Concrete is a building material obtained by a mixture of cement, water, fine aggregate, and coarse aggregate. Concrete work is carried out for monolithic structures or reinforced concrete structures and installations made of cement concrete. Concrete work includes the following activities: preparation of the concrete mix; transportation of the mix to the construction site; and compaction of the mix in the formwork, the curing of the concrete, etc. There are primarily four types of concrete:
Plain Cement Concrete (PCC)
Reinforced Cement Concrete (RCC)
Pre-cast Concrete
Pre-stressed concrete
For further understanding, (Refer course: Understanding of Concrete). Here, the laying of different grades of concrete is described.
Laying M7.5 Grade PCC
Plain cement concrete of 40 mm size graded aggregate with cement and sand in fixed proportion is to be provided. The surface on which the concrete is to be laid should be clean. A mix of 1:4:8 is used and it is mixed thoroughly in the concrete mixer to have a plastic mix of uniform colour. PCC is laid in the layers and it is vibrated by the means of mechanical vibrators till dense concrete is obtained. Compaction should be done and it should be completed before the initial setting starts i.e 30 minutes of addition of water. After 24 hours of laying of concrete, the surface should be cured and curing shall be done for at least 14 days.
Laying M25 Grade RCC
A mixture of 20 mm size graded aggregate with cement and sand in fixed proportion is to be provided. The base on which concrete is to be laid should be clean and loose materials from the sides of the pit should be removed. M25 Grade of cement concrete is to be used and it is mixed thoroughly in the concrete mixer. Concrete is to be laid using a concrete pump and it is vibrated by the means of mechanical vibrators to ensure an even surface. Proper compaction should be done with the help of tamping rods into the corners of the formwork. After the concrete has begun to harden, curing should be done. It should be protected with moist gunny bags or any other materials. Curing should be done for a minimum period of 14 days.
Laying Concrete using Ready Mix Concrete
M25 Grade of concrete is used for ready mix concrete by mixing cement, water, and aggregates: sand, gravel, or crushed stone. Ready-mix concrete is transported and placed at the site. The concrete is to be poured to the surface and it is placed with the help of a concrete pump. Concrete should be placed from the corners of the formwork and compaction should be done immediately after it has been placed. Consolidation is to be done with hand-tampers or iron rods and a vibrator is to be immersed into the concrete at regular intervals. After the concrete has been properly compacted, the top of the concrete is to be levelled for a smooth surface. Curing should be done continuously for 14 days for gaining strength.
Laying RCC flooring
RCC flooring of M:20 grade concrete is to be laid in alternate panels. The panels are formed on four sides with the required MS channel bolted in position for forming the size. The MS channel should have the provision of holes for dowel bars if required. The cement mortar should be laid on a clean surface. The entire mass of RCC flooring should be vibrated with a surface vibrator so as to bring out slurry on top and the top surface should be smooth finished. Curing should be done by ponding for at least 7 days with cement mortar Vata with placing underneath 125-micron polythene sheet. Steel reinforcement should be paid separately as per the relevant item specified in the tender.
Laying Skid concreting
M15 concrete mix is used for skid concreting and cement slurry is spread on the surface. The surface on which concreting is to be done should be clean and leveled. 50 mm thick mortar is prepared and concrete is laid on the prepared surface. Grooves are made with a steel bristle and brooms are used to provide skid-resistant textures. The surface should be kept moist and curing should be done for a minimum period of 14 days as directed.
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