3 Jun 2024

Laboratory Evaluation of Recycled Asphalt Pavement and Engineered Polymer Binder for Small Airfield Repairs

Abstract: Conducting small asphalt repairs on airfields in remote locations can be technically and logistically challenging. An alternative to cold patch products is using an engineered polymer binder (EPB) mixed with recycled asphalt pavement (RAP). This paper presents the results of a laboratory evaluation of EPB with both wet and dry RAP. Compacted specimens were tested for rut resistance, indirect tensile strength (ITS), and Cantabro mass loss (ML). The results indicate that RAP mixed with EPB exhibited substantial rut resistance with ITS and ML similar to that of conventional dense-graded asphalt. Overall, the EPB and RAP blend appears to be a promising alternative for airfield repairs.

31 May 2024

pH Pivoting for Algae Coagulation: Bench-Scale Experimentation

Abstract: Harmful algal blooms (HABs) threaten recreational waters and public supplies across the US, causing detrimental economic and environmental effects to communities. HABs can be mitigated with dissolved air flotation (DAF) treatment, which requires addition of pH-sensitive charged chemicals to neutralize algae, allowing them to attach to microbubbles and float to the surface. During HAB events and photosynthesis, algae raise the pH to levels that are not ideal for DAF. Traditionally, pH is reduced with a strong acid; however, this adds operational cost and permanently adjusts the water’s pH. This study assessed an approach that might allow for infusing CO₂ from diesel-powered electricity generators into the water prior to DAF treatment. It was hypothesized that formation of carbonic acid could temporarily reduce the pH. Results showed that 2.5%–5.0% CO₂ mixed within compressed air can achieve pH levels between 6–7 in algal water with an initial pH of 9–11 and alkalinity of 150 mg/L as CaCO₃. Further, dosing CO₂ before chemical addition yielded a 31% improvement in water clarification. Returning the pH back to natural levels was not achieved using ambient air microbubbles; however, coarse bubble air spargers should be tested to provide more volumetric capacity for CO₂ absorption.

31 May 2024

Hydraulic Load Definitions for Use in Load and Resistance Factor Design (LRFD) Analysis, Including Probabilistic Load Characterization, of 10 Hydraulic Steel Structures: Report Number 1

Abstract: In the past, allowable stress design (ASD) was used to design steel structures. The allowable stresses used were determined from previous practice, with limited understanding of the reliability and risk performance provided by the structure. Engineering methods based on Load and Resistance Factor Design (LRFD) provide more accurate lifetime models of structures by providing risk-based load factors. Besides improved safety, cost savings can be provided through improved performance and, in some cases, by delaying rehabilitation. This research project develops LRFD-based engineering procedures for the evaluation and design of hydraulic steel structures (HSS). Hydraulic loads are a key element to the LRFD analysis. This report identifies the primary hydraulic loads and describes procedures that can be used to determine these hydraulic loads. Existing design guidance for HSS is described and presented in the individual chapters. The appendixes to the report provide examples of the procedures used to compute the hydrostatic, wave, and hydrodynamic loads. A new approach for determining wind-induced wave loads was developed. Design guidance for computing the hydrodynamic load was limited for many of the HSS. Additional research is recommended to improve capabilities for computing hydraulic loads. Details on these recommendations can be found in this report.

29 May 2024

Encryption for Edge Computing Applications

Purpose: As smart sensors and the Internet of Things (IoT) exponentially expand, there is an increased need for effective processing solutions for sensor node data located in the operational arena where it can be leveraged for immediate decision support. Current developments reveal that edge computing, where processing and storage are performed close to data generation locations, can meet this need (Ahmed and Ahmed 2016). Edge computing imparts greater flexibility than that experienced in cloud computing architectures (Khan et al. 2019). Despite these benefits, the literature highlights open security issues in edge computing, particularly in the realm of encryption. A prominent limitation of edge devices is the hardware’s ability to support the computational complexity of traditional encryption methodologies (Alwarafy et al. 2020). Furthermore, encryption on the edge poses challenges in key management, the process by which cryptographic keys are transferred and stored among devices (Zeyu et al. 2020). Though edge computing provides reduced latency in data processing, encryption mechanism utilization reintroduces delay and can hinder achieving real-time results (Yu et al. 2018). The IoT is composed of a wide range of devices with a diverse set of computational capabilities, rendering a homogeneous solution for encryption impractical (Dar et al. 2019). Edge devices are often deployed in operational locations that are vulnerable to physical tampering and attacks. Sensitive data may be compromised if not sufficiently encrypted or if keys are not managed properly. Furthermore, the distributed nature and quantity of edge devices create a vast attack surface that can be compromised in other ways (Xiao et al. 2019). Understanding established mechanisms and exploring emerging methodologies for encryption reveals potential solutions for developing a robust solution for edge computing applications. The purpose of this document is to detail the current research for encryption methods in the edge computing space and highlight the major challenges associated with executing successful encryption on the edge.

29 May 2024

Mesoscale Multiphysics Simulations of the Fused Deposition Additive Manufacturing Process

Abstract: As part of an ongoing effort to better understand the multiscale effects of fused deposition additive manufacturing, this work centers on a multiphysics, mesoscale approach for the simulation of the extrusion and solidification processes associated with fused deposition modeling. Restricting the work to a single line scan, we focus on the application of polylactic acid. In addition to heat, momentum, and mass transfer, the solid-liquid–vapor interface is simulated using a front-tracking, level-set method. The results focus on the evolving temperature, viscosity, and volume fraction and are cast within a set of parametric studies to include the nozzle and extrusion velocities as well as the extrusion temperature. Among other findings, it was observed that fused deposition modeling can be effectively modeled using a front-tracking method (i.e., the level-set method) in concert with a moving mesh and temperature-dependent porosity function.

29 May 2024

Impacts of Invasive Species on Populations of Federally Listed Species on US Army Corps of Engineers Project Lands

Abstract: The US Army Corps of Engineers (USACE) is mandated to meet federal, state, and local environmental laws and organizational regulations pertaining to the protection and conservation of ESA (Endangered Species Act 1973)-listed species and associated critical habitats. USACE is also mandated under Executive Order 13112 to document the presence and status of invasive species on their lands. We examine the status of 50 ESA–listed species prioritized by USACE expenditures for ESA compliance from 2014 to 2018. We review the status of invasive species and assess any evidence from published US Fish and Wildlife Service (USFWS) or National Marine Fisheries Service recovery plans or other government documents that indicate whether invasive species are negatively impacting the status of ESA–listed species on USACE lands. We found that 18 of 50 (36%) USFWS recovery plans for these 50 listed species specifically mention invasive species as a primary factor leading to the species’ decline and listing, or they note the need for management and control of invasive species to meet proposed recovery goals. USACE will need to work collaboratively with other federal and state agencies, universities, and nongovernmental organizations to improve control of invasive species and management and recovery of ESA–listed species.

29 May 2024

Comparing Ecological Models for Assessing Rio Grande Silvery Minnow Response to Environmental Flows

Abstract: The proliferation of continuous streamflow monitoring and spatial data suitable for hydraulic modeling is increasing opportunities to use hydraulic habitat analysis to inform ecological models. However, species population and streamflow data exhibit high variability, making it challenging to identify hydrologic and hydraulic metrics that effectively correlate with ecological outcomes. Metric selection presents a challenge for informing environmental flow decisions and adaptive management of water infrastructure. This study applies models to characterize environmental flows with in-creasing model complexity, including the use of hydraulic models to estimate suitable habitat areas at a given flow. The results are compared to field-measured fish outcomes over the same period using functional data analysis. The variance in model correlation with ecological outcomes aids in identifying the most effective environmental flow parameters while also indicating potential pitfalls from increasing model complexity. This analysis demonstrates techniques that synthesize environmental flows with available habitat analysis and validates the approach. The case study is based on the Rio Grande silvery minnow (Hybognathus amarus, minnow), an endangered fish species in the Middle Rio Grande. Analysis focused on different methods to quantify spring runoff coinciding with the inundation of floodplain nursery habitat necessary for the minnow’s larval and juvenile life stages.

29 May 2024

Publications of the U.S. Army Engineer Research and Development Center; Appendix H : FY23 (October 2022-September 2023)

Abstract: Each year, the US Army Engineer Research and Development Center (ERDC) publishes more than 200 reports through the Information Technology Laboratory’s Information Science and Knowledge Management (ISKM) Branch, the publishing authority for ERDC. Annually since 2017, ISKM has compiled a list of the last fiscal year’s publications. This Appendix H to the original collection includes ERDC publications issued October 2022 through September 2023. The publications are grouped according to the technical laboratories or technical program for which they were prepared, and the preface includes procedures for obtaining ERDC reports. Through this compilation, online distribution, and physical collections, ISKM continues to support ERDC, the Army, and the nation.

29 May 2024

Performance of Army Corps of Engineers Mat System Using Anchorless Connections: A Follow-on Study of Site Stabilization for the Improved Ribbon Bridge Bridge Supplemental Set

Abstract: The US Army Engineer Research and Development Center conducted testing of the Army Corps of Engineers mat system with improved anchorage and connection hardware. Low-profile screw anchors replaced the ground anchorage of the existing system to reduce wear to tracks and wheels of vehicles while trafficking the system. Anchorless connections allowed the system to be placed over soils where the use of screw anchorage would be obstructed or would cause hazards to trafficking vehicles. Test tracks were constructed to evaluate the matting system with new anchorage and connection hardware over three different soils of weak sand and clay. Channelized traffic was applied to the test tracks using a loaded common bridge transporter. Performance of the updated system was evaluated with respect to results from previous testing, indicating that the improved anchorage and connection hardware increased the versatility of the matting system without sacrificing system performance.

29 May 2024

Finite Element, Petrographic, and Mechanical Analyses of Field-Cored Concrete Fairlead Beam Anchor Rods from Luke Air Force Base

Abstract: The fairlead beam is used to accomplish installation of the Barrier Arresting Kit 12 energy absorber for setback aircraft arresting system (AAS) installations at permanent operating facilities. Typical fairlead beams are affixed to a Portland cement concrete (PCC) foundation pad by a series of anchor assemblies made up of steel anchor rods set in grout inside galvanized pipe sleeves. US Air Force Civil Engineering Center (AFCEC) subject matter experts have identified a pattern of premature failures in these steel anchor assemblies when they are nondestructively inspected during AAS overhauls. The US Army Engineer Research and Development Center was tasked by AFCEC to investigate potential reasons for these premature failures. This report outlines methods and results of a finite element analysis of the anchorage, a visual and petrographic analysis of field-cored PCC anchor rods from Luke Air Force Base, and a mechanical analysis of specimens taken from the anchor rods within the PCC cores. Multiple modes of PCC distress were observed, and corrosion was evident in and around the anchor assemblies. Mechanical testing of specimens from the anchor rods indicated that an inferior grade of steel was used to fabricate these particular assemblies. Finally, observed deviations from design intention are discussed.