What material can we add,other than fly ash and pozzolan,to strengthen the strength of concrete?

Adding silica content to the cement will increase the strength of the concrete. Therefore, fine grained silica sand or Montmorillonite Diatomaceous Earth are good additives to improve the compressive strength.

In addition, adding calcium chloride at lower temperatures allows faster curing of the concrete due to the increased rate of hydration. This results in a higher initial strength that can then be preserved against strength retrogression using other additives.