What is concrete?

Concrete is a mixture of cement, sand, gravel, admixtures, and water. It is one of the most common base processes in construction, which is why it is important to know the quantities, the dosage of materials, the type of material to be used, and the type of concrete required.     

Cement

Portland cement, as it is generally known, is a binder material and reacts with water. It is made up of limestone and clay as a base, plus silica, alumina and iron oxide. These compounds give properties to the cement according to the amounts provided. The result of the crushing of these materials produces the Clinker, finally the gypsum is added the small percentages that acts as a retardant and allows setting by adding water and subsequently hardening.     

Gravel and Sand

Gravel and sand are aggregates in construction and taking into account the type of concrete we are going to talk about, a concrete for glue, floors, retaining walls, columns or slabs. Therefore, the type of sand we should use is coarse sand. Fine or medium sand is normally used for finer and more superficial finishes.     

Water

Water is very important in the resistance and consistency of concrete, in its preparation and subsequent curing of the concrete. The water must be clean and must not contain substances such as oils or salts, as this can affect the time it takes for the concrete to reach its maximum strength. The percentage of water in the dosage table is averaged, taking into account if the aggregates sand and gravel are wet, in the dosage per package you can reduce or increase the liters of water, this should be supervised by an experienced builder.     

Concrete batching table

Since cement is usually used together with other construction materials like sand and gravel, we calculate its volume using a mix ratio. With mix ratios, we can tell how many components a concrete mix will need in terms of parts.    

Concrete mix ratio	Resistence	Cement kg	Sand m3	Gravel m3	Water lt	Common Uses
1-2-2	4000psi-28Mpa	440	0.62	0.62	210	Driveways, paths, garage base, structural use
1-2-2.5	3500psi-25Mpa	400	0.56	0.70	200	Beams, Columns, Slabs, Footing, structural use
1-2-3.5	3000psi-21Mpa	340	0.47	0.83	190	Single story foundations,Beams, Columns, Slabs, Footing
1-3-3	2400psi-16Mpa	310	0.66	0.66	180	Drainage Channels, floor slab, Garage Floors, Stairs
1-3-5	2000psi-14Mpa 240	240	0.51	0.85	170	Footing for small walls, Floor Slab, Sidewalks
1-4-7	1560psi-11Mpa	180	0.51	0.89	130	Kerb, Backing, Blinding

What is dry volume of concrete

Volume of Dry mix of different ingredients of concrete like cement sand and aggregate before adding water is known as dry volume of concrete having air voids and pores between particles.    Dry volume of concrete is mixture of cement, sand and aggregate without water in dry condition, their volume is increased by 54% of wet volume due to presence of air voids between cement, sand and aggregate particles.    It means if we have to caste concrete slab of 1 cubic metre size which is wet volume of concrete we have to buy and require dry ingredient of concrete cement, sand and aggregate 1.54 cubic metre.

Sample calculation

Find the percentage of materials needed for a concrete mix of 21Mpa for a 3.1 m3 structural element.   

M21 Mix Ratio = 1 : 2 : 3.5 $\left( 6.5 parts \right)$

1 – Cement    2 – $\left( Sand aggregate \right)$   3.5 – $\left( Coarse aggregate \right)$

Total Concrete Volume= 3.1 m3 x 1.54 $\left( Dry Factor \right)$ = 4.77 m3    

Density of cement – 1440 kg/cum    

Volume of Cement = $\left( 1/6.5 \right)$x4.77=0.7338m3 

Amount of Cement = 1440 kg/ m3 x 0.7338 m3 = 1056.67 kg    

1 Cement Bag Weight = 50 Kg    Then, 1056.67/50 = 21.3 bags     

Sand Quantity

Sand Quantity= $\left( Sand Part/Concrete Part \right)$ x Concrete Volume   

 Sand part = 2 $\left( 1:2:3.5 \right)$   

 Density of sand = 1500–1550 kg/cum    

Volume of Sand = $\left( 2/6.5\right)$  x 4.77m3 = 1.467 m3    

Amount of Sand = 1.467m3 x 1500 kg/m3 = 2201 kg     

Aggregate Quantity

Aggregate Quantity = $\left( Sand Part/Concrete Part \right)$ x Concrete Volume    

Aggregate part = 3 $\left( 1:2:3.5 \right)$   

Density of aggregate = 1520 – 1680 kg/cum    

Volume of Aggregate = $\left( 3.5/6.5 \right)$ x 4.77= 2.568 m3    

Amount of Aggregate = 2.568m3 x 1550 kg/m3= 3981.11 kg     

Water Quantity

According to the table for a concrete of 21 the volume of water per meter is 190 liters    

Volume of water = 190lt/m3 x 4.77 m3 = 906 liters.