This document provides information on concrete practices for construction. It discusses the key ingredients of concrete including cement, coarse aggregates, fine aggregates, water, and admixtures. It describes the types and uses of these ingredients as well as concrete mixing, placing, curing, and testing practices. The document also outlines codes and standards for concrete work and factors that affect the workability of concrete such as temperature, batching tolerances, and admixture dosage.

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CONCRETE PRACTICES

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CONCRETE
 Concrete is a Homogeneous mixture of
Cementitious material,
Water,
Coarse Aggregate,
Fine Aggregate, and
Chemical Admixtures.
 This mixture hardens into a solid material and is mainly used for construction.
 Can be cast into any shape.

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In-gradients of Concrete
 Cement – Pasting material
 Coarse Aggregates – Filler Material
 Fine Aggregates–To fill voids in-between CA.
 Water – For mixing
 Ad-mixtures – For increasing
slump increasing,
retardation of setting time,
water proofing,
accelerating admixture

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Cement
cements :
1.OPC – 33Gr – IS 269
2. OPC – 43Gr – IS 269
3.OPC – 53Gr - IS 269
4.Portland Slag Cement – IS 455.
5.Portland Pozzolona cement – IS 1489.
6.SRPC – Sulphate Resistance Portland cement.
Other different types of cements are also available, based on
usage, type of cement to be selected.

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Coarse Aggregates
 Natural Occurring material.
 Coarse aggregates > 4.75mm size
 Occupy 70 to 80% of the volume of concrete.
 Blue granite stone aggregates, Basalt aggregates.
 Conform to IS 383.
 Single sized aggregates.
 Graded aggregates.

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Size of Coarse Aggregates
As specified in IS 456 - Size of Aggregate:
Not greater than one forth of the maximum thickness of the member.
For most works 20mm aggregates is suitable.
Where there is no restriction to the flow of concrete into the sections,
40mm or larger size may be permited.
In thin sections & closely spaced re-inforcements , consideration should be given to
the use of 10mm nominal size.
Concrete can be placed with-out difficulty so as to surround all re-inforcements
throughly and fill the corners of the form.

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Fine Aggregates
 Natural Occurring material
 Fine aggregates < 4.75mm size.
 Occupy 40 to 45% of the volume of concrete.
 Conforming to IS 383, zone – 1,2,3,4
 Fine aggregates of zone -1,2,3 is suitable for concrete
 Fine aggregates conforming to zone -2 is ideal for concrete.
Fine Aggregates (SOURCES):
 River Sand
 Crushed Stone sand or Mechanical sand.
 Silt content permited as per IS 383 : By weight 3%

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Water
 As IS 456 Potable water suitable for mixing and
curing of concrete.
 The pH value of water shall not be less than 6.
 Imparts plasticity and consistency to concrete.
 Vital role in deciding the strength of concrete.

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Admixtures
 Admixture is used to modify the properties of ordinary
concrete to required quality performance. In such cases,
so as to make it more suitable for any situation.
 Types of admixtures :
1.Slump increasing admixtures.
2.Retardation admixtures
3.Accleration admixtures
4.Water proofing admixtures

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Low tensile strength
Low ductility
Disadvantages of Concrete

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Mixers
 Concrete can be mixed in mixer machines or in batching plants.
 Mixer machines with capacities 10/7, 7/5, 5/3
 RM800
 Batching plants : 0.5m3, 0.75m3, 1m3

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Mixing Time
Concrete mixing time shall be atleast 2 min as per
IS 456 (clause 10.3.1)

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Types of concrete
 Nominal mix concrete
(Based on table-9 proportions given for 50kg of cement for
different gardes of concrete)
 Volumetric mixes : 1:5:10, 1:4:8, 1:3:6, 1:2:4, 1:11/2:3, 1:1:2
Cement and aggregates measured on volumetric basis with respect to
volume of cement in one bag.
 Design mixes
Designed with locally available materials at site and based on tests results
by conducting trial mixes at site. Design mixes are very economical.

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Min cement content and max W/C ratio – IS 456

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Different grades
of concrete

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Water cement ratio
 The free water cement ratio is an important factor
in governing the durability of concrete and
should always be the lowest value.
 Water cement ratio increases workability increases Strength decrease
 Water cement ratio Decreases workability decreases Strength increase

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Workability requirements of concrete

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Factors affecting the workability of concrete
Change in aggregate moisture content
Slump not meeting
requirement for placing
Batching tolerances
Admixture Dosage

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Factors affecting the workability of concrete
Concrete temparature Ambient temparature
Transportation and laying time Aggregate gradings

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Preparatory arrangement before start of concrete.
Take concrete pour card by checking with clients as per drawing for completion of
 Dimensional checks for size.
 Re-inforcements tying completed.
 Bolts,pockets,insert-plates, pipe conducts any, cut-outs for opening fixed and
arrested strongly.
 Cover blocks provided.
 Shuttering completed and required supports given.
 Stagings arrested strongly.
2.Required No of workmen arranged for spreading concrete.
3.Required No of Masons arranged for vibration and finishing of concrete.
4. Availability of transit mixers for continuous supply of concrete.
5.No of vibrators based on the qty of concrete pour planned per day.
6.Masons are to be advised for method of concrete laying and finishing req at top.

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 Availability of operators, electrians,supervisors.
 Lighting arrangements for concrete continuous in night shift.
 Curing arrangements after 24hrs.
 All small gaps in shuttering are closed with cement paste or with tapes to
avoid cement slurry leakages.
 Working of vibrator needles and additional needle for re-placement.
 Clean the concreting area with compressor air or water wash.
 Chutes are properly and tied strongly. Keep the chutes not more than 45deg.
 Maximum permissible free fall of concrete is 1.5m.
 Top level of concrete is marked in all sides permanently.
Preparatory arrangement before start of concrete.

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Standard box for volumetric concrete
Size of the standard box
0.3m x 0.3m x 0.39m=0.0351m3
Equal to volume of 1 bag of cement

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Codes for concrete
IS 456-Code of practice for plain and re-inforced cement concrete.
IS 10262 – Guide lines for concrete mix designs
IS 383 – Coarse and fine aggregates from natural sources for concrete.
IS 269- Specifications for OPC 33Gr cement
IS 8112- Specification for OPC 43Gr cement
IS 12269-Specification for OPC 53Gr cement.
IS 455 – Specification for Portland Slag cement
IS 516 – Methods of tests for strength of concrete
IS 2386 –Pt 1-8 – Methods of tests for aggregates.
IS 9103 – Concrete admixtures – specification.
SP 23 – Hand book on concrete mixes.
IS 1199 – Methods of sampling and analysis of concrete.

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Don’ts in concrete
 Using un-sized and dust mixed aggregates.
 Non-uniform batchings
 Adding of more water for workability required
 Addition of more admixture than dosage
 Delay in laying
 Re-mixing with addition of water.
 laying with-out sequence
 Improper vibration
 Laying of concrete more than required level
 Gaps or hole in shuttering will cause loss of slurry
 Fall of concrete over form works
 Improper preparation of construction joints
 Cold joints to be avoided.

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Test conducted in field
 Slump test – for workability
 Ball test – for cohesiveness of concrete
 Cube sample casting.

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SLUMP CONE WITH TAMPING ROD

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Slump Test

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Cube moulds

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Thank you