IS 456 Most Important Point Part- 1

Metakaolin IMP Point As Per IS 456

• Metakaolin having fineness between 700 to 900 m2/kg may be used as pozzolanic material in concrete. (As Per IS Code-456, P-13, Cl. No: 5.2.1.4)

• Note-Metaknoline is obtained by calcination of pure or refined kaolinitic clay at a temperature between 650^oC and 850^oC, followed by grinding to achieve a fineness of 700 to 900 m2/kg. The resulting material has high pozzolanic.

Aggregates  IMP Point As Per IS 456

• Aggregates should not contain more than 0.5 % of sulfates as SO3 and should not absorb more than 10 % of their own mass of water. (As Per IS Code-456, P-14, Cl. No: 5.3.1)

• For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of the aggregate should usually be restricted to (As Per IS Code-456, P-14, Cl. No: 5.3.3.1)

• 5 mm less than the minimum clear distance between the main bars

or

• 5 mm less than the minimum cover to the reinforcement, whichever is smaller.

Water in Concrete IMP Point As Per IS 456

• Water in Concrete (As Per IS Code-456, P-14, Cl. No: 5.4)

Water used for mixing and curing shall be clean and free from injurious amounts of oils, acids, alkalis, salts, sugar, organic materials, or other substances that may be deleterious to concrete or steel.

Slump Test IMP Point As Per IS 456

• Slump Test  & Workability (As Per Is Code 456, P-17, Cl. No: 7.1)

Placing Conditions	Degree of Workability	Slump  (mm)
Blinding concrete;	Very low	As Per Is 456, P-17, Cl 7.1.1
Shallow sections;
Pavements using pavers
Mass concrete;	Low	25mm -75 mm
Lightly reinforced
sections in slabs,
beams, walls, columns;
Floors;
Hand placed pavements;
Canal lining;
Strip footings	Medium	50mm -100 mm
Heavily reinforced
sections in slabs,
beams, walls, columns;		75mm -100 mm
Slipform work;
Pumped concrete
Trench fill;	High	100 mm -150 mm
In-situ piling
Tremie concrete	Very high	As Per Is 456, P-17, Cl 7.1.2

Water Cement Ratio IMP Point As Per IS 456

• Water Cement Ratio (As Per IS Code-456, P-17, Cl. No: 8.2.4.1)(As Per IS Code-456, Table- 5, P-20)

Minimum Grade of Concrete.	Maximum Free Water- Cement Ratio	Minimum Cement Content  kg/m3
Plain Concrete
–	0.60	220
M 15	0.60	240
M 20	0.50	250
M 20	0.45	260
M 25	0.40	280
Reinforced Concrete
M 20	0.55	300
M 25	0.50	300
M 30	0.45	320
M 35	0.45	340
M 40	0.40	360

• As Per Is 456 P, 20 Cl 8.2.4.1, Cement contains in Concrete for 20 mm aggregate as per the above table &  10 mm & 40 mm aggregate add additional cement as per IS Code as below

Sr No.	Nominal Maximum Aggregate Size mm	Adjustments to Minimum Cement Contents in as per above table kg/m3
1	10	+ 40
2	20	0
3	40	– 30

Standard Deviation for Concrete IMP Point As Per IS 456

• As per Is 456 – Standard Deviation for Concrete. this standard deviation use in concrete after the bulk cube failure of concrete. (As Per IS Code-456, P-22, Cl. No: 9.2.4.1)

• Standard deviation based on the test strength of a sample.

• A number of test results of the samples– The total number of test strength of samples required to constitute an acceptable record for calculation of standard deviation shall be not less than 30.

• Attempts should be made to obtain the 30 samples, as early as possible, when a mix is used for the first time.

• In case of significant changes in concrete:  When significant changes are made in the production of concrete batches(for example changes in the materials used, mix design, equipment or technical control),

• The standard deviation value shall be separately calculated for such batches of concrete.

• Standard deviation to be brought up to date: The calculation of the standard deviation shall be brought up to date after every change of mix design.

Grade of concrete	Assumed Standard Deviation N/mm2
M 10	3.5
M 15
M 20	4.0
M 25
M 30	5.0
M 35
M 40
M 45
M 50

Assumed Standard Deviation (As Per IS Code-456, P-23, Table-8)