- ItemDevelopment of a Recyclable Flax Fiber Reinforced Polymer Composite(Composites in Civil Engineering, 2023-06-28) Das, Shagata; Doshi, Sagar; Millan, Emmanuel; Mendez, Damaris; Luckenbill, Dan; Tatar, JovanThis study compared the mechanical properties of a recyclable flax fiber reinforced polymer composite (FFRP) with a covalent adaptable network (CAN) matrix to an FFRP composite with a conventional (unrecyclable) epoxy resin matrix. The results indicated that composites fabricated via vacuum-assisted resin transfer molding (VARTM) exhibited up to 19% higher tensile modulus and strength compared to those fabricated via hand layup, attributed to reduced air void content and more uniform fiber alignment. Microscopy evidence supported by mechanical property tests revealed superior adhesion of the CAN matrix to flax fibers compared to conventional epoxy resin. Additionally, a solvent-based method was demonstrated for separating fibers from the CAN matrix, facilitating reuse or upcycling.
- ItemModeling the Partitioning of Anionic Carboxylic and Perfluoroalkyl Carboxylic and Sulfonic Acids to Octanol and Membrane Lipid(Environmental Toxicology and Chemistry, 2023-07-13) Torralba-Sanchez, Tifany L.; Di Toro, Dominic M.; Dmitrenko, Olga; Murillo-Gelvez, Jimmy; Tratnyek, Paul G.Perfluoroalkyl carboxylic and sulfonic acids (PFCAs and PFSAs, respectively) have low acid dissociation constant values and are, therefore, deprotonated under most experimental and environmental conditions. Hence, the anionic species dominate their partitioning between water and organic phases, including octanol and phospholipid bilayers which are often used as model systems for environmental and biological matrices. However, data for solvent–water (SW) and membrane–water partition coefficients of the anion species are only available for a few per- and polyfluoroalkyl substances (PFAS). In the present study, an equation is derived using a Born-Haber cycle that relates the partition coefficients of the anions to those of the corresponding neutral species. It is shown via a thermodynamic analysis that for carboxylic acids (CAs), PFCAs, and PFSAs, the log of the solvent–water partition coefficient of the anion, log KSW(A−), is linearly related to the log of the solvent–water partition coefficient of the neutral acid, log KSW(HA), with a unity slope and a solvent-dependent but solute-independent intercept within a PFAS (or CA) family. This finding provides a method for estimating the partition coefficients of PFCAs and PFSAs anions using the partition coefficients of the neutral species, which can be reliably predicted using quantum chemical methods. In addition, we have found that the neutral octanol–water partition coefficient, log KOW, is linearly correlated to the neutral membrane–water partition coefficient, log KMW; therefore, log KOW, being a much easier property to estimate and/or measure, can be used to predict the neutral log KMW. Application of this approach to KOW and KMW for PFCAs and PFSAs demonstrates the utility of this methodology for evaluating reported experimental data and extending anion property data for chain lengths that are unavailable. Environ Toxicol Chem 2023;00:1–12. © 2023 SETAC
- ItemThree-dimensional stress-strain and strength behavior of silt-clay transition soils(Canadian Geotechnical Journal, 2023-04-10) Anantanasakul, Pongpipat; Intharachart, Phimmawat; Kaliakin, Victor N.The effect of silt content on the mechanical behavior of silt-clay transition soils under three-dimensional stress conditions is presented. Undrained true triaxial tests with constant b values were performed on normally consolidated specimens of silt-clay transition soils created from the same base clay and non-plastic silt, however, with systematically varying gradations. With increasing amount of non-plastic silt, the cohesive soils exhibit less contractive tendencies, stiffer stress-strain response and larger shear strength. The magnitude of intermediate principal stress, as indicated by the b value, also strongly influences the stress-strain relations, pore pressure behavior and both total and effective failure surfaces. Although the transition soils exhibit overall clay-like behavior, more pronounced frictional characteristics, as indicated by the shapes of the failure and plastic potential surfaces, were exhibited with increasing silt content.
- ItemPhysiochemical Controls on the Horizontal Exchange of Blue Carbon Across the Salt Marsh-Tidal Channel Interface(Journal of Geophysical Research: Biogeosciences, 2023-06-06) Fettrow, Sean; Jeppi, Virginia; Wozniak, Andrew; Vargas, Rodrigo; Michael, Holly; Seyfferth, Angelia L.Tidal channels are biogeochemical hotspots that horizontally exchange carbon (C) with marsh platforms, but the physiochemical drivers controlling these dynamics are poorly understood. We hypothesized that C-bearing iron (Fe) oxides precipitate and immobilize dissolved organic carbon (DOC) during ebb tide as the soils oxygenate, and dissolve into the porewater during flood tide, promoting transport to the channel. The hydraulic gradient physically controls how these solutes are horizontally exchanged across the marsh platform-tidal channel interface; we hypothesized that this gradient alters the concentration and source of C being exchanged. We further hypothesized that trace soil gases (i.e., CO2, CH4, dimethyl sulfide) are pushed out of the channel bank as the groundwater rises. To test these hypotheses, we measured porewater, surface water, and soil trace gases over two 24-hr monitoring campaigns (i.e., summer and spring) in a mesohaline tidal marsh. We found that Fe2+ and DOC were positively related during flood tide but not during ebb tide in spring when soils were more oxidized. This finding shows evidence for the formation and dissolution of C-bearing Fe oxides across a tidal cycle. In addition, the tidal channel contained significantly (p < 0.05) more terrestrial-like DOC when the hydraulic gradient was driving flow toward the channel. In comparison, the channel water was saltier and contained significantly (p < 0.05) more marine-like DOC when the hydraulic gradient reversed direction. Trace gas fluxes increased with rising groundwater levels, particularly dimethyl sulfide. These findings suggest multiple physiochemical mechanisms controlling the horizontal exchange of C at the marsh platform-tidal channel interface. Plain Language Summary Tidal salt marshes store large amounts of carbon belowground in soils, but there is also a significant amount of carbon flowing into and out of these ecosystems via tidal channels. We investigated the carbon flowing between the channel bank and surface water in a salt marsh in Delaware. We found that soil minerals (i.e., iron oxides) control the mobility of carbon as iron oxides retain carbon during ebb tides and release carbon during flood tides as the minerals dissolve. The gradient between the groundwater and surface water elevation (i.e., hydraulic gradient) controls the flow direction for dissolved carbon, altering the concentration and source of carbon found in the tidal channel across tidal cycles. In addition, gases trapped in channel banks are pushed out of the soils as the tide rises. These findings will improve our understanding of carbon cycles in these critical carbon sinks. Key Points - Physiochemical mechanisms control horizontal exchange of carbon across marsh-tidal channel interfaces, affecting lateral carbon flux - Dissolution and reprecipitation of carbon-bearing Fe oxides during flood and ebb tides control the horizontal mobility of carbon - Hydraulic gradients control the carbon character in the tidal channel, and rising tides push greenhouse gases out of the channel bank
- ItemHazard assessment framework for statistical analysis of cut slopes using track inspection videos and geospatial information(Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2023-06-12) Palese, Michael; Pei, Te; Qiu, Tong; Zarembski, Allan M.; Shen, Chaopeng; Palese, Joseph W.Transportation corridors constructed using through- and side-cuts are susceptible to hazardous slope failures, potentially causing infrastructure damage, operational suspensions and loss of life. To monitor the stability of known geohazards at the local scale, geotechnical investigation of each slope is typically performed to calculate a factor of safety. In many corridors, however, this method is labour-intensive due to the quantity of geohazards and statistical methods are instead used to identify hazardous sections. This paper introduces a new slope failure hazard assessment technique, utilising susceptibility mapping of geospatial information and computer vision-based analysis of right-of-way videos recorded by railroad track inspection vehicles, applied to a section of railroad track near Harrisburg, Pennsylvania. Combining these results, an enhanced relative hazard assessment algorithm was formulated. Using the developed framework, geohazards of primary concern were determined which should be prioritised for future geotechnical investigation and remediation efforts.