Sand and gravel are widely used in construction, transportation and water conservancy. But are they natural raw materials or man-made products? The answer depends on their sources and processing methods.
Sand Making Machine
Natural Sand and Gravel: Nature’s Gifts
Natural sand and gravel are typical natural raw materials, formed by long-term natural forces like weathering, erosion, transportation and deposition of surface rocks.
Sand comes mainly from rivers, lakes and seas (sea sand needs desalination for construction due to high salt content). Gravel, often found in mountains and river valleys, forms via geological movements or glacial impact, requiring only simple screening before use.
Long a top choice for construction due to wide sources and low costs, over-exploitation of natural sand and gravel has caused ecological issues like riverbed collapse and soil erosion. Many countries have restricted its mining, boosting the development of man-made alternatives.
Man-Made Sand and Gravel: Human Ingenuity
Man-made (or machine-made) sand and gravel are typical man-made products, processed by crushing, screening and shaping natural rocks via professional machinery.
With standardized production processes, they boast controllable particle size, stable quality and customizable gradation, effectively compensating for the shortage of natural sand and gravel.
They can also use industrial solid wastes like construction waste and tailings, realizing resource recycling. With advanced processing technology, their quality has improved and they’re widely used in large projects such as high-speed railways and super high-rises.
Conclusion: Coexistence of Two Forms
In summary, sand and gravel can be either natural or man-made. Natural ones have low initial costs but face exploitation restrictions; man-made ones, with controllable quality and recyclable advantages, are important substitutes.
In the future, man-made sand and gravel will take a larger market share. We also need scientific management of natural resources to balance construction needs and ecological protection.
