Grading Of Aggregates for Concrete

—Grading Of Aggregates for Concrete

• Aggregate comprises about 85 % volume of mass concrete—
• —Concrete contains aggregate upto a maximum size of 150 mm

  

• ——Way particles of aggregate fit together in the mix, as influenced by the gradation, shape, and surface texture—
• —Grading effects workability and finishing characteristic of fresh concrete, consequently  the properties of hardened concrete
• —Good grading implies, sample of aggregates containing all standard fractions of aggregate in required proportion such that the sample contains minimum voids
• —Well graded aggregate containing minimum voids will require minimum paste to fill up the voids in the aggregate
• —Minimum paste means less quantity of cement and less quantity of water, hence increased economy, higher strength, lower-shrinkage and greater durability

Gap Grading

• —Voids created by higher size filled up by immediate next lower size—
• —Lower size may not be accommodated in the available gap due to small voids left out which can reduce density
• —Voids created by a particular size can accommodate second or third lower size only—
• —For example voids created by 40mm can accommodate 10mm & 4.75mm but not 20mm, this concept is called Gap Grading