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Category: Publications: Geotechnical and Structures Laboratory (GSL)
  • Computationally Efficient Modeling of Lightweight Expeditionary Airfield Surfacing Systems at Large Length Scales

    Abstract: Expeditionary airfield matting systems are lightweight, portable surfaces that enable the rapid deployment of infrastructure to support aircraft operations. Individual matting components are assembled via interlocking joints to construct arrays that serve as temporary aircraft operating surfaces. The paper outlines the homogenization of the AM2 portable airfield matting system and its interlocking mechanisms to permit computationally efficient analyses toward understanding mechanisms that influence the global behavior of these arrays and underlying subgrade during aircraft maneuvers. An equivalent orthotropic two-dimensional continuum was developed from finite element analysis of a detailed three-dimensional model and its flexural behavior was validated against experimental data and solid finite element models. Interlocking joints were characterized using node-to-node connector elements based on subscale finite element studies. Both components were implemented into a full-scale model representative of a typical test section, and responses to static high tire pressure aircraft loads were analyzed over a soil foundation representing a California bearing ratio of 6%, yielding promising agreement with experimental data. Results of this study reveal an inherent coupling between load transfer, mat deflection, and near-surface subgrade stress with dependence on tire location, mat core shear flexibility, and joint stiffness.
  • 2D Fluorinated Graphene Oxide (FGO)-Polyethyleneimine (PEI) Based 3D Porous Nanoplatform for Effective Removal of Forever Toxic Chemicals, Pharmaceutical Toxins, and Waterborne Pathogens from Environmental Water Samples

    Abstract: Although water is essential for life, as per the United Nations, around 2 billion people in this world lack access to safely managed drinking water services at home. Herein we report the development of a two-dimensional (2D) fluorinated graphene oxide (FGO) and polyethylenimine (PEI) based three-dimensional (3D) porous nanoplatform for the effective removal of polyfluoroalkyl substances (PFAS), pharmaceutical toxins, and waterborne pathogens from contaminated water. Experimental data show that the FGO-PEI based nanoplatform has an estimated adsorption capacity (qm) of ∼219 mg g−1 for perfluorononanoic acid (PFNA) and can be used for 99% removal of several short- and long-chain PFAS. A comparative PFNA capturing study using different types of nanoplatforms indicates that the qm value is in the order FGO-PEI > FGO > GO-PEI, which indicates that fluorophilic, electrostatic, and hydrophobic interactions play important roles for the removal of PFAS. Reported data show that the FGO-PEI based nanoplatform has a capability for 100% removal of moxifloxacin antibiotics with an estimated qm of ∼299 mg g−1. Furthermore, because the pore size of the nanoplatform is much smaller than the size of pathogens, it has a capability for 100% removal of Salmonella and Escherichia coli from water. Moreover, reported data show around 96% removal of PFAS, pharmaceutical toxins, and pathogens simultaneously from spiked river, lake, and tap water samples using the nanoplatform.
  • Dynamic Tensile Behavior of Laser-Directed Energy Deposition and Additive Friction Stir-Deposited AerMet 100

    Abstract: Quasi-static and high-rate tensile experiments were used to examine the strain rate sensitivity of laser-directed energy deposition (L-DED)- and additive friction stir deposition (AFSD)-formed AerMet 100 ultrahigh-strength steel-additive manufactured builds. Electron backscattered diffraction (EBSD) revealed similar as-deposited grain sizes between the two AM processes at approximately 24 µm and 17 µm for the L-DED and AFSD samples, respectively. The strain hardening rate, θ, revealed little change in the overall hardening observed in the L-DED and AFSD materials, with a consistent hardening in the quasi-static samples and three identifiable regions in that of the high-rate tested materials. The L-DED deposited materials displayed average ultimate tensile strength values of 1835 and 2902 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively and the AFSD deposited materials displayed ultimate tensile strength values of 1928 and 3080 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively. Overall, the strength for both processes displayed a positive strain rate sensitivity, with increases in strength of ~1000 MPa for both processes. Fractography revealed significant solidification voids in the laser DED material and poor layer adhesion in the AFSD material.
  • Extreme Cold Weather Airfield Damage Repair Testing at Goose Bay Air Base, Canada

    Abstract: Rapid Airfield Damage Recovery (RADR) technologies have proven successful in temperate and subfreezing temperatures but have not been evaluated in extreme cold weather temperatures near 0°F. To address this capability gap, laboratory-scale and full-scale testing was conducted at these temperatures. Methods developed for moderate climates were adapted and demonstrated alongside methods that used snow harvested on-site as compacted backfill. After only a few days of training, seven experimental repairs were conducted by Canadian airmen at Goose Bay Air Base in Labrador, Canada, and load tested with a single-wheel C-17 load cart. Existing RADR technologies performed adequately despite the freezing temperatures, with the main tactic, techniques, and procedures modification being an increased cure time for the rapid-setting concrete surface material. Compacted snow-water slurry methods also performed well, demonstrating their ability to withstand over 500 passes of single-wheel C-17 traffic after sufficient freezing time.
  • The Influence of Mesoscale Atmospheric Convection on Local Infrasound Propagation

    Abstract: Infrasound—that is, acoustic waves with frequencies below the threshold of human hearing—has historically been used to detect and locate distant explosive events over global ranges (≥1,000 km). Simulations over these ranges have traditionally relied on large-scale, synoptic meteorological information. However, infrasound propagation over shorter, local ranges (0–100 km) may be affected by smaller, mesoscale meteorological features. To identify the effects of these mesoscale meteorological features on local infrasound propagation, simulations were conducted using the Weather Research and Forecasting (WRF) meteorological model to approximate the meteorological conditions associated with a series of historical, small-scale explosive test events that occurred at the Big Black Test Site in Bovina, Mississippi. These meteorological conditions were then incorporated into a full-wave acoustic model to generate meteorology-informed predictions of infrasound propagation. A series of WRF simulations was conducted with varying degrees of horizontal resolution—1, 3, and 15 km—to investigate the spatial sensitivity of these infrasound predictions. The results illustrate that convective precipitation events demonstrate potentially observable effects on local infrasound propagation due to strong, heterogeneous gradients in temperature and wind associated with the convective events themselves. Therefore, to accurately predict infrasound propagation on local scales, it may be necessary to use convection-permitting meteorological models with a horizontal resolution ≤4 km at locations and times that support mesoscale convective activity.
  • Verification of Current Los Angeles (LA) Abrasion Test Criterion for Aggregate Degradation in Airfield Asphalt Pavements

    Abstract: Low-quality mineral aggregates can potentially lead to production, construction, and long-term performance-related problems in asphalt concrete pavements. Therefore, effective qualification criteria for mineral aggregates are paramount. This study was performed to investigate the effectiveness of the Los Angeles abrasion (LAA) test to assess the abrasion resistance of coarse aggregates commonly used in airfield asphalt paving. The LAA test acceptance criteria currently specified by state departments of transportation were examined and compared to the current Department of Defense criterion. Additionally, recent experiences during a forensic evaluation to identify potential sources of excessive presence of foreign object debris on an airfield runway are also briefly discussed in this report. The LAA test and associated acceptance criterion in Unified Facilities Guide Specification (UFGS) 32 12 15.13 were evaluated by testing 24 aggregate sources from various US locations. Also, the Micro-Deval abrasion test was performed as a surrogate abrasion resistance test. Sufficient evidence was not found to suggest adjustments to current LAA test criterion or to recommend the use of an alternative abrasion test. The current UFGS specifications should be improved to provide a more thorough aggregate testing protocol and detailed guidelines regarding aggregate sampling and testing frequency during design and construction of asphalt pavements.
  • Scaled-Up Synthesis of Water-Retaining Alginate-Based Hydrogel

    Purpose: Synthesis of a scaled-up version of a lithium-ion-based alginate/poly(acrylamide-co-stearyl methacrylate) [Li-alginate/P(AAm-co-SMA)] hydrogel with several optimizations for thermal signature investigations on various environmental substrates.
  • Residual Strength of a High-Strength Concrete Subjected to Triaxial Prestress

    Abstract: This study investigates simplified mechanical loading paths that represent more complex loading paths observed during penetration using a triaxial chamber and a high-strength concrete. The objective was to determine the effects that stress-strain (load) paths have on the material’s unconfined compressive (UC) residual strength. The loading paths included hydrostatic compression (HC), uniaxial strain in compression (UX), and uniaxial strain load biaxial strain unload (UXBX). The experiments indicated that the load paths associated with nonvisible microstructural damage were HC and UX—which produced minimal impact on the residual UC strength (less than 30%)—while the load path associated with visible macro-structural damage was UXBX, which significantly reduced the UC strength (greater than 90%). The simplified loading paths were also investigated using a material model driver code that was fitted to a widely used Department of Defense material model. Virtual experiment data revealed that the investigated material model overestimated material damage and produced poor results when compared to experimental data.
  • Instrumented Manikin Data Experiments 1 & 2

    Abstract: In this report, pressure-time histories from a shock front propagating past an instrumented manikin head are presented for two separate experiments. Data represents physical measurements to support an ongoing collaboration between with the US Army Medical Research and Development Center (MRDC) and the US Army Engineer Research and Development Center (ERDC).
  • Graphene in Cementitious Materials

    Abstract: This project aims to determine the influence of laboratory-generated graphene (LGG) and commercial-grade graphene (CGG) on the chemical structure and compressive strength of graphene-cement mixtures. Determining the graphene-cement structure/processing/property relationships provides the most useful information for attaining the highest compressive strength. Graphene dose and particle size, speed of mixing, and dispersant agent were found to have important roles in graphene dispersion by affecting the adhesion forces between calcium silicate hydrate (CSH) gels and graphene surfaces that result in the enhanced strength of cement-graphene mixtures. X-ray diffraction (XRD), Raman, and scanning electron microscope (SEM) analyses were used to determine chemical microstructure, and compression testing for mechanical properties characterization, respectively. Based on observed results both LGG and CGG graphene cement mixtures showed an increase in the compressive strength over 7-, 14-, and 28-day age curing periods. Preliminary dispersion studies were performed to determine the most effective surfactant for graphene dispersion. Future studies will continue to research graphene—cement mortar and graphene—concrete composites using the most feasible graphene materials. These studies will prove invaluable for military programs, warfighter support, climate change, and civil works.