Mixing Of Concrete

-Ingredients should be properly mixed

-Surface of All Aggregate Particle is coated with cement paste & which is homogeneous and macro scale and therefore possessing uniform properties

Consistency & Slump

-The concrete should flow freely around corners & between the reinforcing bars

-Slump test is used to determine the consistency of concrete



 Recommended Slumps :

Concrete Construction	Maximum inches(mm)	Minimum inches(mm)
RCC Fdn. Walls & Footings	3(76)	1(25)
Plain Footing & Substructure Walls	3(76)	1(25)
Beams & Reinforced walls	4(102)	1(25)
Building Columns	4(102)	1(25)
Pavement & Slabs	3(76)	1(25)
Mass Concrete	2(51)	1(25)

Types Of Slump

Water Cement Ratio

-Compressive &Tensile strength and most of the other desirable properties of concrete is inversely related to w/c ratio

-Low w/c ratio increases freeze thaw resistance & decreases shrinkage

-Minimum amount of water is required to completely hydrate the cement (0.27-0.32)

- 0.65 - 0.7 onward - Less Strength

Compressive Strength, psi(MPa)	w/c Ratio By Weight
6000 (41)	0.41
5000 (34)	0.48
4000 (28)	0.57
3000 (21)	0.68
2000 (14)	0.82

-Strength is based on 6”x12” cylinders, moist cured, 28 days at 23+-2C in accordance with section 9B of ASTM C31

Pumping Admixture

-Used for pumping concrete through pipes

Damp Proofing Admixture

-Used to Avoid Dampness

-Zinc Sulphate, Calcium Chloride

Bonding Admixture

-Used to bond old concrete with new concrete

-Poly Vinyl Chloride, Poly Vinyl Acetate

Self Accelerators

-Used to accelerate the setting process

-Calcium Nitrite