Concrete Workability Tests

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Questions and Answers

What is the primary use of the compacting factor test?

Field testing

Determining the slump of concrete

Measuring the density of concrete

Laboratory testing (correct)

What is the range of compacting factor?

0.40 to 0.60

0.90 to 1.00

0.78 to 0.95 (correct)

0.50 to 0.70

What is the formula for the compacting factor?

Weight of fully compacted concrete / Weight of partially compacted concrete

Weight of partially compacted concrete / Weight of partially compacted concrete

Weight of fully compacted concrete / Weight of partially compacted concrete

Weight of partially compacted concrete / Weight of fully compacted concrete (correct)

What is the purpose of the slump test?

Determining the workability of concrete Signup and view all the answers

Which test is more precise and sensitive than the slump test?

Compacting factor test Signup and view all the answers

What is the characteristic of concrete with high fluidity?

High compacting factor Signup and view all the answers

What is the standard height through which the concrete falls in the compacting factor test?

Standard height Signup and view all the answers

Which standard covers the Kelly ball penetration test?

ASTM C360 Signup and view all the answers

What is the primary cause of bleeding in freshly placed concrete?

Sedimentation of solid particles and upward migration of water Signup and view all the answers

What is the result of excessive bleeding in concrete?

A weaker top layer with poor durability Signup and view all the answers

What is the purpose of the hemisphere hammer in the concrete test?

To determine the workability of the concrete Signup and view all the answers

What is one of the benefits of some bleeding in concrete?

Reduced risk of plastic shrinkage cracking Signup and view all the answers

What is segregation in concrete?

The separation of concrete ingredients Signup and view all the answers

Why is it important to mix concrete at the correct speed in a transit mixer?

To prevent segregation of concrete ingredients Signup and view all the answers

Which of the following is a method to reduce bleeding in concrete?

Increase the amount of fines in the sand Signup and view all the answers

What should be done when placing concrete straight from a truck?

Pour the concrete vertically Signup and view all the answers

What is the process of measuring quantities of concrete mixture ingredients by either mass or volume?

Concrete batching Signup and view all the answers

What is the result of a lack of bleed water on concrete flat work?

A dry surface that is difficult to finish Signup and view all the answers

What is the effect of segregation on concrete?

It makes the concrete weaker, less durable, and leaves a poor surface finish Signup and view all the answers

What is the ideal time to mix concrete in a transit mixer?

At least two minutes Signup and view all the answers

What is the purpose of compacting concrete?

To expel entrapped air from the concrete Signup and view all the answers

What can be used to place concrete in inaccessible sites?

Concrete buckets lifted by helicopter Signup and view all the answers

How can concrete be placed in a deep wall or column?

By pumping it vertically Signup and view all the answers

What happens when air is entrapped in the concrete?

The concrete becomes weaker Signup and view all the answers

Why is it important to place concrete as near to its final position as possible?

To prevent damage to the formwork and reinforcement Signup and view all the answers

What can be used to place concrete up to about 12 meters without additional equipment?

A conveyor belt mounted on a truck mixer Signup and view all the answers

What happens to the concrete if the air is not removed fully?

It loses strength considerably Signup and view all the answers

What is the purpose of bullfloating or darbying?

To eliminate high and low spots and embed large aggregate particles Signup and view all the answers

Why should troweling not be done on a surface that has not been floated?

Because the surface would not be prepared for additional finishing operations Signup and view all the answers

What is the purpose of screeding or strikeoff?

To remove excess concrete to bring the top surface to proper grade Signup and view all the answers

What type of vibrators are commonly used to consolidate concrete in walls, columns, beams, and slabs?

Internal vibrators Signup and view all the answers

What is the purpose of floating?

To embed aggregate particles just beneath the surface; remove slight imperfections, humps, and voids; compact the mortar at the surface Signup and view all the answers

Study Notes

Workability Tests

Slump test is widely used due to its simplicity and application.
Compacting factor test is more precise and sensitive than the slump test, particularly useful for concrete mixes of very low workability.
Compacting factor test measures the degree of compaction achieved by a standard amount of work done by allowing the concrete to fall through a standard height.
Compacting factor is measured by the density ratio, i.e., the ratio of the density actually achieved in the test to the density of the same concrete fully compacted.

Compacting Factor Test

The range of compaction factor is from 0.78 to 0.95.
Concrete with high fluidity has a higher compaction factor.
The compacting factor test measures the inherent characteristics of the concrete which relates very close to the workability requirements of concrete.

Kelly Ball Test

The Kelly ball test measures the workability of concrete by measuring the penetration of a 152-mm-diameter hemisphere hammer into the fresh concrete.
A concrete with higher consistency leads to a deeper ball penetration.

Segregation

Segregation is the separation of the constituent materials of concrete.
Segregation makes the concrete weaker, less durable, and leaves a poor surface finish.
To avoid segregation, check the concrete is not 'too wet' or 'too dry', ensure proper mixing, and place the concrete as soon as possible.

Bleeding and Settlement

Bleeding is the development of a layer of water at the top or surface of freshly placed concrete.
Bleeding is caused by sedimentation (settlement) of solid particles and the simultaneous upward migration of water.
Excessive bleeding increases the water-cement ratio near the top surface, creating a weak top layer with poor durability.
The most effective means of reducing bleeding in concrete include reducing the water content, increasing the amount of cement, using finer cementitious materials, and using air-entrained concrete.

Process of Manufacture of Concrete

Batching is the process of measuring quantities of concrete mixture ingredients by either mass or volume and introducing them into the mixer.
Concrete can be placed in its final location by direct chute discharge from a truck mixer, conveyor belt, or truck-mounted pump and boom.
Concrete can be pumped hundreds of meters vertically with these pumping methods.

Placing Concrete

When placing concrete, be careful not to damage or move the formwork and reinforcement.
Place concrete as near to its final position as possible.
Start placing from the corners of the formwork or in the case of sloping site from the lowest level.

Compaction (Consolidation) of Concrete

Compaction of concrete is the process adopted for expelling the entrapped air from the concrete.
The lower the workability, the higher is the amount of air entrapped.
Methods used for compacting the concrete include hand compaction, compaction by vibration, internal vibrator, and external vibrator.

Finishing of Concrete

Concrete can be finished in many ways, depending on the intended service use.
Finishing operations include screeding, bullfloating, floating, and troweling.
Screeding or strikeoff is the process of cutting off excess concrete to bring the top surface of a slab to proper grade.
Troweling should not be done on a surface that has not been floated.

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Description

This quiz covers the slump test and compacting factor test, used to measure the workability of concrete in construction. Learn about the advantages and applications of these tests.