Concrete is a composite material made of water, aggregate, and cement. It has been used widely since Roman times. There are different types of concrete used for various purposes. The key constituents that give concrete its properties are cement, water, aggregates, and sometimes admixtures. Fresh concrete must have adequate workability and undergo proper curing to achieve maximum strength and durability over time. While concrete is economical and durable, it also has some disadvantages like low tensile strength requiring reinforcement.

1. CONCRET
E The Man Made Stone

2. Introduction..
• Concrete is a composite material composed mainly of
water, aggregate, and cement.
• The word concrete comes from the Latin word "concretus"
meaning compact or condensed
• It is believed that romans were the one who introduced
concrete and used extensively from 300 BC to 476 AD.
• After the Roman Empire collapsed, use of concrete became
rare until the technology was re-pioneered in the mid-18th
century

3. Colloseum, Greece

4. Pantheon, Rome

5. Petronas twin Tower Burj Khalifa

6. Types of Concrete
• Light weight concrete: used for load bearing external
walls for building. They are also used for temporary
structures because of low initial cost and can be reused as
aggregate
• High density concrete : They are mainly used in the
construction of radiation shields (medical or nuclear)
• Mass concrete : used in building dams, foundation etc
• Ready mix Concrete : Ready Mixed Concrete is
manufactured under computer-controlled operations

7. Constituents..

8. Constituents..
•Mixture of aggregate
•paste 30 to 40%
• portland cement 7% to 15% by Vol.
• water 14% to 21% by Vol.
•Aggregates 60% to 70%
• coarse aggregates
• Fine aggregates
•Admixtures

9. Portland Cement
• Dry powder of very fine particles
• forms a paste when mixed with water
• chemical reaction-Hydration
• glue
• paste coats all the aggregates together
• hardens and forms a solid mass

10. Water
• needed for two purposes:
• chemical reaction with cement
• workability
• only 1/3 of the water is needed for chemical
reaction
• extra water remains in pores and holes
• results in porosity
• Good for preventing plastic shrinkage
cracking and workability
• Bad for permeability, strength, durability.

11. Aggregates
• cheap fillers
• hard material
• provide for volume stability
• reduce volume changes
• provide abrasion resistance

12. Admixtures
• chemical
• set retarders
• set accelerators
• water reducing
• air entraining
• mineral
• fly ash
• silica fume
• slags

14. Fresh Concrete
Fresh concrete is that stage of
concrete in which concrete can
be moulded and it is in plastic
state.

15. Properties of fresh concrete
•Setting
•Workability
•Bleeding
•Segregation
•Hydration
•Air Entrainment

16. Setting Of Concrete
The hardening of concrete before
its hydration is known as setting of
concrete

17. Factors affecting setting
• Water Cement ratio
• Suitable Temperature
• Cement content
• Type of Cement
• Fineness of Cement
• Relative Humidity
• Admixtures
• Type and amount of Aggregate

18. Water-cement Ratio
The water–cement ratio is the ratio of the weight of water to
the weight of cement used in a concrete mix and has an
important influence on the quality of concrete produced

19. Workability
• Workability is often referred to as the ease with which a
concrete can be transported, placed and consolidated
without excessive bleeding or segregation

20. Factors affecting concrete workability
• Water-Cement ratio
• Amount and type of Aggregate
• Amount and type of Cement
• Weather conditions
• Temperature
• Wind
• Chemical Admixtures
• Sand to Aggregate ratio

21. Test for Workability
Slump Test can be used to find out the
workability of concrete

22. Apparatus for Slump test
• Cylinders
• Small scoop
• Bullet-nosed rod (600 mm
x 16 mm)
• Steel float
• Steel plate 8”
4”
12”

23. Slump Test
slump cone
rod
concrete

24. Procedure
• Clean the cylinder mould and coat the inside lightly with form
oil, then place on a clean, level and firm surface, ie the steel plate.
Collect a sample.
• Fill 1/2 the volume of the mould with concrete then compact by
rodding 25 times. Cylinders may also be compacted by vibrating
using a vibrating table.
• Fill the cone to overflowing and rod 25 times into the top of the
first layer, then top up the mould till overflowing.

25. Procedure
• Level off the top with the steel float and clean any
concrete from around the mould.
• Cap, clearly tag the cylinder and put it in a cool dry place
to set for at least 24 hours.
• After the mould is removed the cylinder is sent to the
laboratory where it is cured and crushed to test
compressive strength

26. Slump test results
• stiff 0-2”
• massive sections, little reinforcement
• use vibration
• medium 2-5”
• columns, beams, retaining walls
• Fluid 5-7”
• heavily reinforced section, flowable concrete

27. Factors affecting slump
• water cement ratio
• w/c = weight of water / weight of cement
example:
weight of water mixed at the plant 292 lbs.
weight of cement 685 lbs./cu.
yard
w/c = 292/685 = 0.43

28. water cement ratio
if you add 10 gallons of water per cubic yard at job site, then:
extra water
10 gallons/cubic yard * (3.8 liters/gallon) * (2.2 lbs./kg)
*( 1kg/liter) = 83.77 lbs.
total water 282 + 83.77 = 365.77
new w/c = 365.77 / 685 = 0.534 >> 0.43

29. Factors affecting slump-
paste content
• constant water cement ratio
• increase paste content
• increase slump
• NO GOOD
• constant cement content
• increase water content
• increase slump
• NO GOOD

30. Factors Affecting Slump-
Water Content
• Add water at the constant cement content, w/c increases,
slump increases.
• Add water at a constant water cement ratio, have to
increase cement as well, slump increases.

31. Factors affecting slump-paste content
Low paste content
Harsh mix
High paste content
Rich mix

32. ball bearing effect-start
starting height

33. ball bearing effect-end

34. Factors affecting slump
• Aggregates
• grading the larger the particle size, the higher the slump for
a given paste content

35. effect of aggregate size
1”
1”
1”
Consider a single aggregate the size of 1”x1”x1”

36. Break it up further

37. Compute the surface area
0.5 in
0.25 in
surface area = 0.25*0.25*6*8*8=24

38. Larger particles, less surface area,
thicker coating, easy sliding of
particles

39. Smaller particles, more surface area,
thinner coating, interlocking of
particles

40. Angularity and surface
texture of aggregates
angular and rough
aggregate
smooth aggregate
river gravel

41. Temperature
fresh concrete
aggregates paste

42. Bleeding
• Bleeding is a form of segregation
where some of the water in the
concrete tends to rise to the surface
of the freshly placed material.

43. Bleeding

44. Prevention of Bleeding in concrete
• Bleeding can be reduced by proper proportioning and
uniform and complete mixing.
• Air-entraining agent is very effective in reducing the
bleeding.
• Bleeding can be reduced by the use of finer cement or
cement with low alkali content. Rich mixes are less
susceptible to bleeding than lean mixes.

45. Curing
• The time needed for the
chemical reaction of cement
with water results in greater
bonding and makes stronger.
• concrete after 14 days of curing has
completed only 40% of its potential.
70 % at 28 days

46. Curing tips
• ample water
• do not let it dry
• dry concrete = dead concrete, all reactions stop
• can not revitalize concrete after it dries
• keep temperature at a moderate level
• concrete with flyash requires longer curing

47. Temperature effects on
curing
• The higher the temperature the faster the curing
• best temperature is room temperature
• strongest concrete is made at temperature around
40 F.(not practical)
• If concrete freezes during the first 24 hrs., it may
never be able to attain its original properties.

48. Temperature effects on
curing
• real high temperatures above 120 F can cause
serious damage since cement may set too fast.
• accelerated curing procedures produce strong
concrete, but durability might suffer.
• autoclave curing.

49. Advantage Of Concrete
• Concrete is economical when ingredients are readily
available.
• Concrete’s long life and relatively low maintenance
requirements increase its economic benefits.
• It is not as likely to rot, corrode, or decay as other building
materials.
• Concrete has the ability to be molded or cast into almost any
desired shape.

50. Advantages Of Concrete
• Building of the molds and casting can occur on the work-
site which reduces cost.
• Concrete is a non-combustible material which makes it
fire-safe and able to withstand high temperatures.
• It is resistant to wind, water, rodents, and insects. Hence,
concrete is often used for storm shelters

51. Disadvantage
• Concrete has a relatively low tensile strength. In order to
over this, steel is reinforced
• low ductility
• low strength-to-weight ratio, and
• Concrete is susceptible to cracking.