foundation system of burj al arab

Pore Size of Aggregate for Concrete

We know that concrete aggregates inherently have pores and their sizes can vary over a wider range. Of these, the largest may be only visible with microscope but sometimes they can be seen by naked eyes. In previous post we have learnt about the importance of pore in assessing concrete strength and durability.


So we have idea about size of pores in aggregates (maximum limit). But get pore of cement paste is smaller than the smallest pore size of aggregates. The common aggregates we used in concrete construction have porosity of (0~5) percent. Here we are providing porosity of some rocks and unconsolidated deposits below:

 
porosity of some rocks and unconsolidated deposits
Pore size less than 4 µm in aggregates is considered especially as such aggregates are susceptible to be badly affected by alternating freezing and thawing.


Some pores don’t comes out to surface remain within solid volume but some pores reach to surface of aggregate particles. Cement paste have high viscosity than water so it cannot penetrate through the pores to a considerable depth.



Porous aggregateUnlike cement paste, water can penetrate pores, thus size and extent of pores affect water demand of concrete. The degree of penetration depends on pore properties such as

-size

-continuity

-total volume


Aggregates, since, occupies three-fourth volume of concrete, it is obvious that a concrete produced from porous aggregate materially becomes porous concrete.

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