Size Gradation

8/16/2019 Size Gradation

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SIZE GRADATION


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Why should wegrade?


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Minimize oids


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Why should we wan!o minimize oids?


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workability


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underflling will resuin entrapped air


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corrosion oreinorcements


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SIE"E ANA#$SIS


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Sieve analysis

• A known weight o material is placed on the top nested sieves

• The top sieve has the largest opening and decredown to the bottom sieve

• Shaken in a period o time

• The material in each sieve is weighed


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Ma%imum and

Ma%imum Nominasize


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Percent Passin

3/4 ! "##$

"/% ! &'$

3/( ! (&$

)4 ! *3$

)( ! 3&$

+T%#%


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&OW TO DE'IDE MA(IM)M SIO* 'OARSE AGGREGATE TO +

)SED IN 'ON'RETE?


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• ,arger si-e . lesser cement• ,esser cement .lesser cost

• ,arger si-elesser 0+ ratiogreater strength


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+12T12S T5AT 6+6 7A8797 S:6 1; +1A


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Grading 'ures

* ll d Th 3 E


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*uller and Thom0son3s E4ua

Where:•

P = percent finer than an aggregate size• d = aggregate size being considered

• D = maximum aggregate size

• n = parameter which adjusts curve for fineness or

coarseness (for maximum particle densit n ! "#$

according to %uller and &hompson'


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Gradation Types

• Dense or well-graded. efers to a gradation that is

near the %)W*+s "#,$ power curve for maximum

densit# &he most common )-* mix designs in the

.#/# tend to use dense graded aggregate# &pical

gradations are near the "#,$ power curve but not righton it# 0enerall1 a true maximum densit gradation

(exactl on the "#,$ power curve' would result in

unacceptabl low VMA.• Gap graded. efers to a gradation that contains only

a small percentage of aggregate particles in the

mid-size range.• Open graded. efers to a gradation that contains onl

a small percentage of aggregate particles in the

small range.• Uniformly graded. efers to a gradation that contains

most of the particles in a very narrow size range#

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Size Gradation