Even if aggregate is available, it may not meet the quality requirements for certain uses.
Suitable aggregate consists of clean, uncoated particles of proper size, shape, and gradation.
It must be strong and resist breakdown during handling, mixing, and in use. It must be able to resist the actions of wetting and drying, and freezing and thawing. It must not react with cement when used in concrete. The aggregate used in the construction of this parapet wall contained minerals that reacted with the cement in the concrete. When the aggregate and cement reacted, the concrete expanded and cracked.