more sensitive to gypsum content than the UCS. CPB deterioration was divided into an initial deterioration stage and a secondary deterioration stage. The evolution curve of the total damage variable presents an ‘S’ shape, with an initial damage stage, an accelerated damage expansion stage, a decelerated damage expansion stage and an end damage stage. The research results provide a basis for improving the recovery rate of resources under highwall conditions, and the extensive utilization of stripping materials, and promote the coordinated development of coal resource exploitation and environmental protection.

Experimental Study on Physical and Mechanical Properties of Lightweight Cellular Concrete Specimens Cast in Field and Laboratory

This paper presents a series of laboratory tests for evaluating the material properties of Lightweight cellular concrete (LCC) with different cement-to-fly ash ratios and at different ages. LCC specimens used in this study were cast in the field and/or laboratory. Large and small direct shear box tests were used to determine the shear strengths of LCC specimens. The test results show that the average wet densities for the LCC specimens cast in the laboratory ranged from 460 to 491 kg/m3, whereas the average wet densities for the specimens cast in the field ranged from 480 to 578 kg/m3 at the age of 28 days. The permeability values for the LCC specimens cast in the field ranged from 5.4 × 10-7 to 7.7 × 10-6 m/s and the permeability values for the LCC specimens cast in the laboratory ranged from 6.8 × 10-7 to 2.5 × 10-6 m/s. The measured peak friction angles of the LCC specimens from the small direct shear box tests ranged from 19° to 63°, whereas the measured peak friction angles of the LCC specimens from large direct shear box tests ranged from 23° to 79°. The average measured compressive strengths for the LCC specimens cast in the field and laboratory ranged from 0.43 to 1.15 MPa and 1.08 to 1.11 MPa at the age of 28 days, respectively. LCC specimens showed shrinkage behavior when subjected to wet–dry cycles and had good resistance to freeze–thaw cycles following ASTM D560/560M. The paper also compares the material properties of LCC measured in this study with those reported in the literature and the comparison shows good agreement overall.

Meso-scale simulation of moisture transport in concrete during wet-dry cycles using 3D RBSM conduit model with variable diffusion model

This paper introduces the 3D RBSM Conduit model, an improved simulation program based on the Rigid Body Spring Model (RBSM), designed to accurately depict the intricate phenomenon of moisture transfer within concrete. This is achieved by incorporating an expanded diffusion model into the simulation framework. The diffusion coefficient is dynamically adjusted at each location and at each time step to accurately represent the precise moisture transfer processes occurring in the concrete. This dynamic adjustment allows the program to efficiently simulate the rate of moisture transport in concrete based on the moisture degree and the dry or wet state of the material. By adapting the diffusion coefficient to the changing conditions in this way, the program achieves simulated moisture transfer rates that align closely with the real-world behavior of moisture in concrete. It offers a dynamic model of the changes in concrete transmission during the switch from drying and wetting conditions. Further, the program exhibits inherent advantages in addressing water transfer problems involving nonlinear boundary conditions and transfer equations. In this study, the program is used to simulate various processes including drying, wetting, local wetting, and combined wet-dry cycles. The results reveal the lag in wet-dry transitions between the interior and exposed surface during the wet-dry conversion process due to retained interior moisture. The simulation captures the moisture variation in the transitional zone.

A Prebiotic Precursor to Life's Phosphate Transfer System with an ATP Analog and Histidyl Peptide Organocatalysts.

Biochemistry is dependent upon enzyme catalysts accelerating key reactions. At the origin of life, prebiotic chemistry must have incorporated catalytic reactions. While this would have yielded much needed amplification of certain reaction products, it would come at the possible cost of rapidly depleting the high energy molecules that acted as chemical fuels. Biochemistry solves this problem by combining kinetically stable and thermodynamically activated molecules (e.g., ATP) with enzyme catalysts. Here, we demonstrate a prebiotic phosphate transfer system involving an ATP analog (imidazole phosphate) and histidyl peptides, which function as organocatalytic enzyme analogs. We demonstrate that histidyl peptides catalyze phosphorylations via a phosphorylated histidyl intermediate. We integrate these histidyl-catalyzed phosphorylations into a complete prebiotic scenario whereby inorganic phosphate is incorporated into organic compounds though physicochemical wet-dry cycles. Our work demonstrates a plausible system for the catalyzed production of phosphorylated compounds on the early Earth and how organocatalytic peptides, as enzyme precursors, could have played an important role in this.

Re-yellowing of chromium-contaminated soil after reduction-based remediation: Effects and mechanisms of extreme natural conditions

Chromium (VI) in soil poses a significant threat to the environment and human health. Despite efforts to remediate Cr contaminated soil (Cr-soil), instances of re-yellowing have been observed over time. To understand the causes of re-yellowing as well as the influence of overdosed chemical reductant in remediating Cr-soil, experiments on excess reducing agent interference and soil re-yellowing mechanisms under different extreme conditions were conducted. The results show that the USEPA method 3060A & 7196A combined with K2S2O8 oxidation is an effective approach to eliminate interference from excess FeSO4 reducing agents. The main causes of re-yellowing include the failure of reducing agents, disruption of soil lattice, and interactions between manganese oxides and microorganisms. Under various extreme conditions simulated across the four seasons, high temperature and drought significantly accelerated the failure of reducing agents, resulting in the poorest remediation effectiveness for Cr-soil (91.75 %). Dry-wet cycles promoted the formation of soil aggregates, negatively affecting Cr(VI) removal. While these extreme conditions caused relatively mild re-yellowing (9.46 %–16.79 %) due to minimal soil lattice damage, the potential risk of re-yellowing increases with the failure of reducing agents and the release of Cr(VI) within the lattice. Prolonged exposure to acid rain leaching and freeze-thaw cycles disrupted soil structure, leading to substantial leaching and reduction of insoluble Cr, resulting in optimal remediation effectiveness (94.37 %–97.73 %). As reducing agents gradually and the involvement of the water medium, significant re-yellowing occurred in the remediated soil (51.52 %). Mn(II) in soil enriched relevant microorganisms, and the Mn(IV)-mediated biological oxidation process was also one of the reasons for soil re-yellowing.

Effect of Wet-Dry Cycling on the Microstructure of Various Weathering Grade Sandstone

This study investigated the effect of rock-water interaction on microstructural properties of various weathering grade sandstone. Sandstone samples were acquired from the Sor-Range coal mine area, Pakistan, and were investigated using a tabletop scanning electron microscope (SEM). The characteristics of microstructures from micrographs were obtained using ImageJ software. According to the findings an increase in wet and dry cycles significantly affects the microstructures (pore spaces and microcracks). The porosity and microcracks density of sandstone increases with the number of wet and dry cycles. Furthermore, the length of microcracks increases as the weathering grade increases. As variation in rock macroscopic mechanical characteristics is directly associated with the deterioration of microstructures. Therefore, analyzing the effect of water-rock interaction in various weathering grades of rock can offer a more accurate reference index for assessing the stability of geotechnical structures.

Performance of concrete superficially treated with nano-modified coatings under sulfuric acid exposures

Protection of concrete surface layer is crucial for preserving serviceability and durability of concrete structures during their service life. Chemical attack by sulfuric acid is an aggressive exposure, commonly causing significant damage to concrete elements such as buildings' foundations and basement walls, buildings and structures affected by acid rain, industrial facilities, and wastewater treatment facilities. Hence, this study endeavored to evaluate the performance of nano-modified composites as surface treatments for concrete under severe chemical exposures. Nano-calcium carbonate and nano-clay particles were dispersed at different dosages (0, 2.5, and 5% by mass) in the neat coatings: vinyl ester (membrane-forming polymer) and silane (hydrophobic agent). Moreover, an amorphous colloidal silica (SiO2>50%) was also used as a superficial treatment for concrete. These coatings were applied to concrete specimens with water-to-binder ratios (w/b) of 0.40 (representing good quality/low penetrability concrete treated for prohibition of deterioration) and 0.60 (representing deteriorated/high penetrability concrete in need for rehabilitation). the wettability and initial transport characteristics of the coated concrete specimens were determined. In addition, the durability of superficially treated concrete specimens was examined under two aggressive exposures: full submergence in a 5% (by volume) sulfuric acid solution, and 5% sulfuric acid solution combined with wetting-drying cycles. During both exposures, the deterioration of concrete specimens was observed by visual inspection and quantified in terms of mass change. Furthermore, the damage mechanisms and coatings’ performance were studied by microstructural, mineralogical, and thermal analyses. The overall results showed that vinyl ester and vinyl ester nanocomposites significantly improved the durability of concrete specimens by an average of around 64% relative to that of the silane and silane nanocomposites; hence, they are recommended for field applications.

Micro-constructive Damage Model of Dry-Wet Cyclic Red Clay Based on Weibull Distribution

Abstract To address the strength damage of red clay under dry-wet cycles, systematic conventional triaxial tests under specific circumferential pressure and scanning electron microscope observation were carried out to describe the damage evolution of soil units under load conditions of dry-wet cycle red clay microunits based on the Weibull distribution. Damage variable expressions obeying the Weibull distribution were established and the micro-parameter pore area ratio and the macro-parameter dry-wet cycle number were introduced. The cross-scale characterization of macroscopic and microscopic parameters was realized by combining the damage mechanics equation of red clay under loading. The microscopic damage intrinsic model of red clay considering the number of dry-wet cycles was constructed. The model was verified to be reasonable and effective based on triaxial tests, in which the calculation errors of the secant modulus damage threshold, probability density function shape parameter, and dry-wet cycle red clay damage stress were within 10 %, 5 %, and 5 %, respectively.