Question

What is the minimum cement content for a reinforced concrete structural member subjected to moderate exposure condition as per IS 456 ∶ 2000? Assume 20 mm nominal maximum size aggregate are used.
1. 350 kg/m³
2. 380 kg/m3
3. 300 kg/m3
4. 280 kg/m3

Answer 1

Correct Answer - Option 3 : 300 kg/m3

Concept:

According to IS 456 : 2000, the Minimum Cement Content, Maximum water-cement Ratio and Minimum Grade of Concrete for different exposures with Normal Weight Aggregates of 20 mm Nominal Maximum Size

SI No.	Exposure	Plain Concrete			Reinforced Concrete
		Minimum cement content kg/m3	Maximum Free-Water-Cement Ratio	Minimum Grade of Concrete	Minimum Cement Content kg/m3	Maximum Free Water-Cement Ratio	Minimum Grade of Concrete
i)	Mild	220	0.60	-	300	0.55	M 20
ii)	Moderate	240	0.60	M 15	300	0.50	M 25
iii)	severe	250	0.50	M 20	320	0.45	M 30
iv)	Very severe	260	0.45	M 20	340	0.45	M 35
v)	Extreme	280	0.40	M 25	360	0.40	M 40

 

It can be seen in the above table, that minimum cement content for various concrete work is dependent on exposure conditions, and the type of concrete i.e plain concrete or reinforced concrete, and it is independent of the grade of cement used.  

Cement content prescribed in this table is irrespective of the grades of cement and it is inclusive of additions such as fly ash or ground granulated blast furnace slag may be taken into account in the concrete composition with respect to the cement content and water-cement ratio if the suitability is established and as long as the maximum amounts taken into account do not exceed the limit of pozzolana and slag specified.