No tags yet.
What's the maximum size of aggregates we can use?
Generally the larger the maximum size of aggregate, the smaller is the cement requirement for a particular water-cement ratio. That means that for the same strength or workability, concrete with large size aggregate will require lesser quantity of cement than concrete with a smaller size aggregate. This is because workability of concrete increases with the increase in the maximum size of the aggregates.
In mass concreting works, the use of larger size aggregates is more cost efficient because of the reduced cement content. Lower cement content will reduce heat of hydration. Thermal stresses will be reduced and thus shrinkage cracks will also be lessened. This is a great feature to have in mass concreting.
With larger aggregates, surface area is smaller and thus the water-cement ratio can also be reduced contributing to higher strength.
However in practice, the maximum size of aggregates is limited by the size of mixing, handling and placing equipment. Also smaller coarse aggregates generally contribute to higher compressive strength because of the higher surface area for bonding with the cement paste. Stress concentration is also higher in the mortar-aggregate interface for when larger aggregates are used.
Therefore, when water-cement content is high, the nominal size of the coarse aggregates must be as large as possible.
For high strength concretes a 10 or 20 mm size of aggregates is preferable. Generally for strengths up to 20 N/mm2, aggregates up to 40 mm may be used and for strengths above 30 N/mm2, aggregates up to 20 mm may be used.