Infuence of Alkali-Silica Reaction on the Shear Capacity of Reinforced Concrete Slabs Without Shear Reinforcement

Søren Gustenhoff Hansen*

*Corresponding author for this work

Research output: ThesisPh.D. thesis

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Alkali-silica reaction (ASR) is a deterioration mechanism that can occur in concrete
structures. It is a chemical reaction between alkalis, silica minerals in the reactive aggregates and water. The reaction causes severe cracking of the concrete, which results in
significant reductions of the strength parameters. This material degradation has raised
serious concerns regarding the safety of ASR-damaged structures; particularly structures,
which may be sensitive to shear failure. The Danish Road Directorate has estimated that
more than 600 Danish road bridges have the potential to develop ASR in the future. The
majority of these bridges has been constructed as slabs without shear reinforcement, i.e.
structures where the shear capacity relies entirely on the strength of the concrete. Unfortunately, there exists no satisfactory method to assess the residual shear capacity of
ASR-damaged slabs without shear reinforcement - in spite of nearly 80 years of research
on ASR.
The aim of this PhD project is therefore to develop an approach that can be used to
determine the shear capacity of ASR-damaged slabs without shear reinforcement. The
approach includes a shear model as well as recommendations and descriptions of how
the relevant strength parameters should be determined by simple tests on samples taken
from the structure. The works that have been undertaken to develop this approach are
as follows.
In the first part of the project, a literature study on how ASR affects the parameters
that are important for the shear capacity is conducted. One of the main findings here
is that ASR affects slabs differently than other types of structures, e.g. the way that
the ASR-induced cracks are orientated. The majority of the existing ASR research on
material characteristics and/or residual capacity of reinforced members is therefore not
directly applicable for this PhD project. Based on the findings as well as shortcomings
in the existing literature, a number of research questions that need answers in order to
develop a shear model for ASR-damaged slabs are formulated.
In the second part of the project, answers to the formulated research questions are found
by means of a thorough experimental investigation, where the effects of ASR on the
material properties as well as on the structural response are studied. The investigation
includes a large shear testing campaign with specimens cut out from two ASR-damaged
bridges. The material properties are investigated by means of standard test methods
and Digital Image Correlation (DIC). By a critical examination of the results and an
optical investigation of the underlying mechanisms, recommendations of testing methods
to obtain the anisotropic residual compressive- and tensile strength are formulated.
In the last part of the project, a model to determine the shear capacity of ASR-damaged
slabs without shear reinforcement is established. The model is based on the upper bound
theorem of plasticity theory, where the specific solutions are derived with inspiration
from the failure mechanisms observed in shear tests with the ASR-damaged slab bridge
specimens. The calculated shear capacity correlates well with test results, both for simply
supported members and for continuous members.
Based on the model, some recommendations are given for how practical assessment of
members subjected to arbitrary loading can be carried out.
Original languageEnglish
  • Hoang, Linh Cao, Supervisor
Publication statusPublished - 4. Apr 2019


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