Mat Density Research Articles

The effects of using soil protective mats of varying compositions and amounts on the intensity of soil disturbances caused by machine traffic

ABSTRACTWe quantified the effectiveness of different soil protective mat compositions (brush, sawdust, combination of brush and sawdust) and densities (light density of 10 kg m−2 and heavy density of 20 kg m−2) on compaction and rutting on skid trails in mountainous forests following one, four, and 10 machine passes on two trail gradient classes (≤ 20% and > 20%). Soil bulk density and rut depth increased markedly with traffic frequency on both slope gradient classes on bare and protected soil, but soil protective mats delayed the onset of adverse soil responses and reduced the level of soil damage. Brush mats provided a more effective protection than sawdust and the combination of brush and sawdust and heavy density brush mats more so than light density mats. Compared to bare soil, heavy brush reinforcement significantly reduced bulk density for up to 10 passes on trail gradients ≤ 20% and four passes on gradients > 20%, regardless of soil protective mat composition. Light and heavy brush mats significantly reduced rut depth at all traffic frequencies on both slope classes. Because the effectiveness of soil protection afforded by the mats diminished with increasing traffic, brush mats provide a particularly effective protection for less trafficked trail segments where brush mats substantially diminished or even eliminated rutting altogether.

Gas permeability of fiberboard mats as a function of density and fiber size

ABSTRACTGas permeability and structure of fiberboard mats are essential properties because of their impact on mat internal gas pressure, moisture content and temperature evolution during the hot-pressing process. The objectives of this work were to determine the effect of fiber size and mat density on the intrinsic gas permeability of the mat. For the study of these mat properties, panels with a homogeneous density profile through the thickness were manufactured at five density levels (200, 400, 600, 800 and 1000 kg m−3) for three different fiber sizes. Fiber refining was performed in a disk refiner at three plate spacings. Gas permeability was measured with an in-house built apparatus. The results showed that the fiber sizes studied had no significant effect on the intrinsic permeability. This was likely due to a more significant impact of the internal porous structure of the mat compared to fiber size. Besides, the intrinsic permeability decreased significantly when the panel density increased from 198 to 810 kg m−3. This suggests that the decrease of the intrinsic gas permeability during the last seconds of press closure plays an essential role in the bulk moisture mass transfer through the fiberboard mat.

Modeling and experimental demonstration of high-throughput flow-through spatial atomic layer deposition of Al2O3 coatings on textiles at atmospheric pressure

Atomic layer deposition (ALD) shows promise for forming thin films on temperature-sensitive materials, such as polymers, for applications in filtration, sensing, etc. However, traditional batch ALD generally proceeds slowly and requires controlled, low-pressure equipment. One approach to combat this limitation is spatial ALD, which uses moving substrates through zones of reactant exposure. To date, studies of spatial ALD have primarily explored growth on planar and nonporous substrates. Here, the authors demonstrate a proof-of-concept atmospheric pressure flow-through spatial ALD reactor specifically designed for through-porous substrates, such as fiber webs. This paper describes detailed gas flow modeling and experimental analysis of their prototype reactor. Model results identify precursor gas flow rates, channel spacing, and the distance between the substrate and reactor surfaces as key factors to achieve uniform deposition. Using a previously developed surface wetting protocol, the authors experimentally verify operating conditions for uniform ALD alumina on polypropylene as a model fiber substrate. Under good ALD conditions, the spatial ALD reactor can complete ∼60 cycles/min over a large substrate area, which is 60 times faster than batch ALD. The authors quantify growth saturation conditions and find that under reduced gas flow rates or slow fiber translation speeds, a transition from ALD to chemical vapor deposition-like growth can be induced. Additionally, the authors demonstrate that fiber mat properties such as mat density and air permeability play important roles in the penetration depth of the precursors and, therefore, the conditions needed to achieve ALD. Overall, this work demonstrates a proof-of-concept reactor for high throughput ALD on porous substrates, and identifies important design challenges and considerations for future high-throughput ALD.

Effects of “lights out” turfgrass renovation on plants, soil arthropod and nematode communities

“Lights out” turfgrass renovation approach is a pesticide-free method of weed and pest management that can reduce weed pressure when replanting turf, switching grass types, or completing a total renovation of a designated grassy area. In this study, we addressed the feasibility of using black, geo-textile weed mats made of woven polypropylene plastic in this alternative turfgrass renovation approach. The specific objectives were: 1) to determine the most effective weed mat density to suppress weeds; 2) to determine the most effective fertilizer treatment (fertilizer × rate) to stimulate weed seed germination and drain the weed seed bank; and 3) to document changes in the biotic communities in the soil including nematodes and insects. This research was conducted in 2016 at Magoon Research Facility on the island of Oahu, Hawai’i. Our results indicated that the “lights out” method was effective, with all cover types providing better weed suppression than control plots treated with glyphosate. There were no significant differences between fertilizer treatments for weed diversity or coverage percent one-month post-fertilization. However, all plots treated with fertilizer had significantly less weed diversity and coverage after the Bermudagrass was planted, indicating that fertilization plays a crucial role in draining the weed seed bank. Soil arthropod and nematode communities were generally altered after each renovation step, indicating that covering and fertilization play a role in shaping the diversity, abundance, and maturity of the soil food web.

Comparison of different erosion control techniques in the Hyrcanian forest in northern Iran

The aim of this study was to evaluate the effects of closure best management practices (BMPs) on runoff volume and soil loss on skid trails that received two densities of soil cover mats and were located on two slope gradients in an Iranian temperate mountainous forest. The treatments included combinations of three closure BMPs (water bar only, water bar + sawdust, and water bar + hardwood slash), two amounts (densities) of mats (7.5 and 15 kg·m<sup>–2</sup>), and two levels of slope gradients (≤ 20% and > 20%). Results showed that the water bar treatment was the least effective erosion control treatment, followed by the hardwood slash and sawdust treatments. Averaged over mat densities and both slope gradients, the average runoff rates and amounts of soil loss from the skid trails with the water bar treatment were 46.7 l per plot and 6.1 g·m<sup>–2</sup>, respectively, 16.8 l per plot, 2.8 g·m<sup>–2</sup>, respectively, with the hardwood slash treatment and 11.7 l per plot, 1.9 g·m<sup>–2</sup>, respectively, with the sawdust treatment. The results indicated that surface cover is a necessary element for controlling erosion losses following a skidding disturbance, particularly on steep slopes.

Improving Nanofiber Production and Application Performance by Electrospinning at Elevated Temperatures

Needleless electrospinning can produce nanofibers on large scales, which is promising for industrial manufacturing. It is known that solution temperature is an important parameter for electrospinning. However, the influence of solution temperature on needleless electrospinning has not been reported much in the research literature, nor has the application performance of needleless electrospun nanofibers. In this study, using a curved slot as the needleless electrospinning spinneret and PVA as the material model, we show that solution temperature has a considerable effect on fiber diameter, packing density of nanofiber mats, and fiber productivity. Increasing the solution temperature from 20 to 60 °C can lead to finer fibers with a larger fiber production rate. The nanofiber mats produced at higher solution temperature show increased air filtration efficiency. Increasing solution temperature may form a new strategy to improve nanofiber productivity and meanwhile increase nanofiber quality.

The photosynthetic responses to stocking depth and algal mat density in the farmed seaweed Gracilaria lemaneiformis (Gracilariales, Rhodophyta).

The branches and mass of Gracilaria lemaneiformis increase with growth season, and the thalli sink to deeper depths with increasing biomass density during maricultivation. The changing depth and algal mat density may affect the physiology of the algae. In the present study, the photosynthetic behaviors regarding different biomass densities in G. lemaneiformis thalli collected from different stocking depths were determined, to examine how photosynthesis of this farmed alga was affected by the growth depths and algal mat densities. Our results showed that the chlorophyll a (Chl a), carotenoids (Car), phycoerythrin (PE) contents, and irradiance-saturated maximum photosynthetic rates (P max) of the deeper layer-grown algae were significantly increased relative to the surface layer-grown algae. The P max, apparent photosynthetic efficiency (α) and dark respiration rate (R d) of G. lemaneiformis thalli, were reduced, whereas the irradiance saturation points (I k) were increased, with the increasing algal mat density. We proposed that appropriate measures are needed to trade off the stocking depth and biomass density, in an effort to maintain a relative high photosynthetic productivity during G. lemaneiformis maricultivation.

Impact of seasonal changes in stream metabolism on nitrate concentrations in an urban stream

Nitrate (NO3 −) dynamics in urban streams differ from many natural streams due to stormwater runoff, sewage inputs, decreased groundwater discharge, often limited hyporheic exchange, increased primary productivity, and limited carbon input. We investigated NO3 − dynamics in a first-order urban stream in Syracuse, NY, which has urbanized headwaters and a geomorphologically natural downstream section. Twice-monthly water sampling, NO3 − injection tests, NO3 − isotopic analysis, filamentous algae mat density, and riparian shading were used to identify processes regulating NO3 − dynamics in the stream over a 12-month period. The urban headwater reach had low NO3 − (0.006–0.2 mg N/L) in the spring through fall, with a minimum uptake length of 900 m, no canopy cover, and high algae mat density. The downstream natural reach (100% canopy cover during the summer and low algae mat density) had nitrate concentrations between 0.6 and 1.2 mg N/L from winter to summer, which decreased during autumn leaf-off. In the urban reach, autotrophic uptake by filamentous green algae is a major NO3 − sink in summer. In the natural reach, the addition of organic matter to the stream at leaf-off led to a decrease in NO3 − concentration followed by an increase in NO3 − concentration in winter as gross primary productivity decreased. This study shows that the balance between autotrophy and heterotrophy in urban streams is variable and depends on an interplay of drivers such as temperature, light, and carbon inputs that are mediated by the riparian ecosystem.

Dynamic characteristics modelling of the tamper–asphalt mixture interaction: application to predict asphalt mat density

ABSTRACTRecently, the study of machinery/medium interaction is becoming increasingly important in terramechanics. In order to maximise the performance of existing equipment and obtaining desired compaction density in road construction, reasonable and effective paving operations are essential. However, the operations always depend on empirical approaches. In this paper, a model based on vibration compaction theory was used to describe the deformation property of asphalt mixture, which can lay a foundation for future analysis. And then, a dynamic model of tamper/asphalt mat interaction, based on the principles of resonance, was developed to predict asphalt mat density during paving operation. The model inputs included excitation frequency, tamper stroke, paver forward speed and asphalt mixture properties parameters for different tamper or asphalt mixture. The numerical simulations are provided to demonstrate how the tamper/asphalt mat interaction model can be used to predict asphalt mixture compaction in the field of road construction engineering.

Thermal Conductivity and Volumetric Specific Heat of Low-Density Wooden Mats

Abstract Using wooden waste as insulation material benefits society by using waste products, reducing building thermal load, and sequestering carbon dioxide. In this study on heat insulating materials, a novel low-density wooden mat was fabricated from wood shavings and kenaf fibers. This research addressed the influences of fabrication conditions on the thermal conductivity and volumetric specific heat of the materials used. The raw materials (wood shavings and kenaf fibers) were mixed with a binder component, and the mixture was thermoformed. The thermal conductivity and volumetric specific heat of the mats were measured, and the influence of mixing ratio, density, and heat flux was evaluated. The results demonstrated that thermal conductivity was largely affected by the mat density and mixing ratio but was largely unaffected by changes in the heat flux. The volumetric specific heat of the mats was largely unaffected by the raw material mixing ratio but was greatly affected by the mat density. The tendency of the thermal conductivity decrease was changed according to the combination ratio of the wood shavings and the kenaf. The wood shavings are flake shaped and curled, and the kenaf is fibrous. It was thought that the internal void was made smaller effectively by mixing two different shaped fibers and the thermal conductivity was minimized. As a result, the thermal performance of the subject mats, as compared with glass wool, exhibited a slightly lower thermal insulation level and higher heat capacity. The results are important in improving efficiency and the commercial design of insulation materials.

Furnish type and mat density effects on temperature and vapor pressure of wood-based panels during hot pressing

The goals of this study were to determine the effects of furnish type and mat density on temperature and vapor pressure inside the mat of wood-based panels during hot pressing and to confirm their effects on panel properties. Two furnish types, hinoki strand (HS) and recycled wood particles (RW), were used for experimental panels using urea–formaldehyde resin at five board densities and 15 % mat moisture content. A monitoring device was used to sense the temperature and vapor pressure during hot pressing. The results from this study showed that furnish type and mat density affected temperature and vapor pressure behaviors. The results also showed the effect on panel properties. HS-board had a higher plateau temperature, longer plateau time, and higher vapor pressure than did Mixed- and RW-board. Higher mat density was associated with higher plateau temperature and vapor pressure and longer plateau time and vapor pressure band. Plateau time and temperature were also correlated with vapor pressure. Furthermore, density showed linear relationships with plateau temperature and internal bonding (IB). A linear relationship was also found between plateau temperature and IB, and non-linear relationships were found for vapor pressure with plateau temperature and IB.

On recycled carbon fibre composites manufactured through a liquid composite moulding process

The recovery of carbon fibres from waste and end-of-life carbon fibre reinforced plastic materials is both economically lucrative and environmentally necessary. Here, we characterise the physical and mechanical properties of recycled carbon fibre reinforced plastics (rCFRPs) composed of random and oriented non-woven recycled carbon fibre mats that were impregnated with liquid epoxy matrices using a vacuum-infusion set-up. The low areal density and poor compactability of the non-woven mats implied that press-moulding upon impregnation was essential to control laminate thickness and improve fibre content; this may limit the applications of the resulting rCFRPs. Moreover, the press consolidation process is thought to degrade fibre length, and is a likely cause for the lower-than-expected tensile properties of the rCFRPs. Expectedly, the oriented rCFRPs exhibited better tensile and compressive properties than the random rCFRPs. Notably, while the tensile strength of the rCFRPs was only up to 2.5 times better than the matrix, the tensile modulus was 4–10 times enhanced. Through a comparative literature survey, we found that the liquid composite moulded rCFRPs were outperformed by rCFRPs fabricated through other manufacturing processes (e.g. prepregging), particularly those employing high compaction pressures, and utilising long fibres recovered through pyrolysis and chemical processes, rather than the fluidised-bed process.

Erratum to: Density dependence in the thermal conductivity of cellulose fiber mats and wood shavings mats: investigation of the apparent thermal conductivity of coarse pores

Thermal conductivities (k-values) of cellulose fiber (CF) and wood shavings (WS) mats were measured, and the density dependence of k-values in the ranges 28–60 and 60–100 kg/m3 for CF mats and WS mats, respectively, was investigated. The k-value of the CF mats tended to increase with increasing mat density, but that of the WS mats showed a much weaker relationship. In order to discuss this density dependence in k-values, the apparent thermal conductivity (k cp) of coarse pores in the mats, which includes the effects of convective and radiant heat transfer, was calculated. The results revealed that the density dependence in the k-values of the CF mats derived only from an increase in the number of heat bridges, consisting of fibers and their contact points. Also, the smaller density dependence of the k-values of the WS mats than that of the CF mats was found to be explicable by the density dependence of k cp in the WS mats, because a lower k cp at higher mat densities contributes to the lowering of mat thermal conductivity in a way that balances the increase in heat bridges as mat density increases.

Assessment of Ichu fibers as non-expensive thermal insulation system for the Andean regions

In the Andean regions, low temperatures (5 to −25°C) combined with the wind effect give the sensation of extreme cold. Besides, in the rural areas, dwelling structures are very rudimentary, being based on adobe walls and galvanized steel corrugated roofs. The combination of weather issues and construction without thermal insulation considerations put people in extreme living conditions. Using local and cheap natural fibers as thermal insulation is a great alternative especially to upgrade/refurbish rudimentary constructions. In areas above 3000m over sea level, natural fibers are vast and cheap (∼0.15USD/kg), especially fibers named “Ichu”. In this study thermal properties of natural fibers were characterized according to the ASTM C177. Results show that the thermal conductivity varies from 0.047 to 0.113W/mK, for mats with unidirectional oriented fibers, being fine Ichu which have the lowest values. For the fine Ichu fiber to be competitive in terms of cost per unit thermal resistance, fiber mat density were reduced, arranging the fibers randomly; results show a significant reduction in density, without increasing significantly the thermal conductivity. According to these results Ichu fibers have exceptional thermal insulation properties. Moreover, this is the first conducted study on the thermal performance of this natural Andeans fiber.

Characterization of porosity, structure, and mechanical properties of electrospun SiOC fiber mats

In this study, silicon oxycarbide (SiOC) ceramic fiber mats obtained by electrospinning of two different preceramic polymers (MK and H44 resin) were evaluated in terms of their total porosity and other structural characteristics using three different characterization tools. The tensile strength and the permeability of the fiber mats were also investigated. The results indicated that the porosity could be easily calculated based on the apparent density and true density of the fiber mats obtained by gas pycnometry. A modified mercury intrusion porosimetry, in which the bulk volume of the fiber mats was calculated based on its independently measured bulk density, also allowed for an accurate evaluation of the porosity and the pore size distribution of the fiber mats. X-ray computed tomography was able to provide various structural characteristics of the 3D morphology of the fiber mats, but it was less effective in the determination of the total porosity due to resolution limits. All results showed that the MK-derived SiOC fiber mats possessed a higher porosity than the H44-derived SiOC fiber mats, resulting in a higher gas permeability. The ceramic fiber mats possessed a suitable permeability for filtration applications in harsh environments.

Structural characteristics of nanofibrillated cellulose mats: Effect of preparation conditions

Nanofibrillated cellulose (NFC) mats, which have porous or dense structures, were prepared in this study. The effects of the number of grinding passes, suspension solids content, and drying conditions on the structural changes of the NFC mats were investigated. Water removal in the NFC suspensions for forming the mats was carried out using pressurized dewatering equipment. The field-emission scanning electron microscope observation showed that the nanofibrils were preserved by solvent exchange drying, whereas the partial aggregation of nanofibrils occurred by freeze drying. Properties such as shrinkage, density, porosity, and specific surface areas of the NFC mats changed depending on the preparation conditions of the NFC mats. The NFC mats, which have low density and high porosity, could be prepared by solvent exchange drying and freeze drying. Porosity of the NFC mats varied from 76 % to 96 %. The specific surface area of the NFC mat increased to 175 m2/g with an increase in the number of grinding passes.

Implications of fiber characteristics and mat densification on permeability, compaction and properties of kenaf fiber panels

In the manufacturing of medium density and high density fiberboards the fiber characteristics and mat density substantially influence mat permeability, compaction pressure and panel's physicomechanical properties. In this paper, the permeability and compaction response of kenaf bast fiber mats are experimentally determined at three fiber lengths for both dry and resinated fiber mats with various levels of mat densification. The mats of long fibers have demonstrated higher permeability and require higher compaction pressure than short fiber mats at the same level of densification. Furthermore, kenaf panels in the density range of 800kg/m3 to 1100kg/m3 are manufactured with commercial melamine urea formaldehyde resin and three fiber categories. The panels are evaluated to demonstrate the effects of these factors on a panel's physicomechanical properties. The higher compaction pressure and good stress distribution with long fibers have resulted in higher mechanical properties than those of short fiber panels. On the other hand, a decrease in fiber length has lowered the mat permeability, resulting in significant improvements in dimensional properties. The panel physicomechanical properties can also significantly improve by increasing the panel density. The high density kenaf panels have shown excellent mechanical properties which are well above the standard requirements of MDF and HDF panels according to (ANSI, A208.2: 2009) and (ANSI, A135.4-2012) standards.

Evaluation of Warm-Mix and Rubber-Modified Open-Graded Friction Course Test Sections Made without Fibers in South Carolina

This paper summarizes the performance of open-graded friction course (OGFC) mixtures used to construct two experimental pavement test sections in South Carolina. The study's main objective was to evaluate OGFC mixtures made without fibers. One test section consisted of three OGFC mixtures [control with cellulose fibers, ground tire rubber modified without fibers, and warm-mix asphalt (WMA) without fibers], and the second consisted of two OGFC mixtures (control with cellulose fibers and WMA without fibers). Material was sampled from the asphalt plant during production. Tests were conducted on the fresh mix as well as specimens compacted at the plant and after reheating in the research lab. Results showed that the removal of fibers from the OGFC mixtures in both projects did not have any detrimental effects on the mix performance (drain down, permeability, abrasion resistance, indirect tensile strength, and fatigue resistance). The WMA mixture made with Evotherm exhibited increased fatigue resistance compared with the control mixture even though the WMA mixture did not contain cellulose fibers. In addition, the WMA mixture showed the potential to reduce heat loss resulting from the startup of the paving operation (i.e., running asphalt mix through a cold material transfer vehicle and then a cold paver). Limiting heat loss could improve the consistency of the OGFC mat density from the beginning transverse cold joint and thus potentially enhance the pavement performance.

Dominant bryophyte control over high‐latitude soil temperature fluctuations predicted by heat transfer traits, field moisture regime and laws of thermal insulation

Summary Bryophytes cover large territories in cold biomes, where they control soil temperature regime, and therefore permafrost, carbon and nutrient dynamics. The mechanisms of this control remain unclear. We quantified the dependence of soil temperature fluctuations under bryophyte mats on the interplay of bryophyte heat conductance traits, mat thickness, density and moisture regimes. For seventeen predominant bryophytes in six typical subarctic ecosystems, we assessed in situ soil temperature dynamics under bryophyte mats in comparison with bryophyte‐removal patches and per‐species mat field moisture. In a complimentary laboratory investigation, we studied how per‐species bryophyte thermal conductivity and volumetric heat capacity depend on mat density and moisture content. Subsequently, we tested whether heat transfer through bryophyte mats could be modelled as a function of mat thickness, thermal conductivity and volumetric heat capacity, the latter two being determined by mat density and field moisture content. Laboratory assessment revealed that bryophyte thermal conductivity and volumetric heat capacity were independent of mat density, and depended linearly on mat moisture content, but the dependencies were not species‐specific. In the field, bryophytes reduced amplitudes of soil temperature fluctuations and freeze–thaw frequency during the growing season, but not mean soil temperature. These effects differed between species and between ecosystems, being strongest in Sphagnum fuscum‐dominated dry tundra, but were well explained by bryophyte mat thickness and field moisture content as affecting thermal conductivity and volumetric heat capacity. We suggest that reduction in soil temperature amplitudes is a generic feature in (sub) arctic ecosystems and should be considered as an important mechanism of bryophyte control on carbon and nutrient turnover. Although heat transfer through bryophyte mats differs greatly among species and ecosystems, species differences are fully explained by differences in mat thickness and moisture content and generally comply with physical laws, without deviations due to biological processes. These results imply that in global vegetation models of carbon and nutrient cycling, the heat transfer through bryophyte mats can be modelled without taking into consideration bryophyte species composition, but considering bryophyte mat depth and moisture availability only. This will allow us to enhance modelling precision through an improved representation of the soil temperature regime.

Electrospun nanofiber mats for evanescent optical fiber sensors

In this work, a study about the optical response of electrospun nanofiber (ENF) coatings for their use in evanescent optical fiber sensors is presented. Several types of ENF mats composed of poly(acrylic acid) (PAA) were developed with different ENF diameters and densities. These ENF mats were deposited onto an optical fiber core in order to fabricate humidity evanescent optical fiber sensors. The devices were exposed to relative humidity (RH) variations from 30% RH to 95%RH. The transfer functions of the devices (transmitted optical power versus relative humidity) presented two well-differenced behaviors depending on the ENF diameter and the ENF mat density. The devices with lower ENF diameters and higher mat density showed an increase in the transmitted optical power when RH increased. On the contrary, the devices with higher ENF diameters and lower mat density showed a decrease in the transmitted optical power when RH increased. In addition to this, sensors with thinner ENF overlays, showed a higher sensitivity. In order to study the response time of these devices, the ENFs sensors were submitted to human breathing cycles and presented a response time around 340 ms (exhalation). In spite of the high RH conditions of this experiment, the devices showed a recovery time around 210 ms and a negligible hysteresis or drift with respect to the initial condition (inhalation).