• 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
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
• 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
•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
• Dry powder of very fine particles
• forms a paste when mixed with water
• chemical reaction-Hydration
• paste coats all the aggregates together
• hardens and forms a solid mass
• needed for two purposes:
• chemical reaction with cement
• only 1/3 of the water is needed for chemical
• extra water remains in pores and holes
• results in porosity
• Good for preventing plastic shrinkage
cracking and workability
• Bad for permeability, strength, durability.
• cheap fillers
• hard material
• provide for volume stability
• reduce volume changes
• provide abrasion resistance
• set retarders
• set accelerators
• water reducing
• air entraining
• fly ash
• silica fume
Fresh concrete is that stage of
concrete in which concrete can
be moulded and it is in plastic
Setting Of Concrete
The hardening of concrete before
its hydration is known as setting of
Factors affecting setting
• Water Cement ratio
• Suitable Temperature
• Cement content
• Type of Cement
• Fineness of Cement
• Relative Humidity
• Type and amount of Aggregate
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
• Workability is often referred to as the ease with which a
concrete can be transported, placed and consolidated
without excessive bleeding or segregation
Factors affecting concrete workability
• Water-Cement ratio
• Amount and type of Aggregate
• Amount and type of Cement
• Weather conditions
• Chemical Admixtures
• Sand to Aggregate ratio
Test for Workability
Slump Test can be used to find out the
workability of concrete
Apparatus for Slump test
• Small scoop
• Bullet-nosed rod (600 mm
x 16 mm)
• Steel float
• Steel plate 8”
• 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.
• 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
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
Factors affecting slump
• water cement ratio
• w/c = weight of water / weight of cement
weight of water mixed at the plant 292 lbs.
weight of cement 685 lbs./cu.
w/c = 292/685 = 0.43
water cement ratio
if you add 10 gallons of water per cubic yard at job site, then:
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
Factors affecting slump-
• constant water cement ratio
• increase paste content
• increase slump
• NO GOOD
• constant cement content
• increase water content
• increase slump
• NO GOOD
Factors Affecting Slump-
• Add water at the constant cement content, w/c increases,
• Add water at a constant water cement ratio, have to
increase cement as well, slump increases.
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 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.
• 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
• 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
Temperature effects on
• 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.
Temperature effects on
• 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.
Advantage Of Concrete
• Concrete is economical when ingredients are readily
• 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
• Concrete has the ability to be molded or cast into almost any
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
• 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.