Porosity :- All aggregate particles contain numerous internal pores. The porosity of aggregate influence such properties of aggregate as the bond between cement and aggregate, resistance of concrete to freezing and thawing, and chemical action. The pores vary in size over a very wide range. The largest pores may be seen with a naked eye but mostly they are visible only under a microscope. The smallest pores are generally larger than the gel pores in the cement paste. Some of the aggregate pores are wholly within the solid, while other open onto the surface of the aggregate.
The cement paste may not be able to penetrate to a great depth but water can enter the pores, the amount and rate of penetration depends on their size and total volume.
