Quality control of concrete

QUALITY CONTROL OF CONCRETE

Prepared by:

Shivkumar M. Goti

What is concrete?Concrete is a most widely used construction material, Commonly

made by mixing of Cement with Fine Aggregate , Coarse Aggregate, Waterand Admixture.

What is quality of concrete?For the building structure to be durable, more strength and also

for aesthetic, accomplishing a quality concrete is of supreme importance.This is because the vital factor which determines or makes a building lookelegant, gives a building more strength and durability the concrete’squality.

Quality control application in concrete construction

Mechanical properties of the reinforcement to be used.

Dimension of the reinforcement.

Location of the reinforcement in construction before concrete poured.

Location of pre-stressing ducts.

Properties of the cement used in the concrete.

Properties of the concrete mix designed of use in the structure.

Control of the coarse aggregates and fine aggregates going into the concrete.

Mixing of the concrete.

Quality control application in concrete construction

Transport of the concrete to the construction site.

Slump of the concrete.

Pouring of the concrete.

Control of water addition.

Vibration/Compaction of the concrete.

Preparation of areas where different concrete pours are done.

Control of compression test samples

Control of formwork removal.

Where does quality control begin?

It begins in the production of material used in concrete ( Sampling and

Testing):

•Portland Cement

•Pozzolana

•Coarse and Fine Aggregate

Uniformity of concrete production will be no greater than the uniformity of

materials used in the concrete.

How does quality control continue?

Handling and stockpiling

Batching and Mixing

Sampling and testing fresh concrete

•Slump

•Air Content

•Unit weight

•Temperature

Transporting and Placing the freshly mixed concrete.

To know the quality of concrete,we can do the several tests.

Tests on Fresh Concrete

• The Slump test

• The Compacting Factor Test

Tests on Hardened Concrete

• Compression Test

• Tensile Strength Test(Split Cylinder Test)

• Flexural Strength Test

Tests on Fresh Concrete

(1)The Slump Test

The mould for the slump test has the shape of frustum of a cone, 300mm

high, the Diameter of the base is 200 mm and at the top is 100mm.

If the slump is:

•25-50 =Low Workability

•50-100 =Medium Workability

•100-150 = High Workability

The Compacting Factor Test

•Compacting factor is less than 0.75 = low workability concrete.•Compacting factor is less than 0.92 = High workability concrete.

Tests on harden Concrete

(a)Compression Test

To determine the characteristic strength of the concrete. Size of concrete cylinder is 150mm Dia 300mm long.

Compression test of concrete Cylinder

Tensile Strength Test(Split Cylinder Test)

when the cylinder split the tensile strength of concrete is determined.

Flexural Strength Test

Test to determine the tensile strength of concrete in flexure have been largely

superseded by the indirect tensile strength test, although it is still specified

occasionally on pavement and other similar projects where the strength of concrete

in flexure, or bending, is of prime importance.

Cement

A mixture of compounds made by burning limestone and clay

together at very high temperature ragging from 1400 C to 1500 C . The

production of Portland Cement begins with the quarrying of

limestone.CaCO3.Then Mixed with Clay(or Shale),sand and iron ore and ground

together to form a homogenous powder.

Material Used in Concrete

Water

Water is the key ingredient. When water mixed with a cement, forms a paste

that binds the aggregates together. water causes the hardening of concrete through

process call hydration. The water needs to be pure in order to prevent side reaction

from occurring which may weaken the concrete or otherwise interfere with hydration

process. The ratio of cement and water is the most critical factor in the production of

‘perfect’ concrete. Too much water can reduces concrete strength but high workability.

Too little water will make the concrete unworkable but high strength.

Aggregate

Chemically inert, solid bodies, held together by the cement. Come in

various shapes, sizes and material ranging from fine particles of sand to large,

coarse rock. Soft, porous aggregate can result in weak concrete with low wear

resistance. Hard aggregate can make strong concrete with high resistance to

abrasion. Should be clean, Hard and strong, Usually washed to remove any Dust,

Silt, Clay, Organic matter.

Admixtures

A material ,other than aggregate ,cement and water added in small

quantities to the mix in order to produce some desired modification, either to the

physical or chemical properties of the mix or of the hardened product. The most

common admixture affect plasticity, air entrainment and curing time.