Strength and compressibility of cement-stabilized sludge under low-salinity dry-wet cycles: effects of cycle number and curing duration

The aim of this investigation was to study the corrosion activity in reinforced concrete exposed to different curing temperatures and durations using a wet–dry cycle corrosion test. Reinforced concrete samples were also tested under an impressed current accelerated corrosion test for comparison. In total, ten curing techniques were conducted by varying curing temperature (hot, normal and cold) and curing duration (1, 3, 7 and 28 d). These curing techniques were evaluated based on the results of wet–dry cycle, accelerated corrosion, rapid chloride permeability and chloride diffusion tests. The chloride threshold, pH value, current measurement, half-cell, mass loss and crack width readings were assessed during wet–dry cycle and impressed current corrosion tests. Heat-cured samples showed the highest chloride diffusion/permeability, shortest corrosion periods, and had the lowest chloride threshold and pH values. This was followed by cold-cured samples (28 d at 3–5°C) and then air-cured samples (28 d at 23°C). Curing samples in water for 28 d at 23°C proved to be the best curing technique. Results also showed that the impressed current accelerated corrosion test can be used effectively to evaluate and compare corrosion activities in different qualities of concrete, but cannot be used after initiation of the first crack.

Developing a low-cost, eco-friendly and sustainable pavement solution is the need of the hour to mitigate the adverse environmental effects. This study evaluates the influence of bio-enzyme stabilisation on the mechanical and durability properties of clayey soils for sustainable pavement construction. The impact of soil type, bio-enzyme dosage, and duration of curing was examined through compaction, unconfined compressive strength (UCS), and California bearing ratio (CBR). Durability was further assessed through wetting-drying (W-D) cycles, with UCS, pH, electrical conductivity (EC), and mass loss recorded after each cycle. The results showed that an optimal bio-enzyme dosage led to an increase in maximum dry unit weight (MDU) and a decrease in optimum moisture content (OMC). Mechanical properties like UCS, CBR, and resilient modulus improved significantly, reducing pavement thickness and construction costs. This study also found a strong correlation between UCS and the elastic modulus (E50) for all soils. However, durability tests revealed that repeated W-D cycles resulted in a strength reduction due to mass loss and destabilisation of calcium silicate hydrate (CSH) gel. Microstructural analyses using XRD indicate the development of cementitious products like CSH gel. Also, FESEM and EDX confirmed aggregation of particles and structural densification, which is responsible for strength gain.

The disposal of stone waste derived from the stone industry is a worldwide problem. The shortage of landfills, as well as transport costs and environmental pollution, pose a crucial problem. Additionally, as a substitute for cement that has high carbon emissions, energy consumption, and pollution, the disposal of stone wastes by utilizing solid waste-based binders as road base materials can achieve the goal of "waste for waste". However, the mechanical properties and deterioration mechanism of solid waste-based binder solidified stone waste as a road base material under complex environments remains incompletely understood. This paper reveals the durability performance of CGF all-solid waste binder (consisting of calcium carbide residue, ground granulated blast furnace slag, and fly ash) solidified stone waste through the macro and micro properties under dry-wet and freeze-thaw cycling conditions. The results showed that the dry-wet and freeze-thaw cycles have similar patterns of impacts on the CGF and cement stone waste road base materials, i.e., the stress-strain curves and damage forms were similar in exhibiting the strain-softening type, and the unconfined compressive strengths all decreased with the number of cycles and then tended to stabilize. However, the influence of dry-wet and freeze-thaw cycles on the deterioration degree was significantly different; CGF showed excellent resistance to dry-wet cycles, whereas cement was superior in freeze-thaw resistance. The deterioration grade of CGF and cement ranged from 36.15 to 47.72% and 39.38 to 47.64%, respectively, after 12 dry-wet cycles, whereas it ranged from 57.91 to 64.48% and 36.61 to 40.00% after 12 freeze-thaw cycles, respectively. The combined use of MIP and SEM confirmed that the deterioration was due to the increase in the porosity and cracks induced by dry-wet and freeze-thaw cycles, which in turn enhanced the deterioration phenomenon. This can be ascribed to the fact that small pores occupy the largest proportion and contribute to the deterioration process, and the deterioration caused by dry-wet cycles is associated with the formation of large pores through the connection of small pores, while the freeze-thaw damage is due to the increase in medium pores that are more susceptible to water intrusion. The findings provide theoretical instruction and technical support for utilizing solid waste-based binders for solidified stone waste in road base engineering.

The structural specificity and hydrological sensitivity of loess have a strong impact on its long-term stability and safety. This topic is being actively researched and focuses on the macromechanical behavior of the shear strength of loess disturbed and its micromechanisms from the perspective of the dry–wet cycle (especially involving soluble salt erosion). In this paper, the correlation between micro-structural shear functional units and macroscopic degradation behavior was established by combining the changes in physicochemical properties of mass loss, surface cracking, strength deterioration, and structural disturbance of the loess with scanning electron microscopy (SEM) microscopic images in different dry–wet cycles and different salt contents. Results revealed that with the increase in dry–wet cycles and salt content, the mass loss of soil deteriorated and the surface crack rate increased. The cohesion of soil showed an overall decreasing trend, which decreased more obviously in the early stage of the dry–wet cycle, followed by a slow decrease, and tended to be constant after nine dry–wet cycles. However, the internal friction angle increased and then decreased during the whole cycle, and its value generally changed little. According to the deterioration and decay of shear strength, it can be concluded that the structural disturbance of loess increased with the increase in dry–wet cycles and salt content. At the same time, further linear quantization fitting of the structural disturbance parameters showed that the structural parameters had a positive correlation with salt content and a power function with dry–wet cycles, where dry–wet cycles seemed to play a dominant role in the loess structural deterioration rather than salt content. The microscopic study demonstrates that the dry–wet cycles and salt content do not directly affect the cohesion and internal friction angle of soil but change the basic shear structural unit of aggregate and then cause an essential impact on c and φ, which in turn have an essential impact on soil strength attenuation. This paper not only helps to elucidate the essence of water–soil–salt structural interactions but also provides theoretical references for sustainable development research in environmental engineering, geological engineering, and other related fields.

Durability of solidified sludge with composite rapid soil stabilizer under wetting–drying cycles

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

This study addresses the durability concerns of concrete subjected to wet–dry cycles, particularly focusing on the impact of different recycled aggregate (RA) replacement percentages. Concrete is increasingly used with RAs for sustainability. However, its long‐term performance under environmental stress is not fully understood. The primary motivation of this study is to provide a comprehensive understanding of how varying replacement percentages of RAs influence concrete degradation, a key factor for improving material performance in real‐world applications. Through a series of wet–dry cycle tests, we analyze key degradation indicators, including surface texture changes, mass loss, and compressive strength. The study findings reveal that wet–dry cycles significantly alter the concrete surface, with higher RA content leading to more extensive pore formation, cracks, and surface roughness. Initially, concrete mass increases slightly due to water absorption, but after several cycles, mass loss becomes significant, particularly for higher replacement percentages, which is attributed to internal pore damage and degradation of the interface between the RAs and cement paste. Furthermore, the compressive strength declines steadily with increasing cycles, with more severe deterioration at higher replacement percentages. This decline is primarily due to microcrack propagation and degradation of the interfacial transition zone. A degradation model is developed to quantify the relationship between RA content and durability loss, offering practical recommendations for optimizing replacement percentages to balance sustainability and durability. This study provides valuable insights into enhancing the long‐term performance of concrete in environments exposed to wet–dry cycles.

This study was conducted on durability of the clayey-sand stabilized using the copper slag (CS)-based geopolymer against wetting-drying (W-D) cycles. In this investigation, the mix of 0, 10, and 15% CS and alkaline activator liquid was used. In this solution, the ratio of NaOH to Na2SiO3 is 70:30 and the weight ratio of CS to solution is 1:1. To evaluate the effects of CS content and NaOH concentration (8 M and 11 M) on the strength, durability, and microstructural variation, a series of experiments were conducted after different cycles. The tests carried out for this purpose include standard proctor compaction test, unconfined compressive strength (UCS), Atterberg limits, accumulative loss of mass, swell and shrinkage, ultrasonic P-wave velocity, pH, toxicity characteristic leaching procedure (TCLP), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) tests. The UCS results demonstrated a remarkable reduction in cycle 2 due to W-D cycles, followed by a decrease in further cycles. As a result of Atterberg limits, lower PI leads to the lower potential to swell or shrinkage; thus, the lower loss of soil mass with a higher amount of CS content is obtained. The microstructure analysis showed that with the increase in cycle number, the abundance of microcracks and voids were increased. Moreover, dissolved geopolymerization products leached due to wet cycles and formed gel becomes weaker. The results showed that all the chosen mixtures were durable and endured all 12 W-D cycles. Furthermore, their mass loss was lower than allowable mass loss content of ASTM D559, suggesting that this stabilization method was appropriate for this soil.

Cyclic wet-dry is one of the influential weathering agents which can rapidly alter the mechanical properties of soils, limiting their durability and consistent performance. This study investigates the effect of wet-dry cycles on the mechanical behaviour of bio-cemented soil. Microbial-induced carbonate precipitation-based bio-cementation is an innovative soil improvement method, which is gaining increasing attention as a potential alternative for stabilizing slope surface. As the treated surfaces are exposed to repeated rainfalls and draughts, durability analysis is essential; cyclic wet-dry tests were therefore performed as a credible indicator of durability. The soil obtained from the Hokkaido expressway slope was treated at laboratory to varying cementation levels (% CaCO3) and subjected to 50 subsequent wet-dry cycles. Physical and mechanical changes were monitored using mass loss, shear wave velocities and needle penetration tests during wet-dry cycles. The results showed that the wet-dry cycles deteriorated the physical and mechanical at two stages. The mass and S-wave velocity of specimens significantly dropped after first few cycles and then tended to reach equilibrium. The second stage of notable deterioration was observed between 30 and 50 wet-dry cycles. It is suggested that the erosion of weak and powdery deposition of CaCO3 causes the degradation at the early stage, whereas the degradation in the late stage was attributed to the microstructural deformations of intact carbonate bonds. It was also found that the increase in cementation level decreases the deterioration of bio-cemented soil under wet-dry cycles.

Wet-dry cycles and cracking are unavoidable problems of concrete structures and reduce durability by enhancing the penetration of harmful ions and water, which may have a synergistic adverse influence with severe surface damage caused by salt freeze-thaw cycles. This study aims to investigate the salt scaling resistance of ultra-high performance concrete (UHPC) under multiple harsh environments including wet-dry cycles and pre-cracking. The relationship between workability, absorption behavior, and scaling resistance with fiber content increases is assessed. Mass loss, chloride binding behavior, pore structure, and pore morphology are analyzed to describe the influences of pre-cracking and wet-dry cycles. The results reveal that the workability of fresh concrete and the distribution of steel fibers are the key factors in determining the salt scaling resistance of UHPC. Pre-cracking and wet-dry cycles inhibit the rapid scaling damage of UHPC by accelerating chloride accumulation, which reduces the icing pressure of pore liquid and refining the micropores (<200 nm) capable of remaining non-frozen at low temperatures through the chemical binding of chloride. However, the combined effect of pre-cracking and wet-dry cycles can lead to the corrosion of internal steel fibers and more scaling damage, and the crack width should not be greater than 0.1 mm.

Clay shale is a sedimentary rock composed primarily of clay particles and is prone to degradation when exposed to wet-dry cycles. Weathered clay shale exhibits low bearing capacity, posing challenges for construction and infrastructure resilience. Improving the engineering properties of such soils contributes to the development of sustainable and resilient infrastructure, aligning with Sustainable Development Goals (SDGs) Industry, Innovation, and Infrastructure and Sustainable Cities and Communities. Soil stabilization with cement is an effective method to enhance its engineering performance. This study examines the effect of cement stabilization on the grain size distribution of clay shale after durability testing. Using sieve analysis, soil gradation was evaluated after each wet-dry cycle. Cement was added to the clay shale at 2%, 5%, 7%, and 10% of the soil’s dry weight, with water content adjusted to the optimum moisture content (OMC). Durability testing involved five wet-dry cycles using the dynamic method. The results demonstrate that higher cement percentages increase the proportion of coarse grains and improve durability. After five cycles, clay shale stabilized with 10% cement exhibited high durability, with coarse-grain content exceeding 50%. This research provides a practical contribution to sustainable geotechnical engineering by quantifying the durability improvement of clay shale through cement stabilization and its potential application for resilient subgrade construction in line with global sustainability goals.

Application of wavelet transform techniques for corrosion assessment of embedded rebars in RC elements using electromechanical impedance

A tale of two very different comets: ISO and MSX measurements of dust emission from 126P/IRAS (1996) and 2P/Encke (1997)

Considering the harsh marine environment characterized by dry–wet cycles, freeze–thaw action, chloride penetration, and sulfate attack, four optimized ultra-high-performance concrete (UHPC) mix designs were developed. Durability was assessed via electric flux, dry–wet cycles, and rapid freeze–thaw tests to evaluate the effects of curing methods, aggregate types, and mineral admixtures on key durability indicators, including chloride ion permeability, compressive strength loss, and mass loss. Scanning electron microscopy (SEM) examined microstructural changes under various conditions. Results showed that curing method significantly affected chloride ion permeability and sulfate resistance. High-temperature curing (70 ± 2 °C) reduced 28-day chloride ion electric flux by about 50%, and the compressive strength loss rate of specimens subjected to sulfate attack decreased by 2.7% to 45.7% compared to standard curing. Aggregate type had minimal impact on corrosion resistance, while mineral admixtures improved durability more effectively. Frost resistance was excellent, with mass loss below 0.87% after 500 freeze–thaw cycles. SEM analysis revealed that high-temperature curing decreased free cement particles, and mineral admixtures refined pore structure, enhancing matrix compactness. Among all mixtures, Mix Proportion 4 demonstrated the best overall durability. This study offers valuable insights for UHPC design in aggressive marine conditions.

Arresting behavior of foamed concrete used in EMAS subjected to wind erosion and wet-dry cycles