Different types of cement concrete are discussed along with their uses.
8.3.1 Plain Cement Concrete
It is the simplest form of concrete made with cement, sand, pebbles or crushed rock and water. It is used for a variety of works where the structural members are subjected to compression. Simple foundations to mighty dams may be constructed with plain cement concrete.
8.3.2 Reinforced Cement Concrete
The cement concrete provided with steel reinforcement for taking on tension, bending, torsion, fatigue, etc., is referred to as Reinforced Cement Concrete (RCC). The steel used in RCC works are: mild steel bars, medium tensile steel bars, hot-rolled deformed bars, cold twisted bars, hard-drawn steel wire fabric or rolled steel. It is used in various structural members, viz., columns, beams, footings, slabs, staircases, shelves, basements, water tanks, retaining walls, folded plates, shells, domes, etc.
8.3.3 Pre-stressed Cement Concrete
Here high tensile steel wires are used as reinforcement instead of mild steel bars. High tensile steel wires are stretched initially to the desired level and concrete is placed. After setting and completion of curing, the concrete is put into use. As the steel wires are initially stretched, the concrete so casted is known as pre-stressed concrete. This concrete is used in the manufacturing of railway sleepers and electric poles and in the construction of large span beams, large span bridge girders, etc.
8.3.4 Light-weight Cement Concrete
This concrete has less density compared to the conventional concrete. Light-weight concrete may be prepared (i) by omitting the fine aggregate, (ii) by using light-weight concrete or (iii) by aerating concrete.
The concrete prepared by omitting the fine aggregate is called no-fine concrete. It has low drying shrinkage. This is used for cast-in-situ external load-bearing walls, small retaining walls, where repetitive loads are expected to occur, etc. This has better insulating properties.
The light-weight aggregates used are pumice, expanded slates, furnace clinker, etc., and the fine aggregates used are crushed light-weight aggregate or natural sand. This type of light-weight concrete has better insulating and fire-resistant properties, is highly water absorptive and economical. This can be used for all the works stated above.
The light-weight concrete obtained by aeration is known as gas, porous or foamed concrete. This is prepared by (i) mixing air-entraining agents with cement or cement mortar in high-speed machines, (ii) mixing a specified quantity of pre-formed foam with cement or cement mortar in an ordinary mixer or (iii) adding aluminium or zinc powder to cement mortar or hydrogen peroxide to concrete. It has a very high drying shrinkage and is used for the manufacture of building blocks.
8.3.5 Precast Cement Concrete
The concrete used for the casting of various structural components with or without reinforcement is called precast cement concrete. Fresh concrete is placed and compacted in moulds made for different structural units. After setting and curing they are removed from moulds and used. This is discussed in detail in the next chapter
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