Day 4

Hello everyone!

On our 4^th day of Orientation period, Dr. Jagbir singh taught us about Concrete technology and design mix.

Concrete is a mixture of cement , fine aggregate , course aggregate  and water. Portland cement is the most common type of cement used in production of concrete. Concrete technology deals wih the study of the property of concrete.

Most common types of concrete

• Plain or ordinary concrete
• Reinforced concrete
• Prestressed concrete
• Precast concrete
• Asphalt concrete
• Lime concrete

Composition of concrete–

1. Cement
2. Fine aggregate
3. Course aggregate
4. Water

CEMENT

• Cement is a binder which is composed of calcareous and argillaceous materials and essentially binds fine aggregate and course aggregate together in concrete
• Cement composition
• Lime (CaO)
• Silica(SiO₂)
• Alumina(Al₂O₃)
• Iron Oxide(Fe₂O₃)

AGGREGATES

• Aggregate includes crushed stones , gravels maybe natural ; manufactured or recycled.Aggregate may take may take 60-80% of concrete mix and provide bulk and compressive strength to concrete.

• Fine aggregate are usually sand i.e size between 75µ to 4.75mm
• Coarse aggregate are usually gravels i.e size greater than 4.75mm 

DESIGN MIX

Design mix is process of selection of suitable ingredient and determine their relative properties to

• Specified compressive strength
• Specified workability
• Durability
• Economy

Data required for Design Mix Concrete.

1. Type of cement.
2. Maximum nominal size if aggregates.
3. Min cement content.
4. Maximum cement content.
5. Maximum water-cement ratio.
6. Workability.
7. Exposed conditions.
8. Method of concrete placing.
9. Type of aggregates.
10. Type of chemical admixture used.

Test required for different materials.

1. Specific gravity of Cement.
2. Specific gravity of Fine Aggregates.
3. Specific gravity of Coarse Aggregates.
4. Specific gravity of Chemical Admixtures.
5. Water absorption of Fine Aggregates.
6. Water absorption of Coarse Aggregates.
7. Free moisture of Fine Aggregates.
8. Free moisture of Coarse Aggregates.
9. Sieve Analysis of Fine Aggregates.
10. Sieve Analysis of Coarse Aggregates.

Procedure for Mix Design(as per IS-10262 2009).

1. Determine the physical proprieties of concrete ingredients.
2. Compute the mean target strength for 28-days ft = fck + 1.65S, where S is the standard deviation and fck is characteristic compressive strength. Select the water-cement ratio of trail mix from table 5 of IS 456: 2000.
3. Select the water-cement ratio of trail mix from table 5 of IS 456: 2000.
4. Select the water content, for the required workability and maximum size of aggregates from table 2 of IS 10262:2009.
5. Compute cement content per cubic meter concrete and check it with permissible limits.
6. Compute proportion of Vol. Of coarse aggregates and fine aggregates using table 3 and clause 4.4 of IS 10262:2009.
7. Measure the slump and adjust the water content and amount of admixture.
8. Carry out two more trails with 10% variation of water content ratio.
9. Plot a graph between three water content ratios and their corresponding 28 days strength. Use this graph to decide the proportion that fulfills target strength.