Aggregates are the important constituents in concrete. They give body to the concrete, reduce shrinkage, and affect the economy. Earlier, aggregates were considered as synthetically inert materials but now it has been perceived that some of the aggregates are chemically active and furthermore that specific aggregates exhibit chemical bonds at the interface of aggregate and paste. The mere fact that the aggregates occupy 70–80 percent of the volume of concrete, their impact on various characteristics and properties of concrete is undoubtedly considerable.
Some of the earliest signs of aggregates in use are from Mesopotamia around 3000 BCE. Antiquated Mesopotamians found the upsides of involving hydraulic lime as concrete. When blended in with water, the crushed lime aggregate would harden, going about as a folio among stones and bricks. Ovens were worked to make the very first burnt bricks. These bricks were a lot more grounded than the dirt and straw bricks well known at that point. With this innovation, antiquated Mesopotamians assembled houses made of solid stone with straightforward concrete floors, and, surprisingly, underground, waterproof frameworks. This was one reason they had the option to flourish in the sweltering desert environment.
Aggregates firmly impact concrete's freshly mixed and solidified properties, mixed proportions, and economy. Thus, the determination of aggregates is a significant process. Albeit some variety in aggregate properties is normal, attributes that are considered include:
- Particle shape and surface texture
- Abrasion and skid resistance
- Unit weights and voids
- Absorption and surface moisture
Types of Aggregates
- Coarse Aggregates - Coarse aggregates are any particles greater than 0.19 inches, but generally range between 3/8 and 1.5 inches in diameter. Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder.
2. Fine Aggregates - Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch sieve.
Differences between Fine & Coarse Aggregates
Brands providing Aggregates
- RoboSandTM - Robo Silicon, for the first time in India, introduced “Manufactured Sand” as a viable, cost-effective, and eco-friendly alternative to the precious and fast depleting natural resource -river sand. Robo Silicon is the first company to brand its sand as “ROBOSANDTM”. It is manufactured in the same way nature has been doing it for over a million years. RoboSandTM is created by a “rock-hit-rock crushing” technique using cutting-edge plant and machinery with top-notch innovation.
- RoboAggregates – Under the same sub-brand of Robo Silicon, RoboAggregates are obtained by crushing of parent rock and exhibit better bonding at the interface of aggregates with cement paste. They are crushed by a three-stage setup comprising of a Jaw Crusher followed by a Cone Crusher and lastly a Vertical Shaft Impactor (VSI) to acquire aggregates that have a cubical molecule shape and are consistent in gradation. RoboAggregates are used as a base material under foundations, roads, railroads, landfills. These aggregates are used as a stable foundation to help prevent differential settling across various applications such as under roads, culverts, bridges, driveways, storm drains, and transformer yards.
- StonaSand - StonaSand is an innovative and progressive mining company, which strives to create a global network of natural resources through responsible partnerships. StonaSand's key agenda includes developing best practices for the extraction process to provide long-term value for all partners involved while maximizing returns from mines that are currently underutilized.
- JSW Slag Sand – JSW’s Slag Sand is a non-metallic product, consisting of glass containing silicates and aluminosilicates of lime, which is a product of metal smelting processes, produced under controlled conditions. They have excluded any materials that may affect the strength as well as the durability of concrete, such as chlorides, organic matter, clay, silt, and shells. The advantages of using this sand over river sand are numerous. It is an environmentally friendly alternative with controlled physical and chemical properties. It can be graded for one’s specific needs and has no deleterious material.
- ThriveniSands – This company manufactures Concrete Sand, Plaster Sand as well as coarse aggregates ranging from 6 – 40mm. The Concrete Sand complies with IS 383 – 1970 Zone 2 standards has advantages over river sand, like excellent texture, no impurities, no scope of concrete deficiencies, all that while meeting industrial standards. The Plaster sand has features like 100% material utilization, consistent and superior quality, uniform shape, and controlled grading over river sand. Their coarse aggregates are manufactured by state-of-the-art machinery that provides zero flakiness and elongation.
Testing of Aggregates
Aggregates play a significant role in the construction area and can be utilized for various projects. Aggregates are a significant component in the making of concrete and offer several advantages. Their essential use is to fortify concrete, strengthening its structure and thus limiting the possibilities of cracks. Therefore, prior to using aggregates for construction purposes they must be tested and checked for quality. Numerous sorts of research on aggregate uncover that the nature of aggregate has a major factor in the quality of concrete and ultimately the construction. The IS Code IS 2386: 1963 contains all the different types of tests regarding the quality of aggregates. Some of the most common tests are mentioned below:
- Crushing test
- Abrasion test
- Impact test
- Soundness test
- Shape test
- Specific gravity and water absorption test
- Bitumen adhesion test
It should be noted that the tests provided above can only be performed in a laboratory with their respective equipment. Therefore, a test sample of the aggregates should be sent to the respective laboratory. Similarly, companies that manufacture these aggregates conduct these tests themselves to confirm the quality of their product.
Storage of Aggregates
Aggregates, like cement, need to be handled and stored very carefully. Faulty or unnecessary handling and inappropriate storage of processed aggregate might bring about one or all three principal problems that may affect the properties of concrete mixtures. The first is segregation, which demolishes the grading uniformity of concrete. The second is contamination or inadvertent inclusion of deleterious material. A third problem is the maintenance of uniform and stable moisture content in the aggregates as a batch. Here are some points that need to be taken care of while handling aggregates.
- Do not heap different sizes of aggregates in such a way that they overflow into each other. This can cause different-sized aggregates to get mixed, making it difficult to obtain the expected mix design.
- Keep the aggregate piles covered with plastic sheets or tarpaulin.
- Store the aggregates on the clean, hard ground away from trees to avoid contamination.
Aggregates are often left over when we talk about the construction industry today. “They are not appealing!” “They are not glamorous!” “They are just rocks after all!” They are the most fundamental material utilized in construction. They give the establishment to streets, bridges, and bridges, while additionally making up more than 90% of asphalt pavement and up to 80% of a concrete mix. By and large, about 24,000 tons of aggregates are important to build one lane kilometre of a highway. The development of an average home requires 400 tons of aggregate, while the normal size of an everyday school requires 15,000 tons.