10 Things to Remember when doing Concrete Mix Design

Good quality concrete starts with the quality of materials, cost effective designs is actually a by-product of selecting the best quality material and good construction practices. Following are 10 Things to remember during Concrete Mix Design and Concrete Trials.

1. ACI and other standards only serves as a guide, initial designs must be confirmed by laboratory trial and plant trial, adjustments on the design shall be done during trial mixes. Initial design “on paper” is never the final design

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2. Always carry out trial mixes using the materials for actual use.

3. Carry out 2 or 3 design variations for every design target.

4. Consider always the factor of safety, (1.125, 1.2, 1.25, 1.3 X target strength)

5. Before proceeding to plant trials, always confirm the source of materials to be the same as the one used in the laboratory trials.

6. Check calibration of batching plant.

7. Carry out full tests of fresh concrete at the batching plant, specially the air content and yield which is very important in commercial batching plants.

8. Correct quality control procedures at the plant will prevent future concrete problems.

9. Follow admixture recommendations from your supplier

10. Check and verify strength development, most critical stage is the 3 and 7 days strength.

Important note:
Technical knowledge is an advantage for batching plant staff, even if you have good concrete design but uncommon or wrong procedures are practiced it will eventually result to failures.

What is the problem of over vibration of fresh concrete ?

Effect of vibration, jigging and pressure on fresh concrete, (Bulletin 3, Structural materials research laboratory, Lewis Institute, Chicago)

             For proper compaction of concrete by immersion vibrators , the vibrating part of the vibrators should be completely inserted into the concrete . The action of compaction is enhanced by providing a sufficient head of concrete above the vibrating part of the vibrators . This serves to push down and subject the fresh concrete to confinement within the zone of vibrating action. Over vibration should normally be avoided during the compaction of concrete . If the concrete mix is designed with low workability, over vibration simply consumes extra power of the vibration , resulting in the wastage of energy .

             For most of concrete mixes, over- vibration creates the problem of segregation in which the denser aggregates settle to the bottom while the lighter cement paste

tends to move upwards . If the concrete structure is cast by successive lifts of concrete pour, the upper weaker layer caused by segregation forms the potential plane of weakness leading to possible failure of the concrete structure during operation . If concrete is placed in a single lift for road works , the resistance to abrasion is poor for

the laitance surface of the carriageway . This becomes a critical problem to concrete carriageway where its surface is constantly subject to tearing and traction forces exerted by vehicular traffic.

Behavior of Fresh Concrete During Vibration/Aci 309.1R-93Recent researches concerning the vibration of fresh concrete =: Recentes recherches sur la vibration du beton frais (Translation - U.S. Army Engineer Waterways Experiment Station)

What is the function of prime coat in bituminous pavement?

The principal function of prime coat in
bituminous pavement is to protect the
subgrade from moisture and
weathering. Since the presence of
moisture affects the strength of
subgrade, the prevention of water
entry
during construction is essential to
avoid the failure of the pavement. In
cold countries, by getting rid of
moisture from subgrade, the danger
of frost heave can be minimized .
Prime coat is an asphalt which, when
applied evenly to the surface of sub-
base or subgrade, serves to seal the
surface to hinder the penetration of
moisture into subgrade. Vehicular
traffic should be avoided on the
surface sprayed with prime coat
because the traction and tearing
action of vehicles would damage this
asphalt layer .

Facts About Construction In India

# Sardar Sarovar Dam being executed by the group is the third largest in the world for volume of chilled concrete to be placed - nearly 7 million cum

# Indira Sagar a 1000 MW Power
house is the second largest surface
power house in the country.

# Nathpa Jhakri a 1500 MW Power
House is the largest underground
power house in India .

# Tehri Dam is the third tallest rockfill dam in the world, and the largest in Asia invloving placement of over 25 million cum of all types of fill material.

# Baglihar Hydroelectric project
involved construction of 30km of
project road along with three bridges.

# Brahmaputra Guide Bund
completed in a record time of 7
months.

# Baspa-II and Chamera -II projects
involved continuous concrete
shuttering for tunnel lining which is
used for the first time in the country.

# Teesta V project has been provided with Jet Grouting curtain is being provided below the coffer dams for the first time in India.

# Alimineti Madhva Reddy Irrigation project is the longest underground face to face tunnel in the world.