TESTS ON QUALITY CEMENT

Quality tests on cements at construction site (also called field tests on cement) are carried to know the quality of cement supplied at site. It gives some idea about cement quality based on colour, touch and feel and other tests.

Tests on Cement at Construction site

The following are the quality tests on cement at construction site:

Color test
Presence of lumps
Adulteration test
Temperature test
Float tests
Strength test
Setting test
Date of packing

 

Color Test of Cement

The color of the cement should be uniform. It should be grey colour with a light greenish shade.

Presence of Lumps

The cement should be free from any hard lumps. Such lumps are formed by the absorption of moisture from the atmosphere. Any bag of cement containing such lumps should be rejected.

Cement Adulteration Test

The cement should feel smooth when touched or rubbed in between fingers. If it is felt rough, it indicates adulteration with sand.

Temperature Test of Cement

If hand is inserted in a bag of cement or heap of cement, it should feel cool and not warm.

Float Test

If a small quantity of cement is thrown in a bucket of water, the particles should float for some time before it sinks.

Setting Test

A thick paste of cement with water is made on a piece of glass plate and it is kept under water for 24 hours. It should set and not crack.

Strength of Cement Test

A block of cement 25 mm ×25 mm and 200 mm long is prepared and it is immersed for 7 days in water. It is then placed on supports 15cm apart and it is loaded with a weight of about 34 kg. The block should not show signs of failure.

The briquettes of a lean mortar (1:6) are made. The size of briquette may be about 75 mm ×25 mm ×12 mm. They are immersed in water for a period of 3 days after drying. If cement is of sound quality such briquettes will not be broken easily.

Date of Packing:

Strength of cement reduces with time, so it is important to check the manufacturing date of the cement. Generally, the cement should be used before 90 days from the date of manufacturing.

 

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concrete durability

Concrete structures are designed to achieve a certain service life. For instance, bridges are designed to achieve a 100 – 120 years of service. However, concrete life can be compromised or ended before the specified life.

A durable concrete will guarantee the achievement of structures with long life. In other words, it can last longer and withstand the environmental attacks without significant defects on the performance of the structures.

Concrete durability is defined as “the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties”.

It is important to mention that achieving the strength requirements for concrete alone can not ensure the durability of the concrete. The relationship between strength and durability is not linearly proportional. In fact, High Strength Concrete (HSC) may be deteriorated under the action of, for example, chemical attack resulting in loss of stability and performance. Of course, higher strength of concrete can improve the resistance against the cracking from the internal stresses but this does not necessary guarantee the durability of concrete.

Increasing the service life of a structure depends on
the quality the material selection, mix design method, production, transportation, placement, finishing and curing of concrete. Moreover, concretes serve in different exposure conditions would require different durability requirements. To summarize, durable concrete must have the ability to withstand the potential deteriorative conditions effectively to ensure the long life as designed.

The most important degradation mechanisms in concrete structures are:

1. Freeze-thaw damage (physical effects, weathering)

2. Alkali-aggregate reactions (chemical effects)

3. Sulfate attack (chemical effects)

4. Corrosion of reinforcing steel embedded in concrete (chemical effects)

Carbonation of concrete
Chloride induced
5. Abrasion (physical effects)

6. Mechanical loads (physical effects)

7. Microbiological induced attack (chemical effects)

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