Freeze-thaw Sensitivity Research Articles

Investigation on mesostructural characteristics of different pore types within asphalt mixtures under freeze–thaw cycles using CT scanning technology

The distribution of water within asphalt pavement contributes to water-induced damage, with pores serving as the primary conduit for water infiltration. However, understanding the microstructural changes in various pore types amid extreme water conditions remains limited. This study focuses on three type asphalt mixtures which common used in the surface-layer of asphalt pavement and utilises Computed Tomography (CT) technology to categorise internal pores in asphalt mixtures into isolated, semi-connected, connected, and open pores. Examining the impact of freeze–thaw cycles, the research quantifies the connectivity and evolution of each pore type in asphalt concrete. The findings reveal that after freeze–thaw cycles, small isolated pores emerge while some larger isolated pores amalgamate with open pores, leading to a reduction in isolated pores. Volumetric alterations predominantly occur in open pores, where semi-connected pores either expand autonomously or merge with existing connected pores. Overall, the pore network enlarges, yet its complexity remains relatively stable. Notably, microstructural parameters of isolated and semi-connected pores exhibit a weaker correlation compared to total and open pores, with the most robust correlation found between average coordination number, volume, and other microstructural characteristics. Among the pore types, open pores demonstrate the highest sensitivity to freeze–thaw cycles. Substantial variations in correlation coefficients and freeze–thaw sensitivity are observed across different pore types and within the same pore type with distinct microstructural parameters. Thus, a comprehensive analysis encompassing multiple microstructural parameters across diverse pore types is imperative for a thorough evaluation of pore micro characteristics.

Effects of particle size distribution of potato starch granules on rheological properties of model dough underwent multiple freezing-thawing cycles

In order to elucidate the mechanism underlying the effect of different-sizes potato starch on dough during freeze–thaw treatment, the rheological properties, moisture distribution, secondary structure, and relative crystallinity of dough were investigated. The results showed that the storage modulus (G′), loss modulus (G″), and complex modulus (|G*|) of dough increased as a result of the freeze–thaw treatment, and the effect was more obvious as the starch granular sizes increased. The higher β -sheet and T22 contents reflected the higher viscoelasticity and freeze–thaw sensitivity, which may be related to the higher degree expansion of amylose. In contrast, dough with small-sized starch had higher intermolecular interactions, and denser structure, lower water migration, showing that this has better resistance and higher stability. The presented mechanisms may contribute to the better understanding of the effects of freeze–thaw process on model dough properties.

Evaluation of polyurethane dense graded concrete prepared using the vacuum assisted resin transfer molding technology

In recent years, the polyurethane (PU) was widely investigated and applied in pavement engineering as a sustainable binder to develop pavment materials with superior mechanical and functional properties. However, the two-component PU binders exhibit rapid curing and thus it is difficult to control the material workability through paving and compaction. Hence, the precast mehtod concept has been proposed to obtain good workability as well as the optimal engineering performances of the polyurethane mixtures (PUMs) used in pavement. In the current study, a method based on the vacuum assisted resin transfer molding (VARTM) technology was developed for the precast PUMs. The results showed that the optimal VARTM-based preparation method is to perfusion the normally compacted specimens with 2 ~ 4 wt% PU content to obtain the optimal compaction uniformity and mechanical properties. Based on the developed methods, the water and freeze-thaw sensitivity of the VARTM-formed PUM samples were evaluated by performing laboratory tests. According to the immersion Marshall stability and freeze-thaw splitting tests, the VARTM-formed PUM samples showed improved Marshall and water stability comparing the performance of samples developed using a conventional compaction method. Given the above excellent performances, the VARTM-formed PUMs were validated to serve as the rapid repair pavement materials or pavement materials with high waterproof performance requirements, for example, the bridge deck paving materials. This research has made a breakthrough in the construction technology of PUMs to a large extent. It has made significant contributions to the further application and promotion of PU binder in transportation infrastructures.

Development of Freeze-Thaw Tolerant Lactobacillus rhamnosus GG by Adaptive Laboratory Evolution.

The industrial application of microorganisms as starters or probiotics requires their preservation to assure viability and metabolic activity. Freezing is routinely used for this purpose, but the cold damage caused by ice crystal formation may result in severe decrease in microbial activity. In this study, adaptive laboratory evolution (ALE) technique was applied to a lactic acid bacterium to select tolerant strains against freezing and thawing stresses. Lactobacillus rhamnosus GG was subjected to freeze-thaw-growth (FTG) for 150 cycles with four replicates. After 150 cycles, FTG-evolved mutants showed improved fitness (survival rates), faster growth rate, and shortened lag phase than those of the ancestor. Genome sequencing analysis of two evolved mutants showed genetic variants at distant loci in six genes and one intergenic space. Loss-of-function mutations were thought to alter the structure of the microbial cell membrane (one insertion in cls), peptidoglycan (two missense mutations in dacA and murQ), and capsular polysaccharides (one missense mutation in wze), resulting in an increase in cellular fluidity. Consequently, L. rhamnosus GG was successfully evolved into stress-tolerant mutants using FTG-ALE in a concerted mode at distal loci of DNA. This study reports for the first time the functioning of dacA and murQ in freeze-thaw sensitivity of cells and demonstrates that simple treatment of ALE designed appropriately can lead to an intelligent genetic changes at multiple target genes in the host microbial cell.

High-Modulus Asphalt Mixtures Modified with Acrylic Fibers for Their Use in Pavements under Severe Climate Conditions

Asphalt pavement properties (strength, durability, bearing capacity, etc.) are considerably affected by environmental conditions. Because of this fact, regions with severe climates (high thermal gradients, abundant precipitation, presence of freeze-thaw cycles, solar radiation, etc.) have serious problems in maintaining the functional integrity of these infrastructures. Thus, it is necessary to develop new materials that could extend the service life of these pavements without increasing the construction costs. Accordingly, the present paper studies the improvement of the mechanical performance of high-modulus asphalt mixtures through the addition of acrylic fibers, for their use under severe environmental conditions. For this purpose, different tests were carried out [thermal stress restrained specimen test, immersed wheel-tracking test, freeze-thaw sensitivity test, and UGR-FACT (University of Granada-Fatigue Asphalt Cracking Test)] under variable conditions (simulating cold and hot scenarios). The results show that the use of acrylic fibers improves the mechanical behavior of high-modulus asphalt mixtures (at high and low temperatures, as well as under the presence of water and ice), and could thus be considered an interesting alternative for extending the service life of asphalt pavements in severe climates.

동결-융해 풍화에 의한 암석 물성 변화 양상과 추정에 관한 연구

화강암(풍화), 석회암, 사암, 응회암, 셰일, 현무암 등 6가지 국내 암석을 대상으로 동결-융해에 의한 암석의 풍화과정을 실험하였다. 동결-융해 시 온도범위는 <TEX>$-20^{\circ}C{\sim}10^{\circ}C$</TEX>로 최대 40회까지 동결-융해를 반복하면서 비중, 공극률, 탄성파 속도, 쇼어경도를 측정하였다. 동결-융해 횟수가 증가함에 따라 공극률이 큰 화강암(w), 셰일, 현무암의 경우 기존의 균열이 성장하는 것이 뚜렷이 관찰되었고 시험편이 상하부로 분리되기도 하였다. 비중의 변화는 뚜렷이 관찰되지 않았다. 화강암(w), 셰일, 현무암의 탄성파 속도와 쇼어경도 값은 동결-융해에 의해 크게 감소하였고 석회암, 사암, 응회암의 경우 그 변화폭이 작았다. 공극률의 경우 인장강도가 작은 화강암(w), 셰일, 현무암이 크게 증가하였고 나머지 암종은 거의 변화하지 않았다. 실험 결과를 이용하여 선형 회귀식을 도출하였고, 각 회귀식의 계수와 동결-융해 풍화 민감도(=초기 공극률/초기 인장강도)와의 상관관계를 살펴보았다. 이를 이용하여 암석의 초기 물성 값만으로도 동결-융해에 의한 풍화를 예측 가능할 것으로 판단된다. Changes in rock properties due to freezing and thawing cycles ranging from <TEX>$-20^{\circ}C$</TEX> to <TEX>$10^{\circ}C$</TEX> were checked for the typical Korean rocks: granite (weathered), limestone, sandstone, tuff, shale and basalt. The porosity, seismic velocity, shore hardness and specific gravity were measured every 10 cycles for each type of rock up to 40 cycles. The specific gravity was rarely changed. Granite (w), shale and basalt decreased gradually in their shore hardness and seismic velocity values, these values for limestone, sandstone and tuff changed only a very little. The porosity increased in the granite (w), shale and basalt, whereas in the others it did not change. Due to the low tensile strength with high porosity, granite (w), shale and basalt were susceptible to the F-T cycles. A linear regression equation was calculated based on the experiment results according to properties and types of rock. The relationship between the freeze-thaw sensitivity (=initial porosity/initial tensile strength) and the coefficients of the regression equation was examined. With additional experimental data, the coefficients of the regression equation can be estimated using the F-T sensitivity. This makes it possible to predict the properties of rock as affected by freeze-thaw weathering by only measuring the initial properties without knowledge of the regression equation coefficients for each type of rock.

Insufficiency of Copper Ion Homeostasis Causes Freeze-Thaw Injury of Yeast Cells as Revealed by Indirect Gene Expression Analysis

Saccharomyces cerevisiae is exposed to freeze-thaw stress in commercial processes, including frozen dough baking. Cell viability and fermentation activity after a freeze-thaw cycle were dramatically decreased due to freeze-thaw injury. Because this type of injury involves complex phenomena, the injury mechanisms are not fully understood. We examined freeze-thaw injury by indirect gene expression analysis during postthaw incubation after freeze-thaw treatment using DNA microarray profiling. The results showed that genes involved in the homeostasis of metal ions were frequently contained in genes that were upregulated, depending on the freezing period. We assessed the phenotype of deletion mutants of the metal ion homeostasis genes that exhibited freezing period-dependent upregulation and found that the strains with deletion of the MAC1 and CTR1 genes involved in copper ion homeostasis exhibited freeze-thaw sensitivity, suggesting that copper ion homeostasis is required for freeze-thaw tolerance. We found that supplementation with copper ions during postthaw incubation increased intracellular superoxide dismutase activity and intracellular levels of reactive oxygen species were decreased. Moreover, cell viability was increased by supplementation with copper ions. These results suggest that insufficiency of copper ion homeostasis may be one of the causes of freeze-thaw injury.

Rom2p, the Rho1 GTP/GDP Exchange Factor of Saccharomyces cerevisiae, Can Mediate Stress Responses via the Ras-cAMP Pathway

The Ras-cyclic AMP pathway is connected to other nutrient-regulated signaling pathways and mediates the global stress responses of Saccharomyces cerevisiae. Here, we show that Rom2p, the Rho1 GTP/GDP exchange factor, can mediate stress responses and cell growth via the Ras-cAMP pathways. ROM2 was isolated as a suppresser of heat and NaCl sensitivity caused by the lack of the Ras-GTPase activator Ira2p or of cAMP phosphodiesterases. Subsequent analysis of strains with a rom2 deletion showed that Rom2p is essential for resistance to a variety of stresses caused by freeze-thawing, oxidants, cycloheximide, NaCl, or cobalt ions. Stress sensitivity and the growth defect caused by the rom2 deletion could be suppressed by depleting Ras or protein kinase A (PKA) activity or by overexpressing the high affinity cAMP phosphodiesterase Pde2p. In addition, overexpression of ROM2 could not rescue cells lacking the regulatory subunit of PKA, indicating that the Ras-adenylate, cyclase-PKA cascade is essential for Rom2p-mediated stress responses and cell growth. Deletion of IRA2 exacerbated the freeze-thaw sensitivity and growth defect of the rom2 mutant, indicating that Rom2p signaling may control Ras independently of IRA2. Increases in cAMP levels were detected in the rom2 deletion mutants, and these were comparable with the effects of an ira2 mutation. The effects of the deletion of ROM2 on sensitivity to hydrogen peroxide, paraquat, and cobalt ions, but not to caffeine, were reduced when a constitutive allele of RHO1 was introduced on a single copy plasmid. However, the effects of the deletion of ROM2 on sensitivity to diamide and NaCl were exacerbated. Taken together, our data indicate that Rom2p can regulate PKA activity by controlling cAMP levels via the Ras-cAMP pathway and that for those stresses related to oxidative stress, this cross-talk is probably mediated via the Rho1p-activated MAPK pathway.

Survival of Escherichia coli O157:H7 after Freezing and Thawing in Ground Beef Patties

Survival of Escherichia coli O157:H7 strains QA 326, and ATCC 43889,43894, and 43895 after freezing (−20°C, 24 h) and thawing (4°C for 12 h, 23°C for 3 h, or microwave heating of 700W for 120 s) in ground beef patties was determined by reference most probable number (MPN), hydrophobic grid membrane filter SD-39 agar, and sorbitol MacConkey agar (SMA) spread-plating methods. Populations decreased from 0.62 to 2.52 log10 CFU/g, with the extent varying significantly by strain. Strain QA 326 populations almost always decreased the most, up to 1.87 log10 CFU/g more than the least sensitive strain. Microwave heating was the most lethal thawing treatment for strain QA 326, and 4°C thawing was the most lethal treatment for strain ATCC 43894. Thawing treatments varied in relative lethality for the other two strains. For strain QA 326 (4°C and microwave thaw treatments) and strain ATCC 43889 (4 and 23°C thawing), the enumeration method significantly affected a population decrease. The SD-39 agar method best recovered strain QA 326 while the SD-39 agar method and the reference MPN method best recovered strain ATCC 43889 after 4 and 23°C thawing, respectively. The greatest difference in population decrease measured by any two methods was 0.58 log10 CFU/g. Results showed (i) a wide range in freeze-thaw sensitivity among E. coli O157:H7 strains, (ii) no thawing method had consistently and significantly greater lethality, and (iii) the reference MPN, SD-39 agar, and SMA methods differed little in ability to enumerate E. coli O157:H7.

Effects of neuraminidase on the phenotype of sindbis virus grown in fibroblasts obtained from patients with I-cell disease

Sindbis virus grown in fibroblasts obtained from patients with I-cell disease shows an exaggerated sensitivity to freezing and thawing. Vesicular stomatitis virus, but not influenza virus, has the same phenotype. Treatment of I-cell Sindbis virus with neuraminidase protects the virus from inactivation and is able to reactivate virus previously inactivated by freezing and thawing. I-cell fibroblasts have been shown to contain increased levels of bound sialic: acid. Although the I-cell viral glvcoproteins contained sialic acid, there was no evidence for excess sialic acid in the glycopeptides isolated from I-cell Sindhis viral glycoproteins. Promise digestion of I-cell viral glycoproteins released four glycopeptides S 1S 4 which co-chromatographed on Bio-Gel P6 with those released from glvcoproteins of control Sindbis virus. In both cases, treatment of the glpcopeptides with neuraminidase caused disappearance of S 1 and S 2, consistent with the removal of 2 and I residues of sialic acid from these glvcopeptides. A second phenotypic abnormality of I-cell Sindbis virus—increased sensitivity to Triton X-100—was not affected by treatment with neuraminidase. Thus, whereas the freeze-thaw sensitivity of I-cell Sindbis virus may be related to an increase in sialic acid containing glvcolipids, the Triton X-100 sensitivity may be associated with other phenotypic alterations in the viral membrane. Sindbis virus obtained from fibroblasts from a patient with mucolipidosis I, a disease associated with an isolated deficiency in neuraminidase, is mildly freeze-thaw sensitive, but (foes not show an increased sensitivity to Triton X-100.

Mechanism of freeze-thaw damage in Pseudomonas F8

Pseudomonas F8 was tested for freeze-thaw sensitivity after being washed several times with water. Survival increased to 85% in the fourth wash. Addition of 1% sodium chloride decreased survival to the level obtained when cells were frozen in brain-heart infusion broth. No differences were observed between cells grown at 5 or 23 °C. The freeze-thaw sensitivity of Pseudomonas may be due to the cell's exposure to concentrated medium salts during cooling and warming.