ZACC-AF Zia Ahmadzai Construction Company

Form work is a sort of dice for reinforced concrete. It gives the shape of concrete. Any tilting of formwork creates tilting of concrete. Formwork is done by using wooden plank or steel sheet. Formwork is designed considering the weight of wet reinforced concrete. A bamboo post generally bears 100 kg vertical weight. In case of wet concrete having weight of 10,000 kg then 10 nos of bamboo post is required to be provided.

The concrete can resist compression, but not tension. For this reason reinforcing rods are provided in the concrete to sustain tension that develops in concrete. The reinforcing material is high strength steel wire, mild steel, high strength plastic fiber etc. the following shall consider while checking reinforcement:

• Appropriate diameter of reinforcement.
• All rods shall be clean and rust free.
• All rods should be straight.
• Appropriate crank in rods is placed at proper place.
• Length of lapping of rods is provided as per requirement.
• Rods as per drawing are placed.
• For maintaining of clear cover chair/ space bar are provided.
• Actual size of rods is used.
• Rods should be uniform in size.
• Rods will have desired tensile strength.

Concrete is produced from cement, coarse aggregates, fine aggregates and water. As a result, quality of concrete will depend on many factors. A few are:

• Properties of the ingredients.
• Proportion of ingredients.
• Water Cement Ratio.
• Mixing, carrying, placing, compacting, curing etc.

After producing fresh concrete slump test should be performed. Slump test should be performed immediately after collection of the sample but not later than 10 minutes after completion of mixing. Molding of test cylinders/cubes should commence within 20 minutes after completion of mixing. The strength requirement of concrete is given in below table. Strength standard deviation not exceeding: 2.1 MN/m2 (3000 PSI). Minimum three samples will be required for testing from each batch.

Placing of Concrete:
It will also be as per the specifications of the project and as stated in SOW.

Ingredients of concrete:
The concrete is composed of coarse aggregate, fine aggregate, cement and water. Cement acts as binding material. A rock chip is used as coarse aggregates whereas sand is used as fine aggregates. Clean water is used to put all the ingredients together to form hardened concrete. Quality of concrete will depend on the quality of its ingredients.

Rock Chips:
Rock chips are the main constituents of concrete and occupy the bulk volume of concrete. The following are the desired qualities of aggregates:
• Aggregates shall be of desired size.
• All aggregates must clean and free from foreign particles.
• All aggregates must be hard and its strength must be desired value.
• Aggregates must be well graded.

Sand:
The following are the desired qualities of sand:
• Sand as fine aggregates must clean and free from foreign particles
• Sand must be well graded
• Finances modulus of sand must be of desired value.

Cement:
Cement is the binding material for the ingredients of concrete. Ordinary Portland cement shall be used in Afghanistan the Cherat - Pakistan made cement gave very good result and used widely. Cement is generally tested before use and the tests are:
• Fineness
• Setting time
• Compressive test

Water:
Water for mixing concrete should have the following qualities:
• Water should be free from impurities
• Water should be clean

Mixing of Concrete:
• The volume of casting is comparatively smaller quantity mixing will be done by hand mix: otherwise mixture machine may be use.
• Mixture shall be homogenous.
• 5-10 % water of total volume shall be put on turning drum before cement, sand and aggregate are applied for mixing.

Carrying and Placing of:
After mixing of concrete it should be carried to the specified sites as quickly as possible. All mixed concrete place with at final position within 45 minute.  Mixed concrete shall not be placed beyond 1m height. Excess water should not add while placing or vibrating the concrete.

Vibration of Concrete:
Concrete should be compacted by means of vibration. It can be done by means of vibratory or poking concrete with the help of rods .all vibration will be completed before initial setting of time, vibration will compact of fresh concrete. In absence of vibrator, 16mm diameter rod can be used as vibrator.

Curing:
Curing increases the strength of concrete. Cement contains some chemical ingredient that require to hydrolysis for chemical reaction to form a rock like substance. The reaction takes place up to 21 to 28 days. For this reason, curing of concrete is required to be done for 28 days. Curing is an environment that helps hydrolysis of cement. It is generally done by spreading water to the concrete surface or covering it with wet sacks so that the water in the concrete does not evaporate. It is generally started after 16 to 24 hour of casting.