Selection of materialsSelecting the right building material is

crucial for any construction. Although the contractor may be arranging the material, yet it is advisable for you as the house owner to be aware of methods to ascertain the quality of the material being used. This is especially important if you are not using ready-mix concrete.

Cement The cement used shall be any of the following and the

type selected should be appropriate for the intended use: 33 grade OPC (IS 269) 43 grade OPC (IS 8112) 53 grade OPC (12269) Other types,Portland slag cement conforming to IS 455 Portland pozzolana cement (fly ash based) IS 1489 (Part

1) Portland pozzolana cement (calcined clay based)IS 1489

(Part 2) Hydrophobic cement conforming to IS 8043 Low heat Portland cement conforming to IS 12600 Sulphate resisting Portland cement conforming to IS

12330

Cement used

Different Tests on cement Fineness (IS 4031 )Soundness: Le-ChatelierConsistency of Standard Cement

PasteInitial & final setting timeCompressive Strength

SandIn technical language, sand is referred to

as Fine Aggregates. Size of particles is less than 5 mm. River sand is cheapest source of natural aggregates. It should be free from dust, clay, silt and organic impurities. 

You can conduct a simple field test for sand: Hold some of the sand in hand, rub it and just throw it. Check your palm. Good sand will not stick to the palm.

COARSE AGGREGATES

Crushed hard stone and gravel are common materials used as coarse aggregates for concrete work in India. Aggregates are available in sizes of 40mm, 20mm and 10mm. For residential slab, beam and column work, 20mm and 10mm size of aggregates are generally used 

20 mm downsize

Tests on Aggregates(IS 2386)

Part 1 particle size and shape

Part 2 Estimation of deleterious & organic Impurities

Part 3 specific gravity, Density, Voids, bulkingAbsorption.

WATER 

Municipal water supplied for drinking purpose is generally considered fit for construction purpose. Additionally, you can check if the water is free of oil, acids, salts and organic impurities. Sea-water and ground water should preferably not be used for construction purposes. 

IS Recommendations for Water To neutralize 100 ml sample of

water, using phenolphthalein as an indicator, it should not require more than 5 ml of 0.02 normal NAOH IS 3025 (Part 22).

To neutralize 100 ml sample of water, using mixed indicator, it should not require more than 25 ml of 0.02 normal H2O,. The details of ‘test shall be as given in 8 of IS 3025

BRICKSBricks should be sound, hard and

well burnt. They should be free from effloresces and be uniform in size, shape and colour.

The bricks when struck together should produce a good metallic ringing sound.

They must not break when dropped from a height of approximately a meter.

SteelIS 432 Mild steel and medium

tensile steel bars and hard-drawn steel wire for concrete reinforcement : Mild steel and medium tensile steel bars

IS 1789 High Strength Deformed Steel Bars and Wires for Concrete Reinforcement

Steel bars used

ConcreteConcrete is a composite

construction material composed primarily of aggregate, cement, and water admixtures.

Concrete has two main stages 1)Fresh Concrete 2)Hardened Concrete

Admixtures Accelerating admixturesRetarding admixturesWater-reducing admixtures

and super plasticizersAir-entraining admixturesFoaming agents

Mixing, placing, finishing and curing of concrete

MIXING Involves weighing out all

the ingredients for a batch of concrete and mixing them together - A six-bag batch contains six bags of cement per batch - Hand-mixing (tools used) - Mixing with stationary or paving mixer - Mixing with truck mixers - Rated capacities of mixers vary from 2cu.ft. to 7cu.yd.

Transits mixer & conventional mixer

Segregation & Bleeding

Segregation can be defined as separating out of the ingredients of a concrete mix, so that the mix is no longer in a homogeneous condition.

Bleeding is due to the rise of water in the mix to the surface because of the inability of the solid particles in the mix to hold all the mixing water during settling of particles under the effect of compaction.

SEGREGATION & BLEEDING

POURING AND CONSOLIDATION

Formwork must be in good condition to prevent leakage.

limit of vertical free fall not more then .5m

Care was taken to ensure that concrete is not over vibrated so as to cause segregation

Pumping and placing Concrete is conveyed to

the construction site in wheel barrows, carts, belt conveyors, cranes or chutes or pumped (high-rise building) - Pumps have capacities to pump concrete

Concrete should be placed as near as possible to its final position - Placed in horizontal layers of uniform thickness (6” to 20”) and consolidated before placing the next layer

Placing of concrete

Placing of concrete

Compaction of concreteConcrete Vibrators

1. Internal vibrators2. External vibrators3. Surface vibrators4. Vibrating table

POOR COMPACTION

Finishing: The concrete must be leveled and surface made

smooth/flat - Smooth finish; Float/trowel finish; Broom finish; Exposed aggregate finish

FINISHING CONCRETE SURFACE

a) All concrete while being poured against form work was worked with vibrator rods & trowels as required so that good quality concrete is obtained.

b) All exposed surface of RCC lintels, beams, columns etc. were plastered to match with adjoining plastered face of walls after suitably hacking the concrete surface.

FINISHING OF SURFACES

Terms related to concreteCompressive StrengthTensile Strength(8-12% CS)Shear Strength (12-13% CS)Bond Strength (10% CS)

RMC concrete Vs Site mix concrete

The quality of concrete is a critical factor in determining the durability and life of your construction. In case of site-mix concrete, the quality is variable and depends upon the limited expertise of the construction supervisor. The process is manual and non-standardised, and hence prone to human error.

Curing of concrete Curing requires adequate —

Moisture Temperature Time

Effect of Adequate Curing on Hardened ConcreteIncreasedStrengthWatertightnessAbrasion resistanceFreeze-thaw resistanceVolume stability

Methods of curingPonding and ImmersionWet CoveringsFogging and SprinklingPlastic SheetsSteam CuringElectrical, Oil, Microwave, andInfrared Curing

Proportions of concreteUse/Application Proportion on volumetric basis

Cement Sand Stone Aggregates

Plain Cement Concrete (PCC)   1 3 6

RCC footing column, beam, slab, (M20) etc.  

1, 1 1.5, 2 3, 4(5,3)

Brick Masonry (23 cm and above)   1 6 -

Brick Masonry (Less than 23 cm)   1 3 -

Cement plaster on wall   1 4 -

Cement plaster on ceiling   1 3 -

Ceramic tiles fixing   1 4 -

 Flooring 1 2 4Cement concrete for footpath/internal roads in housing societies

1 1.5 3

Deshuttering period

Deshuttering period relates to the maturity of concrete and depends on the ambient temperature. Forms shall not struck until the concrete has reached strength at least twice the stress of which the concrete may be subjected at the time of removal of form work.

Assuming standard conditions of workmanship and quality of materials, you can refer to the following time-frames for the removal of forms. 

Deshuttering period

Form Summers Winters (Temp <18° C)  

Walls, columns and vertical faces of structural members  

24 hrs. 48 hrs.

Removal of props under slab Spanning up to 4.5 m  

7 days 14 days

Removal of props under beams and arches spanning up to 6 m  

14 days 28 days