It was shown that the combination of metakaolin (MK) and fly ash (FA) exhibited a significant increase in the characteristics of strength and durability, such as acid and sulphate resistance. The primary reason for this was that the Ca (OH)2 that was formed by the plain concrete reacted with the pozzolans that were added, which resulted in the formation of more calcium silicate hydrates. The Ca(OH)2 that is produced as a byproduct of the hydration of plain concrete does not make a major addition to the concrete's strength and may even be detrimental to the concrete's longevity. Its absence or decrease as a consequence of pozzolans' chemical reaction leads to a significant increase in both strength and durability.