Plasticizer (Water Reducer)

Anionic surfactants like lignosulphonates and their derivatives, salts of hydrocarbons, etc.,

Nonionic surfactants like polyglycol esters, acids of hydroxylated carboxylic acids and their derivatives,

Other compounds like carbohydrates.

Superplasticizer

Sulphonated Melamine- Formaldehyde condensates (SMF)

Sulphonated Naphthalene-Formaldehyde condensates (SNF)

Modified lignosulphonates

Carboxylated acrylic easters copolymers

Retarder

Calcium sulphate (gypsum)

starch / sugar and carbohydrate derivatives

cellulose

lignosulphonic-acids

Soluble zinc salts, borates, etc.

Accelerator

Calcium chloride

Calcium nitrite/ calcium nitrate/ calcium formate

Sodium chloride/ sodium fromate

Barium chloride

Triethanolamine

Air Entraining Admixtures

Natural wood resins, animal or vegetable fats and oils, fatty acids, aluminium powder, etc. are used in manufacture of air-entraining

For construction of Tunnel, the best concrete is shotcrete.

It is concrete with small sized coarse aggregate that is conveyed through hose and pneumatically projected at a high velocity. The momentum of the concrete itself is sufficient to support and compact itself.

Shotcrete can be produce by dry or wet process.

In heavily congested reinforcement area, self-compaction concrete must be used.

It is a special type of concrete that has ability to flow under its own weight through heavily congested reinforcements and thin sections retaining the homogeneity of mix without segregation.

No vibration is needed.

• Good Workmanship and maintain quality on each steps of work.
• Use of Quality Material (Cement, Sand, Aggregate, Water and Admixtures)

In Entrained air, the air is introduced intentionally using air entraining admixtures. But in entrapped air, the air is introduced unintentionally due to insufficient compaction of concrete.

Yes, I know. The right proportioning of ingredients to be mixed for preparation of concrete is called batching of materials for concrete production.

Types: Volume Batching and Weight Batching.

Weight Batching is preferred due to following reasons.

1. Correct method
2. Provide accurate ratio of constituents as per design on the basis of specific gravity of materials.
3. Moisture content presence in the aggregate should also be considered while batching. In case of fully automatic weight batching it can be considered but volume batching is not suitable in such cases.
4. Compressive strength of same concrete mix at 7 days and 28 days is higher for weigh batching concrete mix than volume batching concrete mix.

Shape of Aggregate – Rounded, Angular, Flaky, Elongated

• Rounded – minimum voids, require minimum cement but poor interlocking and bonding.
• Angular – Higher voids, require more cement, but best interlocking and bonding.
• Flaky: Aggregates having its least dimension less than 0.6 times its mean dimension. It has poor bonding and has adverse effect on homogeneity of mix and its strength.
• Elongated: Aggregates having its larger dimension greater than 1.8 times its mean dimension. It has poor bonding and not considered suitable for medium to high strength concrete

Size of Aggregate – Fine, Medium and Coarse

• Fine
• Medium
• Coarse

The maximum size aggregate gives the lower surface area for the development of gel bonds which is responsible for the low strength concrete. Also, non-uniformity in concrete.

Large Aggregate – Lean Mix – High Strength

Smaller Aggregate – Rich Mix –High Strength