Aggregates Final

8/8/2019 Aggregates Final

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AGGREGATES

By,

Shankey contractor and sunny


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DEFINATION

"Aggregate" is a collective term for the mineralmaterials such as sand, gravel and crushedstone that are used with a binding medium (suchas water, bitumen, portland cement, lime, etc.) toform compound materials (such as asphaltconcrete and portland cement concrete

). Byvolume, aggregate generally accounts for 92 to96 percent of HMA and about 70 to 80 percent ofportland cement concrete. Aggregate is alsoused for base and subbase courses for bothflexible and rigid pavements.


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Classififcation

By weightNormal-weight:

Light

Two types of Lightweight Aggregates:

Natural (i.e. Pumice, volcanic rock)

Manufactured (i.e. Fly Ash, blast-furnace slag)

Heavy

(Heavy Rock / Steel)

BY Size coarse >4.75mmfine < 4.75 mm


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Geological Type: sand, gravel, crushed stone, cobbles,

boulders

Geological Origin: sedimentary, igneous, metamorphic

Rock Type: granite, limestone, quartzite, basalt (ASTM C 294

on Nomenclature)

Mineral Class: silica, feldspar, mica, clay (C 294)


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Process: manufactured sand, crushed gravel,

crusher-run, screenings, washed vs. dry processed Grading: dense-graded, open-graded, nominal

maximum size, amount of minus No. 200

Use Categories: aggregate base types, PCC, HMA,

and surface treatment aggregate classes

Particle Shape: flat & elongated, cubical, two-face

crushed gravel, rounded roofing gravel


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Durability Classes: sulfate soundness,

freeze-thaw, durability index Quality Level: in a specific test, such as LosAngeles Abrasion

Hardness, Friction Properties: classes

based on polishing tests in the lab or field Stripping in Bituminous Mixtures: moisture

sensitivity or degree of particle coating


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Reactivity in Concrete Mixtures: potential

alkali-silica reactivity or not Bases & Soil-Aggregate Mixtures: strength

categories,Atterberg limits (PI, LL, and PL)

By texture polish/ dull, smooth/rough,

glassy, granual, crystalline


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Types of Aggregate Gradation

Gradation: The gradual gradation in size

from coarse to fine is a key property ofaggregates. The effects are: Workability

Stability

Drainage

Frost resistance

Others: mix proportioning, economy, porosity,durability, shrinkage, strength


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Normally Graded Aggregate is one that conforms to thegrading limits specified by an agency such as ASTM.

Open-Graded Aggregate has a particle-size distributionthat results in large voids or void content.

Dense-Graded Aggregate has a particle-size distribution

that results in the least voids or lowest void content. G

aped-G

rades Aggregate has a particle-size distributionthat results in a missing some particle sizes


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Aggregate Mixture

Types ofAggregate Mixture

Aggregates with no fines. Its strength from grain-to-graincontact of aggregate particles. Unstable, excellent drainage,completely non-frost susceptible.

Fines just filling the voids of aggregate fraction. Its strengthfrom grain-to-grain contact of aggregate particles. Stablebase coarse material because of fine content, adequate

drainage and can be non-frost susceptible. Fines overfilling the voids of aggregate fraction. Strength is

from grain-to-grain contact of fines rather than theaggregate particles. Reduction in strength, poor drainage,very frost susceptible.


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Aggregates with nofines

Aggregates with justfilling the voids

Aggregates overfillingthe voids


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Aggregate Properties

Physical Properties

Absoprtion, Porosity, and Permeability

Surface Texture Strength and Elasticity

Density and Specific Gravity

Aggregate Voids

Hardness

Particle Shape

Coatings

Undesirable Physical Components

Chemical Properties Composition

Reactions with Asphalt and Cement

Surface Charge

GeneralCharacteristics

Compacted Aggregates

Aggregate for Hot Mix Asphalt

Aggregate for Portland Cement Concrete

Other Aggregates


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PHYSICAL QUALITY REQUIREMENTS

1) Absorption;

2) Abrasion resistance;

3) Soundness;

4) Restrictions on deleterious constituents; and

5) Special requirements.


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Absorption

applies only to coarse aggregates, but this data is necessary on fine aggregate for otherpurposes, such as mix design and water/cementitious ratios.

porous aggregate determines how much liquid can be absorbed when soaked in water.absorption as the increase in the weight of aggregate because of water in the pores of thematerial,Absorption is expressed as a percentage of the dry weight.Absorptionrequirements are of concern only regarding aggregates used in hot mix asphalt andportland cement concrete.

The intent is to avoid usinghighly porous, absorptive aggregates because extra water andcement orasphalt is needed to make a good mix. The maximum percentage of absorptionallowed by the Standard Specifications is 5.0 percent

Measurement of moisture

drying method

displacement method

Automatic measure ment


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Abrasion ResistanceAbrasion resistance applies only to coarse aggregates.

Aggregates vary in their resistance to fracturing under impact (toughness) and breaking downinto smaller pieces from abrasive action (hardness).

The acceptable limits vary from 30.0 to 50.0 percent,

depending on the classification of the aggregate. The percentage is a

measure of the degradation or loss of material as a result of impact and abrasive actions.

Aggregate abbrasion value test wear value

Deval attrition test

Dorry abrasion test - hardness = 20 loss in grain/3

Los angeles test


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Soundness

The quality of soundness applies to both fine and coarse aggregates.Used to check durability

three different test methods to evaluate soundness:

1)The sodium sulfate test2) The freezing and thawing test3) The brine freeze/thaw

The sodium sulfate test requires immersing an aggregate sample in a

sodium sulfate solution for a period of time and then determining theweight loss of particles on a given set of sieves

. The brine freeze/thaw requires the aggregate to be enclosed in a bag containing a 3 percentsodium chloride solution and subjected to 25 cycles of freeze and thaw.

The freezing and thawing test requires subjecting a sample of aggregatessealed and totally immersed in water to freezing and thawing of 50 cycles

before determining the mass loss.


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Freezing and Thawing

Saturated aggregates of low porosity may accommodate pore-waterfreezing by simple elastic expansion. Saturated aggregates of

moderate to high porosity may fail because the particle dimension

exceeds a certain critical size or may cause failure in the paste

immediately adjacent to the aggregate particle because of aggregate

pore-water displacement

Aggregate


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The disruption of concrete by aggregates is a result of hydraulicpressures. The hydraulic pressure is a result of the degree of

saturation (proportional to total void space filled with water) andpermeability and size of the aggregate particles. Upon freezing,water expands 9 percent, and if the degree of saturation of theaggregate particles, 91.7 percent, water will be expelled into thepaste surrounding the aggregate particle, and potentiallydestructive hydraulic pressure may develop there also. So theproperties of paste, its permeability, air content, and porosity are

also involved in the problem. Three additional factors; composition,texture, and structure, also play important roles in freezing andthawing of concrete.


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Strength and Elasticity

Strength is a measure of the ability of an aggregate particle to stand up to

pulling or crushing forces.

Elasticity measures the "stretch" in a particle.

High strength and elasticity are desirable in aggregate base and surface courses. These qualities minimize the rate of disintegration and maximize the stability

of the compacted material.

The best results for portland cement concrete may be obtained by compromising between high and low strength, and elasticity.

Aggregate crushing value 30% to 45 % at 40 ton load Aggregate impact value - 30% to 45 % at 14kg load

Modules of elasticity exponentially varies


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Shape and texture of aggregate

Aggregate shape and surface texture influence the properties of freshly mixedconcrete more than the properties of hardened concrete.

Rough-textured, angular, and elongated particles require more water to produceworkable concrete than smooth, rounded compact aggregate.

Consequently, the cement content must also be increased to maintain the water-cement ratio. However, with rough aggregates, there is better mechanical bond

in the hardened concrete, so strength is higher(if concrete with the same w/cratio is compared).

Hence, when smooth aggregates are replaced with rough aggregates, concrete ofsimilar flow properties and strength can be produced by adding a little bit morewater.


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angular and rough

aggregate

smooth aggregate

river gravel


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Surface Texture

Property Smooth Rough___________________________________Bond Strength Weaker StrongerWater Demand Less HigherW/C Less Higher

Overall Strength Almost equal =Workability Good More

Mortar


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SIEVE ANALYSIS OF FINE

AND COARSE AGGREGATES

scopeThe sieve analysis determines the gradation (the distribution of aggregateparticles, by size, within a given sample) in order to determine compliance with design,

production control requirements, and verification specifications.

summaryA known amount weight of material, the amount being determined by the largest size ofaggregate, is placed upon the top of a group of nested sieves (the top sieve has the largest screen openings

and the screen opening sizes decrease with each sieve down to the bottom sieve which has the smallestopening size screen for the type of material specified) and shaken by mechanical means for a period oftime.After shaking the material through the nested sieves, the material retained on each of the sieves isweighed using one of two methods.

The cumulative method requires that each sieve beginning at the top be placed in a previously weighed pan(known as the tare weight), weighed, the next sieve's contents added to the pan, and the total weighed.This is repeated until all sieves and the bottom pan have been added and weighed.

The second method requires the contents of each sieve and the bottom pan to be weighed

individually. Either method is satisfactory to use and should result in the same answer. The amount passing thesieve is then calculated.

%Retained = 100%

%Cumulative Passing = 100% - %Cumulative Retained.


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Use Wire brush on Coarse Sieve Use Hair Brush on Fine Sieves

Large Tray Shaker Small Sieve Shaker

Aggregates Final

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