What is Moisture Content in Aggregates

1)what is the difference between aggregate absorption (sand,10,20 mm) and moisture content of aggregate(sand,10,20 mm) .
2)It is ok to design a mix without taking moisture of aggregate..
we have only data about absorption of aggregate (sand,10,20 mm). And after that we assume moisture zero and do correction only.. is it ok???
 
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Dnyan Deshmukh

Staff member
There are two type of definitions for water in aggregate

Absorb Water
Water which is absorb by aggregates is called absorbed water, absorption level depends on the porosity and voids in the structure of aggregates.

Adsorb Water
Adsorb water is the excess water present in aggregate on its surface, generally we call it as moisture.

When Mix designing is done the calculation are made to high precision to get the actual out put from it.

When mix design trials are made, the aggregates taken for trials are in SSD Condition (Saturated Surface Dry).
SSD means the aggregate will not absorb the water from mix and also it do not content moisture on its surface.

When aggregates are taken in SSD condition, results of trials gives high precision values.

In general while mix designing we do check for the water absorption property of aggregates and in most of the cases trials done in SSD condition.

When to Calculate Moisture

During actual production of concrete and mostly in rainy seasons or in case water sprinklers are installed on bins to control the dust emission, the actual water present in the aggregates is unknown.

Only the water absorption property of aggregates is known to us.

In this case the sampling of aggregate from bins/stack yard/ stack pile is done.
Those samples are made bone dry in oven and the water content (absorb + adsorb) is calculated and results are written in terms of % weight of aggregates.

Once we knows the value of water present in it.

We can do suitable adjustment in weights of aggregates to ensure the W/C ration remain same and does not affect the properties of concrete.

To compensate the moisture % in aggregates, quantity of aggregates need to be increase by same % and equal amount of water need to be reduce from total water content.

This ensure the correct proportioning of material.

What is total water content in mix
Water as per W/C Ration.
Water demand of aggregates, if not fulfilled, they will absorb the water from W/C ration water quantity. This will affect the workability of concrete.