Effect Of Surface Moisture Research Articles

Boundary slip and lubrication mechanisms of organic friction modifiers with effect of surface moisture

Surface moisture or humidity impacting the lubrication property is a ubiquitous phenomenon in tribological systems, which is demonstrated by a combination of molecular dynamics (MD) simulation and experiment for the organic friction modifier (OFM)-containing lubricant. The stearic acid and poly-α-olefin 4cSt (PAO4) were chosen as the OFM and base oil molecules, respectively. The physical adsorption indicates that on the moist surface water molecules are preferentially adsorbed on friction surface, and even make OFM adsorption film thoroughly leave surface and mix with base oil. In shear process, the adsorption of water film and desorption OFM film are further enhanced, particularly under higher shear rate. The simulated friction coefficient (that is proportional to shear rate) increases firstly and then decreases with thickening water film, in good agreement with experiments, while the slip length shows a contrary change. The wear increases with humidity due to tribochemistry revealing the continuous formation and removal of Si-O-Si network. The tribological discrepancy of OFM-containing lubricant in dry and humid conditions is attributed to the slip plane’s transformation from the interface between OFM adsorption film and lubricant bulk to the interface between adsorbed water films. This work provides a new thought to understand the boundary lubrication and failure of lubricant in humid environments, likely water is not always harmful in oil lubrication systems.

Underground hyperspectral outcrop scanning for automated mine‐face mapping: The lithium deposit of Zinnwald/Cínovec

AbstractThe inherent complexity of underground mining requires highly selective ore extraction and adaptive mine planning. Repeated geological face mapping and reinterpretation throughout mine life is therefore routine in underground mines. Hyperspectral imaging (HSI) has successfully been applied to enhance geological mapping in surface mining environments, but remains a largely unexplored opportunity in underground operations due to challenges associated with illumination, wet surfaces and data corrections. In this study, we propose a workflow that paves the way for the operational use of HSI in active underground mines. In a laboratory set‐up, we evaluated different hyperspectral sensors and lighting set‐ups as well as the effect of surface moisture. We then acquired hyperspectral data in an underground mine of the Zinnwald/Cínovec Sn‐W‐Li greisen‐type deposit in Germany. These data were corrected for illumination effects, back‐projected into three dimensions and then used to map mineral abundance and estimate Li content across the mine face. We validated the results with handheld laser‐induced breakdown spectroscopy. Despite remaining challenges, we hope this study will help establish hyperspectral sensors in the extractive industry as a means to increase the volume and efficiency of raw material supply, advance digitalisation, and reduce the environmental footprint and other risks associated with underground mining.

Numerical and experimental study on the drying process of iron ore in wagons

Dust emissions resulting from handling and transporting particulate materials are a problem in the mining industry. These emissions are more accentuated when the materials are not very humid because the reduced humidity makes the particles lighter and more susceptible to dispersion. Faced with these issues, this study proposes a methodology for the theoretical and experimental study of the drying process that occurs when iron ore fines are transported in wagons. The objective is to clarify the effect of surface moisture in the process of dragging wind iron ores on moist surfaces, such as those found when transporting iron ore in open wagons. In this study, wind tunnel tests were carried out using a wagon model with fine iron ore. A numerical CFD model was developed, and the results agreed well with the experimental results. The numerical model allowed the evaluation of the drying behavior for different values of air flow velocity and the prediction of the thermal conditions that influence the drying process.

Molecular-level investigation on the effect of surface moisture on the bonding behavior of cement-epoxy interface

Epoxy resins are widely used as construction and repair materials. However, their bond with the concrete substrate under wet conditions is of concern as the loss of compatibility will lead to the failure of the bonded system. The reported study investigated the effect of surface moisture at the epoxy/cement interface using molecular dynamics (MD) simulation. The model of the interface was built using calcium silicate hydrate (C–S–H), as a hydrated cement substrate and diglycidyl ether of bisphenol-F (DGEBF) as an epoxy resin. Subsequently, different layers of water molecules were inserted into the model to represent varying moisture concentrations at the interface. The interfacial properties of the dry and wet models were evaluated in terms of adhesion, debonding, and energy ratios. In addition, the radial distribution function (RDF) was employed to deeply investigate the atomic interaction between the cement surface and epoxy. The results of the model indicated that the adhesion properties were adversely affected by the presence of moisture at the epoxy/cement interface. The degradation in the adhesion at moisture contents of 3% and 6% was 37.49% and 72.02%, respectively. Additionally, it was found that the detachment increased, as evident from the values of debonding, at higher moisture contents due to an increase in the adhesion between the C–S–H and water molecules where the latter form hydrogen bonds with the substrate. This work provides valuable molecular-level insights into the epoxy/cement bond that can be used to design new epoxy resins suited for cement and concrete applications.

Experimental Study of the Effects of Moisture on the Performance of Concrete Pavement Joint Sealants

Joint sealants play an important role in maintaining concrete pavement. They reduce or prevent numerous distresses, including spalling, faulting, and subbase erosion damage. The successful maintenance of such joint sealants is closely linked to a satisfactory lifespan for rigid pavement. However, it has been found that many sealants often fail in the early stages, as a result of inadequate or insufficient joint preparation. This study examined the effects of moisture content on bond strength, the main cause of joint sealant failure. Sealant use in various climatic regions throughout the United States was examined and Departments of Transportation were surveyed with regard to how they handled moisture. The survey showed that in cold-freeze areas, hot-pour sealants were preferred over silicone, and most states visually inspected the moisture condition of joint reservoirs. This research evaluated the effects of surface moisture on the tensile bond strength between a joint sealant and reservoir. In addition, an indirect measurement method was applied to estimate the reduction in bond strength in response to excessive moisture on the reservoir wall at the allowable strain. The causes of degradation in adhesion strength were evaluated by measuring the sealant wetting angle. Finally, it was determined that, while the choice of sealant may depend on the climate, those not currently preferred in wet-freeze regions could be used if accompanied by proper pretreatment and moisture control, contributing to the stable lifespan of joint sealants and concrete pavement alike.

Effect of Surface Moisture on Bur-cut Dentin on Bonding of HEMA-free and HEMA-containing Universal Adhesives with or without Methacrylamide Monomer.

The effect of surface moisture on bur-cut dentin on the microtensile bond strength (μTBS) of universal adhesives with various contents of 2-hydroxyethyl methacrylate (HEMA) and methacrylamide monomers was evaluated. Flat mid-coronal dentin surfaces of human molars were exposed, and a standardized smear layer was prepared using a fine-grit diamond bur. The surfaces were either left wet or air dried for 10 s before bonding with Clearfil Universal Bond Quick (UBQ), experimental UBQ without an amide monomer (UBQexp), Scotchbond Universal (SBU), Prime&Bond Universal (PBU), or BeautiBond Universal (BBU). The specimens were built up with resin composite, sectioned into sticks and subjected to the μTBS test after 24 h or 10,000 thermal cycles. The μTBS data were analyzed using three-way ANOVA followed by pairwise comparisons with Bonferroni's correction (α = 0.05). The level of dentin moisture did not significantly affect μTBS of UBQ and BBU (p > 0.05). HEMA-containing UBQ, UBQexp, and SBU exhibited higher μTBS to dry dentin, while HEMA-free PBU and BBU showed higher μTBS to wet dentin. Thermocycling significantly decreased the μTBS of UBQexp (p < 0.01) and BBU (p < 0.001) irrespective of dentin moisture level, while SBU was significantly affected only on dry dentin (p < 0.001). Thermocycling had no significant effect on UBQ and PBU containing methacrylamide monomers (p > 0.05). Dry surfaces enabled obtaining optimal bonding for HEMA-containing adhesives to bur-cut dentin, while wet surfaces enabled optimal bonding for HEMA-free adhesives. Methacrylamide monomers could contribute to the improvement of the initial and long-term bonding performance of universal adhesives to bur-cut dentin.

FDTD Simulation for Moisture Asphalt Pavement Thickness and Density Estimation Utilizing Ground Penetrating Radar

Ground penetrating radar (GPR) has the potential to estimate the thickness and density of asphalt pavement during compaction. However, the surface moisture sprayed by the compactor interferes with the accuracy of data collection significantly. This study proposed an approach based on the extended common midpoint (XCMP) method to minimize the effect of surface moisture. Both the numerical simulation of finite-difference time-domain (FDTD) and laboratory experiments were carried out to study the effect of the surface moisture on the GPR signal. Then, three FDTD models with different incident angles of GPR signal were established, and the difference of time intervals obtained from dry and moisture pavements with each model was studied to propose a proper antennas installation mode. Finally, the thickness and density estimated using the proposed method and surface reflection method were compared to validate the accuracy of the proposed approach. The results show that: 1) FDTD models were verified to simulate the interaction of GPR signal with moisture pavement effectively; 2) the time interval of the GPR signal between the surface and bottom of AC layer increased as the thin wet layer dielectric constant grew, and remained unaffected by the electric conductivity of the thin wet layer; 3) the average error of thickness and density predicted utilizing the proposed method were less than 1.3% and 2.4%, respectively, undercomplicated compaction conditions. This study notes that compaction monitoring in real time could benefit from the proposed method.

Effect of surface moisture on air-permeability kT and its correction

It is a well-known fact that moisture in the pores hinders the flow of gas through them, thus having a strong effect on the gas-permeability of concrete. Contrary to laboratory tests, where specimens can be preconditioned by drying, site air-permeability tests are normally conducted under the natural moisture conditions prevailing at the moment of the measurement. Swiss Standard SIA262/1-E: 2019 prescribes that the site air-permeability test (double vacuum cell or Torrent method) is applicable to measure the air-permeability coefficient, kT, only when the surface moisture content m does not exceed 5.5%, m measured with an electrical impedance-based instrument. This paper analyses 50 sets of parallel data of kT and m, recorded during different drying processes, originated from five independent investigations. The analysis confirms that a relation of the type $$kT = kT_{0} \cdot e^{ - \delta \cdot m}$$ can be fitted to the large majority of the cases ( $$\overline{R} = 0.95)$$ , with δ falling within 1.0–2.0 in 84% of the 50 cases analysed, with a median value of 1.45. This analysis allows the authors to propose a practical method to correct the effect of m on kT, the robustness of which is verified by a sensitive analysis. The correction is of little practical relevance for surface moistures between 4.5% and 5.5%. It is expected that this correction may be included in future versions of standards.

Surface moisture increases microcracking and water vapour permeance of apple fruit skin.

Surface moisture induces microcracking in the cuticle of fruit skins. Our objective was to study the effects of surface moisture on cuticular microcracking, the permeance to water vapour and russeting in developing 'Pinova' apple fruit. Surface moisture was applied by fixing to the fruit a plastic tube containing deionized water. Microcracking was quantified by fluorescence microscopy and image analysis following infiltration with acridine orange. Water vapour permeance was determined gravimetrically using skin segments (ES) mounted in diffusion cells. Cumulative water loss through the ES increased linearly with time. Throughout development, surface moisture significantly increased skin permeance. The effect was largest during early development and decreased towards maturity. Recovery time courses revealed that following moisture treatment of young fruit for 12days, skin permeance continued to increase until about 14days after terminating the moisture treatment. Thereafter, skin permeance decreased over the next 28days, then approaching the control level. This behaviour indicates gradual healing of the impaired cuticular barrier. Nevertheless, permeance still remained significantly higher compared with the untreated control. Similar patterns of permeance change were observed following moisture treatments at later stages of development. The early moisture treatment beginning at 23 DAFB resulted in russeting of the exposed surfaces. There was no russet in control fruit without a tube or in control fruit with a tube mounted for 12days without water. The data demonstrate that surface moisture increases microcracking and water vapour permeance. This may lead to the formation of a periderm and, hence, a russeted fruit surface.

Bond Strength of Self-Adhesive Restorative Materials Affected by Smear Layer Thickness but not Dentin Desiccation.

To use shear bond strength (SBS) testing to determine the effect of surface moisture and smear layer thickness on the adhesion of self-adhesive restorative materials and a universal adhesive. One single-step self-etch universal adhesive, Prime & Bond Active (PA), was used to bond Ceram.x Spectra ST HV composite resin to dentin and enamel using the self-etching technique. Three commercially available restorative materials and one newly developed material with self-adhesive properties, Activa (A), Fuji II LC(F), Equia Forte (E), and ASAR-MP4 (S), respectively, were also bonded to enamel and dentin prepared moist and dry and to dentin prepared with a thick smear layer. Shear bond testing was performed using an Ultradent bonding apparatus. The universal adhesive generated the highest SBS to dentin and enamel, followed by the newly developed material. None of the materials tested were significantly affected by the moisture conditions on enamel or dentin. The thickness of smear layer significantly affected SBS to dentin for S, F, and E. However, S and F still exhibited higher shear bond strength to dentin with the thicker smear layer compared to the other self-adhesive materials. Only the universal adhesive in self-etch mode was not affected by the thicker smear layer and maintained significantly higher SBS. None of the materials tested were affected by bonding to overdried dentin or enamel. All of the self-adhesive materials exhibited lower SBS to specimens with a thicker smear layer. The newly developed material ASAR-MP4 compared favorably to the other self-adhesive materials tested under all test conditions.

Drying and breaking behavior of hot air heavy medium fluidized bed

The drying and crushing behavior of air heavy medium fluidized bed was studied, and the effects of surface moisture, drying temperature, drying time, air volume and other factors on the content of crushed pulverized coal and droped pulverized coal were investigated. A mathematical correlation of crushed pulverized coal content and a mathematical correlation of droped pulverized coal content were established. The results show that the mathematical correlation of crushed pulverized coal content and the mathematical correlation of droped pulverized coal content can well simulate the drying and crushing behavior of fluidized bed. The increase of surface moisture, drying temperature, drying time, air volume and other operating parameters of coal will lead to the increase of crushed pulverized coal content and the decrease of droped pulverized coal content. In the stage of fluidized bed drying, coal does not produce much pulverized coal. The pulverized coal less than 1mm produced by falling coal is much larger than the pulverized coal produced by crushing in the fluidized bed, and the larger the operating parameters are, the more obvious the influence on the pulverized coal content is.

Algorithm development for real-time thin asphalt concrete overlay compaction monitoring using ground-penetrating radar

Ground-penetrating radar (GPR) is an effective, feasible, and non-destructive tool for real-time estimation of the density of asphalt concrete (AC) during compaction. When the AC pavement is thin, however, it is difficult to estimate the density due to the limited GPR signal resolution. In addition, the surface moisture, applied during compaction, has an effect on the GPR signal and hence impacts density prediction accuracy. In this study, a nonlinear optimization approach, based on gradient descent, was used to recover the AC pavement surface reflection. A “modified reference scan” approach was developed to remove the effect of surface moisture on GPR signals during density monitoring. The “modified reference scan” approach was first validated in a laboratory experiment setting, then validated in a field study near Chicago, IL, where GPR antennas were installed on the roller and data were collected during compaction. The results show that GPR is a prospective tool for real-time AC compaction monitoring.

Real-Time Monitoring of Asphalt Concrete Pavement Density during Construction using Ground Penetrating Radar: Theory to Practice

Accurate real-time density monitoring is crucial in quality control and quality assurance during the asphalt concrete (AC) pavement construction process. Ground penetrating radar (GPR) technology has shown great potential in the continuous real-time density prediction of AC pavement. However, it is not accepted as a routine method by transportation agencies in the United States due to the lack of validation under field testing conditions. In this study, three field tests were performed using GPR to estimate AC pavement density. The Al-Qadi-Lahouar-Leng model was used to predict the density from GPR signals. The reference scan method was used to remove the effect of surface moisture during construction. The gradient descent-based non-linear optimization method was used to reconstruct the overlapped GPR signals result from the use of thin AC overlay, which has been widely implemented as an AC pavement rehabilitation technique. Digital filtering and other signal processing methods were used to de-noise the signal. GPR results using the proposed methods were compared with field core data and nuclear gauge results. The results show that the proposed methods were effective in estimating in-situ AC pavement density using GPR. Continuous density estimation by installing GPR on the roller is suggested to provide real-time compaction monitoring during the AC pavement construction process.

Effect of surface moisture on inter-layer strength of 3D printed concrete

The extrusion-based 3D concrete printing is a new technology under development for construction of buildings and structures of complex geometries without the use of expensive formwork. The weak inter-layer strength between printed layers is one of the limitations of this technology when compared with cast-in-the-mold concrete. This study investigates effects of print-time interval on the inter-layer strength, along with compressive and flexural strengths of extrusion-based 3D printed concrete in different directions. Specimens were printed with 10, 20 and 30 min delay times (print-time intervals). Compressive, flexural and inter-layer strengths of the 3D printed concretes were measured. The inter-layer strengths of the specimens printed with 10 and 30 min delay times were comparable but higher than that of the specimens printed with 20 min delay time. A correlation was found between the results of inter-layer strength and the surface moisture content at the interface of the layers. The surface moisture content, in turn, depends on the bleed rate of the concrete and the rate of drying of moisture from the surface among other factors. The results also indicated that the compressive and flexural strengths of 3D printed concrete depended on the testing direction. The orthotropic phenomenon was more pronounced in compressive than flexural strength.

Spatially distinct effects of preceding precipitation on heat stress over eastern China

In many terrestrial regions, higher than usual surface temperatures are associated with (or are even induced by) surface moisture deficits. When in the warm season temperatures become anomalously high, their extreme values affect human beings causing heat stress. Besides increased temperature, rising humidity may also have substantial implications for bodily thermal comfort. However, the effects of surface moisture on heat stress, when considering both temperature and humidity, are less known. In this study, the relationship between the number of hot days in July as indicated by the wet-bulb globe temperature and the preceding three months of precipitation was assessed over eastern China. It is found that the probability of occurrence of above the average number of hot days exceeds 0.7 after a preceding precipitation deficit in northeastern China, but is less than 0.3 in southeastern China. Generally, over eastern China, the precipitation in the preceding months is negatively correlated with temperature and positively correlated with specific humidity in July. The combined effects generate a spatially distinct pattern: precipitation deficits in preceding months enhance heat stress in northeastern China while in southern China these deficits are associated with reduction of heat stress. In the south, abundant preceding precipitation tends to increase atmospheric humidity that is instrumental for the increase of heat stress. These results contribute predictive information about the probability of mid-summer heat stress in eastern China a few weeks ahead of its occurrence.

Effect of surface moisture on chemically bonded phosphor for thermographic phosphor thermometry

This study examined the effect of surface moisture on the calibration lifetime in chemically bonded phosphor paint preparation. Mg4FGeO6:Mn was used as a sensor material, which was excited by a pulsed UV LED. A high-speed camera with a frequency of 8000 Hz was used to conduct phosphor thermometry. Five samples with different degrees of surface moisture were selected during the preparation process, and each sample was calibrated 40 times at room temperature. A conventional post-processing method was used to acquire the phosphorescent lifetime for different samples with a 4 × 4-pixel interrogation window. The measurement error and paint uniformity were also studied. The results showed that there was no obvious phosphorescence boundary between the wet parts and dry parts of phosphor paint. The lifetime increased by about 0.0345% per hour during the preparation process, showing the degree of surface moisture had almost no influence on the lifetime measurement. The lifetime changed only after annealing treatment. There was also no effect on the measurement error and uniformity. These results provide a reference for developing a real-time measurement method using thermographic phosphor thermometry. This study also provides a feasible basis for chemically bonded phosphor thermometry applications in humid and low-temperature environments.

Measuring and modeling the effect of surface moisture on the spectral reflectance of coastal beach sand.

Surface moisture is an important supply limiting factor for aeolian sand transport, which is the primary driver of coastal dune development. As such, it is critical to account for the control of surface moisture on available sand for dune building. Optical remote sensing has the potential to measure surface moisture at a high spatio-temporal resolution. It is based on the principle that wet sand appears darker than dry sand: it is less reflective. The goals of this study are (1) to measure and model reflectance under controlled laboratory conditions as function of wavelength () and surface moisture () over the optical domain of 350–2500 nm, and (2) to explore the implications of our laboratory findings for accurately mapping the distribution of surface moisture under natural conditions. A laboratory spectroscopy experiment was conducted to measure spectral reflectance (1 nm interval) under different surface moisture conditions using beach sand. A non-linear increase of reflectance upon drying was observed over the full range of wavelengths. Two models were developed and tested. The first model is grounded in optics and describes the proportional contribution of scattering and absorption of light by pore water in an unsaturated sand matrix. The second model is grounded in soil physics and links the hydraulic behaviour of pore water in an unsaturated sand matrix to its optical properties. The optical model performed well for volumetric moisture content 24% ( 0.97), but underestimated reflectance for between 24–30% ( 0.92), most notable around the 1940 nm water absorption peak. The soil-physical model performed very well ( 0.99) but is limited to 4% 24%. Results from a field experiment show that a short-wave infrared terrestrial laser scanner ( = 1550 nm) can accurately relate surface moisture to reflectance (standard error 2.6%), demonstrating its potential to derive spatially extensive surface moisture maps of a natural coastal beach.

Algorithm development for the application of ground-penetrating radar on asphalt pavement compaction monitoring

Ground-penetrating radar (GPR) is a promising non-destructive technique to be applied on monitoring the density change during asphalt pavement compaction. The utmost challenge of this application is the unknown effect of surface moisture, sprayed by the compactor during compaction, on GPR signals. To extract density information without the effect of surface moisture, a correction algorithm based on reference scan approach was developed. To evaluate the performance of the algorithm, a full-scale test site was constructed with compaction pass number from 0 to 10, and a large amount of GPR data were collected from the pavement with different surface moisture contents. A total of 22 cores were extracted for validation purposes. After applying the algorithm, it was found that the average density prediction error was reduced significantly. By using correction algorithm together with the density model, the density of asphalt pavement was obtained with high accuracy.

Evaluation of the effect of surface moisture on dentinal tensile bond strength to dentine adhesive: An in vitro study

Aim:To evaluate the effect of surface moisture on dentinal tensile bond strength.Materials and Methods:Forty freshly extracted caries free, unrestored human mandibular molars were selected. The occlusal surfaces of each tooth were ground to prepare flat dentin surfaces at a depth of 1.5 mm. Following acid etching with 37% phosphoric acid for 15 sec, they were randomly grouped, with ten specimens in each: Group I – Over wet, Group II – Blot dry, Group III- One second dry, Group IV- Over dry. Each group was treated with a single bond adhesive system (3M ESPE) as per manufacturer’s instructions. Blocks or cylinders of composite resin were built up using Teflon mould and cured. Tensile bond strengths were tested using Instron universal testing machine. The results were statistically analyzed.Results:The mean tensile bond strength values of group II, Blot dry was highest and statistically significant (P<0.001).Conclusion:After acid etching and rinsing blot drying provided consistently better bond strength.

Stability of wet versus dry bonding with different solvent-based adhesives

Objective To evaluate the effects of surface moisture (wet or dry) and storage (24 h or 3 months) on the microtensile bond strength (BS) of resin/dentin bonds mediated by two water/ethanol based adhesives Single Bond, 3M-ESPE, (SB) and Opti Bond Solo Plus, Kerr, (OB), and two acetone-based adhesives, One Step, Bisco, (OS) and Prime&Bond NT, Caulk/Dentsply, (PB). Materials and methods Flat dentin surfaces were polished with 600-grit SiC paper, etched with 35% phosphoric acid for 15 s and rinsed for 20 s. Half the surface was maintained moist and the other half was air-dried for 30 s. Each adhesive was applied simultaneously to both halves, left undisturbed for 30 s and light-cured. Four-mm resin build-ups were constructed incrementally. After storage in water at 37 °C for 24 h, slabs were produced by transversal sectioning and trimmed to an hourglass shape (0.8 mm 2). Half of the specimens were tested in tension at 0.6 mm/min immediately after trimming and the other half after 3 months of water storage. Data were analyzed by two-way ANOVA and SNK for each material. Results Both moisture and storage affected BS to dentin, and was material-dependent. Dry bonding affected mostly the acetone-based adhesives. Larger reductions in bond strength were associated with dry bonding after 3 months of water storage. Significance Wet bonding resulted in more stable bonds over 3 months of water storage for most of the materials tested.