1. *1.CONCRETE AS A CONSTRUCTION MATERIAL
*CONCRETE
The concrete is obtained by mixing of cement, aggregate and
water in required proportion with or without a suitable
admixture. The subject which deals with the fundamental
principle of concrete is known as concrete technology.
2. Property of concrete-
i) Workability- it is defined as the ease which can be mixed
,transported and placed in proportion in homogenous
state.
ii) Segregation-it is the breaking up of cohesion in a mass of
concrete.
iii) Bleeding- the separation of water or water cement
mixture from the freshly mixed concrete.
*Grade of concrete
-As per Indian Standard code there are seven grades of
concrete i.e M10,M15,M20,M25,M30,M35 and M40.
-In the designation of a concrete mixed , the letter M refers
to the mixed and the number to the specified characteristics
compressive strength of a 150 mm cube at 28days expressed
in N/MM2.
3. -Concrete are mainly divided into
*The grade of the concrete is classified in to 3 types
*Ordinary concrete grade
*Standard concrete grade
*High strength concrete grade
*Ordinary concrete grades
*The grades of the concrete related to the M7.5, M10, M15 and
M20 grade are comes under the ordinary concrete grades.
*Standard concrete grades
*The grades of the concrete related to the M25, M30, M35, M40,
M45 and M50 grade concrete grades are comes under the
standard concrete grades.
*High strength concrete grades
*The grades of the concrete greater than M50 grade concrete
called as the high strength concrete. Example M55, M60 etc.
4. SL. NO GRADE CONCRETE MIX USES
1 M5 1:5:10 Plain cement concrete work such as
levelling course, bedding for footing etc
2 M7.5 1:4:8 Plain cement concrete work such as
levelling course, bedding for footing etc
3 M10 1:3:6 Mass concrete in piers, abutment,
massive reinforced concrete member
4 M15 1:2:4 Slabs and columns
5 M20 1:1.5:3 Self retaining water
6 M25 1:2:2 or 1:4:8 Arches and Lintels
7 M30 1:5:10 Concrete foundation
8 M35 1:6:12 Post tension, pre stressed concrete
9 M40 1: 1:2:0.35 RCC slab, beams, columns, footing etc
5. *Advantages of concrete
-Concrete ingredients are easily available
-Concrete can be pumped and spread to fill into
cracks and lining of tunnels.
-Concrete can be easily transported from the place
of mixing to the place of casting before initial set
takes place.
-Using steels as reinforcement , it is possible to
build any structure.
6. *Disadvantages-
-Concrete posses low tensile strength.
-Due to drying, shrinkage and moisture expansion,
concrete may cause cracks.
-If soluble salt is present in concrete it may lead to
efflorescence when comes in contact with moisture.
-Sustained load developed creep in structures.
7. *Concept of quality control of concrete
-The concrete is generally produced in batches at
the site with the locally available materials.
-The quality control is depending upon several
factors like-
i)Variation of quality of constituent materials.
ii)Variation in the mixed proportion.
iii)Variation in the quality of equipment and
mixing.
iv)The quality of overall workmanship and
supervision at the site
8. -The main aim of quality control of concrete is to
reduce the above variation and produce uniform
Material providing the characteristics designable
for obtaining the good strength concrete.
*Water-Cement ratio
*The ratio of the volume of water to the volume
of cement used to form concrete is termed as
water-cement ratio.
*Optimum Water content
*This is the most suitable amount of water
required for a given proportion of materials to
gain its maximum strength.
9. *Abram's Law
*Abram’s law states that the strength of concrete mix entirely
depends on the water-cement ratio. The increase in water-
cement ratio decreases the strength of the mix i.e. 'the strength
of concrete is inversely proportional to the water-cement
ratio'.
*Abram’s Law is a special case of general rule formulated
by FERET with his experience and experiments.
*Where,
*S = Compressive Strength of concrete
*A & B are empirical constants
*(w/c) is water-cement ratio
10. *Water cement ratio: significance
*The water-cement ratio is a critical factor in determining the strength,
workability, and durability of concrete. It refers to the proportion of
water to cement in the mix, and it plays a crucial role in the hydration
process that occurs when the concrete sets and hardens.
*Concrete that has a lower water-to-cement ratio is denser, stronger, less
porous, and more resistant to chemical and freeze-thaw degradation. A
larger water-to-cement ratio, on the other hand, produces a mix that is
more fluid and workable, simpler to put, and more compact, but it is
also weaker and more prone to cracking and other types of degradation.
*A water-cement ratio that is too high or too low can result in concrete
that is too weak or too brittle, respectively.
*It is important to control the water-cement ratio to produce concrete
with the desired strength and durability.
*A proper water-cement ratio also helps to minimise the amount of water
that is absorbed into the concrete, which can cause it to crack and
deteriorate over time. By selecting the right water-cement ratio for a
given project, engineers and contractors can produce concrete that will
perform well and last for many years.
11. *how much amount of water required in different grades of
concrete for 50kgs of cement.
*For M5 Grade concrete we will use 60 liters of water
*For M7.5 Grade concrete we will use 45 liters of water
*For M10 Grade concrete we will use 34 liters of water
*For M15 Grade concrete we will use 32 liters of water
*For M20 Grade concrete we will use 30 liters of water
*For M25 Grade concrete we will use 25 liters of water
Calculation for Water Cement Ratio
* For proper workability, the water-cement ratio varies from
0.4–0.6. However, maximum strength is derived at w/c = 0.4 at
which minimum capillary are expected to form.
*In arriving at the water-cement ratio values it is assumed that
aggregates are saturated with the surfaces in dry condition.
12. Water cement ratio formula
-Water-Cement Ratio = Weight of water/ Weight of cement.
Let us calculate water quantity for 1 bag of cement.
1 bag of cement = 50 kg
Assuming W/C ratio = 0.50
Water-Cement Ratio = Quantity of water/ Quantity of cement
Quantity of water = W/C ratio * Quantity of cement
Quantity of water= 0.50 * 50
= 25 kg (ltr).
