PhD Defense by Koochul Ji

Event Details
  • Date/Time:
    • Thursday October 22, 2020
      2:30 pm - 4:30 pm
  • Location: REMote
  • Phone:
  • URL: Bluejeans
  • Email:
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    N/A
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Summaries

Summary Sentence: Numerical modeling of mechanical recovery in damaged concrete repaired by epoxy at molecular and metric scales

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Ph.D. Thesis Defense Announcement

Numerical modeling of mechanical recovery in damaged concrete repaired by epoxy at molecular and metric scales

 

by

Koochul Ji

 

Advisor(s):

Dr. Chloe Arson (CEE)

 

Committee Members:

Dr. Susan E. Burns (CEE), Dr. Kimberly E. Kurtis (CEE), Dr. Lauren K. Stewart (CEE), Dr. Olivier Pierron (ME) 

Date & Time: Oct. 22, 2020 at 2.30pm

Location: https://bluejeans.com/854653129?src=join_info

 

 Complete announcement, with abstract, is attached

Almost half of the U.S. bridges will require a major structural investment within the next 15 years. Naturally,
the importance of preventive design and maintenance was stressed in many previous studies that aimed to
assess reparation techniques. Due to its economical and practical benefits, polymer injection is widely
employed to repair cracks in concrete structures. In this thesis, we investigate the mechanisms of
mechanical recovery in concrete repaired by epoxy at atomic and metric scales.
The first part of the thesis presents Molecular Dynamics (MD) models of High Molecular Weight
Methacrylate (HMWM). MD pull-out tests on calcite/HMWM and silica/HMWM interfaces show that the
tensile strength of concrete/HMWM interfaces is optimal in dry conditions and at low temperatures, and
that silica/HMWM interfaces are stronger than calcite/HMWM interfaces. Richeton's model and Johnson-
Cook model are employed to predict the tensile modulus of HMWM and the interfacial strength between
HMWM/concrete minerals at a low strain rate. In order to investigate the effect of interlocking on interface
shear strength, we simulate shear deformation tests with silica/polymer interfaces, in which the substrate is
either smooth or rough. Longer polymer chains promote higher strength but impede notch filling. Rough
interfaces are in average 1.5 stronger than smooth ones. In both mode I and in mode II, MD results
indicate that the work of separation is mostly attributed to van der Waals forces.
In the second part of the thesis, we present a numerical modeling approach based on the Finite Element
Method (FEM), in which HMWM joints and cracks repaired by HMWM are represented by cohesive zone
elements and concrete, by a damage-plasticity model. The model is calibrated against experimental results
obtained on cut and sealed concrete specimens and verified against data on reinforced concrete (RC)
beams and Pre-Stressed Concrete (PSC) beams. Simulation results suggest that HMWM can penetrate
cracks of width 0.01 mm and above by gravity. We also find that HMWM reparation increases concrete
stiffness and strength if cracks in concrete members are over 0.1 mm in width, in which case, the load
capacity of repaired RC beams is 30 to 40% higher than that of as-built RC beams. We also simulate prestressing,
strand release, and four-point loading of PSC girders. We find that the load capacity of a PSC
girder damaged by pre-stressing and then repaired would be about 7% higher than that of the as-built PSC
girder.

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Phd Defense
Status
  • Created By: Tatianna Richardson
  • Workflow Status: Published
  • Created On: Oct 8, 2020 - 4:09pm
  • Last Updated: Oct 8, 2020 - 4:09pm