The presentation that will cover the main topics of concreting methods in cold weather and discussion about the durabiity of concrete and also useful tips for designing the mix of concrete

1. CONCRETE AND TECHNOLOGY
PRESENTATION
Presented To: Dr. Khan Shehzada
Group Members:
1.Muhammad Ismael
2.Moazam Ali
3.Arsalan Khan
4.Abdul Basit
5.Bilal Ahmed

2.  Special care must be taken when concrete is cast in
cold weather.
 Concrete freeze before it gains strength in cold
weather.
 If the concrete which is not yet set allowed to freeze,
the mixing water convert to ice and there is increase
in overall volume of the concrete.
 When water inside concrete freezes than there is no
water available for chemical reaction, the hardening
of the concrete is delayed.

5. To speed up the earlier hydration of concrete can
be obtained by using one or more of the following:
 Never pour concrete over frozen ground, snow
or ice. Use heater to thaw the ground before
pouring concrete.
 Use of chemical admixtures.
 Use of hot water.
 Use of non chloride accelerating admixture.

6.  Prevent damage to concrete due
to freezing at early stages.
 Assure that the concrete
develops the required strength.

8. Concrete mix design is the process of:
 Choosing suitable ingredient
 Producing Economically concrete
 Achieving Notable Workability
 Achieving Strength
 Achieving high Durability

9. It should be explained that an exact
determination of mix proportions by means of
table or computer data is generally not
possible. A Laboratory trial mix does not
provide the final answer even when the
moisture condition of aggregates are taken into
account. The selection of mix proportions is an
art as much as a science. It cannot be stated too
strongly that, competently used, concrete is a
very successful construction material but, in
the literal service of the word, concrete is not
fool proof.

10. Water cement ratio is the ratio of weight of
water to the weight of cement used for mixing
concrete to achieve the desired workability and
strength of concrete. For a designed mix, water
cement ratio is considered based on the
strength and workability requirements for
concrete construction. They consider the free
moisture present in the sand and coarse
aggregates.

11.  Water cement ratio for concrete construction is not
calculated, but it is selected from the various
workability tests suitable for the type of concrete
structural member or type of concrete.
 Different structural members and different types of
concrete construction requires different workability for
proper mixing, transportation, placement and
compaction of concrete. Based on the these slump
value, water cement ratio can be found out.
 If the required strength of concrete is not met, but the
workability is found within the range, then cement
quantity is increased and again mix proportions are
found out and above steps are repeated till the suitable
water-cement ratio and strength and concrete is
achieved.

12. In addition to ordinary cement, following are the other
important types of cement:
1. Acid resistant cement
2. Blast furnace cement
3. Colored cement
4. Expanding cement
5. High Alumina cement
6. Hydrophobic cement
7. Low heat cement
8. Pozzolana cement
9. Quick setting cement
10. Rapid hardening cement
11. Sulphate resisting cement
12. White cement.
13. Air entraining cement

14. Acid-resistant cement is composed of the
following:
 Acid-resistance aggregates such as quartz,
quartzites, etc.
 Additive such as sodium fluosilicate Na2SiF6
 Aqueous solution of sodium silicate or soluble
glass.

15. The addition of additive sodium flousilicate
accelerates the hardening process of soluble glass
and it also increases the resistance of cement to
acid and water.
The acid-resistance cement is used for acid-
resistance and heat resistance coatings of
installations of chemical industry. It is not water-
resistant and it fails when attacked by water or
weak acids. By adding 0.5 percent of linseed oil or
2 percent of ceresin, its resistance to the water is
increased and it is then known as the acid and
water resistant cement.

16. For this cement type, the slag as obtained from blast furnace
is used. The slag is a waste product in the manufacturing
process of pig-iron and it contains the basic elements of
cement, namely alumina, lime and silica. The clinkers of
cement are ground with about 60 to 65 percent of slag.
The properties of this cement are more or less the same as
those of ordinary cement. Its strength in early days is less
and hence it requires longer curing period. It proves to be
economical as slag, which is a waste product, is used in its
manufacture. This cement is durable, but not suitable for use
in dry arid zones.

17. The cement of desired colour may be obtained
by intimately mixing mineral pigments with
ordinary cement. The amount of colouring
material may vary from 5 to 10 percent. If this
percentage exceeds 10 percent, the strength of
cement is affected.

18. The chromium oxide gives green colour. The
cobalt imparts blue colour. The iron oxide in
different proportions gives brown, red or
yellow colour. The manganese dioxide is used
to produce black or brown coloured cement.
These types of coloured cement are widely used
for finishing of floors, external surfaces,
artificial marble, window sill slabs, textured
panel faces, stair treads, etc.

19. This type of cement is produced by adding an
expanding medium like sulpho-aluminate and a
stabilising agent to the ordinary cement. Hence
this cement expands whereas other cements
shrink.
The expanding cement is used for construction of
water retaining structures and also for repairing
the damaged concrete surfaces.

20.  This cement is produced by grinding clinkers
formed by calcining bauxite and lime. It is
specified that total alumina content should not
be less than 32 percent and the ratio by weight
of alumina to lime should be between 0.85 to
1.30.

21.  This type of cement contains admixtures which
decreases the wetting ability of cement grains.
The usual hydrophobic admixtures are acidol,
napthene soap, oxidized petrolatum, etc. Use of
hydrophobic cement considerably increases the
water resistance of an concrete.

22. The considerable heat is produced during the setting of
cement. In order to reduce the amount of heat, this
type of cement is used. It contains lower percentage of
tricalcium aluminate C3A of about 5% and higher
percentage of dicalcium silicate C2S of about 46%.
This cement possesses less compressive strength. The
initial setting time is about one hour and final setting
time is about 10 hours. It is mainly used for mass
concrete work.

23.  Pozzolana is a volcanic powder. It is found in
Italy near Vesuvius. This type of cement is
used to prepare mass concrete of lean mix and
for marine structures. It is also used in sewage
works ad for laying concrete under water.

24.  This cement is produced by adding a small percentage of
aluminium sulphate and by finely grinding the cement. The
percentage of gypsum or retarder for setting action is also greatly
reduced. The addition of aluminium sulphate and fineness of
grinding are responsible for accelerating the setting action of
cement. The setting action of cement starts within five minutes
after addition of water and it becomes hard like stone in less than
30 minutes or so.
 The extreme care is to be taken when this cement is used as
mixing and placing of concrete are to be completed in a very short
period. This type of cement is used to lay concrete under static
water or running water.

25.  The initial and final setting times of this cement
are same as those of ordinary cement. But it
attains high strength in early days. It contains
high percentage of tricalcium silicate C3S to the
extent of about 56%.

26.  In this cement, the percentage of tricalcium
aluminate C3A is kept below 5 percent and it
results in the increase in resisting power against
sulphates.
 This type of cement is used for structures which
are likely to be damaged by severe alkaline
conditions such as canal linings, culverts, siphons,
etc.

27.  This just a variety of ordinary cement and is
prepared from such raw materials which are
practically free from colouring oxides of iron,
manganese or chromium. For burning of this
cement, the oil fuel is used instead of coal. It is
white in colour and is used for floor finish,
plaster work, ornament work, etc.

28.  It is produced by adding indigenous air
entraining agents such as resins, glues, sodium
salts of Sulphates etc during the grinding of
clinker. This type of cement is specially suited
to improve the workability with smaller water
cement ratio and to improve frost resistance of
concrete.

29.  Manufacture of cement
Portland cement is manufactured by crushing,
milling and proportioning the following materials:
 Lime or calcium oxide, CaO: from limestone, chalk, shells,
shale or calcareous rock
 Silica, SiO2: from sand, old bottles, clay or argillaceous
rock
 Alumina, Al2O3: from bauxite, recycled aluminum, clay
 Iron, Fe2O3: from from clay, iron ore, scrap iron and fly
ash
 Gypsum, CaSO4.2H20: found together with limestone

30.  The materials, without the gypsum, are
proportioned to produce a mixture with the
desired chemical composition and then ground
and blended by one of two processes - dry process
or wet process. The materials are then fed through
a kiln at 2,600º F to produce grayish-black pellets
known as clinker. The alumina and iron act as
fluxing agents which lower the melting point of
silica from 3,000 to 2600º F. After this stage, the
clinker is cooled, pulverized and gypsum added to
regulate setting time. It is then ground extremely
fine to produce cement.

31. Concrete is a mixture of cementitious material,
aggregate and water.
Aggregate is commonly considered inert filler, which
accounts for 60 to 80 % of the volume and 70 to 85 % of
the weight of concrete.
Aggregate is a necessary component that defines the
concrete thermal and elastic properties.

32. 1. Increase the volume of concrete,thus reduces
the cost.
2. Provide dimensional stability.
3. Influence hardness,abrasion resistance,elastic
modulus and other properties of concrete to
make it more durable,strong and cheaper.

33.  Size of aggregate
the size of gravel (aggregate) affects
several aspects: mainly strength and workability.
Usually largest maximum size is used because it will
result
a) Reduction of the cement paste
b) Reduction in water requirement
c) Reduction of drying shrinkage
While choosing the maximum size of aggregate it should
not be greater than one-fourth of the minimum
thickness of the structural member.

34.  Shape of aggregate
rounded,angular,flaky,elongated and irregular
are some types of coarse aggregate on shape basis.
At a given w/c ratio,rounded aggregates demands lower
cement content because of its least surface area for a given
volume.
The higher cement demand in case of angular aggregates is
offset to some extant by higher strength and durability.
Flaky and elongated ones having a larger specific surface area
makes very poor concrete because water demand and
cement content for a given strength is higher for such
particles.

35. It is a property of freshly mixed concrete.
A concrete is said to be workable if it is easily
transported,placed,compacted and finished
without any seggregation.
Workability is directly proportional to w/c ratio.

36.  Workability of concrete increases with increase in water
content.higher the water content higher will be the
fluidity of concrete,which is one of the important
factors affecting workability
Adding more water to concrete also has some
disadvantages which are:
a) Increased quantity of water may cause bleeding
b) Strength of concrete may reduced

37.  Unworkable concrete/harsh concrete
it is a concrete with very little amount of water
 Medium workable concrete
this type of concrete workability is used in most of the
construction works.w/c ratio of such concrete is 0.4 to
0.55
 High workable concrete
a high workable concrete is very easy to
mix,transport,place and compact in structures.such
concrete flow easily and settle down without much
effort.w/c ratio for such concrete is more than 0.55

38. DEFINATION
The ability of concrete to resist
weathering action, chemical attack and
abrasion while maintaining its desired
engineering properties.
It normally refers to the duration of
trouble free performance of the concrete
mix

39. 1-The cement paste structure is dense
and of low permeability.
2-it is made with graded aggregate that
are strong and inert.
3-The ingredients in the mix contain
less impurities like alkalies,chlorides
and sulphates etc

40.  Cement content
mix must be designed to ensure
cohesion and prevent seggregation.if cement is
reduced then at fixed w/c ratio ,workability will be
reduced leading to inappropriate compaction
 Compaction
concrete mix contains voids because of
inadequate compaction.Hence proper compaction
makes the concrete durable

41.  Curing
proper curing is needed for strength
development. Hence to make the mix durable, proper
curing is important.
 Permeability
it is consider as the most important factor for
durabilty.it can be noticed that higher permeability is
usually caused by higher porosity.Therefore proper
curing,sufficient cement ,proper compaction could
provide a low permeable concrete.

42. There are two main types of durability
Physical durability
physical durability is against the following
actions.
1-freezing and thawing
2-permeabilty of water
3.High temperature stresses i-e high heat of
hydration

43.  Chemical durability
Its chemical durability is against the following actions
1-alkali aggregate reaction
2-sulphate attack
3-corrosion of reinforcement

44. It is a property of freshly mixed concrete.
A concrete is said to be workable if it is
easily transported,placed,compacted and
finished without any seggregation.

45.  workability of concrete increases with increase
in water content.Higher the water content
higher will be the fluidity of concrete,which is
one of the important factors affecting
workability.
 Adding more water to concrete also has some
disadvantages which are:
 1.increased quantity of water may cause
bleeding
 2.strength of concrete may reduced