Well Graded Aggregate
Dense and well graded aggregates are desirable for making concrete, as the space between larger particles is effectively filled by smaller particles to produce a well-packed structure. A well graded soil is a soil that contains particles of a wide range of sizes and has a good representation of all sizes from the No. 4 to No. 200 sieves. A well graded gravel is classified as GW while a well graded sand is classified as SW.
Gap Graded Aggregate
Gap grading is a kind of grading which lacks one or more intermediate size. Gap graded aggregates can make good concrete when the required workability is relatively low. Advantages of gap grading are more economical concrete, use of less cement and lower w/c ratios. When they are used in high workability mixes, segregation may become a problem. The resulting concrete is very stiff and has low workability. An extreme case is no-fines concrete. This concrete is difficult to handle and compact; developing low strength and high permeability.
Uniformly Graded Aggregate
For uniformly graded aggregate, only a few sizes dominate the bulk material. With this grading, the aggregates are not are not effectively packed, and the resulting concrete will be more porous, unless a lot of paste is employed.
Open Graded Aggregate
Open graded aggregate contains too much small particles and easy to be disturbed by a hole.
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