Crystal Violet Staining for Colitis-associated Neoplasia-guided Delineation of Ulcerative Colitis-associated Neoplasia for Endoscopic Submucosal Dissection: A Four-case Report.

Concrete is the most widely used structural material in civil and protective engineering, and its service environments are increasingly extending toward both ends of the extreme-temperature spectrum. At the low-temperature end, liquefied natural gas (LNG) storage tanks, cryogenic liquid storage and transportation facilities, cold-region and polar engineering structures, and aerospace structures require concrete to maintain load-bearing and sealing capacities under temperatures far below ambient conditions, even under cryogenic conditions such as LNG temperatures of approximately −165 °C [,]. At the high-temperature end, building fires, nuclear containment structures, and metallurgical and energy facilities expose concrete to thermal actions of several hundred degrees Celsius [,,]. In both types of environments, the strength, stiffness, and deformation capacity of concrete vary significantly and non-monotonically with temperature. Therefore, accurate prediction of the mechanical response of concrete over the broad temperature range is a common prerequisite for structural safety design and service-performance assessment. Research on low-temperature, or cryogenic, concrete has attracted attention since the 1970s and 1980s [,] and has recently regained momentum due to the increasing demand from LNG and cold-region engineering [,]. Experimental studies generally show that, as temperature decreases, the compressive strength and elastic modulus of concrete increase, whereas the peak strain decreases and brittleness becomes more pronounced [,,,]. This strengthening is mainly attributed to the freezing of pore water: ice fills and constrains the pore space and participates in load transfer as a load-bearing phase. As a result, the magnitude of strengthening strongly depends on the moisture content and degree of saturation [,]. Moreover, this strengthening can largely recover after rewarming, showing a clear reversible character []. However, because low-temperature testing devices and loading methods have not yet been fully standardized, the available data remain scattered, and the post-peak descending branch of the stress–strain curve is particularly difficult to capture []. This creates substantial difficulty for constitutive model calibration. Moisture content and degree of saturation are therefore essential variables governing the sub-zero mechanical response. However, they are not introduced as independent state variables in the present model because the available dataset does not provide sufficiently detailed moisture histories for their calibration. The resulting temperature-dependent parameter laws should therefore be understood as conditional on the moisture state represented by the source experiments rather than as moisture-independent material laws. It should also be recognized that moisture content and degree of saturation are not secondary variables in the sub-zero response, because they control the amount of pore water available for freezing and load transfer. In the present study, however, moisture content and saturation are not introduced as independent state variables because the available datasets do not provide sufficiently consistent moisture histories for their calibration. The resulting temperature-dependent laws should therefore be understood as conditional on the moisture states represented by the source datasets, rather than as moisture-independent material relations. In comparison, the behavior of concrete at high temperatures has been more extensively investigated [,]. With increasing temperature, evaporation of free water, dehydration and decomposition of hydration products such as C–S–H gel and Ca(OH), and microcrack propagation induced by thermal incompatibility between aggregates and cement paste generally lead to reductions in strength and stiffness, a pronounced increase in peak strain, and possible explosive spalling [,]. In the temperature range of 200–400 °C, however, a non-monotonic recovery of strength is often observed due to moisture migration and re-densification of the gel structure [,]. Unlike the reversible strengthening at low temperatures, the degradation caused by dehydration and microcracking at high temperatures is irreversible after cooling and should therefore be regarded as irreversible damage [,]. It is thus evident that the temperature domains below and above 0 °C are governed by fundamentally different mechanisms, and the mechanical properties of concrete evolve non-monotonically over the entire temperature range.