Aggregates gradation also have an influence on the compressive strength of concrete. Concrete strength increases when using dense gradation and increasing fines modulus of aggregates. By increasing fines modulus surface area of aggregates goes on increasing. With the increase in surface area more bond surface will be available and due to this stronger bond will be formed and also this requires less mixing water. Now when there is decrease in amount of mixing water at the same consistency lead to higher compressive strength, this is because of less number of air voids in between the concrete volume.
Fines modulus is actually a number that defines gradation of aggregates, by increasing fines modulus mean coarser gradation and with the decrease in fines modulus means finer gradation. Using smaller number of fines modulus, particles surface area is small and hence requires more amount of mixing water, which will lead to increment in voids due to this weak point’s in concrete increases and due to this compressive strength graph of concrete falls down.
Using higher number of fines modulus without decreasing amount of mixing water, decrease the compressive strength of concrete.
Shape And Size Effect On Concrete Strength
Aggregates shape and size has a strong influence on properties of concrete. Rough surface textured particles increase the compressive strength of concrete up to 20-30%, instead of using natural gravels that is obtained from river beds. Rough surface have pores which have ability to form bond or create resistance against the applied load. In case of size, mainly there are two types of aggregates.
- Coarse aggregates
- Fine aggregates
Aggregates having size larger than 4.75mm are categorized as coarse aggregates and aggregates whose size is less than or equal to 4.75mm are known as fine aggregates.