Civil Engineering Reference
In-Depth Information
2 The petrographic
examination of concrete
and concrete repairs
Mike Eden
2.1 Introduction
The most commonly employed methods of testing concrete for concrete
repairs such as measuring compressive strength or cement content or pull-
off testing for bond strength, leave many unanswered questions when it
comes to assessing the condition of the concrete in a structure, or the overall
effectiveness of a concrete repair. For example, the bond strengths measured
by pull-off testing may be low but it is often not possible to determine why
this is so without further testing. The measured cement content may be
unexpectedly low, but it is not possible to determine without further testing
whether or not the repair material contains a cement replacement material
such as PFA that might affect the cement content measurement.
The key questions that can be answered by petrographic examination in
evaluating a concrete structure in need of repair are:
•
What is the current condition of the concrete?
•
Is the concrete undergoing on-going deterioration?
•
What depth of concrete needs to be removed before repair materials can
be applied?
For evaluating an existing concrete repair, the following additional
questions can be answered from petrographic examination:
•
In what condition is the bond between the repair and the substrate?
•
Has the repair material deteriorated?
This chapter introduces petrographic examination as a cost-effective
method capable of providing information about many different aspects of
the condition of a concrete repair, the substrate and the bond between the
repair and the substrate. It describes how cementitious repair materials may
be identified petrographically and describes the diagnosis of problems with
concrete repair durability.
