Introduction

In this modern savvy world, concrete have the big interaction with the

environment and it is significant as you can see without concrete there are no

buildings. According to Robrtson. S (n.d), concrete is a mixture of cement and

water plus the combination of sand and water which harden into an artificial

stone in few minutes but some will takes up to hours or even weeks if some

substances added in the mixing stage. However, there are concrete

degradation and defects.

The meaning of degradation is a turning down process that low in condition,

quality and level. In a simple explanation means the condition of something

getting worse. Moreover, the word ‘defect’ means the lacking of something

essential or can be indicate as an imperfection that causes failure. So the

concrete degradation and defects means that the concrete is undergoing the

damaging stimuli.

Since in this report concrete degradations and defects is the topic discussed

about, all the details about should be briefly explained. First issue is finding

the reasons that can cause concrete degradation and defects, then explaining

the process one by one plus discussing about characteristics of them. Next

level is to find the preventions and solutions for concrete degradation and

defects, how to repair them, and what their effects are, then at the end giving

some examples of structure failure.

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Types of defects and degradation

There are so many types of concrete degradation and defects, from a minor

cracking to a major structural failure. The examples are cracking, corrosion of

reinforcement bar, concrete spalling, honeycombing, scaling, delamination

and popouts. The followings are the common types of defects that we usually

meet.

1. HoneycombingHoneycomb is the phenomena that we found a void on the surface of the

concrete slab. This phenomenon is named as concrete honeycomb because

the void looks alike with the honeycomb that made by the honeybees.

"The honeycomb is formed because of the failure of the mortar to effectively

fill the spaces among coarse-aggregate particles” (Honeycomb, 2014). The

failure of filling spaces among coarse-aggregate is due to the ineffective of

vibration. Furthermore, there are few more reasons that lead to this defect

such as poor sampling, incorrect placement of reinforcement bars, and

inaccurate cement to water ratio that causes poor workability (Schultz, 2014).

The honeycomb can be repaired by removing the affected area and then

clean the area thoroughly to remove all the loose materials. Then, the non-

shrink grout should be applied to the affected surface, while a larger affected

area may need the bonding agent.

2. Concrete cancer Honeycombs found on the surface of concrete. Retrieved from (Honeycomb, 2014)

Honeycombs found on the surface of concrete. Source from: http://www.jfanjoy.com/blog/?p=3885

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The correct term for concrete cancer is actually concrete spalling, it is one of

the phenomena of concrete degradation. This phenomenon is the breaking

away of the concrete surface and it will usually happen on top of the slab, slab

edge, soffit and façade.

It happens with the presence of water penetration and salt from the

atmosphere. These two elements will cause the reinforcement bar inside the

concrete to rust and thus the corroded steel will normally expand few times

from its original size. This situation then makes the concrete to spall (break

away). The lack of concrete cover, poor quality of concrete, carbonatation and

Alkali – Silica reaction are also the factors that cause concrete cancer.

Concrete cancer must be treated immediately once it happened. “This is

because the rusting reinforcement bar may cause the concrete around the

steel to become more displaced, and more water penetrates into the steels

thus causing more rusting” (Fitzgerald, 2010).

The areas of concrete that affected by spalling can be repaired if the

damaged top pavement is not more than 1/3 while full-depth repair is needed

if the damage is more than the top 1/3 of the pavement (Concrete Slab

Surface Defects: Causes, Prevention, Repair, 2001). First of all, all the

affected concrete and rust on reinforcement bar must be removed. Then, anti

corrosives should be applied to the steel or waterproofing can be added to

prevent further rusting. And, lastly applying a fresh render on the concrete

surface (Fitzgerald, 2010).

Corroded steel in concrete. Source from: http://corrosion.ksc.nasa.gov/corr_forms.htm

The concrete spalled and left the ugly pits. Source from: http://www.concretenetwork.com/fix-spalled-concrete/fixing-a-spalled-driveway.html

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3. Cracking

Cracking of concrete is the most frequently defect that happens among all the

concrete defects. The cracking usually happens on the top of surface of

concrete. “Some types of the cracking will not affect the structural stability and

durability of the building, but the use and serviceability of the building will be

affected in some serious cracking and that is why this defect should be

prevented to its minimum” (Cracks in concrete, 2014).

There are so many types of cracking and different type of cracking may be

caused by different factor. Besides, “cracking can be caused by one or a

combination of numerous reasons such as drying shrinkage, thermal

contraction, external or internal restraint, subgrade settlement, and applied

loads” (Concrete cracking, 2005). Other than that, cracking of concrete may

also happen because of the friction between the element and the casting

mould forms during the lifting.

Types of cracking Reasons

Transverse Crack Shrinkage due to low temperature

Longitudinal Crack Poor joint construction

Plastic Shrinkage Crack Quick loss of water (especially during

hot weather) before hardening

Plastic Settlement Crack Ineffective vibration

Shear Crack Structural loading or movement

Craze Crack Improper curing, excessive floating

Table 1: The types of cracking and its causes.

Cracking of concrete is usually unpreventable, but definitely can be reduced.

There are several repair methods that can be applied. But, as normally the

affected area need to be chipped off at first, then sealing and grouting will be

done to the cracks according to its seriousness. On the other hand, the

cracking that caused by corroded steel bar should be treated by removing the

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rusts from the corroded steel and then apply anti corrosives on the steel. And,

finally sealing and grouting will be done to the affected area.

Preventions and Solutions

Longitudinal cracking from poor longitudinal joint construction. Retrieved from (Longitudinal Cracking, 2008)

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Concrete is kind of different from other materials used in construction and it is

because at the same it is one of the strongest, however it is relatively fragile

material. One of the hardest parts in construction is to know how to prevent

concrete defects and finding solutions. For this reason solutions can be

divided into two types of concrete degradation including chemical and

physical.

There are some solutions for concrete chemical degradation such as using

fibers in concrete composition to remove the concrete tends to crack and also

reducing corrosion and rust. However acids penetrating inside the concrete

and concrete efflorescence can be prevented too, just by adding concrete

densifires. Furthermore many measures can control corrosion in concrete

such as:

Using a high quality concrete with adequate coverage. There must be a

minimum of 2 inches of concrete covering the metal

Coating the steel with epoxy

Using a corrosion inhibitor in the concrete

Employing a cathodic protection system

Keeping the concrete dry

Physical degradation is understood to mean all the causes of concrete spall

and can be prevented during mixing process by adding air entertaining agents

for creating microscopic air bubbles in the concrete so penetrate water can

expand in these bubble instead of concrete material. Also adding concrete

densifires can prevent further infiltration.

Sulfate attack is a chemical and physical reaction between sulfates usually in

soil or ground water and concrete or mortar, primarily with calcium aluminate

hydrates in the cement-paste matrix, often causing deterioration. There are

factors that can affect concrete sulfate attack so can be prevented by

considering some factors:

Cement type and content

Fly ash addition

Sulfate type and concentration

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Chloride ions

Effects of Concrete Degradation and Defects

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Different types of concrete degradation have different effects on

infrastructures such as concrete cracks and rusts, which can cause many

problems, troubles, and at the end disasters may occur, but some of them

happens more common.

One of the most dangerous effects of concrete degradation is on bridges

which in this case they usually start deteriorating within 5 to 10 years of

construction which is because of corrosion in reinforcement steels resulting

cracks and crumbles. The other case happens for structures built in contact

with water such as in rivers or marine environments when salt water can

directly contact with reinforcement concrete plus reinforcing steel corrodes

resulting in cracks and crumbles. However failure attributed to corrosion is not

common in buildings, but because of inaccurate or incomplete site

investigation, poor design, and poor workmanship they have occurred causing

problems and structural failures.

All of this failures can result in falling piece of concrete and probably hit

people underneath or larger disasters such as collapsion of buildings, bridges,

and etc., which can put many people life in danger plus loss of huge amount

of money.

Examples of Structure Failures

Example 1: Terminal 2E at

Charles de Gaulle Airport

Bangladesh's Rana Plaza factory collapsed on April, 2013 (source from: http://news.nationalgeographic.com/news/2013/13/130425-bangladesh-dhaka-building-collapse-world/ )

6-storey building collapse on October, 2011 in Maryland, Lagos, Nigeria (source

http://nigeriatrends.com/why-buildings-in-nigeria-collapse/ )

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On 23rd of May 2004, the concrete roof of Terminal 2E at Charles de Gaulle

airport in Paris, France caused a structure failure leading to collapse. The

stretch of the roof because of cyclical loads is one of the main reasons, but

reports say that wrong position of reinforcements or lack of enough

reinforcements in concrete blocks are the most effective reasons of this

damage. However rapid thermal expansion is an important factor too.

.

In 2004 part of the roof of terminal 2E of Charles de Gaulle airport in Paris collapsed (source from: http://www.dailymail.co.uk/news/article-1341419/Chaos-European-airports-Charles-Gaulle-roof-risk-collapse-heavy-snow-mass-cancellations-continue.html )

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Example 2: Dolphin Tower

A huge crack observed in Dolphin towers convoyed by bucking walls plus

some floor tiles, which were broken, forced all the residences, an emergency

evacuation on 1st of July 2010. This 15 stories residential building, including

116 units was built in 1974 in Sarasota, Florida, United States. Due to wrong

movements and high pressure of concrete members and slabs the strength of

them became lower and also the live loads are much lower than dead loads

on the transfer slabs and columns. Furthermore the most possible reason of

failure of the transfer blocks is use of low strengthening concrete where high

resist concrete is required.

Example 3: Seabrook Nuclear

Power Plant

Dolphin tower condominium, built in 1974, Florida United States (source from: http://www.buysarasota.com/dolphin-tower-sarasota.html )

Stands for keeping the building (Dolphin tower) away from collapsing while repairing (source from https://failures.wikispaces.com/Dolphin+Towers+Condominiums+-+Transfer+Slab+Failure )

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In Seabrook, New Hampshire, United States, 2009, due to entering moisture,

concrete degradation observed by specialists on section walls of Seabrook

nuclear power plant which could be very dangerous. They found the main

reason high chemistry activities on the structure of this nuclear power plant,

which is always in contact with soil and ground water (Special NRC Oversight

at Seabrook Nuclear Power Plant: Concrete Degradation, 2014).

Seabrook nuclear power plant, New Hampshire, United States (source from:

http://www.nrc.gov/info-finder/reactor/seabrook/concrete-degradation.html )

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