Free Online Education Presentations

Fiber Orientation in Ultra High-Performance Concrete: Quantification, Characterization, and Implications for Design and Performance, Part 2 (ACI Spring 2024, New Orleans, LA) Fiber orientation in ultra-high performance concrete (UHPC) is a critical factor that relates to both material- and structural-level behavior. Many techniques have been studied to quantify fiber orientation including but not limited to computer vision-aided image analysis, computerized tomography (CT) scanning, and electromagnetic methods. This presentation will discuss a pilot study on the application of electrochemical impedance spectroscopy (EIS) to determine fiber orientation and fiber volume in UHPC-class materials. A series of prismatic beam samples were created with different fiber volume fractions. Different casting methods were employed to create random and aligned fiber orientations. Specimens were scanned using EIS and subsequently subjected to 4-point bending to assess tensile resistance. Additionally, a limited parametric study was completed using a commercially available multiphysics modeling platform. This aimed to determine how different parameters such as fiber orientation and fiber volume fraction influence the impedance response. The presentation will provide an overview of this work and its preliminary findings.

FRP Bond and Anchorage in Concrete Structures, Part 1 (ACI Spring 2024, New Orleans, LA) The American Concrete Institute (ACI) 440.1R-15 Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars linearly reduces the bar stress and thereby pull-out capacity of FRP bars to zero from an embedment length at 20 bar diameters (db) or less. Most experimental research and data examine the development length of various FRP bars at longer, more traditional, embedment lengths. A database was created from select available data in literature to compare to empirical standards. This investigation examines the bond performance of short embedded FRP bars into concrete considering a pull-out failure mode to expand the understanding of short embedded FRP bars into concrete. Based upon the database collected, for the glass fiber-reinforced polymer (GFRP) rebars, the current 440.1R appear quite conservative. For the basalt fiber-reinforced polymer (BFRP) rebar database collected, the current ACI 440.1R-15 provisions appear unconservative for a statistically significant number of the specimen test results within the database. In the case of the carbon fiber-reinforced polymer (CFRP) database, which is quite limited, the data appears to develop considerably less bond strength than the current 440.1R provisions might suggest which requires deeper investigation for the case of short embedment length bonded CFRP bars.