主题：Microstructural characterization and wave-modulus simulation of concrete materials
主持人：Professor Lizhi Sun
摘要：This seminar presents a quantitative analysis of microstructural damage evolution of concrete materials under freeze-thaw (F-T) action using three-dimensional (3D) X-ray computed tomography (CT). The microstructural damage evolution as well as pore network (porosity, pore size, and pore distribution) are specifically investigated. The concrete microstructures of different F-T action show that the interfacial transition zone (ITZ) is most likely to be damaged first under frost attack. Pores and cracks can nucleate during the F-T action, and further accumulate and grow in the paste and aggregates, eventually leading to concrete failure. It is demonstrated that 3D X-ray CT is capable of acquiring microstructures of concrete and revealing existence of internal pores and cracks in different phases of concrete, and effective to characterize accumulated damage of concrete due to F-T action. Based on the nanoCT microstructure, we further conduct micromechanics-based numerical simulation of effective wave-moduli of concrete materials. The effects of heterogeneous aggregate size and shape are investigated on the wave-moduli. Finite element results are also compared with experimental data from smart aggregate technique to demonstrate the dependence of overall wave-moduli on material heterogeneity.
个人介绍：Dr. Lizhi Sun is Professor of Department of Civil and Environmental Engineering (CEE) at University of California, Irvine (UCI). He received his B.S. degree in Engineering Mechanics from Zhejiang University in 1987, M.S. degree in Solid Mechanics from Peking University in 1990, and Ph.D. degree in Civil Engineering from University of California – Los Angeles (UCLA) in 1998. Dr. Sun’s primary area of research is the micro/nano-mechanics of heterogeneous composite materials, with applications in structural, aerospace, and biomechanical engineering. He has published more than 160 papers including 90 peer-reviewed journal papers in the fields of mechanics and materials. He wins academic and research awards such as ASCE Engineering Mechanics Institute Fellow (2014), UCI Civil and Environmental Engineering Professor of the Year (2013), AFRL Faculty Fellow (2011), UCI School of Engineering Fariborz Maseeh Best Faculty Research Award (2008), and Honda Research Initiation Award, (2006). He is an editor for International Journal of Damage Mechanics, and associate editor for ASCE Journal of Engineering Mechanics and ASCE Journal of Nanomechanics and Micromechanics. He is a member of ASCE, ASME, MRS, and AAAS and has been the committee chair for ASCE Committee on Inelasticity Modeling and Multiscale Behavior (2009-2011), ASCE Committee on Nanocomposites (2012-2013), and ASCE Committee on Nanomechanics and Micromechanics (2014-2017).
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