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.