Aggregate grading is crucial in economically obtaining a concrete mix with adequate strength, reasonable workability, and minimal segregation. There are four types of aggregate gradation: well-graded, uniformly (or one-sized) graded, gap-graded, and open-graded.

Well-graded aggregates include a complete range of necessary size fractions that fit together to create a dense matrix with minimal voids, represented by a smooth, continuous gradation curve. This type of grading ensures good workability and stability for the concrete.

In contrast, one-sized or uniformly graded aggregates consist predominantly of particles of the same size, which is evident from a nearly vertical gradation curve. While these aggregates provide good permeability, they lack stability and are typically used in specific applications like chip seals in pavements.

Gap-graded aggregates are characterized by the absence of certain size fractions, causing a significant portion of particles to pass through two vastly different sieves. This results in a gradation curve with a nearly horizontal section, indicative of missing intermediate sizes. Due to the missing material sizes, these aggregates can lead to issues with concrete stability.

Open-graded aggregates, missing smaller sizes that fill voids between larger aggregates, exhibit a flat gradation curve with minimal values in the smaller size range. These aggregates are highly permeable but have reduced stability.

Figure 1

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5.5 : Types of Aggregate Grading

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5.1 : Unsoundness of Aggregate due to Volume Change

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5.2 : Deleterious Substances in Aggregate

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5.3 : Sieve Analysis and Grading Curves

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5.4 : Fineness Modulus

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5.6 : Maximum Size of Aggregate

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5.7 : Quality of Water

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5.8 : Testing Water Quality

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5.9 : Aggregates Classification

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5.10 : Shape and Texture of Coarse Aggregate

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5.11 : Bonding and Strength of Aggregate

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5.12 : Toughness and Hardness of Aggregate

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5.13 : Specific Gravity of Aggregate

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5.14 : Bulk Density of Aggregate

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5.15 : Porosity and Absorption of Aggregate

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