• Durability and Smart Condition Assessment of Ultra-High Performance Concrete in Cold Climates

      Qiao, Pizhong; Zhou, Zhidong; Allena, Srinivas (Center for Environmentally Sustainable Transportation in Cold Climates, 2016-12-31)
      The goals of this study were to develop ecological ultra-high performance concrete (UHPC) with local materials and supplementary cementitious materials and to evaluate the long-term performance of UHPC in cold climates using effective mechanical test methods, such as “smart aggregate” technology and microstructure imaging analysis. The optimal UHPC mixture approximately exhibited compressive strength of 15 ksi, elastic modulus of 5,000 ksi, direct tensile strength of 1.27 ksi, and shrinkage of 630  at 28 days, which are characteristics comparable to those of commercial products and other studies. The tensile strength and modulus of elasticity in tension, dynamic modulus, and wave modulus show slight increases from the original values after 300 freeze-thaw (F-T) cycles, indicating that UHPC has excellent frost resistance in cold climates. Although porosity deterioration was observed in the F-T cyclic conditioning process, no internal damage (cracks or fractures) was found during imaging analysis up to 300 cycles. Since structures for which UHPC would be used are expected to have a longer service life, more F-T cycles are recommended to condition UHPC and investigate its mechanical performance over time. Moreover, continuum damage mechanic-based models have the potential to evaluate damage accumulation in UHPC and its failure mechanism under frost attack and to predict long-term material deterioration and service life.
    • Freeze-Thaw Durability and Long-Term Performance Evaluation of Shotcrete in Cold Regions

      Qiao, Pizhong; Zhou, Zhidong (Center for Environmentally Sustainable Transportation in Cold Climates, 2017-12-31)
      This study’s aim was to evaluate the freeze-thaw durability of shotcrete in cold regions and predict its long-term performance. One benchmark mix design from the WSDOT was chosen to prepare samples for performance evaluation. Shotcrete specimens were conditioned in accordance with ASTM C666. The long-term freeze-thaw performance after certain cycles was evaluated using the dynamic modulus of elasticity test (ASTM C215), fracture energy test (RILEM 50-FMC), and X-ray CT microstructure imaging analysis. Probabilistic damage analysis was conducted to establish the relation between the durability life and the damage parameter for different probabilities of reliability using the three-parameter Weibull distribution model. The fracture energy test was found to be a more sensitive test method than the dynamic modulus of elasticity for screening material deterioration over time and for capturing accumulative material damage caused by rapid freeze-thaw action, because of smaller durability factors (degradation ratios) obtained from the fracture energy test. X-ray CT imaging analysis is capable of detecting microcracks that form and pore evolution in the aggregate and interface transition zone of conditioned samples. Moreover, the continuum damage mechanic-based model shows potential in predicting long-term material degradation and the service life of shotcrete.
    • Smart FRP Composite Sandwich Bridge Decks in Cold Regions

      Hulsey, J. Leroy; Qiao, Pizhong; Fan, Wei; McLean, David (Alaska University Transportation Center, 2011)