Temperature:
The strength of concrete increases with increase in temperature of casting and curing of concrete because the rate of hydration, particularly at early age, is faster at higher temperature. That is why we use steam curing when early gain of strength is required. However, at the later stage (i.e. after months or a year), as the rate of hydration becomes very slow the effect of temperature on the strength does not remain much effective. For example, let a concrete sample 'A' is casted and cured at 46oC and another sample of the same concrete 'B' is casted and cured at 4.5oC, then 7 days' strength of sample 'A' will be about 45% higher than that of 'B'. But if we compare28 days' strength of sample 'A' and 'B' then the difference of 28 days' strength between 'A' and 'B' reduces to 20% only.