Dear reader in our last post we have learnt about water absorption of aggregate for concrete. Our present discussion is also related to this. In case of concrete mix design, after all considerations for strength and durability, a water-cement ratio is fixed which is followed by necessary adjustment due to moisture deficiency or excess in aggregate mass. The normally adjustment is deficiency or excess amount of water is either added or cut off from water-cement ratio.
But this calculation is not so easy; as dry aggregate mass cannot absorb all moisture that is deficient in aggregate. Now several questions may be asked:
If not how much moisture is absorbed?
What are the effect of this on reach and lean concrete mix?
In case of coarse aggregate there have also movement of moisture form surface to interior mass of aggregate, which is not usual in fine aggregate. We have provided idea about pore size and porosity of aggregate in our previous posts.
Now why should we discuss about dry aggregate?
We can change in moisture condition before mixing in concrete. In case of dry and hot climate, excessive moisture may be loosed from aggregate before mixing and in some batching plant where conveyor belt is used; the dry air can absorb moisture from aggregate. Dear reader we have provided ACI code provision for hot weather concreting and also requirements for using conveyor belt in concrete production.
Dear reader we will find the answer of above questions in next part, coming just after it; please stay with us.