CONCRETE 1:2:4, Grade 25 N/mm2 (MPa)

CONCRETE 1:2:4, Grade 25 N/mm2 (MPa)
1.COMPOSITION
Ingredient				Specification		Quantity
Cement				Ordinary Portland Cement		1 part in 7 of dry volume
Coarse sand				Coarse sand used for concrete mixing doesn’t have clay or organic matter. The fine sand shall not be used in concrete mixing.		2 parts in 7 of dry volume
Aggregate 10x20 mm				Minimum stone size 10 mm, maximum size 20 mm. No dust, clay or organic matter.		4 parts in 7 of dry volume
Water				Clean and free water from any organic or inorganic matter in solution or suspension. It shall not contain any grease or greasy particles, clay or salt ( Drinking water).		149 litres per m3 of mix or 23 litres per 50 kg bag of cement, but anyway the minimum amount needed to mix and pour concrete
1.OTHER REQUIREMENTS
Cone size: 10x20x30 cm				The consistency of fresh concrete shall be monitored by slump test: Minimum slump: 80 mm Maximum slump:120mm Concrete compressive strength should be Strength Grade   25 N/mm2
3.CONSTRUCTION TECHNIQUES
Concrete mixing 1:2:4				The type of this concrete should be mix by machine.
Compaction				This type of concrete should be compact by mechanical vibrator.
Construction joint				The construction joints shall be made where concrete placing operation send for the day or where one concrete structural element is cast against a previously placed concrete structural element. The construction joint shall extend entirely through the concrete element. In a normal contraction joint load transfer, additional to that provided by reinforcing steel when present at the joint, shall by aggregate interlock. This requires the first placed concrete to have a rough and irregular surface at the join. If the roughened surface is prepared by scab bling then the joint must be thoroughly cleaned with compressed air or other effective means before placing fresh concrete. Keyed joints shall not be used because this method has poor load transfer, especially for unreinforced concrete. If the construction joint is made smooth in unreinforced concrete then dowel bars shall be used to achieve load transfer across the joint.
Finishes				All exposed finished surface shall be smooth. Honeycombed surfaces and superficial water and air holes shall not be made good immediately on removal of the formwork and shall only be filled in with mortar on the instructions of the Technical Supervisor. The faces of concrete for which formwork is not provided, other than slabs, shall be floated to provide a smooth surface. Faces of concrete to receive render or plaster shall be roughened to provide a good key for the applied finish. A good key can be provided if the concrete surface is scratched and roughened with a sharp tool, this will be most effective with young concrete. Alternatively and/or additionally a ‘dash coat’ may be applied by throwing a mixture of mortar and added bonding agent against the wall. The scratch and dash coat shall be left 24 hours before the floating/render coat is applied. The surface of building floor slabs shall be polished when nearly set with a dusting of cement powder to ensure a smooth horizontal surface. Pathways and concrete areas shall be coarse broom-finished to ensure that the surface is non-slip.
Curing				Newly placed concreteafter 6 hours shall be protected from drying wind,rain and sun by completely covering it with plastic (or other) sheeting. The concrete, including exposed faces, shall be frequently wetted by approved means for at least 7 days after placing. During the curing period, the concrete shall be left undisturbed other than works to be covered.
Plastering			Structural concrete shall not be plastered unless required by the drawings.
4.USES
Concrete 1:2:4 used for		Reinforced concrete beams, columns and slabs for small buildings Bridge foundations, abutments and piers (but not bridge decks and beams).
5.CALCULATION OF MATERAIL QUANTITIES PER 1m3 OF CONCRETE					Concrete 1:2:4
Material	Amount			Unit
Cement	325			kg
Coarse Sand	0.43			m3
Aggregate 10x20mm	0.86			m3

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