Freeze-thaw Research Articles

Gelatin hydrolysate in freeze–thawed shrimp model system: retardation of weight loss and muscle protein denaturation

SummaryThis research explores the cryoprotective potential of gelatin hydrolysate by determining weight loss and physicochemical changes in the muscle protein of freeze–thawed shrimp. Shrimp treated with gelatin hydrolysate exhibited significantly higher and lower weight gain (9.20%) than those treated with distilled water (0.93%) and mixed phosphates (16.99%), respectively. Gelatin hydrolysate could lower the increasing rate of thawing and cooking loss and freezable water content in freeze–thawed shrimp (P < 0.05) and comparable to those of mixed phosphates treated shrimp (P > 0.05). As the shrimp were subjected to freeze–thawing, gelatin hydrolysate slowed the decline of protein solubility and Ca2+‐ATPase activity and mitigated the rise of surface hydrophobicity and disulfide bond content. It also delayed the shear force increase. These findings suggest that gelatin hydrolysate could be an effective alternative to traditional cryoprotectants, retarding weight loss and protein denaturation to preserve shrimp quality during freezing and frozen storage.

Phytic acid extracted cellulose nanocrystals for designing self-healing and anti-freezing hydrogels’ flexible sensor

Phytic acid (PA), a naturally occurring organic acid, has been extensively researched in various fields such as flame retardants, electroactive materials, metal coatings and flexible sensors. This study proposes a method for extracting cellulose nanocrystals (CNCs) utilizing PA and ingeniously applies them to hydrogels, endowing the hydrogels with exceptional mechanical properties, anti-freezing capabilities and high electrical conductivity. First of all, the CNCs@PA and PA were integrated into a multi-component network consisting of hyperbranched polyethyleneimine (HPEI), polyvinyl alcohol (PVA), and zinc chloride (ZnCl2), and their complex interactions resulted in the formation of a robust three-dimensional structure. Consequently, the hydrogels formed after just a single freeze–thaw cycle exhibited exceptional mechanical properties (2.6 MPa) and a significant self-healing ability (92.3 %). Moreover, the strategic addition of PA to the hydrogels effectively immobilizes H2O, providing anti-freeze properties and enabling the hydrogels to maintain their structure and performance even at −20.0 °C. Notably, following hydrolysis, PA generates a substantial number of hydrogen ions, markedly enhancing the conductivity (2.3 S/m) and a sensitivity gauge factor (GF = 2.5) of the hydrogels. This work offers a cost-effective, eco-friendly, and scalable method for the manufacturing of nanomaterials, and opens new avenues for creating anti-freeze wearable flexible sensors.

Oilfield Brine as a Source of Water and Valuable Raw Materials—Proof of Concept on a Laboratory Scale

Oilfield brine is the largest byproduct stream generated during the extraction of crude oil and natural gas and may be considered a resource for the production of potable water and valuable raw materials. The high salinity of such waters limits the application of typical membrane-based techniques. In most oilfields, waste cold energy from the process of the low-temperature separation of natural gas is available and may be used as a source of cold for the freezing desalination (FD) of brine. As a result of the FD process, two streams are obtained: partially desalinated water and concentrated brine. The partially desalinated water may be suitable for non-potable applications or as a feed for membrane desalination. The concentrated brine from the FD could be used as a feed for the recovery of selected chemicals. This paper focuses on verifying the above-described concept of the freezing desalination of oilfield brine on a laboratory scale. The brine from a Polish oilfield located in the Carpathian Foredeep was used as a feed. Four freezing–thawing stages were applied to obtain low-salinity water, which subsequently was treated by reverse osmosis. The obtained permeate meets the criteria recommended for irrigation and livestock watering. The concentrated brine enriched with iodine (48 mg/L) and lithium (14 mg/L) was subjected to recovery tests. Ion exchange resin Diaion NSA100 allowed us to recover 58% of iodine. Lithium recovery using Mn- and Ti-based sorbents varies from 52 to 93%.

Seasonal freeze‒thaw processes impact microbial communities of soil aggregates associated with soil pores on the Qinghai–Tibet Plateau

BackgroundSeasonal freeze‒thaw (FT) processes alter soil formation and cause changes in soil microbial communities, which regulate the decomposition of organic matter in alpine ecosystems. Soil aggregates are basic structural units and play a critical role in microbial habitation. However, the impact of seasonal FT processes on the distribution of microbial communities associated with soil pores in different aggregate fractions under climate change has been overlooked. In this study, we sampled soil aggregates from two typical alpine ecosystems (alpine meadow and alpine shrubland) during the seasonal FT processes (UFP: unstable freezing period, SFP: stable frozen period, UTP: unstable thawing period and STP: stable thawed period). The phospholipid fatty acid (PLFA) method was used to determine the biomass of living microbes in different aggregate fractions.ResultsThe microbial biomass of 0.25–2 mm and 0.053–0.25 mm aggregates did not change significantly during the seasonal FT process while the microbial biomass of > 2 mm aggregates presented a significant difference between the STP and UTP. Bacterial communities dominated the microbes in aggregates, accounting for over 80% of the total PLFAs. The microbial communities of soil aggregates in the surface layer were more sensitive to the seasonal FT process than those in other soil layers. In the thawing period, Gram positive bacteria (GP) was more dominant. In the freezing period, the ratio of Gram-positive to Gram-negative bacterial PLFAs (GP/GN) was low because the enrichment of plant litter facilitated the formation of organic matter. In the freezing process, pores of 30–80 μm (mesopores) favored the habitation of fungal and actinobacterial communities while total PLFAs and bacterial PLFAs were negatively correlated with mesopores in the thawing process.ConclusionsThe freezing process caused a greater variability in microbial biomass of different aggregate fractions. The thawing process increased the differences in microbial biomass among soil horizons. Mesopores of aggregates supported the habitation of actinobacterial and fungal communities while they were not conducive to bacterial growth. These findings provide a further comprehension of biodiversity and accurate estimation of global carbon cycle.

Microbially-mediated reductive dissolution of Fe-bearing minerals during freeze-thaw cycles

Constraining the role of microbes in the structural iron (Fe) reduction of iron-bearing minerals improves our understanding of sediments and ice sheets as a source of dissolved Fe (dFe) to the oceans. However, bio-mediated structural Fe-reduction has yet to be studied in cryospheric environments. Here, we show that the Fe reducing psychrophile bacterium Shewanella vesiculosa, isolated from sea ice in Antarctica, reduced structural Fe in nontronite (NAu-2) and maghemite (γ-Fe2O3), common mineral phases in glacial ice, and marine sediments in Antarctica, during two freeze–thaw cycles (−10 °C to +15 °C), resulting in the release of dFe. The modification of turbostratically disordered nontronite (ferric iron dominant phase) to discrete ordered illite-like structure (ferrous iron dominant phase), and the aggregation of altered small maghemite particles with neoformation of vivianite (Fe3(PO4)2·nH2O) indicated the microbially induced reductive dissolution of nontronite and maghemite, respectively. The biotic Fe-reduction gradually decreased and ceased as the temperature approached freezing (−8 °C), however the rection reactivated in the thawing cycle (−7 to +15 °C). No discernable biotic Fe-reduction was measured for either mineral under freezing conditions, suggesting that temperature limits the activity of the microbes. Further, and regardless of temperatures during two freeze–thaw cycles, Fe-reduction was not observed in abiotic control. Overall, these results highlight the importance of microbially induced Fe reduction during seasonal freeze–thaw cycles of ice and sediments in continuous supplying bioavailable dFe to cryospheric environments and the often Fe-limited polar oceans.

Freeze–thaw damage analysis and life prediction of modified pervious concrete based on Weibull distribution

An assessment of the freeze–thaw durability of pervious concrete was conducted using a rapid freezing method to investigate the durability of modified pervious concrete within a freeze–thaw environment. The optimal proportion of the modified material was determined by evaluating the mass-loss rate and the relative dynamic elastic modulus as indicators of freeze–thaw performance. Scanning electron microscopy (SEM) was employed to observe microcrack propagation and reaction products. A freeze–thaw damage model, based on the Weibull probability distribution, was formulated. Freeze–thaw damage analysis and life prediction assessment were carried out using curves such as freeze–thaw damage velocity curves, freeze–thaw damage acceleration curves, failure rate curves, and reliability life curves. The outcomes revealed that the inclusion of polyacrylonitrile (PAN) and silica ash had a favourable impact on improving the frost resistance of pervious concrete at later stages. The optimal proportions for PAN fibre and silica ash were determined as 0.6 % and 8 %, respectively. As the number of freeze–thaw cycles approached approximately 52.03 times, the freeze–thaw cycle velocity peaked. Subsequently, the freeze–thaw damage velocity was categorised into three stages based on the freeze–thaw damage acceleration curve. The degradation of pervious concrete due to freeze–thaw cycles followed a typical loss-type failure pattern. Notably, a 50 % increase in PAN fibre content resulted in a 62.92 % reduction in failure rate. Furthermore, a predictive analysis was conducted to estimate the lifespan of pervious concrete in a representative freeze–thaw region in China was performed.

Bioinspired chitin/gelatin composites with enhanced mechanical property

AbstractThe defensive tissues such as insect epidermis and crustacean exoskeleton in nature displayed characteristics of high strength and high toughness via multi‐level structure, which shed light on the designation of natural polymer‐based composites with enhanced mechanical property. Herein, a bioinspired strategy was used to prepare chitin/gelatin composite with improved mechanical property. Chitin hydrogels were first prepared by dissolution in NaOH/urea via freezing–thawing and then regeneration in sodium propionate, to form a heterogeneous nanofibrous structure. After coating gelatin on the chitin nanofibers, a hierarchical structure was obtained, leading to more compact and homogenous morphology. The coating process significantly strengthened the chitin nanofibrous structure and reduced the weak defect, which enhanced the tensile strength and toughness of the composite. The present work not only supplies a chitin/gelatin composite with high mechanical property but also offers a facile approach to prepare strengthening and toughening materials based on natural polymers.

Experimental study and numerical simulation verification of the macro- and micromechanical properties of the sandstone–concrete interface under freeze–thaw cycles

In cold-region tunnel engineering, the bonding surface between concrete and surrounding rock is highly susceptible to engineering disasters such as the cracking of support structures under the influence of freeze-thaw cycles, which severely affects the stability of tunnel engineering. This study investigates the macroscopic and microscopic mechanical properties of the sandstone–concrete interface under freeze–thaw cycles and reveals the microdamage and fracture evolutionary laws during the freeze–thaw loading process via the coupled expansion of water–ice particle phase changes via particle flow numerical simulation methods, aiming to provide theoretical support for the design and construction of rock–soil and tunnel engineering in high-altitude frozen soil areas. The results indicate that the interface strength characteristics of the sandstone–concrete specimens exhibit a stable decreasing trend with an increase in the number of freeze-thaw cycles and a decrease in roughness. Taking the most unfavorable condition as an example, the exacerbation of freeze-thaw deterioration resulted in shear strength reductions of 16.53%, 27.01%, and 37.17% for specimens (JRC=3.727), while an increase in roughness led to shear strength increases of 11.00% and 15.14% for specimens (NT=60 cycles). The acoustic emission characteristics during the loading process of the sandstone–concrete interface specimens reflect the microcracking evolutionary activity of the specimens quite well, and setting 1.0 as the recommended value for the precursor determination of the b-value and CV(k) index is most reasonable. Under freeze-thaw cycles, cracks first initiate partial microcracks at the interface and on the outer side of the specimen, primarily dominated by tensile cracks and evolving with a "slow–fast" trend toward both sides of the interface. Under shear stress, particles at the interface first undergo slip dislocation due to their lower bonding strength, generating cracks, subsequently inducing significant displacement of particles on both sides of the interface, resulting in crack propagation toward both sides of the interface, ultimately penetrating and forming shear bands leading to macroscopic failure.

Analysis of damage evolution and study on mesoscopic damage constitutive model of granite under freeze–thaw cycling

Analysis of damage evolution and study on mesoscopic damage constitutive model of granite under freeze–thaw cycling

A broad-spectrum broth rapidly and completely repairing the sublethal injuries of Escherichia coli caused by freezing and lactic acid alone or in combination for accurate enumeration

Pathogenic and spoilage bacteria undergo various stresses during food preservation and processing, leading to sublethal injuries. This emphasizes the need for a versatile repair broth. Furthermore, the broth should quickly revive all sublethal cells within 20 min to prevent the proliferation of intact cells for accurate counting. For this purpose, we developed a new repair medium called ERBMn in this study. After systematically examining various factors affecting sublethal injuries in both Escherichia coli K-12 and O157:H7, we identified the freezing and thawing (FT) treatment that resulted in the highest sublethal ratio for each strain. Then, five treatments were used to induce various numbers, types, and degrees of sublethal injuries for both strains: FT, lactic acid (LA), pretreatment with LA followed by FT, concurrent exposure to LA and FT, and pretreatment with FT followed by LA. Our results demonstrated that ERBMn rapidly and completely recovers all sublethal injuries within 20 min. Additionally, we confirmed no observable proliferation after a 20-min incubation in ERBMn. To the best of our knowledge, ERBMn is the first broad-spectrum repair broth for precise enumeration. It is expected to become the preferred repair broth for accurately quantifying E. coli in food for food safety.

Finite element modeling of thermal‐hydro‐mechanical coupled processes in unsaturated freezing soils considering air‐water capillary pressure and cryosuction

AbstractThis paper presents a comprehensive computational model for analyzing thermo‐hydro‐mechanical coupled processes in unsaturated porous media under frost actions. The model employs the finite element method to simulate multiphase fluid flows, heat transfer, phase change, and deformation behaviors. A new soil freezing characteristic curve model is proposed to consider the suctions from air‐water capillary pressure and water‐ice cryosuction. A total pore pressure with components from liquid water pressure, air pressure, and ice pressure is used in the effective stress law. Vapor and dry air are considered miscible gases, utilizing the ideal gas law and Dalton's law. The governing equations encompass the linear momentum balance equation, the energy balance equation, and mass conservation equations for water species (ice, liquid, and vapor) and dry air. Weak forms are formulated based on primary variables of displacement, water pressure, air pressure, and temperature. The spatial discretization is achieved through the finite element method, while temporal discretization employs the fully implicit finite difference method, resulting in a system of fully coupled nonlinear equations. To verify the proposed computational model, a numerical implementation is developed and validated against a set of experimental data from the literature. The successful verification demonstrates the robustness of the model. A detailed discussion of the contributions from phase change strain and different sources of pore pressure is also addressed.

Proof of stability of an RSV Controlled Human Infection Model challenge agent

In 2018, SGS Belgium NV developed RSV-NICA (Respiratory Syncytial Virus-Nasobronchial Infective Challenge Agent), an RSV type A challenge agent for use in RSV Controlled Human Infection Model (CHIM) studies.It is widely recognized that the stability of RSV can be influenced by a variety of environmental parameters, such as temperature and pH. Consequently, our objective was to evaluate the stability of the viral titer of RSV-NICA following five years of controlled storage and to determine the uniformity of the viral titers across different vials of a GMP-qualified batch of RSV-NICA. In addition, we examined the capacity of RSV-NICA to infect human primary airway epithelial cells (MucilAir™), the principal target cells of RSV, and evaluated the influence of single and recurrent freeze–thaw cycles on the infectious viral titer of the challenge agent.The aliquoted RSV-NICA virus stock was subjected to standard virological and molecular methods to gather data on the titer and consistency of the viral titer contained within 24 representative vials of the stock. Our findings illustrate that over a span of five years of cryo-storage, the infectious viral titer in 75% of the tested vials exhibited a comparable average infectious viral titer (4.75 ± 0.06 vs 4.99 ± 0.11; p-value = 0.14). A considerable reduction down to an undetectable level of infectious virus was observed in the remaining vials. RSV-NICA demonstrated its capacity to effectively infect differentiated human airway epithelial cells, with active virus replication detected in these cells through increasing RSV genome copy number over time. Virus tropism for ciliated cells was suggested by the inhibition of cilia beating coupled with an increase in viral RNA titers. No discernable impact on membrane barrier function of the epithelial lung tissues nor cytotoxicity was detected. Pooling of vials with infectious titers > 4.0 log10 TCID50/ml and freeze-thawing of these combined vials showed no deterioration of the infectious titer. Furthermore, pooling and re-aliquoting of vials spanning the entire range of viral titers (including vials with undetectable infectious virus) along with subjecting the vials to three repeated freeze–thaw cycles did not result in a decrease of the infectious titers in the tested vials.Taken together, our findings indicate that long-term cryo-storage of vials containing RSV-NICA challenge agent may influence the infectious viral titer of the virus, leading to a decrease in the homogeneity of this titer throughout the challenge stock. However, our study also demonstrates that when heterogeneity of the infectious titer of an RSV stock is observed, rounds of pooling, re-aliquoting and subsequent re-titration serve as an effective method not only to restore the homogeneity of the infectious titer of an RSV-A stock, but also to optimize patient-safety, scientific and operational aspects of viral inoculation of study participants during at least the period of one RSV CHIM trial. RSV-NICA is a stable, suitable CHIM challenge agent that can be utilized in efficacy trials for RSV vaccines and antiviral entities.

Enhancing concrete’s durability with graphene nano platelets insights on its freeze–thaw performance

Purpose Durability of concrete can be enhanced by reducing the pore size/volume of pores or by entrapping the pores. This can be achieved by adding concrete admixtures that have particle size finer than cement. In this study, GNP, having particle size much smaller than cement, has been introduced/added to concrete mix to control the pore size in concrete to tape out the contribution of GNP in the durability enhancement of concrete. Design/methodology/approach Different concrete mixes, at various water–cement ratios and amounts of graphene, have been manufactured to produce concrete containing three different %ages of GNP, i.e. 0%, 0.05% and 0.1%. To demonstrate the effect on durability of the concrete through the addition of GNP, these concrete samples have been subjected to repeated Freeze-Thaw cycles. Followed by testing after 28 days of curing, including weight loss, water absorption and strength, which are directly related to the durability aspect of concrete. Findings It has been observed that the addition of GNP to concrete mixes reduces the weight loss and pore size distribution and enhances tensile and compressive strength of concrete, thereby increasing the durability of concrete in unfavorable circumstances like freeze-thaw i.e. alternate hot and cold weather conditions. Originality/value This investigation presents original piece of experimental work conducted on modified concrete (GNP-based concrete). The aim is to construct the civil infrastructure in deep-cold region with increased life span and better performance.

Exploring freeze-thaw damage distribution of asphalt mixture through DIC in combination with CT

Open graded friction course (OGFC) is highly susceptible to environmental impacts such as load and clogging, due to its rich void structure and exposure to environments. Especially in cold regions, freeze–thaw (F-T) damage is inevitable for OGFC. While the existing analysis methods cannot specifically describe the material's micro-response to load or environment. Therefore, the digital image correlation (DIC) in combination with computed tomography (CT) was applied to closely examine the intricate process of F-T damage of OGFC in this research. Principal strain and strain energy were used to describe the F-T damage process and distribution. In addition, the effects of initial void content and immersion conditions on the temporal and spatial distribution of damage were discussed. The data demonstrated that the spatial distribution of F-T damage strain was uneven. During F-T cycles, the principal strain inside the OGFC during F-T cycles was generally increased, and the deformation of the sample gradually accumulated. According to the strain energy growth rate variation, the F-T damage could be divided into two stages during the 18 F-T cycles, namely, the development stage and the deceleration stage. Moreover, the crucial parts of F-T damage were determined to be at the end of the voids connected with the outside or the void interface between the aggregates and asphalt mortar. The larger initial void content would increase the strain of OGFC during F-T cycles, as well as the inhomogeneity of the strain. Furthermore, the strain energy increased considerably, and the development of F-T damage of OGFC accelerated. Under partial immersion conditions, the immersed part has large strain and strain energy due to the direct effect of F-T, and the increase in immersion depth aggravates the F-T damage.

Evaluation of fracture indices of warm mix asphalt (WMA) modified with nano-additive under pure shear and pure tear deformations

Cracks located on the road edge and curve are two pavement crack types that can reduce road safety. Providing a solution to control this type of crack can solve a large part of the concern in this case. This study innovatively bridges the research gap by evaluating the efficacy of nano-reduced graphene oxide powder (NRGOP) in enhancing the fracture resistance of warm mix asphalt (WMA) under various environmental conditions, a critical aspect previously unexplored in the pavement engineering literature. For this goal, asphalt mixtures containing different ratios of NRGOP were constructed. Then, a level of aging and damage induced by freeze–thaw were applied to the semicircular bend (SCB) and edge-notched disc bend (ENDB) specimens to understand how the changes in fracture strength, fracture crispiness, and fracture stiffness are under modes III and II (at + 15 °C and −15 °C). The finding revealed that the introduction of NRGOP increased the fracture properties of WMA mixtures, such as fracture energy (FEII or FEIII) and fracture toughness (KIIC or KIIIC), as well as fracture stiffness under pure shear and pure tear deformations. Laboratory findings at low temperatures showed that it is necessary to investigate KIIC and FEII for asphalt mixtures under non-conditions and freeze–thaw conditions. However, KIIC and FEIII were suggested for aging conditions. Therefore, in two-thirds of the results, FEII was critical, and in 100 % results, KIIIC was critical. At + 15 °C, KIIC and FEIII were more crucial for non-treated and freeze–thaw conditions, while KIIC and FEII were more critical for aging, respectively. Therefore, in two-thirds of the results, FEIII was critical, and in 100 % results, KIIC was critical. The results of this research provide insights to advance the socio-economics of pavements by controlling surface cracks in tropical and subtropical regions, which in turn increases ride quality, driver safety, and pavement maintenance costs.

Pore structure expansion and evolution in sandstone with prefabricated crack under freeze-thaw cycles based on CT scanning

Pore structure expansion and evolution in sandstone with prefabricated crack under freeze-thaw cycles based on CT scanning

The Bolt Anchorage Performance of Fractured Rock under a Freeze–Thaw Cycle Load

In circumstances influenced by freeze–thaw cycles, the strength of rock diminishes, necessitating an in-depth investigation into its corresponding anchoring support schemes. This study conducted experiments on rocks with and without fractures at angles of 0°, 45°, and 90° subjected to freeze–thaw cycles of 0, 10, 20, and 30 iterations. It explored the effects of fracture inclination, anchoring conditions, and freeze–thaw cycles on the mechanical properties of rock. The primary findings from the experiments are as follows: (1) fracture inclination significantly impacts rock strength, with the most pronounced deterioration observed in samples with a 45° fracture, exhibiting strengths and elastic moduli at 28.4% and 73.4%, respectively, of those of fracture-free samples; (2) anchoring effectively controls deformation but concurrently induces stress concentrations, resulting in Y-shaped crack formation around the anchoring rod; (3) the degree of strength reduction due to freeze–thaw cycles is angle-dependent, with fracture-free and 90° fracture samples exhibiting diminished strength post freezing, while the 45° fracture samples’ strength remains largely unchanged. Additionally, this study employed a numerical model, coupling a discrete element method (DEM) with a finite difference method (FDM), to simulate experimental conditions, yielding conclusions consistent with experimental outcomes, and notably revealing a prevalence of tensile cracks over shear cracks within samples under uniaxial compression.

Effect of Nano-TiO2 and Polypropylene Fiber on Mechanical Properties and Durability of Recycled Aggregate Concrete

In order to promote the engineering application of recycled concrete, the effects of PPF and nano-TiO2 dioxide on the mechanical properties and durability of recycled concrete were studied.Polypropylene fiber recycled concrete(PRAC) and nano-TiO2 recycled concrete(TRAC) were prepared by adding different volume contents of PPF and nano-TiO2. The experimental findings demonstrated that the PPF and nano-TiO2 improved the splitting tensile strength of RAC better than the compressive strength. When the volume content of nano-TiO2. and PPF is 0.8% and 1.0%, respectively, the corresponding splitting tensile strength of concrete reaches the maximum value(3.4 and 3.7 MPa). The contribution rates of nano-TiO2 and PPF with different volume contents to the mechanical properties of RAC have optimal values, which are 0.4 and 1.0%, respectively. The incorporation of nano-TiO2 and PPF can effectively inhibit the loss of RAC mass and the generation of pores under freeze–thaw conditions, and slow down the decrease of dynamic elastic modulus. When the volume content of PPF is 1.0% and the volume content of nano-TiO2 is 0.4%, the protection effect on the internal structure of RAC is better, and its carbon resistance is better. The results of RSM model analysis and prediction show that both PPF and nano-TiO2 can be used as admixture materials to improve the mechanical properties and durability of RAC, and the comprehensive improvement effect of PPF on RAC performance is better than that of nano-TiO2.

Laboratory Study of Liquid Nitrogen Cryo-Fracturing as an Environmentally Friendly Approach for Coalbed Methane (CBM) Reservoirs

This study evaluated two distinct cryo-fracturing techniques using liquid nitrogen (LN2). The evaluation included tests for peak compression strength, acoustic emission, and energy absorption. The experiments compared single-exposure freezing time (FT) and multiple-exposure freezing–thawing cycle (FTC) processes on dried specimens. The outcomes indicated that FTC experiments demonstrated lower uniaxial compression stress (UCS) values compared to FT experiments because, during the thawing phase, the ice inside the pores reverts to liquid as the temperature rises. The difference between average baseline experiments versus FT180 and FTC6 indicated a reduction in stress of 14.5% and 38.5%, respectively. The standard error of our experiments ranged from 0.58% for FT60 to 5.35% for FTC6. The damage factor follows a downward trend in both FT and FTC experiments as the time of LN2 treatment augments. The amount of energy that can be absorbed in elastic or plastic deformation before failure is less for FTC specimens with the same total LN2 exposure time. Samples undergoing the freezing time process demonstrate a greater and denser quantity of acoustic emissions in comparison to freezing–thawing cycle processes, suggesting a positive correlation with uniaxial compressive strength outcomes. The large network of fractures formed by the FTC and PFTC techniques indicated that they have the greatest potential as stimulation approaches. The engineering results were improved by adding the geological context, which is essential to apply these findings to coals that have comparable origins.

A laboratory study on the durability of limestone wastes in harsh environments for their suitability as aggregate in concrete

One of the critical environmental issues in the Chegeni area (Lorestan Province, western Iran) is the production of a large volume of limestone wastes during the quarrying operations. Releasing limestone wastes in the areas neighboring the quarries has caused visual damage to the environment, and adverse effects on the quality of the soil, running water, and groundwater used for agricultural and drinking water purposes. One solution to this issue can be recycling limestone wastes to produce building materials. In the present study, a comprehensive laboratory program is planned for the durability evaluation of the limestone wastes under harsh environments for their suitability as aggregate in concrete. For this purpose, five aging tests, including freeze-thawing (F-T), salt crystallization (SC), acid attack (AA), wetting-drying (WD), and heating-cooling (HC), were conducted on the limestone sample up to 60 cycles. After every 10 cycles, the physico-mechanical characteristics of the sample, including porosity (n), Brazilian tensile strength (BTS), point load index (PLI), and P-wave velocity (Vp) were determined. Moreover, the pores structure modification of the sample subjected to aging tests was examined through scanning electron microscopy (SEM). Data analyses revealed that the sample is highly vulnerable to the AA and SC processes but is durable against FT, WD, and HC actions. These results were in good agreement with the SEM data such that the sample exposed to AA and SC underwent more changes in their pore structure compared to FT, WD, and HC. Among the physico-mechanical characteristics, the Vp and PLI had the highest and the lowest accuracy, respectively, in the durability evaluation of the sample exposed to aging tests. Based on the data analysis, limestone wastes can be used as aggregate in concrete in environments with the possibility of FT, WD, and HC. However, this type of concrete is not suitable for conditions with occurrences of the AA and SC. Finally, in addition to reducing the environmentally harmful impacts of the study area, using limestone wastes as aggregate in the construction of concrete can also be a practical solution for sustainable development from an economic viewpoint. The results of the present study can be used for assessing limestone wastes produced in other areas of Iran and the world.