A discrete transport-mechanical approach for modelling the durability of concrete

Fahy, Caroline (2014) A discrete transport-mechanical approach for modelling the durability of concrete. PhD thesis, University of Glasgow.

Abstract

Reinforced concrete is one of the most commonly used structural materials in the world and
is used for buildings and many different types of civil engineering structures, such as bridges,
tunnels and airports. The majority of these structures are required to remain in service for
at least 50 years while some are expected to last well over 100 years. Fracture of these
structures leads to an increase in the permeability of the concrete which in turn can result in
increased ingress of water and other aggressive agents, such as chlorides or carbon dioxide,
that accelerate the deterioration of these structures. Likewise, the mechanical properties of
the concrete can be affected by the transport of moisture into the structure. The increase in
moisture can lead to a reduction of the strength and the stiffness of the material.
The costs arising from structural failure are extremely high and in practice repair work tends
to be implemented even when it is not entirely necessary. Therefore reliable approaches that
can describe the interaction between the transport and mechanical properties of concrete and
predict resulting structural degradation are of great benefit for practising engineers. Numerical
models, such as the one proposed in this work, could be used for predicting when a
repair is really necessary.
In this work, a transport-mechanical lattice approach to modelling the durability of concrete
is proposed. The discretisation of the specimen domain is based on a dual Delaunay and
Voronoi tessellation in which the edges of the Delaunay triangles form the mechanical elements
and the transport elements are placed along the edges of the Voronoi polygons. The
mechanical response of the concrete is described using an isotropic damage constitutive law,
while the transport of moisture through the specimen is described using constitutive laws
developed for mass transport through porous materials.
Both the mechanical and the transport models are assessed individually before the coupling
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between the two models is implemented. The accuracy of the proposed coupled approach
is validated through the analysis of an elastic thick-walled cylinder, in which the numerical
results are compared with an analytical solution derived as part of this work. The proposed
coupled approach is then applied to the case of corrosion-induced cracking of reinforced
concrete structures. In this approach, the corrosion products are assumed to behave as a
fluid and therefore values of fluid properties are required. A value of viscosity is determined
based on the analysis of a concrete specimen containing a single reinforcement bar. Finally,
the proposed approach is applied to a concrete specimen containing four reinforcement bars
to assess the approach as a predictive model.
As expected with the concrete specimen containing a single reinforcement bar, very good
agreement between numerical and experimental results is obtained. In the case of a specimen
containing four reinforcement bars, it is observed that for small attack penetration
depths the proposed approach is in very good agreement with experimental results. As the
analysis continued, however, the numerical approach under-estimated the crack width when
compared to experimental results.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Reinforced concrete Coupled transport-mechanical Computational modelling Cracking Hydraulic fracture
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Grassl, Dr. Peter
• Date of Award: 2014
• Depositing User: Caroline Fahy
• Unique ID: glathesis:2014-5761
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 13 Nov 2014 11:06
• Last Modified: 13 Nov 2017 13:20
• URI: https://theses.gla.ac.uk/id/eprint/5761