Wet-dry Cycles Research Articles

Effects of bacterial strains on undrained cyclic behavior of bio-cemented sand considering wetting and drying cycles

The microbial-induced calcite precipitation (MICP) technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils. However, the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions. Furthermore, the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented. Moreover, the effect of wetting-drying (WD) cycles on the cyclic characteristics of MICP-treated sand is not readily available, which may contribute to the limited adoption of MICP treatment in field applications. In this study, strain-controlled consolidated undrained (CU) cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains: Sporosarcina pasteurii and Bacillus subtilis. The treatment durations of 7 d and 14 d were considered, with an interval of 12 h between treatments. The cyclic characteristics, such as the shear modulus and damping ratio, of the MICP-treated sand with the different bacterial strains have been estimated and compared. Furthermore, the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months. The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand, considering the influence of different bacterial strains, treatment duration, and WD cycles.

Multi-scale investigation on staged deterioration mechanism of sliding-zone soils induced by reservoir fluctuations

Water level fluctuations in the reservoir deteriorate soils and rocks on the bank landslides by drying-wetting (D-W) cycles, which results in a significant decrease in mechanical properties. A comprehensive understanding of deterioration mechanism of sliding-zone soils is of great significance for interpreting the deformation behavior of landslides. However, quantitative investigation on the deterioration characteristics of soils considering the structural evolution under D-W cycles is still limited. Here, we carry out a series of laboratory tests to characterize the multi-scale deterioration of sliding-zone soils and reveal the mechanism of shear strength decay under D-W cycles. Firstly, we describe the micropores into five grades by scanning electron microscope and observe a critical change in porosity after the first three cycles. We categorize the mesoscale cracks into five classes using digital photography and observe a stepwise increase in crack area ratio. Secondly, we propose a shear strength decay model based on fractal theory which is verified by the results of consolidated undrained triaxial tests. Cohesion and friction angle of sliding-zone soils are found to show different decay patterns resulting from the staged evolution of structure. Then, structural deterioration processes including cementation destruction, pores expansion, aggregations decomposition, and clusters assembly are considered to occur to decay the shear strength differently. Finally, a three-stage deterioration mechanism associated with four structural deterioration processes is revealed, which helps to better interpret the intrinsic mechanism of shear strength decay. These findings provide the theoretical basis for the further accurate evaluation of reservoir landslides stability under water level fluctuations.

Influences of Wetting–Drying Cycles on Expansion and Shrinkage, Crack, and Leaching Behaviors of Lime Solidified Pb(II) Contaminated Expansive Soil

Influences of Wetting–Drying Cycles on Expansion and Shrinkage, Crack, and Leaching Behaviors of Lime Solidified Pb(II) Contaminated Expansive Soil

Enhanced nitrous oxide emission factors due to climate change increase the mitigation challenge in the agricultural sector.

Effective nitrogen fertilizer management is crucial for reducing nitrous oxide (N2O) emissions while ensuring food security within planetary boundaries. However, climate change might also interact with management practices to alter N2O emission and emission factors (EFs), adding further uncertainties to estimating mitigation potentials. Here, we developed a new hybrid modeling framework that integrates a machine learning model with an ensemble of eight process-based models to project EFs under different climate and nitrogen policy scenarios. Our findings reveal that EFs are dynamically modulated by environmental changes, including climate, soil properties, and nitrogen management practices. Under low-ambition nitrogen regulation policies, EF would increase from 1.18%-1.22% in 2010 to 1.27%-1.34% by 2050, representing a relative increase of 4.4%-11.4% and exceeding the IPCC tier-1 EF of 1%. This trend is particularly pronounced in tropical and subtropical regions with high nitrogen inputs, where EFs could increase by 0.14%-0.35% (relative increase of 11.9%-17%). In contrast, high-ambition policies have the potential to mitigate the increases in EF caused by climate change, possibly leading to slight decreases in EFs. Furthermore, our results demonstrate that global EFs are expected to continue rising due to warming and regional drying-wetting cycles, even in the absence of changes in nitrogen management practices. This asymmetrical influence of nitrogen fertilizers on EFs, driven by climate change, underscores the urgent need for immediate N2O emission reductions and further assessments of mitigation potentials. This hybrid modeling framework offers a computationally efficient approach to projecting future N2O emissions across various climate, soil, and nitrogen management scenarios, facilitating socio-economic assessments and policy-making efforts.

Unfolding the dynamics of ecosystems undergoing alternating wet-dry transitional states.

A significant fraction of Earth's ecosystems undergoes periodic wet-dry alternating transitional states. These globally distributed water-driven transitional ecosystems, such as intermittent rivers and coastal shorelines, have traditionally been studied as two distinct entities, whereas they constitute a single, interconnected meta-ecosystem. This has resulted in a poor conceptual and empirical understanding of water-driven transitional ecosystems. Here, we develop a conceptual framework that places the temporal availability of water as the core driver of biodiversity and functional patterns of transitional ecosystems at the global scale. Biological covers (e.g., aquatic biofilms and biocrusts) serve as an excellent model system thriving in both aquatic and terrestrial states, where their succession underscores the intricate interplay between these two states. The duration, frequency, and rate of change of wet-dry cycles impose distinct plausible scenarios where different types of biological covers can occur depending on their desiccation/hydration resistance traits. This implies that the distinct eco-evolutionary potential of biological covers, represented by their trait profiles, would support different functions while maintaining similar multifunctionality levels. By embracing multiple alternating transitional states as interconnected entities, our approach can help to better understand and manage global change impacts on biodiversity and multifunctionality in water-driven transitional ecosystems, while providing new avenues for interdisciplinary studies.

Preparation and properties of ultra-high performance concrete incorporation multi-mineral admixtures

Abstract The impact of multi-mineral admixtures on the sturdiness of ultra-high performance concrete (UHPC). In this study on the premise that multi-mineral admixtures can be utilized in UHPC, we optimized the percentage of three admixtures(limestone powder,slag, and pumice powder) that can replace cement using the Box-Behken design response surface method, and prepared UHPC specimens with multi-mineral admixtures. The rationality of the multi-mineral admixtures approach proposed in this study was confirmed by characterizing the mechanical properties and porosity of the prepared specimens. Durability was also investigated through relevant tests. The results showed that the porosity of the prepared UHPC decreased by 49.4%, the mechanical properties improved by 14.7%, the self-shrinkage and drying shrinkage decreased by 9.8% and 6.2%, respectively, and the volume stability improved. Moreover the resistance to sulfate dry-wet cycling, chloride ion permeation, and carbonization improved significantly. This study, thus, demonstrates a new type of multi-mineral admixture for UHPC with excellent mechanical properties and durability.

Investigation of the effect of relative humidity on micro lime consolidation of degraded earthen structures

Micro lime, hydrated lime (Ca (OH)2) with particle sizes of 1-3μ dispersed in isopropanol, can be used to reinforce deteriorated earthen structures. The consolidation effect depends on the amount of moisture present in the structure or in the ambient air. This study investigates the influence of different levels of relative humidity (RH) on the consolidation effect of micro lime on earthen structures, the chemical processes responsible for the consolidation and the physical changes to the structure. The aim is to gain a deeper understanding of the underlying chemical reactions and to identify a potential limit to the applicability of this consolidation method in low RH environments. The fact that many of these sites are located in arid climates greatly influences the practical application of micro lime in the conservation of historical earthen structures. To characterize the consolidation effect of micro lime, unconfined compressive strength and exposure to wet and dry cycles were used. The properties of the reaction products and the bonding between soil particles and micro lime were investigated using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). At RH levels of 25%, 45%, 65% and 90%, the unconfined compressive strength (UCS) and the modulus of deformation at 50% strength (E50) of the micro lime-reinforced specimens demonstrated an increase with humidity. This led to a significant improvement in their ability to resist the effects of dry–wet cycles. Results from thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) indicate that micro lime interacts with the soil matrix via carbonation, with the reaction rate increasing with humidity. At 25% RH, vaterite was produced and residual free lime was observed, whereas at humidity levels of 45% and above, the reaction yielded vaterite and aragonite. The lime treatment did not significantly alter the pore structure of the soil specimens. The total porosity of the specimens was only slightly reduced, with the main effect of the lime treatment being a reduction in the number of large pores.

Influence in the mechanical properties and salt erosion resistance of recycled sand UHPC made from fly ash content

This study aims to explore the impact of fly ash (FA) as a partial replacement for cement on the durability of recycled sand (RS) ultra high performance concrete (UHPC). The effects of FA content on the mechanical properties, resistance to chloride salt freezing-thawing coupling, and resistance to sulfate dry-wet cycling coupling of F-RUHPC were investigated. The results showed that FA improved the mechanical properties of F-RUHPC, with a compressive strength of up to 120.8 MPa. It also resulted in higher tensile strength compared to the control group and demonstrated excellent resistance to chloride salt freezing-thawing and sulfate dry-wet cycling. Microscopic analysis revealed a low content of free chloride ions within F-RUHPC, all below 0.08 %. Additionally, the permeability coefficient of F-RUHPC with 10 % FA was found to be the lowest under chloride salt freezing-thawing conditions. Microstructural characterization demonstrated the dense structure of UHPC. The addition of 10 % FA was found to be beneficial in improving the mechanical properties and durability of F-RUHPC, providing a theoretical reference for the development of environmentally friendly UHPC.

Microscopic simulation of mechanical tests on red-bed soft rock based on the evolutionary law of mineral composition under dry-wet cycles

The macroscopic mechanical behavior of red-bed soft rock under different drying-wetting cycles was analyzed by uniaxial/triaxial compression tests, and the evolution of mineral components was analyzed by x-ray diffraction. Considering the characteristics of porosity and mineral composition, PFC2D was used to establish the meso-particle calculation model for mechanical tests. The macro-meso cracking characteristics and mechanism of rock treated by dry-wet cycle were discussed. The results show that the content of quartz and clay minerals in rock increases under dry-wet cycle treatment. Cementation degradation between mineral particles and dissolution leads to micro-cracks between and within particles. Under compressive load, the essence of the change of the macroscopic failure mode is the change of the dominant type of the micro-crack.

Damage Characteristics and Degradation Mechanism of Silty Mudstone Under Wet–Dry Cycling

Damage Characteristics and Degradation Mechanism of Silty Mudstone Under Wet–Dry Cycling

Efficient optimization parameter calibration method-based DEM simulation for compacted loess slope under dry–wet cycling

Dry–wet cycles can cause significant deterioration of compacted loess and thus affect the safety of fill slopes. The discrete element method (DEM) can take into account the non-homogeneous, discontinuous, and anisotropic nature of the geotechnical medium, which is more capable of reflecting the mechanism and process of instability in slope stability analysis. Therefore, this paper proposes to use the DEM to analyze the stability of compacted loess slopes under dry–wet cycles. Firstly, to solve the complex calibration problem between macro and mesoscopic parameters in DEM models, an efficient parameter optimization method was proposed by introducing the chaotic particle swarm optimization with sigmoid-based acceleration coefficients algorithm (CPSOS). Secondly, during the parameter calibration, a new indicator, the bonding ratio (BR), was proposed to characterize the development of pores and cracks in compacted loess during dry–wet cycles, to reflect the impact of dry–wet action on the degradation of bonding between loess aggregates. Finally, according to the results of parameter calibration, the stability analysis model of compacted loess slope under dry–wet cycling was established. The results show that the proposed optimization calibration method can accurately reflect the trend of the stress–strain curve and strength of the actual test results under dry–wet cycles, and the BR also reflects the degradation effect of dry–wet cycles on compacted loess. The slope stability analysis shows that the DEM reflects the negative effect of dry–wet cycles on the safety factor of compacted loess slopes, as well as the trend of gradual stabilization with dry–wet cycles. The comparison with the finite element analysis results verified the accuracy of the discrete element slope stability analysis.

Optimization of All-Desert Sand Concrete Aggregate Based on Dinger–Funk Equation

In recent years, with the development of the construction industry and the wide application of concrete materials, the demand for natural resources such as sand and gravel in China has continued to grow. The Xinjiang region is rich in natural desert sand resources due to its large desert area, which are inexpensive and easy to obtain, providing new possibilities for the production of concrete materials. The use of natural desert sand as concrete aggregate not only reduces the cost of construction but also contributes to the protection of the environment and the rational development and utilization of natural resources. However, poor particle gradation in natural desert sand leads to poor concrete properties. In this study, the Dinger–Funk equation was used to optimize the aggregate gradation of natural desert sand from Toksun, Xinjiang, and concrete specimens were prepared for mechanical properties and sulfate erosion resistance tests. The test results show that the four groups of aggregates optimized by the Dinger–Funk equation are better than the single gradation and natural gradation in terms of apparent density, bulk density, void ratio, mechanical properties, and durability of concrete. Where the distribution modulus n = 0.3 was the best, the compressive strength, splitting strength, and flexural strength were increased by 13.14%, 15.71%, and 11.08%, respectively, as compared to the natural gradation. After 90 sulfate erosion and dry–wet cycles, the mass change rate and relative dynamic elastic modulus of concrete specimens first increased and then decreased, and at the distribution modulus n = 0.3, the aggregate particles of 0.3–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm accounted for 26.98%, 32.33%, and 40.69%, respectively, and the smallest of the mass change rates of durability was the best.

Mechanical properties and durability analysis of CS-CG stabilized soil: Towards sustainable subgrade soil enhancement

In this study, carbide slag (CS) and coal gangue (CG) powder were utilized to enhance the properties of the subgrade soil. CS-CG stabilized soil underwent lab experiments to assess its mechanical properties and durability. Tests included unconfined compressive strength (UCS), compressive resilient modulus (CRM), and California bearing ratio (CBR) at stabilizer dosages of 5 %, 10 %, and 15 %. Additional tests, such as dry-wet cycling, salt solution immersion, permeability, leaching, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP), were conducted specifically for the 10 % dosage. The mechanical properties and durability were comprehensively analyzed, with a microscopic investigation into pore size. Furthermore, the soil-water characteristic curve (SWCC) of CS-CG stabilized soil is derived through MIP, providing insights into its impact on the material's strength. Results showcased favorable bearing capacity and durability of CS-CG stabilized soil. The optimal mixing dosage is 10 %, with the best ratio being CS: CG= 70: 30. After 6 dry-wet cycles, UCS loss rate was 18.6 %, comparable to 4 % Portland cement (PC) stabilized soil. Dry-wet cycle characteristics surpassed PC and Lime stabilized soils. Immersion in a 5 % NaCl solution for 30 days yielded a UCS of 3.8 MPa at 28-day age, while exposure to 5 % Na2SO4 solution led to an 11.6 % strength decrease compared to NaCl. Permeability coefficient indicated low permeability akin to PC and Lime stabilized soils. Heavy metal content met standards, with minimal increase during cycles. Hydration products mainly comprised C-S-H gel, Ca(OH)2 crystals, and carbonate modification. Analysis suggested capillary and transition pores predominantly, with minimal macropores presence. Dry-wet cycles induced a marginal increase in pore size, with negligible overall impact. SWCC predicted water content (θs) ranged from 30 % to 32 %, with a slight increase in matrix suction during dry-wet cycles. CS-CG stabilized soil shows favorable mechanical properties, durability, and environmental sustainability, indicating its potential as a substitute for traditional cement and lime treatments in subgrade soil reinforcement.

Development Characteristics and Mechanism of Crack in Expansive Soil under Wet–Dry Cycling

Development Characteristics and Mechanism of Crack in Expansive Soil under Wet–Dry Cycling

Experimental study on the degradation of sandstone-petroglyph carriers in Helankou: Effects of freeze-thaw and wet-dry cycles

The Helankou petroglyphs offer precious data for understanding the lifeways of ancient pastoralists. However, in Helankou, the combination of unique climate conditions and complex hydrochemical environments has accelerated the weathering of the sandstone-petroglyph carriers, leading to numerous petroglyphs at risk of vanishing. In response, this study employed freeze-thaw and wet-dry cycle experiments to simulate the actual environmental conditions for sandstone. Subsequently, the sandstone that underwent the experiments was subjected to further testing and analysis. The goal was to comprehensively understand the performance change patterns and micro-mechanisms in sandstone under environmental stress, thus providing scientific theoretical support for Helankou petroglyph conservation. The results indicate that under the effects of freeze-thaw and wet-dry, the degradation processes can be attributed to a diverse combination of mechanisms such as swelling-shrinkage, hydrolysis, frost heave, dissolution, and salt crystallization, which alter the physical parameters, particle size distribution, mineral composition, and structural integrity of the sandstone.

Study on the effect of deformation and strength characteristics of microencapsulated phase change materials on modified silty clay under dry and wet cycles

To prevent the cracking of silty clay under cyclic wet-dry cycling (W-D), which leads to the increase of deformation and strength attenuation of silty clay, microencapsulated phase change material (mPCM) was used to improve it. The deformation and strength characteristics of silt with different dosages (1 %, 2 % and 4 %) of mPCM and their changing patterns were analyzed and studied by indoor compaction test, crack observation test, consolidation test and straight shear test, and compared with silt without modifier. The results showed that with the increase of mPCM dosage, the optimum water content of silt and the maximum dry density decreased. A 2 % dosage of mPCM inhibited the development of silty clay cracks, reduced crack width and deformation, and increased the compression modulus of the soil samples by nearly 2.3 times. Under dry and wet cycling conditions, the cohesion decay of silty clay is greater than the angle of internal friction. The addition of 2 % mPCM significantly increased the shear strength of silty clay, cohesion by nearly 2.1 times, and internal friction angle by 1.4 times. The mPCM inhibits crack development mainly by regulating the internal temperature field of soil samples, thus improving soil strength. This study provides a reference for inhibiting soil cracking from a new temperature perspective.

Properties evolution and deterioration mechanism of steel fiber reinforced concrete (SFRC) under the coupling effect of carbonation and chloride attack

Carbonation of concrete and chloride-induced corrosion of steel fiber are two potential threats to the durability of steel fiber reinforced concrete (SFRC). In this study, the properties evolution of SFRC under the coupling effect of carbonation and chloride attack was investigated, and the deterioration mechanism was also explored. Results showed that the compressive strength of SFRC increased during the 360 days under the coupling effect of carbonation and chloride attack. However, the flexural properties exhibited an increasing trend before 120 days, with peak strength and flexural toughness rising by 60.8 % and 43.9 %, respectively, followed by a subsequent decline, which were lower than initial flexural properties after 360 days. Compared to the single chloride attack, the coupling effect of carbonation and chloride attack accelerated the corrosion process of SFRC. After 360 dry-wet cycles of chlorides, the inner steel fibers within approximately 10 mm from the SFRC surface were severely corroded, while steel fibers at the deeper depths remained uncorroded despite the chlorides ions penetration depth exceeding 40 mm. Furthermore, the deterioration process and potential mechanism of SFRC was elaborated upon, which provides empirical evidence and establishing a theoretical foundation for the development of highly corrosion-resistant SFRC.

Compressed stabilised earth block synergistically valorising municipal solid waste incinerator bottom ash and sisal fiber: Strength, durability and life cycle analysis

Compressed stabilized earth blocks (CSEB) represent an eco-friendly substitute for traditional building materials, predominantly utilizing earth. Municipal Solid Waste Incineration Bottom Ash (MSWIBA) is a by-product of municipal waste treatment that can be creatively repurposed in construction projects. This research explores integrating MSWIBA as a substitute for Earth in CSEB production to conserve natural resources and repurpose waste, potentially reducing its landfill disposal. The sisal fibers (SF), often regarded as by-products of agricultural processes, offer an intriguing research material. The SF was treated with a 5 % NaOH alkaline solution to improve the CSEB bonding, increasing the flexural strength. The study aims to determine the optimal mix of stabilizers, in addition to a 10 % cement content, using various percentages of MSWIBA (10–40 % by weight of dry sand) and SF content (0.25–1 % by weight of dry soil). These blocks undergo comprehensive tests to determine their strength and durability. Wet and dry compression, flexural tests and indirect tensile tests were used to assess strength qualities, while wetting-drying cycles and acid exposure were used to determine durability. MSWIBA replaces 20 % sand in CSEB satisfying the strength. However, exceeding this amount increases void content and lowers strength, emphasizing the importance of balanced proportions for best performance. The 20 % MSWIBA and 0.75 % SF combination enhanced the compressive strength by 6.45 MPa, flexural strength by 0.92 MPa and water absorption by less than 18 %. The durability test displayed increases in compressive strength of 14.7 % and flexural strength of 93.48 % and optimized water absorption rate. Furthermore, microstructural analysis has been performed on CSEBs and the results highlight the importance of balanced cement and SF proportions for structural integrity. Life Cycle Analysis (LCA) investigation shows that construction costs using CSEB are 12.24 % higher than those with FCBs. Additionally, the study suggests that CSEB with MSWIBA and SF will be an environmentally sustainable construction material, considering factors such as energy usage, Global Warming Potential, and other environmental considerations

Strength and durability characteristics of geopolymer treated pond ash as pavement material

This study evaluated the strength and durability characteristics of pond ash (PA) treated with geopolymer (3%, 6%, 9%, 12%, and 15%, by dry weight of PA) and compared them with Portland cement and hydrated lime stabilizations at same additive contents. Unconfined compressive strength of specimens was evaluated at curing durations of 1, 3, 7, 28, and 90 days. The durability of 28-day cured stabilised specimens against wet-dry cycles, freeze-thaw cycles, water slaking cycles, water immersion, capillary action, and dispersion was assessed. Geopolymer-stabilized PA achieved higher strength and durability than cement and lime-stabilised PA. It is due to the formation of a dense microstructure with significant reaction products. PA stabilised with 3% geopolymer and 15% cement satisfies the strength properties of the cementitious subbase in flexible pavements. Whereas, 6% geopolymer content fulfils the requirements of the cementitious base in flexible pavements and the cementitious subbase in rigid pavements as per IRC: 37-2018 and IRC: 59-2015, respectively.

Durability analysis of metakaolin recycled concrete under sulphate dry and wet cycle

This study aims to enhance the durability, cost-effectiveness, and sustainability of recycled fine aggregate concrete (RFAC) subjected to the combined effects of wet-dry cycles and sulfate erosion. Dry–wet cycle tests were conducted in RFAC with different admixtures of biotite metakaolin (MK) and 15% fly ash (FA) mix (M) under 5% sulfate erosion environment. The effect of 0%, 30%, 60% and 90% recycled fine aggregate (RFA) replacement of natural fine aggregate on mass loss, cubic compressive strength, relative dynamic modulus test of RFAC, damage modeling and prediction of damage life of concrete were investigated. The results showed that the concrete cubic compressive strength and relative dynamic modulus were optimal for recycled concrete at 15% MK biotite dosing and 60% RFA substitution, and its maximum service life was accurately predicted to be about 578 cycles under 5% sulfate dry–wet cycling using Weibull function model. This study is pioneering in addressing the durability of RFAC under sulfate attack combined with wet-dry cycling, employing a novel approach of incorporating MK and FA into RFAC. The findings highlight the practical application potential for using MK and FA in RFAC to produce durable and sustainable construction materials, particularly in sulfate-exposed environments. This research addresses a critical challenge in the construction industry, providing valuable insights for developing more durable and eco-friendly construction materials and contributing to long-term sustainability goals.