Download - 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