Loss of Fines During Pouring of concrete, Thessaloniki, Greece Ref no: 111

Please do not use page numbers

LOSS OF FINES DURING POURING OF CONCRETE: DEFECTS AND CORROSION

ON STRUCTURES

MS ARIADNE TSAMBALI

UNIVERSITY OF WESTMINSTER, 35 MARYLEBONE RD. LONDON, NW1-5LS, U.K,

tsambani@hotmail.com

EXTENDED ABSTRACT

Many concrete buildings show corrosion damage at the base of columns and walls.

This research investigates a form of segregation where the fine particles are left behind, while some other

glue to the either sides of the formwork and reinforcement while the coarse material falling to the base of the

formwork.

From the results it was observed that due to the loss of fines, the concrete becomes permeable and allows the

water to reach the steel reinforcement and appears to cause corrosion reinforcement.

The concrete then becomes less durable, and cracking and spalling of concrete and that occur as the

corroding reinforcement expands.

To evaluate the behavior of the reinforced concrete during construction, it is normally important to

understand the phenomena of segregation, as explained wholly on this paper.

1. INTRODUCTION This research investigates the Loss of Fines during Pouring of Concrete.

These days, there is two commonly used of structural materials: concrete and steel.

They sometimes complement one another and stand by themselves, so that many structures of a similar type

can be built in either of these materials.

Steel is manufactured under carefully controlled conditions. The properties of every type of steel are

determined in a laboratory and described in a manufacturer's certificate.

The designer of a steel structure needs only specify the steel dimensions and the constructor need only

ensure that the correct steel is used and the connections between the members are properly executed.

On concrete building sites, the whole situation is totally different. Even where that the manufacturer

guarantees the quality of the cement, but cement is not the building material: while concrete is.

Design faults, lack of skilled workmanship, inadequate site control and the low standard. Of some of the

materials used has caused structural or non-structural problems to appear in many years buildings after only

a fraction of their anticipated life.

Transporting, placing, compacting are factors, which influence the final product.

The properties of hardened concrete are durability, strength, the modulus of elasticity and density.

Fortunately, most of the desirable properties will be present if, and only if; concrete of adequate strength and

durability is made.

Durability consists of resistance to weathering, resistance to erosion and impact and resistance to chemical

attack, both internal and external. Results, which came from a questionnaire to members of the Concrete

Society, showed that: the principal cause of poor performance of concrete in the U.K. was the rusting of

reinforcement; usually in association with the presence of chloride.

Where the performance of reinforced concrete is in question, we can say that the most interesting

part of the concrete is that within 50mm of the outside. This is because the outer steel bars will

almost invariably be located within this region.

1.1 CONCRETE DURABILITY: -

This research program tries to prove that the loose of fines is responsible for some of the

problems, which appear in concrete structures.

During this research, we found different ways with which the concrete suffers. When

the concrete has insufficient fines (cement) then we can see holes in the mass of the concrete.

Through these holes the water gets straight to the steel and corrosion of the steel may appear

rabidly; or concrete being more permeable may slowly allow the water in, due to the loss of fines.

Also, the air can easily reach the steel reinforcement. The steel is no longer alkaline protected

and corrosion starts to appear.

Also, carbonation proceeds more quickly because of the reduced alkalinity created by insufficient cement.

The durability of concrete is one of the most important properties of the material.

The reason for this is because the concrete must be strong enough to withstand the conditions for

which it has been designed throughout the life of a structure.

The factors, which reduce the durability of concrete, are both external and internal. By the word

external, we include all the problems are created by the environment.

These factors have been categorized as physical, mechanical and chemical. Physical causes,

arise from the action of frost and from the differences between the thermal properties of the

aggregate and of the cement paste. Impact, abrasion, erosion or cavitations causes mechanical

damage.

By the phrase chemical causes, we also mean the attack by sulphates, acids, and seawater

chlorides, which induce electrochemical corrosion of steel reinforcement. It should be noted that

this attack takes place within the concrete mass.

Therefore, the attacking agent is capable of penetrating throughout the concrete. Thus, the

Concrete permeable at this stage. It will be seen then that, the durability of concrete largely

depends on the ease with which the fluids, (both gases and liquids) can enter and move through

the concrete. This is what we called permeability.

1.2 CORROSION OF REINFORCEMENT: -

Its resistance to the corrosion of the reinforcing steel influences the composition of concrete.

Corrosion of steel in concrete is a very complex phenomenon.

Usually occurring an electrochemical action it is usually encountered when two dissimilar metals are in

electrical contact with the presence of oxygen and moisture.

The strongly alkaline nature of Ca (OH)2 (pH about 13) in cement prevents the corrosion of the

steel reinforcement by the formation of a thin protective film of iron oxide on the metal surface.

Also the same process takes place even when the steel is alone.

And that is because of the differences in Electro-chemical potential on the surface, in the form of

anodic and cathodic regions.

However, if the concrete is permeable and the carbonation reaches the concrete in contact with

the steel, with the presence of water and oxygen then corrosion of reinforcement will take place.

The passive iron-oxide layer is destroyed when the pH falls below about 11.0 and carbonation

lowers the pH to about 9.

The formation of rust results is an increase in volume compared with the original steel so that

swelling pressures will cause cracking and spalling of the concrete. In all cases, oxygen is

present.

The water is regenerated and is needed for the continuity of the process.

Therefore, there is no corrosion in a dry atmosphere, probably with relative humidity of 40%. It

believed that the relative humidity for corrosion is 70% - 80%.

The causes, which are responsible for the corrosion of reinforced steel, are:

Chloride attack

Acid attack

Inadequate cover

Cracks.

1.3 THICKNESS OF COVER: -

The cover of the reinforcement can control the transport of the chloride ions.

Thus, the thickness of the cover is a very important factor. The greater the cover the longer the

time is required before the chloride ions concentrate at the surface of the steel.

Therefore the quantity of the concrete (in terms of its relation to low permeability) and the

thickness of the cover were critical in determining the emergence, or otherwise, of structural

problems.

However, the purpose of the cover is not only to provide protection to the reinforcement, but also

to ensure a composite structural action in the steel and concrete.

In some cases the cover provides fire protection. Reducing the thickness of the cover may have

as result in the appearance of cracking or local damage or misplaced reinforcement in places

where the chloride ions can rapidly be transported to the surface of the steel. In practical terms

the thickness of the cover should not exceed 80 to 100mm.

Therefore by providing an adequate depth of cover, we can prevent the corrosion of steel due to

carbonation.

1.4 SEGREGATION: -

Segregation of concrete means the separation of coarse aggregate from the mortar, so that their

distribution is no longer uniform. In the case of concrete, it is the differences in the size of

particles and in the specific gravity of the mix that are the primary causes of segregation.

Concrete is not a homogeneous material, but rather a mixture of material of different specific

gravities.

Forces are always acting on these materials to separate them. Some of the failures in bonding, at

joints and the cracking belong to the segregation effect. Segregation can be controlled by the

choice of suitable grading.

There are two main forms of segregation. In the first form, the coarser particles tend to separate

out because they tend to travel further along the slope. The second form of segregation occurs

mainly in wet mixes and is known as separation of (cement + H2 O) from the mix.

1.5 CARBONATION: -

Discussion of the durability of concrete is mainly based on the facts that air contains CO2, which

in the presence of moisture reacts with hydrated cement; the actual agent being carbonic acid as

gaseous CO2 is not reactive.

The action of CO2 takes places even with small concentrations such as are the present in rural

air. Where the content of CO2 is about 0.03% by volume. In any laboratory, the content for CO2

may rise above 0.1%; however in large cities it is on average of 0.3% - 1%.

In fact carbonate of concrete is generally found to be less permeable than the same concrete,

this has not carbonated and is therefore more resistant to the ingress of aggressive fluids.

Carbonation has important effects on concrete.

When the carbonation takes place then the alkalinity of the concrete is much reduced and

therefore, if the carbonation front approaches reinforcement or other embedded metal, protection

against corrosion is much reduced and the steel may be exposed to corrosive attack.

It is therefore important to ensure that the quality and thickness of the concrete cover is sufficient

to prevent the steel ever succumbing to corrosion during the life of the structure.

Cement has free lime but carbonation reduces it so much that the pH values can fall from the

normal value of 13.5(highly alkaline) to about 8.5(nearly neutral), making steel in it likely to rust or

corrosion.

Carbonation shrinkage is the first important effect. The second important consequence is

corrosion of reinforcement.

1.6 FACTORS INFLUENCING CARBONATION: -

There is a fundamental factor, which controls carbonation. And that is the diffusivity of the

hardened cement paste.

Diffusivity is a function of the pore system of the hardened cement paste during the period, in

which the diffusion of CO2 takes place.

The type of cement, the water/cement ratio and the degree of hydration are factors very relevant

to diffusion. The strength of concrete is also influenced by these factors.

Therefore, we can say that the rate of the carbonation is simply a function of the strength of the

concrete.

1.7 CARBONATION SHRINKAGE: -

Shrinkage occurs through loss of water either by evaporation, or by hydration of the cement and

also by carbonation.

Loss of water through evaporation occurs both on concrete where surface of concrete is wet, and

concrete whose surface is dry. When the hydrated cement fixes the carbon dioxide paste, the

mass of the latter increases.

Also, the mass of the concrete increases, when it dries, at the same time as it carbonates.

Carbonation shrinkage occurs when crystals of Ca (OH)2 dissolving under compressive stress, and, at the

same time, causes a deposition of CaCO3, which is free from stress. After that the compressibility of the

hydrated cement paste is temporarily increased.

Therefore, if the carbonation continues to the stage of dehydration of C-S-H, then it produces

carbonation shrinkage. Sometimes, the shrinkage in structures is largely related to cracking.

1.8 ACID ATTACK: -

Concrete is generally resistant to chemical attack. However, there are some exceptions.

One of these is, concrete containing Portland cement, which is not resistant to attack by acids. In

damp conditions, sulphur dioxide (SO2) and carbon dioxide (CO2) are present in the atmosphere

and attack concrete by dissolving and removing a part of the cement paste.

In practice, the degree of attack increases as acidity increases.

Generally, attack occurs at values of pH below about 6.5; a pH of less than 4.5 leading to severe

attack.

1.9 CHLORIDE ATTACK: -

General corrosion takes place where large amounts of chloride are present in the concrete. It is

important to emphasize that in the presence of chlorides, just as in their absence, electrochemical

corrosion proceeds only when water and oxygen are available.

There is no corrosion in a dry environment, even if a large amount of chloride is present. Only the

soluble chlorides are relevant to corrosion in steel.

As a rule, chlorides can be present in concrete because they have been incorporated in the mix

through the use of contaminated aggregate or of seawater or brackish water or admixtures

containing chlorides, since seawater contains chlorides, the use of seawater for mixing is not

permitted, because of the dangers of corrosion in reinforcement steel.

None of these materials should be permitted in reinforced concrete.

The code generally prescribes strict limits to the chloride content. For example BS8110: Part 1:

1997 limits the total chloride-ion content in reinforced concrete to 0.4% by mass of cement.

Above 1% of chloride-ion the risk is classified as 'severe'.

The presence of chloride-ions increases the electrical conductivity of the pore water. A result of

thus is to create a corrosive current, which accelerates the dissolution of the iron in the steel

reinforcement.

Corrosion of the steel creates bulging or cracking of the concrete and appears as rust on the

surface of the concrete.

2. METHODS AND MATERIALS

'A research was carried out over the period of three months in order to established clearly the

specific paper.

This research was mainly based on what happens to concrete columns, we created a specific place in the

laboratory area. In this area, we placed three steel column formworks, which we used for our tests. The

initial results were not very good since the aggregate glue to the sides of the columns, because of the small

width of cover within the 150mm x 150mm formwork.

The procedure was altered by increasing the formwork size to 200mm x 200mm, giving an extra

depth (now about 35mm). The result of the change proved excellent. After a month and a half, we

finally ascertained that when we pour the concrete into the column some materials, mainly fines

glue to the sides of the column.

On the later test we found that the concrete within the column had a composition similar to that in

mixing for most of its height but the lowest 200mm contained far fewer fines. This phenomenon is

mainly observed at the lower horizontal.

Concrete is made from cement, aggregate and water with the occasional addition of an

admixture. During the project most of the concrete mixes used were standard mixes based on a

20mm maximum aggregate size.

For this first part of the test we used steel formwork. The formwork has one meter high and

150mm wide.

The formwork was in pieces and we set it together with bolts, in order to take a column of

200mm x 200mm in cross section area. For the first part we used three columns, each has one

meter length and was 150mm x 150mm in cross section area.

The main reinforcement used was high yield steel with 12mm diameter.

For the stirrups, we used high yield steel with 8mm diameter. The columns were prepared with

four bars of main reinforcement, with 10links at 100mm centers.

Then reinforcement cage for each column was one meter long and was hung from the top of the

formwork into the column. The columns were fixed on the side of a table with the column base

open.

The total distance from the ground to top of the column was 1.5m.For the second part of the test

we used formwork one meter high and 150mm wide with a cross-section area of 150mm x

150mm.

For this test we used the same main reinforcement as in first case. Finally, we took three pieces

of formwork with one meter high, and we placed the one above the other, connected with bolts in

order to make a three meters column with 150mm x 150mm in cross section area.

This column was fixed on top of a 0.5 meter high at rectangular form.

Therefore the total height was 3.5 meters. The main reinforcement has the same properties as

the in other cases, but now we have four bars of three meter length and links at 100mm centers.

The reinforcement was hung from the top of the formwork into the column.

Before the pieces of formwork were connected together, were first marked and weighed them

individually. The balance, which was used, was a 25Kg maximum load capacity with accuracy

of ±1gr.The reinforcement cages were marked and weighed using the same balance.

Four formwork pieces were assembled all together, to give a column of one meter high and with

100mm x 100mm in cross-section area.

We made a set of three columns. Each column was marked. The first column has the label A, the

second the label B and the last has the label C.

The reinforcement cages were then hung from the top of the formwork into each column. A

concrete mix typically weighting 80Kg approximately was prepared for pouring into the columns

from the top of the column by using a bucket. (Note: The value of 80Kg an average).

The concrete, which passed through the column, was collected at the base in a pre-weight

bucket. The difference in weight was material left within the formwork, on the walls on the

reinforcement. The concrete left in the original bucket was also weighed. Samples were taken

both before and after pouring for strength, sieve analysis and permeability.

As a check the weight of fine concrete left on the reinforcement cage and on each side of the

reinforcement was also measured.

This procedure was then repeated by pouring the remaining concrete (fewer fines left in the first

Column) through the next column and so on. The test measurements, which were obtained by

using different types of mixing concrete are given on Table 38.

A similar procedure was followed for the 3m long formwork with 150mm x 150mm cross-section

area and with the greater cover depth.

Approximately, 14Kg of concrete was placed in a bucket and poured through the column in small

quantities. The first 2cm of the concrete were collected in one bucket and then the next 2cm, and

the next 2cm.

The remainder was then poured through in one pour. The first three samples were tested for

moisture content and sieve analysis and the remainder cured under water and kept for usual

examination. The fines on the 3m cages and formwork were also recorded.

The mix used was mix type C. Details of these mixes are given in Table 3.1.

Also mix D; mix E and a special mix were cast once.

The special mix was without coarse aggregate. Details of these mixes are given in Table 3.1.

The aggregate and cement were weighed, and mixed dry. Water was then added to give the

needed water/cement ratio. The balance used to weigh the aggregates, cement and water was

accurate to ±1Kgr.

TABLE 3.1. Mix Proportions

Mix

R.H.P.C Sand

5–10 mm

aggregate

10-20 mm

aggregate

Water/

Cement

ratio

C 1 2 1 2

0.5

D 1 2 1 2

0.4

E 1 2.25 1

2

0.75

Special 1 2 3

0 0.5

3.0 COMPRESSIVE STRENGTH - TEST CUBES:-

Before the fresh concrete was poured into the column, four cubes with 150mm sides were

prepared. There was prepared one 150mm cube for each stage of the test.

These means that the first cube was prepared before the wet concrete was poured into the first

column.

As the material passed through the first column we have kept a small amount of the concrete to

fill the cube.

Then the next cube was prepared for the material passing through the second column.

Finally from material passing through the third column, the last cube was prepared. All cubes were

vibrated using an electric hammer.

After casting the concrete, the cubes were cured under polythene for 24 hours. Then, the samples were

removed from moulds.

The samples marked for identification. After that, we put the samples into a tank of fresh water, in

order to continue the curing, for the 28th day, on which they tested.

All the cubes were crushed in accordance to BS1881: Part 116:1983.The compressive strengths,

Fcu were calculated from:-

Where: N = maximum crushing force (in N)

Ac = cube cross sectional area (in mm2)

4.0 CYLINDER TEST:-

Two 100 x 200 mm cylinders were prepared for each stage of the test.

The first cylinder was prepared before the wet concrete was poured into the first column, then the

next cylinder was prepared for the material passing through the column. All cylinders were

vibrated using an electric hammer.

After preparation, the cylinders were kept under polythene for 24hrs. Then they were removed

from the moulds and marked for identification.

Curing was then continued under fresh water inside a tank for the twenty-eight days. The

Cylinders were split according to BS1881: Part 117:1983. The tensile strength, Ft was calculated from:

Where:

Ft = splitting strength (in N/mm^2

)

F = maximum load (in N)

L = length of specimen

D = diameter of the cylinder

Fcu = N/Ac

Ft = 2*F/ *L*D

5.0 CONCRETE MIX SIEVE ANALYSIS TEST:-

Wet concrete samples were collected for each stage of the test as in the case of the test cube.

Then the wet concrete samples were weighed.

The analysis of the fresh concrete was according BS1881: Part 2. We placed the concrete in the

5mm sieve over the 150 micron sieve spraying with water for 2 minutes. The material left on the

5mm sieve after washing was then weighed as before and put into oven to dry for 24hrs at

105C.

Next a sample of fines was placed in the 150 micron sieve. It was sprayed with water for at least

ten minutes until the water passing through was clear and stirred gently with brush. The material

left on the 150mm sieve, transferred into a clean dry tray and covered with water and weighed.

Also, we put it into an oven to dry for 24hrs and at 105ºC.

After 24hrs we removed the samples from the oven and weighed them again. From this

procedure we can calculate the content of each part of the material as a percentage.

The purpose of this procedure is to verify the loss of fines from the wet mix at each stage.

6.0 CONCRETE MIX - MOISTURE CONTENT:-

Wet concrete samples were collected for each stage of the test as in the cases before.

Then, we take a clean tray and we weighed it. We placed the wet concrete sample was placed

into the tray and weighed it again.

Then the samples were marked and put into the oven to dry for 24hrs. After 24hrs, they were

removed from the oven and we weighed them again, in order to verify the water content.

Results for all the moisture content tests made on three types of mixes are given on Table 28.

7.0 RESULTS

Description: Mix type: C. Type of specimens: Metal

Size of column:200mm x 200mm % Gravel % Sand % Fines

After casting 39.68 38.58 21.6

After passing column A 42.83 35.55 21.6

After passing column B 49.38 35.55 15.052

After passing column C 35.9 37.85 26.2

Amount of fines glue on

Formwork and reinforcement 5.44 32.89 61.65

TABLE 28. DATE OF CAST: 06-04-1998

CUBE AND CYLINDER CRUSHING

Dimensions Cubes: 150mm x 150mm

Cylinder: 100mm x 200mm

Average Fcu

Average Ft

Date of Cast Date of Test Type of Mix No (N/mm^2) (N/mm

^2)

13-03-1998 22-05-1998 D Before 70.66

13-03-1998 22-05-1998 D After 64.04

23-03-1998 22-05-1998 Special Before A 50.14

23-03-1998 22-05-1998 Special After A 55.47

23-03-1998 22-05-1998 Special After B 56

23-03-1998 22-05-1998 Special After C 51.73

30-03-1998 22-05-1998 C Before 4.178

30-03-1998 22-05-1998 C After 3.74

06-04-1998 22-05-1998 C Before A 45.25

06-04-1998 22-05-1998 C After A 49.83

06-04-1998 22-05-1998 C After B 49.29

22-05-1998 C After C 48.98

06-04-1998

TABLE 38. Type of Tests.

Notes: The value of Fcu is obtained by crushing one cube;

The value of Ft is obtained by splitting 1 cylinder

WATER/

DATE OF CAST AMOUNT GLUE(Kgr)

CEMENT RARATIO TYPE OF FORMWORK

11-03-1998 4.494 0.4 METAL

23-03-1998 16.78 0.5 METAL

30-03-1998 2.72 0.5 METAL

06-04-1998 5.054 0.5 METAL

19-05-1998 1.84 0.75 METAL

TABLE 39. Amount of fines glue on formwork and reinforcement. It has calculated the total

Formwork weight plus reinforcement weight.

8.0 CONCLUSION

We start the research first by using formwork with 150mm x 150mm in cross section area.

After three tests it was found that both fines and gravel were glue to the sides. If this retained

material came from the first batch and pass down the column then 1Kg is a significant amount

fines say the first 3Kg of concrete, as it would represent the whole fines content.

This happened because the cover was 15mm to 20mm, which trapped larger patches as well as

fines stick to the sides. It was then decided to use 200mm x 200mm (with the same formwork

cage) firstly in short lengths and then in one long length.

The tests showed only small differences in grading of the concrete passing through the

formwork, although up to amount 1Kg of fines was left on the formwork sides.

However, this was not detected in the samples taken (in which were somewhat larger), so it is

clear that the pubbles does not apply to most of the column, only the very first part.

It was also noted that a significant amount of fines were lost in the mixer, and in the skip or buckets, used to

carry the concrete. It was also noted that the concrete with fewer fines in is less workable and may compact

so easily, leaving more cavities after unbratched.

The purpose of this research was to investigate the effect of losing fines at column bases during

pouring concrete. An investigation on the amount of fines which sticks on the formwork and

reinforcement at different column positions was made.

Throughout this project, three different types of concrete mixes were used. The table shows the

percentage of fines from the wet mix at each stage of the mixing. All the aggregates were mixed

dry together with the cement and water was then added to give the required water/cement

ratio. The balance of materials was not sufficiently consistent.

The accuracy of the balances was ±1 Kgr which in fact was not good enough. The accuracy of the

balance used for weighing the reinforcement cage and the formworks was ±1gr which was very

good, but a better way of weighing the formworks and the cage after the casting must be

found.

During the procedure of removing the cage from the column for weighing and the

procedure of stripping off the formwork, some fines were dropped and this made the values less

accurate.

At the beginning, we used 150x150mm, with 1m long, steel formwork. After the first three tests,

we decided to use 200x200mm formwork. In both cases, the steel formworks were very

heavy. Especially when they had to be stripped off in pieces and weighed one by one.

The procedure weighing the formwork could not be improved. It was impossible to weigh each

column formwork at one time because of its great weight.

Each column formwork weighed of about 50Kgr.However; we could replace the steel formwork by

using wood formwork, as the second were lighter in comparison with the steel ones.

A similar behavior can be observed for the relation between the percentage of fines in each mix and the

percentage of fines which glue on the formwork and reinforcement. That is, the percentage of fines glue on

the formwork is inversely proportional to the percentage of fines in the mixes, whereas the former is directly

proportional to the latter in the case of the reinforcement.

The loss of fines at each stage is clearly shown on table 28.From the results of the sieve analysis,

it can be seen that the grading curve is near enough to the required grading.

The procedure for pouring the wet concrete into the columns was improved by using a funnel on

top of the formwork. We can see the percentage of the fines which glue on the formwork and

reinforcement. It can be observed that the percentage of fines glue on the reinforcement is

decreases from column A to column C.

This might be due to the fact that the percentage of fines in the mix poured to the next column, is

less each time as some fines are lost on the previous column. But on the other hand, we can see

that in the formwork there is a small increase on the percentage of fines which stick on the sides

of the formwork.

From Tables, we can see for the mixing C on 06/04/98, the percentage of the gravel which was

passed through the column and collecting into buckets is increasing from column 1 to column

2. Suddenly at the last column that percentage decreases.

This is not quite good. This might be happen because the concrete which passed through the

first column was collected in three buckets. When the samples of concrete for sieve analysis were

collected, I had taken only from the first bucket. Then the concrete pass through the second

column.

Similar with the first column I collected that concrete into 3 buckets and I keep samples

from the first bucket. Finally, I left the concrete to pass through the third column, and collected in

two buckets, samples were kept only from the last bucket.

The different water/cement ratio has a significant effect on the amount of fines which glue on the

reinforcement cages. During the last test, we decided to use one column of 3m long with 200mm

X200mm sides.

The first problem was to find a place to fix it. After finding a place, we repeated the test with a

small amount of concrete.

Comparing the specimens from the first four tests with the last test, we could reach a conclusion.

This was that the strength of the concrete at the top of the column is approximately 85% - 95%.

The problem of segregation appears mainly few centimeters below the end of the column.

Examples from real cases defects on concrete structures appeared on the next 2 photographs.

In case of Photo 1, it shows an extensive corrosion on reinforcement due to

loss of fines on concrete, on base of beam and on the middle of the column.

While in case of Photo 2, it appears extensive corrosion reinforcement due to

loss of fines near the sides of the window frame.

REFERENCES

1. J Hinks. The Technology of Building Defects, E & FN Spon

2. R Whitlow., (1998).Basic Soil Mechanics, Third edition, Longman.

3. M L Poyiatzis, (1989), Segregation in Concrete Columns, Thesis, University of Westminster.

4. A C I Manual of Concrete Practice, 1982 - Part 1.

5. A.M. Neville & J.J. Brooks. Concrete Technology, Longman, Updated.

6. A.M. Neville. Properties of Concrete, Fourth Edition, Longman.

7. D. Campbell - Allen. (1991), Concrete Structures: Materials, Maintenance and Repair, Longman

Scientific Technical.

8. Concrete Society Technical Report No 44. 'The relevance of cracking in concrete to corrosion of

Reinforcement'.