🔹 Methods of Curing -

1. Curing by spraying water -

Spraying of water continuously on the concrete surface provides an efficient curing. It is mostly used for curing floor slabs. The concrete should be allowed to set sufficiently before sprinkling is started. The spray can be obtained from a perforated plastic box. On small jobs sprinkling of water may be done by hand. Vertical and sloping surfaces can be kept continuously wet by sprinkling water on top surfaces and allowing it to run down between the forms and the concrete. For this method of curing the water requirement is higher.

2. Curing using wet Gunny bags -

This is a widely used method of curing, particularly for structural concrete. Thus exposed surface of concrete is prevented from drying out by covering it with hessian, canvas or empty cement bags. The covering over vertical and sloping surfaces should be secured properly. These are periodically wetted. The interval of wetting will depend upon the rate of evaporation of water. It should be ensured that the surface of concrete is not allowed to dry even for a short time during the curing period. Special arrangements for keeping the surface wet must be made at nights and on holidays.

3. Curing by Ponding Method -

This is the best method of curing. It is suitable for curing horizontal surfaces such as floors, roof slabs, road and air field pavements. The horizontal top surfaces of beams can also be ponded. After placing the concrete, its exposed surface is first covered with moist hessian or canvas. After 24 hours, these covers are removed and small ponds of clay or sand are built across and along the pavements. The area is thus divided into a number of rectangles. The water is filled between the ponds. The filling of water in these ponds is done twice or thrice a day, depending upon the atmospheric conditions. Though this method is very efficient, the water requirement is very heavy. Ponds easily break and water flows out. After curing it is difficult to clean the clay.

4. Steam Curing -

Steam curing and hot water curing is sometimes adopted. With these methods of curing, the strength development of concrete is very rapid.

These methods can best be used in pre cast concrete work. In steam curing the temperature of steam should be restricted to a maximum of 750C as in the absence of proper humidity (about 90%) the concrete may dry too soon. In case of hot water curing, temperature may be raised to any limit, ay 1000C.

At this temperature, the development of strength is about 70% of 28 days strength after 4 to 5 hours. In both cases, the temperature should be fully controlled to avoid non-uniformity. The concrete should be prevented from rapid drying and cooling which would form cracks.

5. Curing using chemicals -

Curing compounds are chemical products usually sprayed directly over the concrete surface and allowing it to dry. The compound forms an impermeable membrane that retards the loss of moisture from the concrete.

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📌 Bleeding & Segregation in Concrete -

🔹Bleeding -

Bleeding is a form of segregation in which water present in the concrete mix is pushed upwards due to the settlement of cement and aggregate. The specific gravity of water is low, due to this water tends to move upwards. Bleeding ordinarily occurs in the wet mix of concrete.

The Prime factor for bleeding in concrete is the high dosage of Water cement ratio. Higher water-cement ratio weakens concrete and leads to excessive bleeding.

The bleeding in concrete is not harmful if the rate of evaporation of water is equal to the rate of bleeding. Normal bleeding is quite good, and it enhances the workability of concrete.

When the concrete is fully plastic, bleeding may not cause much harm. However, concrete is still in the plastic stage later it is subsidized and compacted.

🔹Segregation -

Segregation is the “Separation of constituent materials in concrete.” In concrete technology, segregation is of three types:-

1. Separation of Coarse aggregate from the concrete mixture,

2. Separation of Cement pastes from the concrete during its plastic stage.

3. Separation of water from the concrete mix (Bleeding in concrete)

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🔹Important concept -

TMT bars -TMT stands for "Thermo Mechanically Treated".
Generally we use TMT bars for the construction purposes where we need high strength and high corrosion resistance as compared to normal steel.

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🔹Important concept -

Main bars in the slabs shall not be less than 8 mm (HYSD) or 10 mm (Plain bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.

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🔹Important concept -

Main bars in the slabs shall not be less than 8 mm (HYSD) or 10 mm (Plain bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.

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🔹Mild Steel Bar -

The mild steel bars are smooth and round in shape having diameter ranges from 6mm to 50mm used for small scale construction works.

Mild steel is also known as low carbon steel having 0.1% to 0.25% of carbon. But mild steel is not considered as an alloy steel though it doesn't contain other elements in it compared to different steel varieties. As carbon content increases, ultimate strength and hardness will increase but ductility and toughness decreases. Though mild steel contain very less carbon, it is ductile and weldable but having low stength. Also mild steel is highly prone to corrosion.

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