Final_Paper-libre.pdf

Shayna L. Scott

1/29/2015

THE MAINTENANC E & REPAIR

O F REINFO RC ED C O NC RETE

HIPR -709 Conservation Science & Preservation Technology

The goal of this paper is to demonstrate that reinforced concrete structures have the

potential to last for prolonged periods when properly cared for using the technology and knowledge that is currently available, and that will become available in the future.

During the 20th century, reinforced concrete became an increasingly popular building

material for everything from houses to highways, resulting in a new breed of historic structures that will need specialized care. The main three sub-topics that are addressed

in this paper are how to properly maintain reinforced concrete, how to recognize

failures, and the treatment options available to remedy them.

The Maintenance & Repair of Reinforced Concrete

INTRODUCTION

The field of architectural conservation is one that must constantly evolve to include the study of

non-traditional materials and building practices.

In the mid-1900s, reinforced concrete (RC) became a prominent construction material for both residential and commercial buildings

because of its strengths and versatility.

As construction evolved, concrete became

tantamount with modern architecture and its use

became more popular and widespread. In order to preserve and protect historic RC buildings

today and in the future, it is necessary to

understand its maintenance requirements,

failures and treatment options.

THE COMPOSITION & HISTORY OF CONCRETE

Concrete is a mixture of water, cement and

aggregate. Portland cement was patented in 1842; this formula has dominated the concrete

industry because of its success in construction.

The ratios of cement, aggregate and water used in a concrete mix will greatly affect its

durability, strength and overall performance. A

concrete mixture that has too much water will

crack easily, while a mix with too little water

will be overly porous. A good concrete mix

consists of 10-15 parts cement, 60-75 parts aggregate and 15-20 parts water. A well-proportioned concrete mix will be pliable when

1 Tensile strength is the ability to resist breaking under

tension.

wet, and strong when cured. (Portland Cement Association 2014)

Concrete has been in use for thousands of years

because of the many advantages it offers as a

construction material. Concrete can be shaped in almost any manner, making it suitable for almost

anything, it is a good insulator (which makes it more sustainable), and it can resist fire, rain, wind, insects, and biological attacks. (Civil Engineers Forum 2015)

Figure 1. Egyptian Pyramids Constructed w/ Concrete.

Figure 2. The Pantheon in Rome. Built w/ Concrete-like Substance

A major drawback to concrete is that it has low tensile strength and ductility, but the addition of steel reinforcement bars or fibers helped to

improve these properties.1

Ductility is the ability to take on a new form.

S. L. Scott HIPR 709 Conservation Science & Preservation Technology P a g e | 1


Chemist and engineers led the innovation of RC;

unlike other building materials, it required a

thorough understanding of how steel and concrete work together. (Forty 2012) Accordingly, the maintenance and repair of this

composite material is a science that requires the

expertise of a professional.

In 1860, S.T. Fowler took out the first patent in the U.S. for a RC wall. It was not until the

1880s that the use of RC became more

widespread. (Coney 2012) In Europe, a few designers patented systems for the proper use of RC in an attempt to regulate its use in

construction. The Monier system was prevalent

in Germany & Austria, and in France, the

Hennebique system served as models to many RC buildings of the 19th and early 20th century.

(Forty 2012)

Figure 3. Crown Hall, Illinois Institute of Technology, Chicago, 1956.

Today, RC is one of the most commonly used

construction building materials. Leading

architects of the 20th century advocated the use of RC and it was instrumental in the

development of the modern architecture

movement. Iconic buildings such as Crown Hall

at the Institute of Technology in Chicago by

Ludwig Mies Van der Rohe, and the

Guggenheim Museum by Frank Lloyd Wright

increased the popularity and use of RC in both

residential and commercial sectors.

Figure 4. The Guggenheim Museum: Spiral Ramp and Glass Dome, 1959.

CYCLICAL MAINTENANCE

Regular maintenance is vital to the preservation

of RC. It allows for the early detection of

physical, chemical and mechanical damage.

Other components such as gutters, downspouts and roofs must also be up-kept, if not they can

contribute to the deterioration of RC. For

example, a clogged gutter or a leaky roof can

cause water damage to RC. Factors that might determine the maintenance schedule for a

structure include materials, geographic location,

building use, and the age of the building.

The thorough analysis of a building must be

complete before a maintenance or repair schedule is developed. Existing cracks,

efflorescence, spalling, and other findings that

indicate failure must be recorded for future

reference. The review of existing maintenance

and repair records is recommended prior to the

commencement of new repairs or the

development of maintenance schedules. Old



records may contain valuable information about

the buildings history such as previous

maintenance schedules, former repairs and

alterations.

CLEANING METHODS

It is necessary to test small, discrete areas of the

RC prior to cleaning any large surface. The cleaning method selected should be appropriate

for the level of soil on the surface. It is

recommended to use the gentlest cleaning

method possible; the purpose of cleaning is to prolong the life of a structure, not make it look

new.

The use of harsh chemicals or abrasive methods

such as sand blasting to clean RC is not

advisable; it can accelerate failure of the RC, and result in the loss of historic integrity. It must

also be decided if cleaning is even required;

some stains are part of the historic fabric of the

building and have bonded to the concrete, providing a protective barrier.

Figure 5. Pressure Washing on Exterior Concrete Wall.

Low-pressure water is one of the most common

methods of cleaning RC, the stream should not

exceed 200 psi for historic edifices; higher

pressures are acceptable only on high-strength,

sound concrete when there is no danger of causing damage. (Slaton 2015) Micro abrasive

treatments can be effective for the removal of

heavy soil, but only when applied by a

professional as they can alter the surface of RC if used incorrectly. Wet blasting uses small

particles of limestone and other similar material

in the water stream at pressures of around 35 to 75 psi. (Slaton 2015)

A third method of cleaning RC is with the use of chemicals. Mild detergents and water may

remove heavy soils when paired with light

scrubbing with a natural bristle brush. Strong

substances such as muriatic acids are inappropriate as they may affect the RC

adversely, causing etching, bleaching or other

undesirable reactions to occur.

SURFACE TREATMENTS

If the walls of a building are comparable to the bones in a human, then paint and sealants are

equivalent to skin. Without the protection of

paints and sealers, moisture, salts and acids permeate the porous network, causing damage to

the concrete and the embedded steel. There is a

surfeit of paints and other surface treatments available on the market, but only some are

appropriate for use on concrete.

Paints should be used that are 100% acrylic-latex

because of their water resistant properties; oil

based paints should never be used. (California Paints unknown) Elastomeric paint is a good choice for concrete surfaces because it has a

plasticity that helps to bridge surface cracks.

The best elastomeric paints are breathable to

allow water vapors to escape.



Figure 6. Cracks in Concrete Wall.

Surfaces should always be clean and dry prior to

the application of any paint. Existing layers of

paint should not be removed unless they are

bubbling up, and have lost adhesion to the surface. Older layers of paint are part of the

historic fabric of the building, see Figure 7. The

forceful removal of paint by mechanical means such as sandblasting could expose the concrete,

making it vulnerable to invasion by moisture and

chemicals.

Waterproof coatings can improve a concrete

surfaces ability to resist external elements. Waterproof treatments do not function the same

as water repellents. With water repellents, the

objective is to change the nature of the concrete by filling the pores. Concrete needs to remain breathable to allow the escape egress of water

vapors. In regions that have saturated soils, a

condition called damp rising can cause austere

impairment of the RC if the moisture does not

have a path of egress, see Figure 8.2

2 Damp rising is when moisture from water saturated

soil below the grade, penetrates a wall. The moisture then rises vertically up the wall, causing damage both inside the wall and to adjacent materials.

SUB-SURFACE TREATMENTS

The application of water repellants and impregnations that are not hydrophobic, are

only suitable for isolated areas.3 These coatings

should be used sparingly because they often

leave a film on the concrete surface and are

irreversible.

Hydrophobic impregnations penetrate the

surface of concrete and line the capillaries and

pores network, making it water repellent. (Sika n.d.) These products typically do not leave a film on the surface, but require periodic

reapplication in order for the product to remain

effective. Unlike water repellent treatments,

they do not block the egress of water vapors and

are safe for use on RC. Under the advice of the

Secretary of the Interior, it is advisable to test all

products prior to use; not doing so could cause

irreversible damage to the concrete surface.

Figure 7. Layers of Historical Paint on Wall.

3 Impregnation is the treatment of concrete to make

the surface stronger and less porous by partial or complete filling of the capillaries. (Sika n.d.)



Figure 8. Rising Damp on Concrete Wall.

Corrosion inhibitors can protect the embedded steel from oxidizing; when steel expands, it causes damage to the concrete by exerting too

much force. Traditionally, corrosion inhibitors

were applied to rebar prior to implanting them

into concrete. Today, formulas exist that inhibit corrosion of the rebar via impregnation of the

surrounding concrete. These products prolong

the life of RC structures by shielding the rebar

post-construction. A regular maintenance task

may include the application of an impregnable

corrosion inhibitor to areas of the concrete that

are prone to water and/or chemical damage.

PREVENTATIVE MEASURES

Surface treatments are just one method of protecting RC from damage; other preventative

measures can thwart repairs. Downspouts can be re-positioned if the water runoff is too close to

the structure. In regions where it snows, deicing

salts that are used to catalyze the melting of the

snow can be problematic to RC. The salts penetrate concrete and deposit chloride ions that

can cause corrosion of the embedded rebar, and

efflorescence or sub florescence in the concrete.

It is best to stipulate that deicing salts be

prohibited from use adjacent to RC structures.

Figure 9. Efflorescence.

Figure 10. Water Absorbing Tree.

Windows, doors and other openings with

improper seals can also invite water damage.

Modern heating and cooling systems can pose a problem when temperatures and humidity levels

vary too greatly between interior and exterior

environments and cause condensation. (Park n.d.)

A site can be used and manipulated as an unobtrusive tool to control moisture and minimize

damage to a structure. Sloping the grade down,

away from a structure is an effective way to

prevent water from becoming stagnant adjacent to foundation walls. Paved areas contiguous to the



structure prevent water from saturating the soil

beneath the foundation, which can lead to damp

rising as discussed earlier. The planting of trees and plants that soak up water a safe distance from

a structure is another effective method to reduce

saturated soil near the foundation of a building.

DIAGNOSING DAMAGE

Reinforced concrete is susceptible to three different classes of attack: physical, mechanical

and chemical. Shrinkage, thermal movement,

erosion, abrasion and freeze/thaw cycles are examples of physical attack. Impacts to the

structure, overloading, movement, vibration,

earthquakes and explosions are mechanical

attacks. Chemical attacks are perhaps the most injurious of the three categories of attackers; they can cause destruction to both the concrete and the

rebar. This class of attacks includes damage that

results from alkali-aggregate reactions, sulfates,

chlorides, acids, carbonation, efflorescence and

mold. (Sika n.d.)

One of the most recognizable signs of failure is a

crack in a vertical or horizontal surface. Spalling,

mold, rust stains and efflorescence are also signs of failure. In cases where damages are severe, it

is usually the result of extended periods without

maintenance, unfamiliarity with RC structures or insufficient funds. Early detection of failure is

critical and may be the difference between a

minor and major repair.

PHYSICAL ATTACKS

Figure 11. Cracks Indicative of Shrinkage.

Shrinkage can occur during the drying process and may produce a random pattern of fine cracks

that are not of much consequence. RC structures are less susceptible to shrinkage cracks than

concrete buildings that do not have

reinforcements. A greater ratio of aggregate in a

concrete mix can reduce shrinking during the curing process. Concrete that cures under hot

and/or dry conditions will have a greater

percentage of shrinkage than if it were cool and

consistently wet throughout the curing process.

Figure 12. Thermal Expansion Crack

Thermal expansion is the process of concrete expanding due to an increase in temperature.

Cracks may form on the surface of the concrete



that are vertical and/or diagonal; the cracks

usually originate from the corner of an orifice.

These cracks are not of great concern and can be easily remedied; they only detract from the

aesthetics of a building.

Figure 11. Erosion Damage.

Erosion is the deterioration of the concrete

surface by physical or mechanical means. One of the most common causes of erosion is the

application of water at pressures that are too high

during surface cleaning. Cleaning concrete

surfaces with water pressures higher than 400 psi is a common cause of erosion. Lower pressures

are more appropriate, especially for damaged or

weakened surfaces.

Figure 12. Abrasion Damage.

Abrasion damage is generally limited to floors

and is the result of constant traffic. Abrasion can

wear down horizontal surfaces and ultimately

change the texture. Constant wear and tear can

also lead to cracks and/or pieces of the concrete breaking off, especially near edges. Surface

treatments are available to help resist abrasion

and prolong the life of concrete floors.

Figure 13. Freeze/Thaw Damage.

Freeze/thaw damage is a problem in regions that have snow and can result in cracking, spalling

and delamination. (Penn State Uniersity nd.) Concrete made with a high ratio of water is at a

higher risk of freeze/thaw damage. As the

excess water dries out, more voids are created within the concrete, those voids trap water, and

more tension is put on the concrete as it expands.

Freeze/thaw expansion is a serious concern that

requires action; if it is not addressed, the severity of the damage will increase due to the already

compromised state of the concrete.

MECHANICAL ATTACKS

Overloading, can cause severe damage to RC structures and is not always foreseeable.

Overloading can occur when too much weight

from machinery or other equipment is loaded

onto a floor. This is imperative to remember



when historic buildings are re-purposed for a

new use, an engineer should always be consulted

to make sure that the structure has the load capabilities to support the new use. Sagging

concrete is an indication of overload.

Figure 14. Overload Structural Beam.

Earthquakes and other movements are also

examples of overloading. (Portland Cement Association 2002) Damage from these incidents can range from small cracks in the structure, to

chunks of concrete completely breaking off.

Cracks that are the result of overloading are

usually diagonal and extend the length of the

surface.

A third type of overloading can result from impacts. An example of an impact is a tree that

has fallen onto a building or a car that has

crashed into it. Impacts are unpredictable, but

the positive side is that damage caused by these attacks is isolated to the area where the impact

occurred.

CHEMICAL ATTACKS

Like any other building material, RC is vulnerable to attack by chemicals. Alkali-

4 Hydroxides occur naturally in concrete.

aggregate reactions, sulfates, chlorides, acids and

carbonation contribute to the ruin of RC.

Hydrochloric acid, hydrofluoric acid, aluminum-chloride and calcium-bisulfite are among the

chemicals that cause the greatest amount of

damage to RC.

Alkali-aggregate reactions are chemical attacks

that occur when certain aggregates have a

negative reaction with hydroxides.4 There are

two distinct type of alkali-aggregate reactions:

alkali-silica reactivity (ASR) and alkali-carbonate reactivity (ACR). Water initiates the reaction in ASR. The following chemical

equation defines the reaction sequence (Portland Cement Association 2002):

Alkalis + Reactive Silica Gel Reaction Product

Gel Reaction Product + Moisture Expansion

Figure 15. Map Cracking from ASR Damage.

The product of the silica and water create a gel

that expands with moisture, creates pressure within the concrete, and produces map pattern

cracking. If the problem is not resolved, it can

lead to spalling or complete deterioration. The

best way to prevent this type of damage is to



maintain the concrete as dry as possible. In

regions with high humidity, aggregates that

contain silica should not be used.

ACR is a reaction that can occur when

aggregates that contain calcium magnesium

carbonate [CaMg (CO 3) 2] are used; the compound is more commonly referred to as

dolomite. (Merriam-Webster Inc. 2015) Like ASR, this reaction results in expansion due

crystallization of the minerals. It is not common

to encounter this damage because modern

technology has nearly eliminated the use of aggregates containing dolomite through

advanced filtering processes. Dolomite may be

present in historic RC structures; map pattern

cracking may also be an indicator that ACR is

occurring.

Sodium, potassium, magnesium and calcium are

all sulfates that attack concrete in various

different ways. (Portland Cement Association) Sulfates can mix with chemicals in concrete to produce new compounds that deteriorate the

concrete. These new compounds manifest as

solids near the surface of the concrete. Sulfates

can also break the chemical bonds in the cement causing the concrete to become weak. A low

water to cement ratio will decrease the potential

for sulfate damage to concrete. (Portland Cement Association)

Chloride is extremely destructive to rebar, and most commonly come from deicing salts and

seawater. Structures in maritime communities

like Miami, as well as those in regions of heavy

snow such as Chicago are at the highest risk of

corrosion.

Figure 16. Oxidation Process

Once the rebar begins to corrode, oxidation

produces rust, which takes up more volume than

the rebar and puts pressure on the concrete.

Cracking, spalling and delamination may indicate the presence of chloride ions. Rust

colored stains on the concrete are clear proof of

rebar corrosion.

Figure 17. Rust Stains from Corroded Steel.

Figure 18. Spalling Damage.

Acids are often used to clean concrete surfaces,

but if they have a pH level above 3.0, they can



cause etching. Acids combine with water to

create a new, destructive compounds such as

acid rain, which has a pH level of 4.0 4.5. (Portland Cement Association 2002) Soil and animal waste may contain acids that are harmful

to concrete. It is best to protect concrete with

surface treatments if acid exposure is plausible.

Carbonation can also result in the corrosion of embedded metals. This occurs most often in

areas with high levels of air pollution and/or high

humidity. (Portland Cement Association 2015) Carbonates are created when carbon dioxides from the air react with hydroxides in the

concrete. Areas that are shaded from the sun,

constantly moist, or where the metal is

embedded too close to the surface of the concrete are more vulnerable susceptible to damage from

carbonation. (Portland Cement Association)

Efflorescence is a condition that occurs when

salts are trapped in the walls of concrete. This is

usually the result of damp rising. A white discoloration at the base of a wall is usually

indicative of efflorescence.

Figure 19. Efflorescence.

Mold can occur on concrete directly, or on top of

an exterior coating such as paint. Mold is most

prevalent where there is moisture and food.

Nearly anything can be considered food,

including microorganisms that are found in dust. Black and/or green colored stains indicate the

presence of mold. Mold and/or fungi should be

removed as soon as possible because it can be

hazardous to human health. It can also be a fall hazard because it creates a slippery surface on

stairs and other horizontal surfaces.

Figure 20. Mold & Soil Stains.

REPAIR METHODS FOR RC

Thanks to technology, repairs to RC structures can now be completed without diminishing the

integrity of the building. Concrete has an

advantage over other materials because it is

uniform, as opposed to other construction methods that rely on large quantities of small

units such as bricks or wood. Another advantage

that concrete has is that new mortars and/or

concrete can be matched to existing materials,

creating an almost seamless repair.

With petrography, the size, amount, type and

quantity of aggregates used in existing concrete

can be determined. Likewise, ratios of water to

cement, lime content and the presence of



admixtures can be determined prior to repairs to

RC structures for better matching.

Repairs to RC structures are divided into two

categories: concrete and rebar repairs. A

concrete repair can be as simple as filling in a crack, or as detailed as re-casting or replacement.

Similarly, rebar repairs can be as simple as

slowing down the rate of corrosion, or as

complex as the rebar being replaced.

Each case is unique and no two repairs will be the same. By analyzing the damage that needs

repairing, and the history of a structure, the most

appropriate repair method can be determined. It is also important to investigate and rectify the

cause of the damage prior to making repairs to

prevent the problem from reoccurring.

CONCRETE REPAIRS

Fine cracks are the result of thermal expansion,

or shrinkage during the curing phase. These

cracks are usually dormant and only require

minor repair. These cracks are typically not a

threat to the structure, but it is advisable to fill

them to prevent the infiltration of moisture and

chemicals. Cracks should be exposed and filled

with a waterproof sealer, or other appropriate

sealing agent.

Figure 21. Repair of Small, Dormant Crack.

Cracks that are or greater, are active, or are

the result of more serious damage such as

settlement and load bearing issues are concerning. (CFA- Tech Notes TN004 Cracking n.d.) Cracks typically occur where tension is greatest, but and an experienced professional can

transfer those cracks into joints to accommodate movement in the structure and prevent further

damage. (Sika n.d.)

Large cracks should be filled or injected with materials that have plasticity, consist of a one-

compound polyurethane and are durable. (n.d., 16-17)

Figure 22. Transfer of Crack to Contraction Joint.

Severe damage to concrete, such as spalling, may require mortar patching or replacement. The

most appropriate mortar to use for patching large

voids in RC surfaces is M90 mortar. (Speiwick n.d.) Mortars that have very low shrinkage, are corrosion inhibiting, lightweight, and have a

quick dry time are ideal for patch repairs.

In the case that an entire section needs to be re-

cast or replaced, it may be necessary to remove a

sample of the existing concrete to analyze its

chemical and physical composition. Once the

new concrete and existing concrete match

properties, the new cast is attached with high



strength grouts, and/or cement mortars that

contain epoxy.

Products used in the repair should have good

strength, be able to expand during the curing

process, be pliable for good workability, and provide a moisture barrier. The repair should be

blended to be as seamless as possible to retain

the integrity of the structure. (Sika n.d., 20-21) Mortars used for structural repairs should have

all of the same qualities as mortars used in

patching repairs, and additionally they should

have a high density with the ability to resist

carbonation.

In the case that mortars, epoxies and grouts alone

are insufficient to repair severe damage to

concrete, a method called stitching can be

employed. Stitching is not ideal because it decreases flexibility in the concrete, but it may

be a better option than replacement. Staples span

the affected area in varying lengths after holes

are drilled into the concrete on either side of the

crack. (The Constructor 2014)

Figure 23. Stitching Repair of Concrete.

5 Flexural strength is a measure of tensile

strength of concrete.

External steel plates are used specifically to

restore and/or increase the load carrying capacity

of beams in RC structures. These plates have been in use since 1990 and have gained popularity for their ease of installation, low cost

and ability to increase the flexural property of

concrete.5 The plates are secured using collar anchors and can extend the life of a RC structure.

They are suitable for use in historic structures

because the treatment is reversible.

Figure 24. Installation of External Plates.

REBAR REPAIRS

Electrochemical chloride extraction (ECE) is a temporary, non-invasive method used to prevent

the corrosion of rebar inside the concrete. It uses

a power supply and monitoring system to apply 50 volts of direct current to the rebar, see Figure 24. The current from the power supply forces

the negative ions to move towards the surface of the concrete and away from the passive layer,

which protects the steel. The treatment takes

approximately 4-6 weeks to be fully effective

and is reversible. (Bromfield 1996)



ECE can decrease the rate of corrosion

significantly by decreasing the level of chemical

saturation in the pore network. However,

because this treatment is not permanent, heavy

precipitation can interrupt the effectiveness of

the treatment and it may have to be repeated.

(Bastidas n.d)

Another way to control corrosion of the rebar is by converting the surface of the metal into a

cathode; this is called cathodic protection

(CP).6 The corrosion of steel and other metals is an electrochemical reaction that only occurs with

a presence of negatively charged or anodic ions.

CP requires the permanent installation of a

power supply and control systems to maintain a

constant negative charge around the embedded metal, see Figure 26. The positive charge is re-directed to an anode that is isolated and will not

cause damage to the RC structure. (Coney 2012) CP has been very successful in the repair of historic RC structures. The implementation of a

CP system creates new hydroxyl ions in the

concrete, re-builds the passive alkaline layer that

protects the rebar and repels chloride ions.

(Bromfield 1996)

Re-alkalization can reverse damage caused by

carbonation, and restore the passive layer created

by hydroxyl ions in concrete, which protect the

embedded steel. The same principles as cathodic protection are applied to this treatment see

6 A cathode is the positively charged area in an

electrochemical reaction.

Figure 27. The difference is that a wet anode is

placed at the surface of the concrete that contains

calcium carbonate. Positive ions travel from the surface inwards under electro-osmotic-pressure

and re-alkalize the concrete. (Bromfield 1996)


Figure 25. Electrochemical Chloride Extraction.

Figure 26. Cathodic Protection System.

Figure 27. Re-Alkalization Process.

SUMMARY

Reinforced concrete has strengths and weaknesses just like any other building material. The negative aspect of RC is that the combination of concrete and metal make the material vulnerable to a multitude of

physical, chemical and mechanical attacks. If the embedded steel rebar corrodes, it directly affects the

concrete by expanding and can causing the concrete to crack, spall or break off from pressure. Likewise, the concrete is a protective barrier to the embedded steel; damage to the concrete will expose the steel to

attacks from the elements. The positive aspect of RC is that it is a manufactured material based on

engineering and science. Admixtures, surface treatments and impregnations are available that greatly

reduce the risks of attacks by moisture and chemicals.

Maintenance is the key to sustaining RC structures now and in the future. Regular cleanings of RC structures are essential and it provides an opportunity to inspect previous repairs and recognize failures.

The roof, gutters and downspouts should be checked frequently to assure they are in proper working order,

and water should be diverted away from the structure whenever possible. It is imperative that exterior

paints and coatings be well preserved to maintain the barrier that protects concrete from various attacks.

Professionals such as contractors or architectural conservators should always perform repairs. The least invasive treatment should always be chosen to preserve the integrity of a structure whether it is historic or

not. As discussed earlier, the plasticity and uniform nature of concrete allows repairs to blend in a seamless

way that is not possible with other building materials. There is a vast amount of information in books,

online and in professional journals that can be used to make intelligent decisions about the care of this unique composite material.

Based on the information that has been reviewed, it is understandable why RC has been used to build

everything from small residential homes to massive highway systems. Technology and scientific research

has already provided non-destructive ways to maintain and repair RC that will preserve the integrity of the

material. There is no doubt that experts in the study of RC will continue to advance and create new and improved methods of sustaining RC structures. RC is a flexible, strong, and valuable building material that

is worth all the time and effort that scientists, engineers and builders have dedicated to its development.

There are already historic RC structures that are valuable to our history, and in the future, more will be

recognized and preserved for centuries to come with proper care.


LIST OF FIGURES

Cover Image. Accessed January 30, 2015. http://technicalstudiescsat.myblog.arts.ac.uk/2013/04/28/task-5-reinforced-concrete-failures/

Figure 1. Egyptian Pyramids Constructed w/ Concrete. Accessed February 3, 2015. http://www.culturefocus.com/egypt_pyramids.htm

Figure 2. The Pantheon in Rome. Built w/ Concrete-like Substance. Accessed February 3, 2015. http://en.wikipedia.org/wiki/Panth%C3%A9on

Figure 3. Crown Hall, Illinois Institute of Technology, Chicago. Accessed February 7, 2015. http://0-www.britannica.com.library.scad.edu/EBchecked/topic/381736/Ludwig-Mies-van-der-Rohe

Figure 4. Guggenheim Museum: Spiral Ramp and Glass Dome. Accessed February 7, 2015. http://0-www.britannica.com.library.scad.edu/EBchecked/topic/649476/Frank-Lloyd-Wright

Figure 5. Pressure Washing on Exterior Concrete Wall. Accessed February 11, 2015. http://www.sodablast.ca/sand-blasting

Figure 6. Cracks in Concrete Wall. Accessed February 14, 2015. http://www.stellarpaintingandremodeling.com/tag/colorado-painting-contractors/

Figure 7. Layers of Historical Paint on Wall. Accessed February 14, 2015. http://kk.org/streetuse/2007/11/layers-of-time/

Figure 8. Rising Damp on Concrete Wall. Accessed February 15, 2015. http://www.wisepropertycare.com/rising-damp/what-is-rising-damp/

Figure 9. Efflorescence. Accessed February 15, 2015. http://www.retrofittingcalifornia.com/efflorescence-problem/

Figure 10. Water Absorbing Tree. Accessed Online February 15, 2015. http://www.houseplantsguru.com/absorption-of-water-through-roots-in-flowering-plants

Figure 11. Erosion Damage. Accessed Online February 21, 2015. http://saberconcrete.com/services/other-services/

Figure 12. Abrasion Damage. Accessed Online February 21, 2015. http://www.techcoat.com/abrasionresistance.html

Figure 13. Freeze/Thaw Damage. Accessed Online February 17, 2015. http://www.engr.psu.edu/ae/thinshells/module%20III/concrete_behavior_text.htm#_Toc5593991



Figure 14. Overloaded Structural Beam. Accessed Online February 21, 2015. http://www.structural.net/case-study/pre-stressed-beam-repair-washington-dc-parking-structure

Figure 15. Map Cracking in ASR Damaged Concrete. Accessed Online February 22, 2015. http://www.bam.de/en/aktuell/presse/bildarchiv/fotoachiv_material_umwelt.htm

Figure 16. Oxidation Process. Accessed Online February 22, 2015. http://www.cement.org/for-concrete-books-learning/concrete-technology/durability/corrosion-of-embedded-materials

Figure 17. Rust Stains from Corroded Steel. Accessed Online February 22, 2015. http://corrosion.ksc.nasa.gov/corrincon.htm

Figure 18. Spalling Damage. Accessed Online February 16, 2015. http://civildigital.com/spalling-concrete-causes-prevention-repair

Figure 19. Efflorescence. Photographed by Author.

Figure 20. Mold & Soil Stains. Photographed by Author.

Figure 21. Repair of Small, Dormant Crack. Accessed Online February 23, 2015. http://www.earndig.com/extraordinary-easy-how-to-repair-walls-cracked/stucco-dry-wall-repair-sheetrock-

cracked-foundation-ceiling-drywall-hole-diy-concrete-crack-in-basement-ideas-patching-holes-cost-floor-

contractor-wall-cracks-repair-by-experts-554x415/

Figure 22. Transfer of Crack to Contraction Joint. Accessed Online. February 23, 2015. http://www.cement.org/for-concrete-books-learning/concrete-technology/concrete-

construction/contraction-control-joints-in-concrete-flatwork

Figure 23. Stitching Repair of Concrete. Accessed Online. February 23, 2015. http://theconstructor.org/concrete/repair-of-active-cracks-in-concrete/7726/

Figure 24. Installation of External Plates. Accessed Online February 20, 2015. http://www.felix.by/news/118/consulting/

Figure 25. Electrochemical Chloride Extraction. Accessed Online February 22, 2015. http://www.jpbroomfield.co.uk/ace/resources/chlorem-1-w640h480.jpg

Figure 26. Cathodic Protection System. Accessed Online February 24, 2015. http://remedialtechnology.com.au/themes/VSRTTheme/resources/flash/cathodic%20protection_flv.png

Figure 27. Re-Alkalization Process. Access Online. February 24, 2015. http://patentimages.storage.googleapis.com/US6258236B1/US06258236-20010710-D00000.png



REFERENCES

Bastidas, Cobo, Otero & Gonzalez. n.d. "Electrochemical rehabilitation methods for reinforced concrete

structures: advantages and pittfalls." Corrosion Engineering, Science & Technology.

Bromfield, John. 1996. "The Repair of Reinforced Concrete." Buildingconservation.com. Accessed 01 06,

2015. http://www.buildingconservation.com/articles/concrete/concrete.htm.

California Paints. unknown. Choosing The Right Type of Paint. Accessed 01 07, 205. http://www.californiapaints.com/Project-Guides/Painting-Basics/Before-You-Begin/Choosing-Paint-Type.aspx.

Civil Engineers Forum. 2015. Concrete: Advantages and Disadvantages of Concrete. 01 16. Accessed 02 02, 2015. http://civilengineersforum.com/concrete-advantages-disadvantages/.

Concrete Foundations Association of North America. n.d. "CFA- Tech Notes TN004 Cracking." cfawalls.org. Accessed 01 30, 2015. http://www.cfawalls.org/downloads/cfa_cracking_flyer_v08.pdf.

Coney, William B., AIA. 2012. "Preservation Briefs: 15 Preservation of Historic Concrete: Problems and General Approaches." U.S. General Services Administration. 09 10. Accessed 02 05, 2015. http://www.gsa.gov/portal/content/111618.

Forty, Adrian. 2012. Concrete and Culture: A Material History. London: Reaktion.

International Association of Certified Home Inspectors. 2015. Visual Inspection of Concrete. Accessed 02 23, 2015. http://www.nachi.org/visual-inspection-concrete.htm.

Merriam-Webster Inc. 2015. Dolomite. Accessed 02 22, 2015. http://www.merriam-webster.com/dictionary/dolomite.

Merriam-Webster, Inc. 2015. Dictionary and Thesarus - Merriam-Webster Online. Accessed 02 2015. http://www.merriam-webster.com/dictionary/.

Park, Sharon C. n.d. Holding the Line: Controlling Unwanted Moisture in Historic Buildings. Accessed 01 20, 2015. http://www.oldhouseweb.com/how-to-advice/holding-the-line-controlling-unwanted-moisture-in-historic-buildings.shtml.

Penn State Uniersity. nd. "Concrete Behavior." engr.psu.edu. Accessed 02 17, 2015. http://www.engr.psu.edu/ae/thinshells/module%20III/concrete_behavior_text.htm#_Toc5593991.



Portland Cement Association. 2015. Corrosion of Embedded Metals. Accessed 02 22, 2015. http://www.cement.org/for-concrete-books-learning/concrete-technology/durability/corrosion-of-

embedded-materials.

. 2014. "How Concrete is Made." Cement.org. Accessed 02 04, 2015. http://www.cement.org/cement-concrete-basics/how-concrete-is-made.

. 2002. "Types & Causes of Concrete Deterioration." cement.org. Accessed 02 21, 2015. http://www.cement.org/docs/default-source/fc_concrete_technology/durability/is536-types-and-causes-of-concrete-deterioration.pdf?sfvrsn=4.

Raluca Sarla, Cristina. 2013. "Reinforced Concrete Failures." Technical Studies Blog. http://technicalstudiescsat.myblog.arts.ac.uk/2013/04/28/task-5-reinforced-concrete-failures/, 04 28.

Rediff India Abroad. 2006. "Pyramids were built with concrete: Study." Rediff India Abroad: India as it Happens, 12 01. Accessed 02 03, 2015. http://www.rediff.com/news/2006/dec/01look.htm.

Servet, Kayar &. 2013. "Strengthening and Repair of Reinforced Concrete Beams Using External Steel

Plates." Journl of Structural Engineering 929-939.

Sika. n.d. "Technology and Concepts - Repair and Protection of Reinforced Concrete."

Ribaproductselector.com. Accessed 01 19, 2015. http://www.ribaproductselector.com/Docs/0/06790/external/COL806790.pdf.

Slaton, Gaudette and. 2015. "Preservation f Historic Concrete." National Park Services. Accessed 02 08, 2015. http://www.nps.gov/tps/how-to-preserve/briefs/15-concrete.htm.

Speiwick, Mack &. n.d. "Preservation Brief #2: Repointing Mortar Joints in Historic Masonry Buildings." nps.gov. Accessed 02 18, 2015. http://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htmhttp://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm.

The Constructor. 2014. Repair of Active Cracks in Concrete. Accessed 02 18, 201. http://theconstructor.org/concrete/repair-of-active-cracks-in-concrete/7726/.

The Universiy of California Berkley. n.d. "Repair of Reinforced Concrete Structures." Accessed 01 15, 2015. http://www.ce.berkeley.edu/~paulmont/165/repair.pdf.

United States. 2012. Types of Cracks in Concrete and Typical Causes. 02 24. Accessed 01 28, 2015. http://www.gsa.gov/portal/content/112806.


IntroductionThe Composition & History of ConcreteCyclical Maintenancecleaning MethodsSurface TReatmentsSub-Surface TreatmentsPreventative Measures

Diagnosing DamagePhysical AttacksMechanical AttacksChemical Attacks

Repair Methods for RCConcrete RepairsRebar Repairs

SummaryList of FiguresReferences

Final_Paper-libre.pdf

Documents

Transcript of Final_Paper-libre.pdf