full text is available online.
|Title:||Environmental Durability of Hybrid Braided Polymer Matrix Composites for Infrastructure Applications|
|Committee Chair:||Roberto A. Lopez-Anido, Professor of Civil Engineering|
|Committee Members:||William Davids, Professor of Civil Engineering ; Edwin Nagy, Instructor of Civil Engineering|
|Date of Defense:||2011|
The composite arch technology developed by researchers at the University of Maine is being implemented in several bridges throughout New England. These bridges use concrete-filled structurally integrated stay-in-place fiber reinforced polymer (FRP) composite forms. The FRP composite arch form confines the concrete and provides tensile strength traditionally gained with steel rebar. The composite system durability and maintenance requirements need to be evaluated and compared to that of traditional bridge structures. An asymmetric hybrid carbon and E-glass fiber braided reinforced composite laminate was selected. This hybrid composite laminate is representative of the material used to fabricate the composite arch forms. The hybrid composite laminate was adopted for evaluation of the effect of various environmental conditions on the material properties. First, the proposed asymmetric hybrid composite laminate was investigated to determine if the experimental procedure would produce accurate and consistent measurements of material properties. A rectangular composite coupon reinforced with one layer of braided carbon fibers and one layer of braided E-glass fibers embedded in vinyl ester epoxy resin was used to determine the elastic properties. A notched composite coupon, made of the same materials, was adopted to produce a fiber rupture failure mode in order to determine the ultimate tensile strength in the longitudinal direction of the arch. First a model was implemented using micromechanics equations and classical lamination theory to predict the elastic properties of the composite under a tensile load. Second, a phenomenological damage model was proposed to predict the strength of the hybrid composite based on the properties of individual carbon and E-glass fiber reinforced layers. The model is bilinear to account for damage in the layer that fails at the lower tensile strain. After the initial failure the model can consider either a brittle or a yielding response of the damaged layer. Furthermore, the model considers the efficiency of the carbon fiber tows in the notch specimen to determine the ultimate tensile strength. The asymmetric hybrid composite laminates were subjected to different environmental conditions to assess the durability of the composite arch forms. The environmental factors investigated include: water resistance, saltwater resistance, dry heat resistance, alkali resistance, freeze thaw resistance, UV resistance, and gasoline fuel resistance. After being exposed to a particular environmental condition coupons were cut from the laminate sheets and tested in tension to determine their tensile strength and elastic properties. Selected environmental conditions had coupons tested for multiple exposure durations to determine the rate of change of material properties over time. The change of elastic properties over 1000 hours was less than 10% and the corresponding change of tensile strength was less than 15% when comparing mean values. The environmental durability studies showed that after exposure to seven separate environmental conditions, most tensile material properties retained at least 90% of the control values. Water, saltwater, alkali, and dry heat exposure was also evaluated based on Acceptance Criteria 125 (ICC Evaluation Service) as recommended by AASHTO (2009). It was found that most conditions passed the acceptance criteria after the initial round of testing as described in this study. Studies were also done on the abrasion resistance and ignition resistance of the composite system. A test for ignition resistance showed that a small flame was not able to ignite the outer surface of the arch material after a 10 min exposure time. Furthermore, tests for abrasion resistance lead to the conclusion that an additional abrasion protection layer would provide a significant increase in abrasion resistance.
Demkowicz, Mackenzie, University of Maine, CIE2011-004