CIV1201_Project2_Final

Nouha Javed
Arman Khabbazian
CIV 1201 Project 2
Non-Destructive Evaluation of Historic
Buildings

Contents
1. Introduction ................................................................................................................. 2
2. Deterioration mechanisms........................................................................................... 2
2.1 Abrasion................................................................................................................. 2
2.2 Corrosion ............................................................................................................... 3
2.2.1 Corrosion by Carbonation................................................................................ 3
2.2.2 Corrosion by Chloride ...................................................................................... 3
2.3 Excessive loading .................................................................................................. 4
2.4 Potential for silica reaction or alkali silica reaction ................................................. 4
2.5 Fire and Heat ......................................................................................................... 4
3. Non-Destructive Testing.............................................................................................. 5
3.1 Half-cell potential mapping..................................................................................... 5
3.2 Rebound hammer .................................................................................................. 5
3.3 Linear Polarization ................................................................................................. 5
3.4 Infrared Thermography .......................................................................................... 5
3.5 Resistivity............................................................................................................... 5
3.6 Phenolphthalein ..................................................................................................... 6
3.7 Visual examination................................................................................................. 6
3.8 Petrography ........................................................................................................... 7
4.0 Challenges ................................................................................................................ 7
5.0 Codes/Guidelines...................................................................................................... 9
6.0 Conclusion .............................................................................................................. 10
References.................................................................................................................... 11

Sound
Optical
Radiation
Electro-
magnetic
1. Introduction
Historic buildings have a unique set of challenges due to a potential lack of information
about the structure and any modification made since the time of construction. Some
historic building may also be in a fragile state, and may not be able to withstand robust
testing. The use of non-destruction testing is best suited to tackle these challenges, and
can be used to find irregularities, differences in material and other forms of deterioration
without influencing the integrity of the structure. NDT can also be used to detect
potential environmental hazards to the structure. This report will explore the types of
commonly found types of degradation, and identify which NDTs are appropriate and the
situations in which they are used in context of historical buildings. Information obtained
by NDT testing can provide valuable information to owners with respect to conservation,
repair and maintenance programs. NDT testing can be categorized in one of the four
categories shown below.
2. Deterioration mechanisms
2.1 Abrasion
Abrasion damage occurs when the surface of concrete is unable to resist wear caused
by rubbing and friction typically caused by foot traffic in historical building over long
span of time. As the outer paste of concrete wears, the fine and coarse aggregate are
exposed and abrasion and impact will cause additional degradation that is related to
aggregate-to-paste bond strength and hardness of the aggregate

2.2 Corrosion
In literature the corrosion is “the corrosion process for reinforced concrete can be
simplified into a two-stage process namely, the ‘initiation phase’ and the ‘propagation
phase’. By definition the initiation phase is the time taken for conditions to become
conducive to corrosion and the propagation phase is the period in which the accelerated
corrosion of the steel reinforcement ultimately leads to rust staining, cracking and
spalling of the cover concrete’’ (Crevello, et al., 2015). NDT testing can be used to
determine the potential for corrosion and rate at which corrosion occurs. Half-cell
potential mapping and linear polarization are two NDTs than evaluate corrosion which
are later discussed in this report.
Figure 1: Example of corrosion
2.2.1 Corrosion by Carbonation
Carbonation occurs when carbon dioxide from the air penetrates the concrete and react
with cement matrix. The chemical reaction causes depassivation of protection layer for
the reinforcement. Reinforcement gradually oxidizes and causes spalling.
2.2.2 Corrosion by Chloride
Chloride can introduce into concrete by coming into contact with environments
containing chlorides such as sea water or de-icing salt. High concentration of chloride in
the concrete causes the reinforcement to corrode. Corrosion is volume expansive
process that causes spalling in historical buildings.

2.3 Excessive loading
Loading service condition can cause deterioration of historical buildings. For example
loading a floor of historic building with books can introduce cracks in floor slabs due
excessive loads.
2.4 Potential for silica reaction or alkali silica reaction
Alkali agreeagate reaction may create expansion and servere caracking of concrete
structure and pabments. The mechanism are not fully understood. What is known about
the the type of reaction is certain types of aggregate react with cement costititunents
and for gel around aggregastes. When the concrete is exposed to moisture the gel
expands causing cracking to occur.
2.5 Fire and Heat
It is not too rare to find a historical building that survived fire in its past. Compressive
strength of concrete cam ne drastically effected when its temperatures exceed 300
degrees celeries.
Figure 2: Temperature v. concrete strength

3. Non-Destructive Testing
3.1 Half-cell potential mapping
Half-cell potential test measure voltage of concrete surface, areas where the potential
difference is highly negative are indication high probability of corrosion.
3.2 Rebound hammer
Rebound hammer is cheap and quick way correlating surface hardness to compressive
strength of materials in historical buildings. It is advisable that historical building owners
develop a ‘correlation chart’ to obtain more reliable results
3.3 Linear Polarization
Linear Polarization Resistance can provide useful information that no other NDT test
can provide. Using electromagnetic field principals one can estimate instantaneous rate
of reinforcement corrosion. This rate can be used to extrapolate range for expected
service of life of historical buildings
3.4 Infrared Thermography
Infrared picture of surfaces can reveal information about the heat flow and localized
differences in surface temperature. The test can be used to detect anomalies such as
delamination in the historical buildings structures
3.5 Resistivity
Four probe methods for measuring concrete resistivity in KΩ.cm. Feilid and Bungey
developed two relationship concrete resistivity and corrosion rate in 1996 and 2006
respectively

Figure 3: Graphic of resistivity test
3.6 Phenolphthalein
Phenolphthalein's common use is as an indicator in acid-base. Phenolphthalein can be
used to measure depth of carbonation on freshly exposed concrete. Phenolphthalein
turn pink if PH is more than 10, and is colorless when concrete is carbonate (PH<8).
The figure below indicates that carbonation is present near the top since it is pink.
Figure 4: Phenolphthalein Test
3.7 Visual examination
Visual examination is one of most crude test yet important method of concrete
evaluation. ACI 201.1R-08 GUIDE FOR CONDUCTING A VISUAL INSPECTION
developed standard for more systematic approach to visual inspection.

3.8 Petrography
Petrography is one of more advance NDT testing being done on concrete. It is prudent
to have trained technician to determine properties of cement and aggregate and
composition of cement matrix and many other properties of concrete that might be of
interest to investigation.
4.0 Challenges
In many cases, the intended design life and desired service life of historic buildings are
several years apart. These buildings are usually still functioning well beyond their
intended service life. For this reason, there are several challenges associated with
working with historic building, including those that the original designers didn’t account
for.
The primary challenge for the rehabilitation of historic structures is working around the
imposed restrictions. These may be in the form of local codes and standards, or based
on the fragility of the existing structure. Examples include landmark restrictions, which
minimize interventions, preserve historic details and replace certain materials. In some
cases “the philosophy of minimal intervention in prevalent throughout the conservation
community which is not in agreement with the general concrete repair industry”
(Crevello, et al., 2015). This difference in opinion between professions is especially
apparent with landmark and iconic buildings. ‘Traditional’ building and repair methods
are often seen as contradictory to conservation standards. Limitations on destructive
testing are commonplace as a result of these standards. Because of this, alternative
methods such as non-destructive testing and degradation models need to be
incorporated into the project plan, and may be need to become the primary source to
rely upon. An effective restoration strategy needs to view the problem from different
points of view, and needs to preserve the structure for future generations while still
maintaining structural integrity and minimizing impact.
Economic considerations are usually also limiting factors as the cost of the rehabilitation
can be more expensive than the cost of replacing the structure. Substantial

contingencies must also be built into the budget as “uncertainties inherent in
rehabilitation [can] result in expensive problems being discovered in the middle of the
repair contract that could not be identified during the evaluation phase” (Davis, et al.,
2001).
Another challenge when working with historic buildings is the potential limitations in
historic building codes. As innovations were introduced over the 19th and 20th
centuries, they were assimilated into the codes and standards. At that time their benefits
were well recognized, but their limitations were identified decades later. Therefore, it is
key to understand what the code requirements were at the time a particular building was
constructed, and identify potential risks. An example of this is the use of alternative (non
Portland) cements at the beginning of the 20th
century, before the use of Portland
cement concrete became the norm. Reinforcing technologies have also varied over
time, with some early systems using wrought and cast iron bars, and twisting the bars to
improve anchorage (Brueckner & Lambert, 2013). Welding modern mild steel to these
older steel can be challenging, as can establishing electrical continuity for the installing
of a cathodic protection system.
In some cases, historic buildings can be neglected for years before a decision was
made to restore it. This lack of maintenance presents a unique set of challenges
concerning the safety of the building, the team performing the assessment and all other
workers involved in the preliminary stages of the project. Safety concerns may also
arise when performing non-destructive testing on a historic bridge. As with any work
done near an active road or highway, there are always risks related to the proximity to
vehicles.
The understanding of the properties of historic building materials is hard to trace or
confirm. Standardization of modern engineering materials is the norm, and the material
properties needed for structural design can usually be found out from a reference
manual or by contacting the manufacturer. For historic buildings, it is possible to also
refer to some historic text, or in rare cases trace construction documents. It could also
be possible to locate a possible manufacturer based on proximity to the construction

site, but that may not always be possible. If no information can be found, the engineer
may have to rely solely on the results of concrete cores, which would increase the
amount of destructive testing needed.
Finally, the nature of the non-destructive testing industry can lead to decreased use of
these methods for projects involving historic buildings. Often testing instrumentation is
used with minimal or no standardization. This leads to results that don’t match
expectations, and the NDT loses credibility with the professionals involved and
“consequently, once an NDT method is perceived to have failed, it is very difficult to
persuade this community that the method may be appropriate for other conditions
(Livingston, 2001). There is also a prevailing attitude that NDT methods are simply too
expensive to be used by a smaller firm, as the cost of the instruments and technicians
can be very high. This attitude fails to take the short and long term benefits of having a
better understanding of the structure into account. Building codes and practices can
encourage the use of NDT, and conservation professionals should have further
education concerning the use of NDT methods.
5.0 Codes/Guidelines
Several reference texts exist to guide the conservation of historic buildings. Canada’s
Historic Places publishes the “The Standards and Guideline for the Conservation of
Historic Buildings in Canada”, which outlines the process for understanding, planning
and intervening projects involving historic structures. Additional standards and
guidelines apply to the restoration and rehabilitation of structures. The National Institute
of Building Sciences’ “Standards for the Treatment of Historic Properties” is a similar
text for use in the United States. This text also has guidelines and standards for the
reconstruction of historic structures. These standards have been created for
conservationists, but all professionals involved in these kinds of projects “should
embrace the tenets of the Interior Guidelines…or the governing conservation body of
the respective country. While standard practices outlined by the American Concrete
Institute, the Corrosion Prevention Association, or the Concrete Society provide a

baseline for surveys, they do not address the sensitivity required to assess historic
concrete” (Brueckner & Lambert, 2013).
The International Code Council publishes the “International Existing Building Code”, and
Chapter 12 of this code specifically applies to historic buildings. The code outlines
standards for safety, accessibility requirements and changes in occupancy. The chapter
mandates that all structural changes made to the existing building must follow existing
building code.
6.0 Conclusion
Non-destructive testing (NDT) is a particularly useful tool in the assessment and
rehabilitation of historic structures. The fragility of these structures and the inherent
uncertainty associated with their history are well suited for NDT methods. Historic
concrete structures are exposed and vulnerable to the same deterioration mechanisms
as with modern concrete structures, but the results may be exacerbated. Abrasion,
corrosion of reinforcing steel, excessive loading, potential for silica reactions and
extreme temperatures all pose a risk to the structure. A variety of NDTs can be used to
identify the potential, or the extent, of deterioration including half-cell potential tests,
rebound hammer, linear polarization, infrared thermography, resistivity, phenolphthalein,
visual examination, and petrography. There are several issues regarding the restoration
methodology for historic buildings, and care must be taken to balance structural integrity
and safety with consideration for the history and preservation of the structure.

References
Brueckner, R. & Lambert, P., 2013. Assessment of historic concrete structures. WIT
Transactions on The Built Environment, Volume 131, pp. 75-86.
Cohen, J. S., 2012. Evaluation of a Historic High-Rise Reinforced Concrete Building.
FORENSIC ENGINEERING, pp. 1198-1207.
Concrete Research and Testing, 2016. Petrographic Examination of Concrete. [Online]
Available at: http://www.concretetesting.com/petrographicexaminationsconcrete/
Crevello, G., Hudson, N. & Noyce, P., 2015. Corrosion condition evaluations of historic
concrete icons. Case Studies in Construction Materials, pp. 2-10.
Davis, A. G., Olson, C. A. & Michols, K. A., 2001. Evaluation of Historic Reinforced
Concrete Bridges. Structures 2001.
Livingston, R. A., 2001. Nondestructive Testing of Historic Structures. Archives and
Museum Informatics, Volume 13, pp. 249-271.
Portland Cement Association, 2002. Types and Causes of Concrete Deterioration.
Concrete Information, Issue 2617.

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