Sand, gravel and hard-rock aggregates
Almost every item of infrastructure around us contains stone construction materials. It can either be as sand, which is stone crushed by nature, or stone crushed by machines, known as hard-rock aggregates (or crushed stone)
Sand, gravel and hard-rock aggregates are used as stone construction materials, which after modification are used to build roads, railway lines, buildings etc.
Geological materials with different grain sizes, such as sand, gravel, clay and crushed rock (hard-rock aggregates) have exploited by humans for thousands of years. These materials are considered non-renewable, although recycling has recently become more common. In some countries, there has been a recent shift towards using gradually more hard-rock aggregates in the materials mix, instead of sand and gravel.