Hi Bhupes, I assume the grade of concrete you are going to make with the 350 kg/m3 cement content and w/c of 0.45 should be f'c28=32 MPa .

As a generic solution, when the cement content is constant, the increase of W/C results in the increase of paste volume therefore the proportion of fine aggregates should be increased. In addition, for grade 32 MPa the proportion of coarse aggregates is better to be higher than fine aggregates.

When the volume of matrix (fine + coarse) is considered fixed, then the volume of binder is also fixed because: the total volume 1 m3 = volume of matrix (fixed) + volume of binder + air content AC (fixed) and therefore : volume of binder = 1 - AC (fixed) - volume of matrix (fixed). In such cases, the increase of W/C results in the decrease of cement content in a way that the total volume of binder remains same.

Your question can be more complex, if you introduce fly ash or slag to your mix, or want to keep the workability (slump) of mix similar. in those cases you have a combination of  cementitious materials rather than cement and you should consider the effects of adjustments in workability and short-term strength of concrete.

In addition if you use a combination of manufacture sand and natural sand you need to consider that natural sand are round in shape and mixes that have higher proportion of natural sand are more workable. Accordingly, for higher W/C ratios (more workable mixes) you can increase the proportion of man sand to adjust the target slump.

You can easily perform all calculations in spreadsheet. Please find attached a sample spreadsheet, provides solution for your question.

You can find more information on the library section of the CCAA web site www.ccaa.com.au

Let me know if you need more information. 

Basically i want to judge water reduction capacity of admixture .so i proposed a few dosages SBWC for admixture WRM  as well as control with any w/c which would give me air content 3.5%max. on base of 3.5% aircontent constant for also admixture containing concrete, i want to change concrete volume by keeping constant air content ,i am using a flyash also.which may effect on workability as well as air content. how should i compare my product water reduction by keeeping air as well as slump constant? i want to clerify the sesitivity of my concrete using a no admixture.means percent of water cut.i want to do a mix by keeping constant binder wt. & at constant matrix volume at diferent w/c ratio.will 0.125 micron sieve size retained material effect on my concret matix volume? 

Your descriptions were not clear for me. However, I think you need to define a reference mix design, then only increase the content of admixture and see the effect of that on the slump and air content.

In the next stage, keeping the content of cement (or cement + fly ash) fixed, you should reduce W/C ratio and plot the effect of change in W/C ratio on the slump and AC.

Having data from stage one and two, enables you to formulate a correlation between W/C and admixture, also AC and admixture.

0.125-micron sieve size retained has an influence on AC, but it is not the only variable. It is complex, and I suggest you to study on this matter. The content of cement inert minerals also the volume of binder have the effect on the AC. You can adjust the AC using air-entraining admixtures.

Thanks A lot Iman Sir,

the simplest and practical method is considering the concrete mix proportion such as:

`1:2:4

can use the formula

Volume = 0.67 (C+S+G), (Cement, Gravel, Sand by volume)

solved for upper mix using G=4C,  S= 2C

find all volumes

regards

the simplest and practical method is considering the concrete mix proportion such as:

`1:2:4

can use the formula

Volume = 0.67 (C+S+G), (Cement, Gravel, Sand by volume)

solved for upper mix using G=4C,  S= 2C

find all volumes

regards

where this 0.67 comes from? will u please explain in more details?

i want to keep constanst cement say 350 @ 0.5,0.55,0.6 W/C for this what will be the matrix volume? also when i keep constant matrix volume say 315 @ 0.5,0.55,& 0.6 W/c ratioo what will be the cement Quantity i have to take?