How do you think the ratio of cement to sand affect the concrete strength?

well, although it is very general question and to explain the relation between concrete materials which affect the strength will take long time..
but in brief I can say it is known that increasing of cement content will increase the strength of concrete but on the other hand will affect other physical properties as it will increase the shrinkage of concrete and will affect also the workability and at the end it is un economically process.
so there is proportions comes through researches shows the ideal contents gives the proportions for desired strength according the structure purpose of use.

the ratio according to Egyptian code is cement:sand:aggre1:2:4 so if you use more sand you must increase cement to achieving required strength but don't neglect aggre ration because more sand and more cement well make week concrete because most of cement will encases small particles of sand and this make non homogenous concrete and you will need more water and it will take much time in mixing

it is advisable to work on specifications of certain project..........if there is reduction or increment in cement/sand ratio contrary to the specification, then the efficiency,safety,life span and profit on such project are not guaranty.

Cement sand ratio may affect concrete depending on different factors for example, increasing cement may increase its chances of failure due to shrinkage.
On the other hand, increasing sand content may decrease the bonding between cement and aggregates.
 

well, although it is very general question and to explain the relation between concrete materials which affect the strength will take long time..
but in brief I can say it is known that increasing of cement content will increase the strength of concrete but on the other hand will affect other physical properties as it will increase the shrinkage of concrete and will affect also the workability and at the end it is un economically process.
so there is proportions comes through researches shows the ideal contents gives the proportions for desired strength according the structure purpose of use.

The way that concrete is mixed is very important in determining the quality of the final product after it is poured.
The exact materials used and the proportion of those materials are both very important.
Knowing what ratio of sand to cement to use depends partly on what the concrete is being used for.
Standard Mixture A pretty standard recipe for mixing concrete calls for one part of cement to every two parts of sand.
The result of this recipe, assuming that four parts of gravel are also included in the mix, is a C20-rated concrete.
Concrete is rated on a number system that indicates how strong the mix is after it has cured for approximately a month.
C20 concrete would be considered a medium-strength concrete mix.
Higher numbers indicate a stronger concrete.
Increasing the Strength Adjusting the strength of concrete based on the ratio of sand to cement is easy to do.
The closer you bring the ratio to an even one-to-one ratio of sand to cement, the stronger you will make the concrete.
On the other hand, if you push the ratio in the other direction you will get a product that has slightly less strength.
Quality While concrete mixes all contain Portland cement, the actual type of sand used varies.
In addition to the ratio, the type of sand that you use in the concrete mix also affects the strength of the concrete.
Using unwashed beach sand, for instance, is likely to create a concrete mixture that is not as strong as products made with sand that has been cleaned in order to produce a consistent quality.
Other Factors It is important to realize that the ratio of sand to cement is not the only factor that affects the strength of concrete.
Concrete is typically made from four ingredients, not just two.
In addition to the cement-to-sand ratio, the ratio of gravel to sand must also be considered.
Finally, the amount of water added to the mixture is also important in the strength of the final product.

Well, if you have a ratio of cement, water and sand that is about1:1:2, it can make it stronger.
However, add any more sand to that, and the concrete can become brittle, making it weak and easy to

THE RELATION BETWEEN CEMENT AND SAND IF YOU MEAN SAND AS A FINE AGGREGATE YOU SHOULD NOW THAT IT'S PARALLEL RELATION WHEN YOU INCREASE SAND YOU MUST INCREASE CEMENT RATIO TO KEEP SAME STRENGTH E