وهي تقرير بحث بسيط عن تاكل الخرسانة وطرق علاجها
Reinforced concrete is the most multiform, economical and successful constraction
material. It can be moulded to a variety of shapes and finishes. Usually it is durable
and strong so it is a widely used for bridges, buildings, utility and marine construction,
and underground structures such as tunnels and reinforced concrete pipe lines.
There are still a large number of failures of concrete structures as a result of
reinforcement corrosion. The corrosion of reinforcing steel in concrete is a major
problem facing civil engineers and surveyors today.
In this report, the types of cracks and method of repair will be definite.
2 Basics of corrosion of reinforcement in concrete
Some engineering says the concrete is alkaline that means it contains microscopic
pores with high concentration of soluble calcium, sodium and potassium oxides (when
Concrete is alkaline the PH number between 12-13) and if concrete is high alkaline
that means the concrete contains high PH.
The alkaline condition creates a passive layer, which is a dense and prevents the
steel from corrosion, around the steel surface. Through the permeability of the
concrete many different kinds of gases such as carbon dioxide, sulphr dioxide and
calcium chloride will penetrate into concrete. As a result, the reinforcing steel
will be rusted
2.1 The corrosion processes
The processes, which will destroy a passive layer, may be classified on the basis of
whether they belong to the carbonation or the chloride attack. The first process is
carbonation which is the result of the interaction of carbon dioxide gas in the
atmosphere with the alkaline hydroxides in the concrete. This reaction occurs when
there is a low cement ******* , high water cement ratio , poor curing of the concrete and
a little concrete cover over the reinforcing steel.
Carbonation is common in old structures but it is rare on modern highway
bridges and other civil engineering structures where water cement ratio (W/C) are low,
cement *******s are high with good compaction and curing. wet and dry cycling on the
concrete and high of temperature will accelerate carbonation. As a result, coastal areas
and the Middle East which the temperature excess of 40 degrees Celsius throughout
The second process chloride attack when the chloride ion attacks the passive layer
but unlike carbonation, there is no overall drop in ph. According to John (1997) there
are three sources of chlorides, use of sea water in the mix, contaminated aggregates and
use of chemical materials in the mix.
3 Corrosion damage
Corrosion leads to many cracks in the reinforcement concrete and it will be do
to remove the concrete cover. Which cause many problems that often result of
corrosion which lead to significant problems that may cause a big collapse in many
deterioration building particularly near the coast and underground facilities. Therefore
engineers are now examining and analysing the concrete to determine the types of
cracks to treat the situation based on the type of cracking.
3.1 Type of cracks
Cracking can be an important sign that reinforcement is rusting. Because the
significance of each type of crack is different. Cracks can be classified according to its
direction into tow types, longitudinal cracks which caused by corrosion of reinforcing
steel and transverse cracks which caused by shrinkage, thermal contraction , structural
overloading , movement of the foundation and accident damage.
No all cracks result from rusting so some cracks such as transverse cracks do
not normally indicate that the reinforcement is rusting but transverse cracks, which
caused by structure overloading , need immediately action to keep the structure safe .
4 repairing cracks
Inspection and testing of the structural will defined the kind and cause of cracking.
The repair cracks can be classified according to the type of the cracks. First, repair
transverse cracks which caused by overload should all the overload are removed then
should the cracks are injected with special materials to product reinforcement from
weather facts . Second repair longitudinal cracks, which run directly over
reinforcing bars and this cracks caused by corrosion so it will be leads to removing of
cover concrete . It is a symptom of deterioration and it seems that they cannot be
treated without removing and renewing the concrete cover and deterioration concrete
with used special materials.
4.1 Removing concrete cover
The concrete cover, which is damage, must be cut away until the affected
reinforcement and usually up to 50 mm beyond it . This distance depends on
contaminated concrete because the chloride can spread from contaminated concrete
into new concrete . As a result, all contaminated concrete are removed.
Before removing any concrete should support the structure first by add the
temporary support for the transfer of loads from section that will be treated.
4.2 Cleaning reinforcement
When the concrete cover has been removed the reinforcement can be inspected. Then
the reinforcement will be cleaned by special material and must be removed all rust
from the reinforcement . But according to John (1997), if rusting reduced cross-sectional
area of reinforcement by more than 20 % extra reinforcement must be added.
4.3 Replacing and curing concrete
Before adding new concrete, the old one must be very clean so that the new
paste can bond with it . And must be saturated so that water needed for curing is not
sucked from the new concrete. And also the concrete must be contains polymer
admixtures or other special materials to bond old and new concrete together.
All types of cementations repair need curing by spray water for at least 3 days
in temperate weather or 7 days under hot drying conditions.
Although many older structures still not need repair, there are many other structures
which built during last three decade are showing signs of deteriorations. In many causes
early deterioration can be linked to chloride in the concrete. Such as in cold regions,while
the engineers in this countries add more chloride to the mix because the chloride
accelerate the time of sitting. And the States that suffer from severe weather conditions
such as high temperature and high humidity .So should engineers have to deal
with deteriorating buildings as soon as possible and to maintain modern structures with
decrease the percent of a mount of chloride in the mix and decrease the permeability of