A model of unfrozen water content in rock during freezing and thawing with experimental validation by nuclear magnetic resonance

The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties. This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process, considering the influence of unfrozen water film and rock pore structure, which can reflect the hysteresis and super-cooling effects. The pore size distribution curves of red sandstone and its unfrozen water content under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance (NMR) to validate the proposed model. Comparison between the experimental and calculated results indicated that the theoretical model accurately reflected the water content change law of red sandstone during the freezing and thawing process. Furthermore, the influences of Hamaker constant and surface relaxation parameter on the model results were examined. The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10^?19 J to 10^?18 J; and when the relaxation parameter of the rock surface was within 25–30 μm/ms, the calculated unfrozen water content using the proposed model was consistent with the experimental value.     

Hysteresis in the ultrasonic parameters of saturated sandstone during freezing and thawing and correlations with unfrozen water content

Determining the mechanical properties of frozen rock is highly important in cold-area engineering.These properties are essentially correlated with the content of liquid water remaining in frozen rock.Therefore, accurate determination of unfrozen water content could allow rapid evaluation of mechanical properties of frozen rock. This paper investigates the hysteresis characteristics of ultrasonic waves applied to sandstone(in terms of the parameters of P-wave velocity, amplitude, dominant frequency and quality factor Q) and their relationships with unfrozen water content during the freeze-thaw process.Their correlations are analysed in terms of their potential for use as indicators of freezing state and unfrozen water content. The results show that:(1) During a freeze-thaw cycle, the ultrasonic parameters and unfrozen water content of sandstone have significant hysteresis with changes in temperature.(2)There are three clear stages of change during freezing: supercooled stage(0℃ to -2℃), rapid freezing stage(-2℃ to -3℃), and stable freezing stage(-3℃ to -20℃). The changes in unfrozen water content and ultrasonic parameters with freezing temperature are inverse.(3) During a single freeze-thaw cycle, the ultrasonic parameters of sandstone are significantly correlated with its unfrozen water content,and this correlation is affected by the pore structure. For sandstones with mesopores greater than 50%,there are inflection points in the curves of ultrasonic parameters vs. unfrozen water content at -3℃ during freezing and at -1℃ during thawing. It was found that thermal deformation of the mineral-grain skeleton and variations in the phase composition of pore water change the propagation path of ultrasonic waves. The inflection point in the curve of dominant frequency vs. temperature clearly marks the end of the rapid freezing stage of pore water, in which more than 70% of the pore water freezes. Consequently,the dominant frequency can be used as an index to conveniently estimate the unfrozen water content of frozen rock and, hence, its mechanical properties.     

Thermal effects on fracture toughness of cracked straight-through Brazilian disk green sandstone and granite

Cracked straight-through Brazilian disc (CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700 °C. Uniaxial splitting experiments were performed using an automatic electro-hydraulic servo press to study the evolution laws of physical and fracture properties of different deep rock materials under high-temperature geological conditions. The fracture characteristics were measured using an industrial camera and digital image correlation technology to analyze the effect of high temperature on fracture properties and failure modes of the CSTBD samples after different thermal treatments. The micro-damage properties of green sandstone and granite materials were obtained using a scanning electron microscope (SEM). The following conclusions were drawn from the test results: (1) With the increasing temperature, the fracture characteristics of green sandstone and granite change from brittle fracture to plasticity fracture, the longitudinal wave velocity of granite decreases sharply at 600 °C, and the damage factor reaches 0.8748 at 700 °C. (2) The fracture toughness of green sandstone and granite decreases with increasing temperature; however, the decreasing range of granite is larger than that of green sandstone. (3) As the temperature increases, the fracture morphologies of green sandstone and granite materials become rougher, whereas thermal damage cracks of granite and intergranular fractures inside sandstone as well as pores of sandstone increase. (4) The crack tip opening displacement and peak strain corresponding to peak load increase with the temperature.     

Methods for quantifying Staphylococcus aureus in indoor air

Staphylococcus aureus has been detected in indoor air and linked to human infection. Quantifying S. aureus by efficient sampling methods followed by appropriate sample storage treatments is essential to characterize the exposure risk of humans. This laboratory study evaluated the effects of sampler type (all‐glass impinger (AGI‐30), BioSampler, and Andersen one‐stage sampler (Andersen 1‐STG)), collection fluid (deionized water (DW), phosphate‐buffered saline (PBS), and Tween mixture (TM)), and sampling time (3–60 min) on cell recovery. Effects of storage settings on bacterial concentration were also assessed over 48 h. Results showed BioSampler performed better than Andersen 1‐STG and AGI‐30 (P < 0.05) and TM was superior to PBS and DW (P < 0.05). An increase in sampling time negatively affected the recoveries of cells in PBS of BioSampler and AGI‐30 (P < 0.05), whereas cell recoveries in TM were increased at sampling of 6–15 min compared with 3 min. Concentrations of cells collected in PBS were decreased with storage time at 4 and 23°C (P < 0.05), while cells stored in TM showed stable concentrations at 4°C (P > 0.05) and increased cell counts at 23°C (P < 0.05). Overall, sampling by BioSampler with TM followed by sample transportation and storage at 4°C is recommended.     

Linking the mechanical properties of frozen sandstone to phase composition of pore water measured by LF-NMR at subzero temperatures

Water-bearing porous rocks can be greatly strengthened by freezing; its microscopic mechanisms lie in how subzero temperature modifies pore structure but have not yet been clearly defined. In this study, we link the mechanical properties of frozen sandstone to phase composition of pore water (i.e., relative amount of unfrozen water and ice). Both the strength (uniaxial compressive strength and tensile strength) and the phase composition of pore water (tested through the nuclear magnetic resonance (NMR) method) of frozen sandstone at nine subzero temperatures were measured. The results showed the following: (1) subzero temperature strengthened saturated sandstone significantly, both the strengths increased in a three-stage mode and each stage showed an approximately linear trend as temperature decreased from 0 to – 20 °C; and (2) change of phase composition with freezing displayed two distinct stages: the rapid decreasing stage of unfrozen water content (0 to – 4 °C), when bulk water and capillary water froze almost completely, and the slow decreasing stage (? 4 to – 20 °C), when adsorbed water froze partially. Based on direct observations on microscopic pore structure of sandstone and detailed discussion on the mechanical interactions between water, ice, and pore wall, phase composition may modify the mechanical properties of frozen rocks through the following effects: the supporting effect of ice under compression, the crack-filling effect of ice, the cementing effect of unfrozen water film under tension or under shearing load, and the frost damage effect. The former three are strengthening effects, while the latter one is weakening effect.

     

Effects of thermal cycles on mechanical properties of an optimized polymer concrete

The aim of this study is the design, fabrication and experimentally characterization of an optimized polymer concrete (PC). To this end, three factors, namely: the aggregate size, epoxy resin weight percentage, and chopped glass fiber percentage; are considered as the influencing factors on the compressive strength, bending strengths and interfacial shear strength between the PC and steel. The number of tests which are necessary to simultaneously optimize three above strengths of the PC are reduced based on the design of experiment using the orthogonal array technique or so-called Taguchi method. Comparison of the predicted strengths based on the Taguchi approach with the measured experimental results shows a good correlation between them. Afterward, the effect of three freeze/thaw thermal cycles; 25 °C to ?30 °C (cycle-A), 25 °C to 70 °C (cycle-B) and ?30 °C to 70 °C (cycle-C) for 7 days; on the strengths of the optimized PC is experimentally investigated. Comparison of the experimental results for the mechanical strengths measured at room temperature (RT) and above thermal cycles shows that the compressive strength of the optimally designed PC is not affected by heating and cooling cycles. On the other hand, the bending strength is more affected by exposing PC to the thermal cycle-B. The interfacial shear strength becomes affected by exposing the PC to cycles-A and -B, whereas no changes are observed on this strength by exposing to the thermal cycle-C. In general, among the three thermal cycles, cycle-B exerted the most deteriorating effect on the strengths.     

Shear strength of RC beams subjected to cyclic thermal loading

The experiments were performed for assessing the influence of cyclic thermal loading on the shear strength of reinforced concrete (RC) beam specimens. One hundred eleven RC beams of 100 × 150 × 1200 mm size reinforced in tension zone with two bars of 8, 10 and 12 mm diameters were tested under four point loading. The beams were subjected to a number of thermal cycles varying from 7 to 28 cycles with peak temperature taken as 100, 200 and 300 °C. The effects of thermal cycles on the crack pattern, failure mechanism, first crack load and the shear strength of beams have been discussed. The shear strength of the beams has been found to increase by up to 10% at lower temperature cycles of 100 and 200 °C but reduces by up to 14% at higher temperature (300 °C) depending on the severity of thermal loading. The results of study emphasize the need for developing appropriate guidelines for the design of RC structural elements used in comparatively high temperature environment with cyclic thermal loading conditions.     

Damage of concrete experiencing flexural fatigue load and closed freeze/thaw cycles simultaneously

The damage evolution of concrete subjected to 4-point flexural fatigue load and closed freeze/thaw cycles simultaneously was experimentally studied. The responses on a separate fatigue load at 20 °C and ?25 °C were tested to simulate the specimens with “thawed” or “frozen” pore water respectively. This damage, characterized by the residual strain, is 15.7% lower of the “frozen” state and 30.8% higher caused by the two loads than that of the “thawed” state. More interfacial cracking related signals were observed in the frequency domain using acoustic emission. The micrographys illustrate the cracks originate from the two damage sources, referring to the pores and the interfacial zones.     

Experimental research on the evolution laws of soil fabric of compacted clay liner in a landfill final cover under the dry–wet cycle

This paper aims to investigate the structural damage in compacted clay liner (CCL) caused by the dry–wet cycles in a landfill final cover. Experimental research is performed on the microstructure evolution of CCL under repeated dry–wet cycles and different initial compactness (90, 94, and 98 %). Results show that the pore size distribution of CCL has multifractal characteristics which can be classified into five self-similar intervals: macropore (>15 μm), medium-pore (8–15 μm), small-pore (0.3–8 μm), mesopore (0.04–0.3 μm), and micropore (<0.04 μm). The compression proportion of the different intervals is not equal and constant with the increase in compactness. Maximum compression interval is observed among small-pores and mesopores, with compactness ranging from 90 to 94 % and from 94 to 98 %, respectively. The effect of the dry–wet cycles mainly focuses on small-pores, medium-pores and macropores, while having little effect on meso-pores and micro-pores. The increase of macropores is one of the reasons for increase in the permeability of CCL, but it is not the main reason. Cracks causing by the irreversible shrinkage of pores is the main reason leading to permeability with an orders of magnitude increment, and improving the compactness can reduce the structural damage of CCL under the function of dry–wet cycles.     

Predicted percentage dissatisfied with ankle draft

Draft is unwanted local convective cooling. The draft risk model of Fanger et al. (Energy and Buildings 12 , 21‐39, 1988) estimates the percentage of people dissatisfied with air movement due to overcooling at the neck. There is no model for predicting draft at ankles, which is more relevant to stratified air distribution systems such as underfloor air distribution (UFAD) and displacement ventilation (DV). We developed a model for predicted percentage dissatisfied with ankle draft (PPD_AD) based on laboratory experiments with 110 college students. We assessed the effect on ankle draft of various combinations of air speed (nominal range: 0.1‐0.6 m/s), temperature (nominal range: 16.5‐22.5°C), turbulence intensity (at ankles), sex, and clothing insulation (<0.7 clo; lower legs uncovered and covered). The results show that whole‐body thermal sensation and air speed at ankles are the dominant parameters affecting draft. The seated subjects accepted a vertical temperature difference of up to 8°C between ankles (0.1 m) and head (1.1 m) at neutral whole‐body thermal sensation, 5°C more than the maximum difference recommended in existing standards. The developed ankle draft model can be implemented in thermal comfort and air diffuser testing standards.     

Window/door opening‐mediated bedroom ventilation and its impact on sleep quality of healthy,young adults

This work examined window/door opening as means of bedroom ventilation and the consequent effect upon occupants’ sleep, using data from 17 healthy volunteers. Bedroom CO₂ level, temperature, and relative humidity were measured over 5 days, for two cases: open window or door (internal, bedroom door), and closed window and door. Participant filled questionnaires and sleep diary provided subjective measure of sleep quality. Actigraphy objectively monitored the participants during sleep. Additionally, a FlexSensor, placed under pillows of participants, detected movement during sleep. Average CO₂ level for the Open conditions was 717 ppm (SD = 197 ppm) and for Closed conditions was 1150 ppm (SD = 463 ppm). Absolute humidity levels were similar for both conditions, while Open conditions were slightly cooler (mean = 19.7°C, SD = 1.8°C) than Closed (mean = 20.1°C, SD = 1.5°C). Results showed significant correlations (P < .001) between actigraphy data and questionnaire responses for: sleep latency (r = .45), sleep length (r = .87), and number of awakenings (r = .28). Of all analyzed sleep parameters, questionnaire‐based depth of sleep (P = .002) and actigraphy‐based sleep phase (P = .003) were significantly different between Open and Closed conditions.     

不同含水率冻融后红砂岩剪切蠕变特性

针对高海拔地区岩体在冻融作用及含水状态下的劣化特征及长期稳定性,对不同含水率红砂岩进行了冻融后核磁共振检测及剪切蠕变试验,揭示了冻融循环及含水率变化对红砂岩细观结构及蠕变特性的影响机制,据此构建合理的剪切蠕变模型。研究结果表明:在冻融作用下,饱水红砂岩呈现出由小尺寸孔隙增长向中小尺寸孔隙共同增长的趋势,而饱和红砂岩主要以中、大孔隙增长为主。在长期荷载作用下,随着含水率的增加,冻融后红砂岩的蠕变量普遍增大,而长期强度及长期折减系数显著降低,破坏前试样更易出现加速蠕变特征,破坏后试样宏观形态更为碎裂。根据红砂岩的冻融损伤及时效性损伤效应,建立了红砂岩冻融剪切蠕变模型,并对模型进行了参数优化辨识,借此验证了模型的正确性及合理性。研究结果对于冻融岩质灾害的防控和评价具有参考价值。     

Coupling effect of landfill leachate and temperature on the microstructure of stabilized clay

This paper studies the microstructure of stabilized clay polluted by landfill leachate at different temperatures. For this purpose, dynamic corrosion-stabilized clay was used to prepare mercury intrusion porosimetry and scanning electron microscopy samples by lyophilization. The results showed that a rise in temperature affects the pore structure of corrosion-stabilized clay. Macropores are easily produced when the temperature ranges from 40 to 60 °C, while cryptopores and ultramicropores appear in significant numbers if the temperature reaches 80 °C. The corresponding micrographs show a dispersed structure at temperatures of 40 to 60 °C and a clearly flower-like structure at 80 °C. Landfill leachate has obvious effects on the microstructure of stabilized clay. After corrosion processes, pore size is reduced while average pore radius is increased. Macropores increase and span a wider range. The peak of the pore size distribution curve shifts from the middle to both ends; porosity initially decreases and then increases. From the chemical point of view, this corrosion mechanism is mainly due to the growth of new material such as calcium chloro-aluminates, ettringite or dihydrate gypsum that were generated by the reaction between landfill leachate and stabilized clay.

     

Human responses to high levels of carbon dioxide and air temperature

In this study, 30 subjects were exposed to different combinations of air temperature (T_a: 24, 27, and 30°C) and CO₂ level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to T_a = 24°C, exposure to 30°C at all CO₂ levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of T_a on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO₂ from 8000 to 12 000 ppm at all T_a caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of T_a and CO₂ concentration on human responses was identified.     

Applications of glaze and decor on dimensioned andesites used in construction sector

This report presents initial results of the development process of a new product using andesites obtained from Afyon/Iscehisar region as an alternative to traditional ceramic wall and floor tiles used in construction sector. The series of characterization tests were conducted on andesite samples. Then, the samples were applied glaze for trial purposes. Analysis indicated that the andesite samples consisted of sanidine, mica and pyroxene minerals and its apparent porosity, density, water absorption and compressive strength values were 15.75%, 2610 g/cm³, 7.43% and 40.7 MPa, respectively. In heat microscope measurements, maximum sintering was recorded at 1138 °C. Linear expansion coefficient (α) of the andesite at 400 °C was 3.26 × 10^?6 K^?1. Firing performed by using the prepared glaze recipe at approximately 1160 °C produced good results in terms of body-glaze harmony. In addition, different decorative surface finishes to be used in indoor and outdoor spaces were obtained via under glaze decorative technique.     

Comparison of fibrous insulations – Cellulose and stone wool in terms of moisture properties resulting from condensation and ice formation

Cellulose fibres are often used as thermal insulation in buildings. The organic nature of cellulose fibres, however, makes the insulation sensitive to high moisture content. This study investigates the moisture performance of cellulose insulation when exposed to a subzero environment. The paper is focused on the condensation and freezing in the material and includes comparison with the authors previous studies on stone-wool insulation. While the used stone-wool samples were water-repellent due to resin binders, cellulose is a typical representative for hydrophilic thermal insulation to which any contact with water condensate can be crucial.Test specimens of loose-fill cellulose were placed in a special laboratory device providing high moisture load. During a period of 100 h the specimens were subjected to a continuous load of moisture at atmospheric conditions on one side while the other side of the specimen faced a surrounding temperature of 0, −10 and −20 °C and the laboratory tests were repeated three times for each set of the specific thermal conditions (T_i = +20 °C, T_e = 0, −10 and −20 °C). The results indicate that there are minor changes in the water vapour permeability of the specimens. The experimental data from the investigation is compared with a mathematical model that simulates moisture diffusivity of cellulose together with accumulation due to sorption and freezing, using the actual climatic data.     

Cyclic threshold shear strain in pore water pressure generation in clay in situ samples

The threshold level of the cyclic shear strain required for pore water pressure generation in clay samples is examined through the results of torsional hollow cylinder cyclic shearing tests according to JGS 0543-2009. The study confirms the previous results, namely, that the threshold cyclic shear strain is dependent on the effective consolidation stress and plasticity index (I_p). The average and standard deviations in the estimated threshold strain levels are 0.038?±?0.023% (I_p?<?30, σ′_c?$\leqq$?100?kN/m²), 0.047?±?0.016% (I_p?<?30, σ′_c?>?100?kN/m²), 0.079?±?0.028% (30?$\leqq$?I_p?<?5?0), and 0.143?±?0.041% (I_p?$\geqq$?50). As was found in past research, the levels of threshold strain for pore water pressure generation for clay are larger than those for clean sand. An increase in pore water pressure is only observed when the stiffness is reduced to around 80% of its initial value. This delay occurs because there is a difference between the cyclic threshold strain of the pore water pressure generation, γ_tp, and the cyclic threshold strain of the stiffness degradation, γ_td. Since the test procedure of JGS 0543-2009 is a standard scheme in the practical design process, it is expected that more data will become available in the near future which will allow for further discussions on threshold strain.     

A study of the thermal buckling behavior of a circular aluminum plate using the digital image correlation technique and finite element analysis

In this study, the thermal buckling behavior of a circular aluminum plate that results from thermal loading was investigated using a digital image correlation (DIC) technique. The aluminum plate was placed in a titanium ring and the structure was heated from room temperature 25 °C to 160 °C. Due to the differences in the coefficients of thermal expansion (CTEs) between aluminum and titanium, the aluminum plate buckles at a certain temperature. The buckling temperature was determined from the full-field deformation shape and temperature-displacement curve that were obtained using the DIC-based ARAMIS^® software. In order to obtain an appropriate full-field deformation, a polarized light filter was used to reduce the out-of-plane displacement error, which is an unavoidable error in the experiment. Using this method, the standard deviation of the z directional displacement was reduced from ±3.14 μm to ±2.70 μm. In addition, the results demonstrated that the measured buckling temperature was close to the theoretical buckling temperature of the circular plate in a simply supported boundary condition. In order to verify the proposed measurement method, a finite element analysis of the structure was performed using the ABAQUS software. The results of the DIC-based measurement and finite element analysis were in good agreement regarding the deformation curve tendency. The buckling temperature from the finite element method (FEM) was slightly larger than that from the experimental results due to the initial imperfections of the aluminum specimen. These results provide a good method for studying thermal buckling for the design and analysis of engineering structures in diverse fields such as aerospace engineering, oil refineries, and nuclear engineering.     

Meta-analysis of indoor temperatures in new-build housing

ABSTRACT

Despite growing concerns about overheating, a lack of evidence exists on the scale of the problem, particularly in contemporary UK housing. This paper presents the results of a meta-analysis of indoor temperatures in selected low-energy housing. Temperature data recorded at five-minute intervals in 60 dwellings across 19 demonstration projects (2012–14) were collated and analysed to investigate the prevalence of overheating. Findings evidence high summertime temperatures, with 27% of living rooms exceeding 28°C during August. Based on the Chartered Institution of Building Services Engineers (CIBSE) threshold of 5% annual occupied hours > 25°C, 57% of bedrooms and 75% of living rooms were classified as having overheated. Overall, 30% of living rooms exceeded the adaptive comfort threshold of > 3% occupied hours ΔT?≥?1?K. The results suggest a fundamental relationship between ventilation and indoor temperatures. The higher minimum and average summertime temperatures observed in mechanical ventilation with heat recovery (MVHR) homes (p?<?0.05) and lower temperature range (p?<?0.001) suggest the need for greater attention to adequate summertime ventilation provision in airtight homes. The results demonstrate a high prevalence of overheating in exemplary housing, indicating the need for greater efforts to ensure the effective implementation of strategies to minimize overheating and improve ventilation in low-energy homes.     

Ermittlung des Wasserdampfdiffusionswiderstandes von Baustoffen in Abhängigkeit von der Baustofftemperatur

Determination of the water vapour diffusion permeability of building materials in dependency on the temperature. Investigations concerning the correlation between the water vapour diffusion permeability (μ ‐value) and the temperature were done at two wood based panels (MDF and OSB), an external thermal insulation compound system, a plaster system and an EPS‐insulation. The investigations were made by analogy to the measurement method described in ISO 12572 but at the chosen temperature levels from –10, –5, 0, 10 up to 50 °C. Based on the measured results, it can be concluded, that the μ ‐value is influenced by the temperature.