Cost of construction will vary depending upon the type of finish, quality desired and also on the cost and availability of materials as well as labour.
Approximate Estimate of the cost of construction
Other Expenses 10%
Sand (FINE AGGREGATES)
For fine aggregates, river sand is used on a large scale. The dividing line between fine and coarse aggregates is 4.75 mm sieve size. Particles passing through the sieve are categorized as fine aggregates
Sand should be clean without silt or clay, salt and other organic materials and shells.It should neither be too fine nor very coarse.
How to check for silt and clay in sand
Rub a sample of the sand between your hands. Clean sand will leave your hand only slightly stained. If your hands become dirty, it means that there is too much silt or clay in the sand.
Fill a glass container up to half of its capacity with sand and pour clean water till the container is three quarters full. Shake it vigorously and let it settle for half an hour. Clean sand will settle at the bottom while the clay and silt will slowly settle on top of the sand. The thickness of the silt or clay layer should not be more than 3- 4% by volume. If it is more, the sand must be washed before use.
20mm/12mm Jelly/Blue metal (Coarse Aggregates):
Crushed rock is the commonly used coarse aggregate in the country. and particles retained on the 4.75 mmsieve would qualify as coarse aggregates.
Metal must be clean, dense, hard, and durable. It should not have organic impurities or salt deposits.
Fine aggregates (sand) and gitti or coarse aggregates (below 10mm is grit and below 20mm is kapchi) constitute nearly 70- 75% of the total volume of concrete and are essentially inert in nature. They give body shape to the concrete, reduce shrinkage and are economical to use.
The aggregates used to make concrete must be clean, dense, hard, durable, structurally sound (neither flaky nor elongated), capable of developing good bond with the cement, weather-resistant, and unaffected by water. Hence, use of well-graded aggregates, free from silt, organic matters, and other unsuitable impurities is always preferable.
Aggregates should be stored properly and different fractions (sizes ) shouldn’t be mixed together.
Proper storage of cement permits easy access for inspection and identification. Cement should be stored in suitable weather-tight structures to protect it from dampness. It should not be piled higher than ten bags in a stack and has to be arranged in header and stretcher fashion as far as possible. While removing the bags for use, the”First in, first out” rule should be applied.
Water distributes through the cement evenly so that every particle of the aggregate is coated with it. It reacts chemically with the cement, the reaction being called hydration of cement, and brings about the setting and hardening of cement. Water also lubricates the mix and gives it the workability required to place and compact it properly.
It is preferable to use potable quality of water that is free from impurities and harmful ingredients. Seawater is not recommended for reinforced and pre-stressed concrete. The water fit for mixing is fit for curing too. Use of minimum quantity of mixing water, consistent with the degree of workability required to enable easy placing and compaction of concrete, is advisable. Ensure that the quantity of water added at the construction site is measured first. Low water-cement ratio is essential for the strength of the structure in the long run.
Reinforcement steel as per IS 1786 should be free from loose rust, oil paints, mud etc. It should be cut, bent and fixed properly. The reinforcement steel rods should be placed and maintained in position by providing proper cover blocks, spacers, supporting bars, laps etc. It should be placed and tied such that concrete placement is possible without segregation, and compaction possible by an immersion vibrator.
Placing of Concrete
Walking rails should be provided on slabs before concrete placement so that Reinforcement steel will not get disturbed or damaged.
Concrete should not be poured from more than 1m of height to avoid segregation.
Compaction refers to removing air from concrete. It reduces the voids since lesser the voids, stronger the concrete. Proper compaction will ensure water tightness too. For manual compaction of slab use a wooden float and a 16 mm bar.
Curing is essential for strength and durability of the concrete structure. Do not start plastering before completion of brickwork curing.
Curing is the process of preventing loss of moisture from the concrete and maintaining the required humidity within the structure to facilitate high strength development in concrete and other works where cement is used.
Application of water should begin when the exposed surfaces start drying out. Concrete surfaces should be kept continuously moist preferably for a period of 10 to 14 days. It should be ensured that all the exposed surfaces including sides, edges are kept moist throughout the curing period.
Bricks should be well burnt and of uniform size and color. Striking two bricks together should produce a metallic sound. A good brick will not break if dropped in its standing position from 1m above ground level. Bricks must be well soaked in water for a minimum of 8 hours before use or it will absorb moisture from the mortar. A good brick should not absorb moisture more than 15-20% by weight.
Plastering is done to protect the surface of masonry from atmospheric influences, especially rain. It also binds all bricks or stones and provides some lateral stability. It protects the joints of masonry and presents a good appearance with white or color wash.
Mortar from the joints should be raked off and the surface wetted. Mortar with cement and fine sand in the ratio of 1:4 should be used. For coarse sand the ratio can be changed to 1:6. However, the 1:4 mix is preferred for a better result. It should be ensured that the mix is not prepared for the whole day at one go. Only the amount that will be consumed within an hour should be prepared at once.
Concrete needs protection. It is constantly under attack of environmental pollution, moisture ingress, penetration of chlorides and sulphates and other deleterious chemicals. The durability of concrete is then affected.
Preventive measures are always better than curative ones. Using the right quality of materials in the right proportion supported with good workmanship will give good results and require less repair and maintenance. Considering this, the life cycle cost of the structure is greatly reduced and makes it economical.
While repairing, it is advisable to know the reasons for failure or defect first. Proper diagnosis is important.
Since there are many materials and methods for effective repair of damaged concrete structures, repair works should be carried out under expert guidance only.