When it comes to concrete, the type of aggregate used is a key factor in determining its properties. Aggregates are categorized into gravel, sand, recycled concrete, slag, topsoil, ballast, type 1 MOT, and geosynthetic aggregates. The alkali content and type of aggregate in the system are likely to be unknown, so it is important to ensure that the materials used are suitable. Aggregates must be solid, clean, hard, durable, and free of excessive fines or contaminants that could affect cement hydration or alter the paste-aggregate bond.
It is essential to make sure that your concrete producer purchases good quality aggregates, as verified by regular aggregate test results in accordance with ASTM C 33, Standard Specifications for Concrete Aggregates. Variation in the size, leveling, texture, shape, and strength of the aggregates means a variation in the properties of the resulting concrete. As a natural material, the aggregate will sometimes include worn or unstable particles in the supplied product. The shape of your aggregates is important to the workability of the concrete, the quantity you want to place, and the strength of the concrete you want to make.
Using larger coarse-grated aggregates generally reduces the cost of a concrete mix by reducing requirements for cement, the most expensive ingredient. Both gravel and crushed stone are generally acceptable for manufacturing quality concrete (Photo), although gravel is generally preferred for exposed aggregate. For greater workability and economy, as reflected in the use of less cement, the fine aggregate must have a rounded shape. But a closer look reveals the primary role and influence that aggregate plays on the properties of fresh and hardened concrete.
Photo 5 - Maximum aggregate size recommended to traverse the clearance between the reinforcing steel and the roof dimension. This is typically achieved through proper storage of aggregates and reprocessing stockpiles to counteract excessive segregation (Photo). If there is a deficiency in a locally available fine aggregate, concrete may benefit from the addition of air entrainment, additional cement, or a supplemental cementitious material (SCM) to address these deficiencies. Vermiculite concrete aggregate is used to create a lightweight, insulating concrete that can be used in various forms of foundations suitable for a variety of engineering designs.
Glass aggregate can replace some or all of the sand and gravel in concrete, for effects ranging from colorful terrazzo, to granite or marble finishes, to concrete that reflects light like a mirror. In conclusion, it is important to understand that different types of aggregates can have an impact on both fresh and hardened concrete properties. It is essential to ensure that good quality aggregates are purchased from reliable sources and tested regularly according to ASTM C 33 standards.