Civil Engineering Reference
In-Depth Information
• Aggregate and binder contents
• Water/cement ratio
• Aggregate type
• Aggregate deterioration such as ASR
• Binder type
•
Binder deterioration such as leaching or sulphate attack
•
Porosity and microcrack distribution
Evidence for deterioration at the repair/concrete contact.
2.1.3 Electron microscopy and X-ray microanalysis (SEM/EDXA)
Electron microscopy and X-ray microanalysis techniques are capable of
providing information about chemical composition and microstructure at
magnifications that are much higher than those that can be achieved with
the petrological microscope. Electron microscopy is often most successfully
employed when used in conjunction with conventional petrographic
examination. Some examples of the application of the techniques of electron
microscopy and X-ray microanalysis in the examination of concrete repairs
would include:
•
Mapping the penetration of chloride and sulphate ions
•
Measuring PFA or GGBS contents
•
Identifying the products of chemical attack
•
Assessing the effectiveness of cathodic protection systems (Eden, 2003a).
The scanning electron microscope (SEM) uses a scanning beam of
electrons to form an image of a sample. The electron microscope has the
advantage that it is capable of operating at very high magnifications and can
resolve objects that are much less than 1 μm in diameter. X-rays emitted as
the electron beam interacts with the surface of the sample can be collected
using an X-ray microanalysis system (EDXA) attached to the SEM and can
be used to make quantitative chemical analyses of objects as small as 3 μm.
The X-ray microanalysis system can also be used to map the distribution of
elements around cracks or at interfaces with substrates.
2.2 Identifying the causes of concrete deterioration
Concrete repairs are commonly carried out in response to concrete
deterioration. When examining concrete repairs that have been in place for
several years, the original reason for the repair may not be obvious from a
visual inspection of the structure, yet establishing the cause of the concrete
deterioration is vital if reliable judgements are to be made about the potential
life-span of a repair and the selection of appropriate repair materials.
Petrography is an effective means by which the causes of concrete
deterioration can be established. Reinforcement corrosion is probably the
