Concrete work in a Nut-Shell for Building Construction
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
further understanding, (Refer course: Understanding
of Concrete). Here, the laying of different grades of concrete is described.
- Laying M7.5
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
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.
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
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
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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