Compaction of concrete

Placing and compaction: 

The following points are considered while placing and compaction of concrete over roof slab and in beams. 

• Always use chutes lesser than 4.5 m in length or angle of inclination at 45° to horizontal in order to pour concrete.
• Fill concrete to the required depth only and vibrate it until the entrapped air inside concrete is released.
• First Pour concrete into beams and then over the slab portion.
• Beams having more than 500 mm depth, concrete to be done in layers. By adopting this, for each layer,  good compaction of concrete can be achieved. Columns, beam, slab level of the concrete top should be pre-marked before starting of concreting works.
• Checking the slab levels are very important, before and during concreting with line thread method and also with Dumpy level. Suitable adjustable Level Gauges can be used as reference marking for the required depth of concrete, made from good quality MS bright bars is highly advisable.
• It is always recommended to use appropriate needles for vibration depending on the aggregate size, reinforcement spacing and concrete element. Hence, for bigger size footings use a 60 mm needle for compaction of concrete, for medium size footings, columns and slabs use a 40 mm needle, and for starters and precast lintels use a 25 mm needle for compaction of concrete.
• Caution: Over vibration for concrete is very bad, gives horrible results in leakages of concrete slurry. Therefore gentle vibration for each layer is necessary, but don’t go for vibrating the concrete again, which was already vibrated and compacted.
• Always Use wooden mallet with gentle ramming, so as to form slurry on top of the concrete surface, which indicates the uniform compaction of concrete with even packing.
• Immediately after concreting clean the surfaces of shuttering works, wherever spilled concrete found.
• Leave vertical construction joints after consultation with the structural engineer.
• All surfaces of shuttering like beam and slabs shall be moistened with water sprinkling before placing of concrete to reduce water loss due to absorption.