you have to take 1.52 as constant for calculating concrete 
mix ,let me explain it this 1.52 is the quqntity of total 
dry aggregate which is required.so when ever u require to 
know the quantity for any given mix .u need to add up the 
ratio of mix and divide 1.54 by the sum of mix ratio u ll 
get the quantity of cement for one cum 
eg: suppose m20 mix u need to calculate the concrete then
simply add the ratio of m20 i.e 1:1.5:3 so the total is 5.5
and divide 1.52 by 5.5 u ll get 0.27 cum of cement which ll 
b required for 1 cum of concrete and if u multiply it(0.27) 
by 30 u ll get the no. of cement bags .follow the same rule 
for diff type of mix

curing

Divide the sum of ratio of any mix to dry cofficient eg. 
1:1.5: 3= 1+1.5+3= 5.5, 1.54/5.5*3 you can find c.a.

Estimating Quantities of material needed.

   1. Calculate the volume of concrete needed.
   2. Estimate the total volume of dry material by
multiplying the required volume of concrete by 1.65 to get
the total volume of dry loose material needed (this includes
10% extra to compensate for losses).
   3. Add the numbers in the volumetric proportion that you
will use to get a relative total. This will allow you later
to compute fractions of the total needed for each
ingredient. (i.e. 1:2:4 = 7).
   4. Determine the required volume of cement, sand and
gravel by multiplying the total volume of dry material (Step
2) by each components fraction of the total mix volume (Step
3) i.e. the total amount cement needed = volume of dry
materials * 1/7.
   5. Calculate the number of bags of concrete by dividing
the required volume of cement by the unit volume per bag of
cement (0.0332 m3 per 50 kg bag of cement or 1 ft3 per 94 lb
bag).

For example, for a 2 m x 2 m x 10 cm thick pump pad:

   1. Required volume of concrete = 0.40 m3
   2. Estimated volume of dry material = 0.4 x 1.65 = 0.66 m3
   3. Mix totals = 1+2+4 = 7 (1:2:4 cement:sand:gravel)
   4. Ingredient Volumes: 0.66 x 1/7 = .094 m3 cement
      0.66 x 2/7 = .188 m3 sand
      0.66 x 4/7 = .378 m3 gravel
   5. # Bags of cement: 0.094 m3 cement / .0332 m3 per 50 Kg bag
      = 2.83 bags of cement (use three bags)