Wet-dry Cycles Research Articles

Identifying the influencing factors of soil nitrous acid emissions using random forest model

Gaseous nitrous acid (HONO) plays an important role in atmospheric chemistry, but there is still controversy regarding its sources. Recent studies have shown that soil can emit significant amounts of HONO. In order to further investigate the impact mechanism of soil HONO emissions and refine the estimation model of soil HONO emissions fluxes, this study employed a random forest model to estimate soil HONO emission fluxes and identified key influencing factors. By measuring in the laboratory and integrating global literature on soil HONO emissions, this study analyzed the characteristics of soil HONO emissions and their relationship with environmental factors. The results indicated that croplands emit significantly more HONO than other land use types. Furthermore, during wet-dry cycles, total soil HONO emissions showed a significant positive correlation with NO2- content and clay content, and also correlated significantly with maximum HONO emissions, total NO emissions, and maximum NO emissions (P<0.001). Using a random forest model, a mapping relationship between soil environmental factors and total HONO emissions was constructed, with soil pH, NH4+, NO3-, NO2-, clay, silt, sand, total nitrogen, total carbon, total organic carbon, carbon-nitrogen ratio, and soil texture as input features. The results indicated that the model accounts for 56% of the variance in total soil HONO emissions within the test set. Feature importance analysis of the model indicated that soil texture, pH, NH4+, NO3- and NO2- were key factors in predicting soil HONO emissions. This finding provides valuable information for future predictions of soil HONO emissions.

Properties at Corrosion Sites Formed on Pure Iron during Wet-dry Cycling Test and on Steel during Exposure Test

Properties at Corrosion Sites Formed on Pure Iron during Wet-dry Cycling Test and on Steel during Exposure Test

The Impact of Soil Dry–Wet Cycles on the Mineralization of Soil Organic Carbon and Total Nitrogen in Check Dams of the Loess Plateau

Frequent soil drying and wetting cycles significantly affect the mineralization processes of soil organic carbon (SOC) and total nitrogen (STN), impacting soil quality and contributing to nutrient loss. However, the effects of these dry–wet cycles on SOC and STN mineralization in dam soil are not well understood. This study simulated four consecutive wet–dry cycles under five soil moisture gradients of 0% (CK), 5%, 10%, 15%, and 100%, and 100%, across four cycles of 7, 14, 21, and 28 days, to investigate the effects on soil aggregates, enzyme activities, and the mineralization of SOC and STN. The results indicated that soil enzyme activity peaked after two dry–wet cycles and then began to decline. The dry–wet cycles reduced the proportion of soil macro-aggregates while also decreasing the proportions of small and micro-aggregates. In contrast, the 100% treatment conditions exhibited the opposite effect. Dry–wet cycles enhanced the mineralization rates of SOC and STN, with the average mineralization rates under the 10% soil moisture content being the highest—1.78 and 2.38 times greater than the CK treatment for SOC and STN, respectively. The impact of dry–wet cycles on SOC and STN mineralization through the enzyme pathway was greater than through the aggregate pathway. These research findings provide theoretical insights and scientific references for the efficient operation and ecological protection of sedimentation dams in the Loess Plateau.

Long short term memory networks for predicting resilient Modulus of stabilized base material subject to wet-dry cycles.

The resilient modulus (MR) of different pavement materials is one of the most important input parameters for the mechanistic-empirical pavement design approach. The dynamic triaxial test is the most often used method for evaluating the MR, although it is expensive, time-consuming, and requires specialized lab facilities. The purpose of this study is to establish a new model based on Long Short-Term Memory (LSTM) networks for predicting the MR of stabilized base materials with various additives during wet-dry cycles (WDC). A laboratory dataset of 704 records has been used using input parameters, including WDC, ratio of calcium oxide to silica, alumina, and ferric oxide compound, Maximum dry density to the optimal moisture content ratio (DMR), deviator stress (σd), and confining stress (σ3). The results demonstrate that the LSTM technique is very accurate, with coefficients of determination of 0.995 and 0.980 for the training and testing datasets, respectively. The LSTM model outperforms other developed models, such as support vector regression and least squares approaches, in the literature. A sensitivity analysis study has determined that the DMR parameter is the most significant factor, while the σd parameter is the least significant factor in predicting the MR of the stabilized base material under WDC. Furthermore, the SHapley Additive exPlanations approach is employed to elucidate the optimal model and examine the impact of its features on the final result.

The Mesoscopic Damage Mechanism of Jointed Sandstone Subjected to the Action of Dry–Wet Alternating Cycles

The effect of the dry–wet cycle, characterized by periodic water level changes in the Three Gorges Reservoir, will severely degrade the bearing performance of rock formations. In order to explore the effect of the dry–wet cycle on the mesoscopic damage mechanism of jointed sandstone, a list of meso-experiments was carried out on sandstone subjected to dry–wet cycles. The pore structure, throat features and mesoscopic damage evolution of jointed sandstone with the action of the dry–wet cycle were analyzed using a-low-field nuclear magnetic resonance (NMR) technique. Subsequently, the impact on the mineral content of dry–wet cycles was studied by small angle X-ray scattering (SAXS). Based on this, the mesoscopic damage mechanism of sandstone subjected to dry–wet cycles was revealed. The results show that the effects of the drying–wetting cycle can promote the development of porous channels within sandstone, resulting in cumulative damage. Besides, with an increase in dry–wet cycles, the proportion of small pores and pore throats decreased, while the proportion of medium and large pores and pore throats increased. The combined effects of extrusion crush, tensile fracture, chemical reaction and dissolution of minerals inside the jointed sandstone contributed to the development of mesoscopic pores, resulting in the increase of porosity and permeability of rock samples under the dry–wet cycles. The results provide an important reference value for the stability evaluation of rock mass engineering under long-term dry–wet alternation.

Evolution of solidified municipal sludge used as landfill cover material under wet–dry cycles: mechanical characteristics, microstructural, and seepage properties

Evolution of solidified municipal sludge used as landfill cover material under wet–dry cycles: mechanical characteristics, microstructural, and seepage properties

Study on the Development Rule of Mudstone Cracks in Open-Pit Mine Dumps Improved with Xanthan Gum

The stability of open-pit mine slopes is crucial for safety, especially for spoil dump slopes, which are prone to cracks leading to landslides. This study investigates the use of xanthan gum (XG) to enhance the stability of mudstone in spoil dumps. Various concentrations of xanthan gum were mixed with mudstone and subjected to dry–wet cycle tests to assess the impact on crack development. Pore and crack analysis system (PCAS) was utilized for image recognition and crack analysis, comparing the efficiency of crack rate and length modification. The study found that xanthan gum addition significantly improved mudstone’s resistance to crack development post-drying shrinkage. A 2% xanthan gum content reduced the mudstone crack rate by 45% on average, while 1.5% xanthan gum reduced crack length by 46.2% and crack width by 26.3%. Xanthan gum also influenced the fractal dimension and water retention of mudstone cracks. The optimal xanthan gum content for mudstone modification was identified as between 1.5% and 2%. Scanning electron microscopy imaging and X-ray diffraction tests supported the findings, indicating that xanthan gum modifies mudstone by encapsulation and penetration in wet conditions and matrix concentration and connection in dry conditions. These results are expected to aid in the development of crack prevention methods and engineering applications for open-pit mine spoil dump slopes.

Surface instability driven by wetting-drying cycles hinders the colonization by biocrusts in Tabernas Desert

AbstractCatchment asymmetry in the Tabernas Desert suggests a relatively greater instability in the sunnier hillslope in a very early stage of catchment development due to abiotic factors, which would hinder the biocrust colonization. In the absence of erosion, such a difference in stability between opposite hillslopes could be due to differences in wetting-drying cycles. To verify this, as biocrust types assumed as successional stages are associated with different microhabitats, the surface movements of three types of physical crusts (Structural, Depositional and Island) and four biocrust types, representative of different stages of succession (Incipient, Cyanobacteria, Squamarina and Lepraria), were analyzed based on the distances calculated between markers placed on a grid on the soil surface. Two sample groups were analyzed: in situ samples, with four plots per crust type, and ex situ, with four unaltered samples per crust type extracted from the field site to control the effect of slope angle, orientation, trampling by animals, etc. Physical crusts showed greater surface instability compared to biocrusts, and this instability was influenced by the amount and frequency of precipitation. Biocrusts were more stable and elastic to surface movements, often recovering their initial position, and this stability increased throughout succession. Furthermore, the results showed that reducing instability (when sediment deposition ceases) favors colonization. Our results support the hypothesis that, in absence of erosive events, larger surface instability due to wetting-drying cycles hinders biocrust colonization on the relatively sunnier hillslopes with physical crusts; however, it is unknown where (or when) biocrust can develop.

Consolidation Enhancement of Weathered Coal Gangue Utilized for Aggregate Filling of Cement Pavement in Mining Area

The large-scale, open-air storage of coal gangue often leads to oxidation and decomposition due to natural weathering, resulting in decreased strength and instability, which limits its wider application in concrete pavement. To address these issues, this paper proposed a composite consolidation treatment for weathered coal gangue (WCG), assessing its effectiveness and enhancement mechanisms through aggregate performance tests, mixture performance tests, and microscopic visualization analyses. Results indicated that the initial and post-20 dry–wet cycle crushing values of WCG were 23.96% and 47.94%, respectively, failing to meet required standards. However, applying a composite consolidation treatment using a lithium curing agent and cement paste significantly improved WCG’s robustness and stability. After 4 days of treatment, the crushing value, impact value, and Vickers hardness of WCG had reached 18.3%, 6.58%, and 113.52 kgf/mm², respectively, fully meeting the standards for aggregate filling in mini concrete pavements. Furthermore, tests demonstrated that the lithium curing agent induced the formation of hydrated calcium silicate and calcium aluminate on both the surface and interior of the WCG, enhancing its structural stability. Approximately 5–12 wt.% of the curing agent penetrates and encapsulates the WCG, strongly bonding and reinforcing its internal weak surfaces. These findings offer potential solutions and technical insights for the large-scale management of weathered coal gangue.

Numerical simulation of strengthening/deterioration and damage development of cementitious materials under sulfate attack environment

Cementitious materials exposed to sulfate environments often suffer from the combined effects of external sulfate attack and dry wet cycling. In order to predict the long-term performance of cement-based materials in sulfur rich environments, this paper aims to establish a numerical model that can reasonably characterize the degradation process of cementitious materials in sulfate environments. Using this model, we can address durability problems common to cementitious materials in real sulphate environments, such as determining the degree of corrosion, predicting the durability life of materials, and calculating the time to failure. The model consists of three parts: transportation, chemical reactions, and material damage. We establish the degradation model for cement-based materials in sulfate environments by considering ion diffusion, water convection, chemical reactions, accumulation of corrosion products, and the development of material strengthening/degradation. Compared with existing sulfate corrosion models, this model not only considers ettringite, but also takes into account the volume changes of gypsum formation, calcium leaching, and salt crystallization precipitation, which can more reasonably simulate the sulfate corrosion process in real environments. The model can reasonably simulate the distribution pattern of ion concentration, hydration products and corrosion products in the cementitious material, and on this basis calculate the porosity of the cementitious material. In order to make the simulation results more applicable to experimental and non-destructive testing results, the model uses easily obtainable relative dynamic elastic modulus to evaluate the degree of material strengthening/degradation and predict the durability life of the material.

Role of bentonite in improving the anti-seepage durability of fly ash-based geopolymer cutoff wall backfill under dry–wet cycles

Role of bentonite in improving the anti-seepage durability of fly ash-based geopolymer cutoff wall backfill under dry–wet cycles

A straw-soy protein composite (SSPC) material: preparation, physical properties and wetting drying stability

The use of bio-based biomass construction materials has the advantage of helping to reduce fossil energy demand, protecting the environment from carbon dioxide emission and reducing the production of non-degradable waste. This paper used resin-modified soy protein (SP) adhesive to combine rice straw stalks, and made straw-soy protein composites (SSPC) material. The physical properties, compressive behavior and stability during wetting drying cycles of SSPC were measured. Due to water evaporation, the SP matrix is full of connected pores, resulting to its physical properties of small density, high shrinkage ratio and low thermal conductivity, which are 0.24 g/cm3, 16.2%, and 0.065 W/(m•K), respectively. Adding straw is helpful to the physical properties of SP matrix, leading to an obvious decrease in shrinkage ratio and thermal conductivity of SSPC, which are 8.51% and 0.075 W/m•K. Furthermore, the compressive load–displacement curves of SSPC groups divide into two types: divergent and convergent. The compressive strength of divergent samples is decided by the critical displacement determined according to the convergent specimens. It shows that straw stalk proves the positive effect on the compressive property of SP matrix. As to the mass of SSPC samples during the wetting drying cycles, it drops apparently in the initial three cycles, and becomes negligible from the fifth cycle, meaning that the stability of SSPC during wetting drying cyclic process is quite good. The research result would be helpful for using SSPC as building material, especially as thermal insulation material.

Thermo-hydro-mechanical modelling of the heterogeneous subsidence and swelling in the desiccation cracked clayey strata

Soil desiccation cracking as a consequence of severe environmental changes alters soil deformation mechanisms significantly. Therefore, this study aims to explore the effect of crack characteristics and environmental conditions on the heterogeneous deformation of desiccation-cracked soils using thermo-hydro-mechanical analyses. The model framework consists of balance equations, thermal, hydraulic, and mechanical constitutive equations, while the model scenarios were determined based on statistical analyses. The meteorological record of Qom city was used for three years, from 2015 to 2017, to capture long-term behaviour under wetting-drying cycles. Findings revealed that cracks extend the deformation range, potentially up to six times, with variation based on crack dimensions and spacing. Notably, narrower cracks experienced more pronounced deformation than wider ones. The cracked soil with a crack depth of 2.5 m showed 1.5 times higher swelling and subsidence than crack depth of 1 m. Furthermore, the wider cracks indicated a lower rate of increase in their dimensions compared to the initial state during drying. The investigation also highlights the mechanisms of soil surface shape due to swelling and shrinkage, resulting in concave and convex surfaces, respectively. The results provide new perspectives on the behaviour of fine-grained deposits in arid to semi-arid climates with deep groundwater levels.

Prediction model for equivalent exposure time in indoor dry-wet cycling tests for concrete in marine tidal zones

Chloride ion erosion poses a major threat to the durability of concrete structures in coastal environments, particularly in tidal zones with periodic seawater exposure. This study developed a predictive model based on Fick's second law, utilizing data from over 20 coastal structures across six countries. The model, grounded in the principle of equivalent free chloride ion concentration at a certain depth after a given exposure time, estimates the number of dry-wet cycles required in accelerated laboratory testing to simulate real-world conditions. It has been validated using data from actual marine structures. Key environmental factors such as temperature and humidity, along with regional climate differences, are incorporated to predict the relative deterioration rates of concrete in various marine environments. Additionally, an accelerated indoor dry-wet cycle test was designed based on the theory of environmental similarity, tracking the performance evolution of concrete. The model was verified through experiments, showing that 30 indoor dry-wet cycles correspond to 79 years of exposure in a coastal environment. The physical property changes observed in the accelerated tests further confirmed the model’s reliability and accuracy. This research provides critical insights into the impact of environmental factors on concrete degradation and offers a scientific basis for the application of accelerated laboratory testing.

Aging properties of bamboo scrimber after cyclic dry-wet exposure

In outdoor applications, bamboo scrimber structures are inevitably expose to prolonged cyclic dry-wet environments. To ensure the service life, it is necessary to understand how the bamboo scrimber behaves during dry-wet cycles. This study presents the aging properties of bamboo scrimber subjected to six cycles of dry-wet exposure. The tensile, compressive and flexural behavior of bamboo scrimber specimens were evaluated at the 1, 2, 4 and 6 cycles. The microstructures of bamboo scrimber specimens before and after the exposure were observed by scanning electron microscopy (SEM). Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) tests were conducted to identify the chemical changes in scrimber fibers and quantify the crystallinity of cellulose, respectively, which was projected to explain the reduced mechanical properties of bamboo scrimber after the exposure. The results indicated that after six aging cycles, the bamboo scrimber specimens showed mass loss (5.32 % - 6.22 %) and thickness expansion (tensile 17.97 %, compression 4.87 %, flexural 3.98 %). From SEM images, after the aging, the interfacial bond between the bamboo fibers and matrix was weakened and the cell walls of the thin-walled cells became thinner; gaps appeared between cell walls, and the inter-cellular arrangement was less compact. Regarding the tensile and flexural strengths of bamboo scrimber, after the first cycle, there was a significant decrease (29.50 %, 17.15 %); in subsequent cycles, no apparent changes were observed. It is worth mentioning that the compressive strength of the specimens after six accelerated aging cycles was slightly improved by 16.17 % due to the expansion of the specimen.

Effect of anionic polyacrylamide amendment on the climatic durability of solidified waste rock fine

In order to improve the climatic durability of solidified waste rock fine (WRF), anionic polyacrylamide (APAM) was innovatively introduced to amend solidified WRF in this study. The effects of APAM content, freeze-thaw (F-T), and wet-dry (W-D) cycles on the mechanical behaviors of solidified WRF were explored. After that, zeta potential, fourier transform infrared (FTIR) spectroscopy, and scanning electron microscope (SEM) tests were initiated to understand the behavioral mechanisms of APAM. The results show that APAM can significantly improve the mechanical properties and durability of solidified WRF, and there exist a threshold content of APAM (0.3%~0.8% in this study), beyond which the strength will decrease. The microscopic test shows that the bridging effect and the filming effect induced by APAM are considered to be the two decisive factors affecting the mechanical behavior of S-WRF. On the one hand, the linear APAM long chain enables the cohesion between particles to be stronger through ion bridging, on the other hand, the long chains cross-link with each other to form a network interwoven inside the structure, thus playing a microfabric reinforcement role and enhancing the crack resistance of the solidified matrix. In addition, life cycle assessment (LCA) further confirmed the advantages of using industrial by-products combined with APAM to amend solidified-WRF. These results provide a theoretical basis for using APAM as trace additives to mitigate climatic durability-related issues.

Effect of impact loading and acidic drying-wetting cycles on fragmentation and energy dissipation characteristics of sandstone

Effect of impact loading and acidic drying-wetting cycles on fragmentation and energy dissipation characteristics of sandstone

Macro-micro tests of cohesive soil under varied normal and shear stresses subjected to drying-wetting cycles

Macro-micro tests of cohesive soil under varied normal and shear stresses subjected to drying-wetting cycles

Experimental Study on the Mechanical Properties of C30 Molybdenum Tailings Concrete after High-Temperature and Sulfate Corrosion

In order to study the durability of molybdenum tailings concrete after a specific period of wet-dry cycle tests and exposure to high temperatures, this paper investigates the rule of change of the mechanical properties of molybdenum tailings concrete under the coupled influence of sulfate corrosion and high-temperature environmental conditions. A total of five C30 concrete prisms with molybdenum tailings content (0%, 25%, 50%, 75%, and 100%) were considered in the tests, with sulfate solution concentrations of 0 g/L, 20 g/L, and 50 g/L, and exposure temperatures of 25° at room temperature and 400° at high temperature, respectively. The test results showed that the mass loss rate of concrete prisms with different molybdenum tailings substitution rates under sulfate corrosion and high temperature environment showed an increasing and then decreasing trend. The specimens with 25% molybdenum tailings content still maintain high mechanical properties after wet-dry cycle tests of sulfate solution and high temperature, and the reduction of peak stress in this group is only 11%, and the reduction of elastic modulus is 1%; the rest of the molybdenum tailings content has a reduction of peak stress of about 25%, and the reduction of modulus of elasticity is more than 10%. The plastic deformation capacity of molybdenum tailings concrete decreases under the single-factor effects of wet-dry cycle tests of sulfate solution and high temperature effects, but the plastic deformability capacity of the specimens is enhanced under the combined effects of multiple factors. The stress-strain curve formulas for molybdenum tailings concrete under high temperature, wet-dry cycle tests of sulfate solution, and coupled wet-dry cycle tests of sulfate solution and high temperature were fitted. The results of this study can provide experimental data and valuable references for the engineering application of molybdenum tailings concrete under wet-dry cycle tests of sulfate solution and high temperature conditions, laying a foundation for further research.

Corrigendum to “Prediction model for equivalent exposure time in indoor dry-wet cycling tests for concrete in marine tidal zones” [Constr. Build. Mater. 451 (2024) 138778

Corrigendum to “Prediction model for equivalent exposure time in indoor dry-wet cycling tests for concrete in marine tidal zones” [Constr. Build. Mater. 451 (2024) 138778