Question

1- Give information about the stages of concrete production. Discuss any two stages in detail.

Answer 1

Stages of concrete production are:

1. Batching: measurements of water, cement, fine aggregates and coarse aggregates is done.
2. Mixing: all the measured components are mixed
3. Transportation: mixed concrete is transported to the required site
4. Placing: at the site transported concrete is placed
5. Compaction: to the required and specified degree compaction is done
6. Curing: proper moisture and temperature condition is ensured

Batching:

For concrete mix, materials have to be measured and mixed, so batching is done. Quality of concrete depends very much on batching. It is of two types

• Weight batching
• Volume batching

Weight batching: It is based on weight measurements. It is more accurate than volume batching. Manual or electronic weight batchers are employed to measure the weights.

For preparation of 1:2:4 concrete mix, 50 kg cement, 100 kg fine aggregates and 200 kg coarse aggregates have to be taken.

Volume batching: It is based on volume measurements. It is less correct than weight batching. Gauge boxes are used to measure materials. 50 kg cement bag is equal to 35 litres in volume. To make 1:3:6 concrete mix, 50 litres cement, 150 litres fine aggregates, and 300 lites coarse aggregate have to be taken.

Weight batching is preferred over volume batching because it is difficult to measure appropriate volume due to voids and loose materials. Often volume batching proves to be wrong bacause of moisture present in the particles whereas moisture content is inherent to weight batching. Weight batching requires skilled labour but it is not so in volume batching.

curing:

Fresh Concrete needs proper temperature and moisture conditions to harden and attain compressive strength. All such processes which provide the concrete necessary moisture and temperature conditions is called curing of concrete. Curing period depends on the nature of concrete work and for OPC concrete it is 7-14 days.

advantages of curing:

• Improved flexural and compressive strength
• Improved durability of concrete
• Weathering and Abrasion resistance of concrete increases
• Curing prevents the concrete from the adverse effects of wind, dust, sun etc.
• Shrinkage reduces and impermeability of concrete increases, thus crack formation is low.

methods of curing:

• Water ponding can be better option for flat surfaces like roofs, floors etc .
• Application of Jute bags to cover the Concrete surface like in columns.
• Using wet sand and saw dust and polythene sheets to cover the surface of concrete.
• Continuous sprinkling and intermittent spraying of water
• Some curing compounds can also be applied. Example: bitumen, linseed oil, sodium silicates, acrylates and some other compounds.
• Steam curing can be used where early removal of shuttering and formwork is required.