AGGREGATE MATERIALS

AGGREGATES (cont’d)

Overview

Definition: Usually refers to mineral particles but can relate to byproducts or waste materials. (i.e. vitrified soils)

Natural aggregates are formed from rocksor the decomposition and transport of rock(see fig 2-2)

Natural sources include underwater, land( stripping) , Glacier Outwash.

Note:Disadvantage of natural aggregate deposits is:• the content of impurities and dust. •Rounded shapes and smooth surfacesare found with natural aggregates which is undesirable. However in some locationsit may be more economical.

AGGREGATES TESTING (cont’d)

Advantage of crushed stones: Size of the particle can be manufactured

as needed Also angular shapes and rough surfaces

are formed which is better suited for industry

AGGREGATES TESTING (cont’d)

Rock TypesIgneous Rock - Volcanic Rock which was molten at one time and then cooledi.e. Granites(CG), Basalt(FG) & DiabaseTrap Rock is Basalt and Diabase•Pumice and Scoria are rock filled with bubbles which are good for lightweight aggregate•Trap Rock is an excellent aggregate

AGGREGATES TESTING (cont’d)

Sedimentary Rock - Shows a lot of stratification from its natural deposition

•If it is a sand deposit formed rock it is known as sandstone or quartzite

•If it is a gravel deposit formed rock it is known as a conglomerate

Note: Shale is not a great aggregate because of cleavage

AGGREGATES TESTING (cont’d)

Metamorphic Rock - Formed from Sedimentary or Igneous under heat and pressure

•i.e Shale turns into slate•i.e. Limestone turns into marble

AGGREGATES TESTING (cont’d)

What qualities do we want in Aggregates?Weight- Prevents erosion of banks or for gabion retaining wallsResistance - •For weathering and freeze/thaw•To breaking and crushing•To resistance to abrasionAbility-•to transmit compressive forces as a mass•to adhere to a cement agentPermeability- potential as a filtering or drainage system

AGGREGATES TESTING (cont’d)

STRENGTH OF MATERIAL REVIEW

COMPRESSION TENSION

TORSION THIRD POINT LOADING

SPLIT TENSILE

ELASTIC LIMIT

PROPORTIONAL LIMIT

YIELD POINT

ULTIMATE STRENGTH

STRAIN

ST

RE

SS

STEEL VS CONCRETE

Elastic Modulus(slope)or Young’s Modulus (E)

f’c:5700 psi

f’c:4700 psi

f’c:4100 psi

f’c:3300 psi

f’c:2600 psi

strain(x10-4)

Str

ess

(psi

)Stress - Strain Diagram of various concretes

Aggregates

Usually refers to a soil that has in some way been processed or sorted.

Excavation

Crushing

Transportation

Sizing

Stockpiling

Desired Aggregate Properties

Toughness

Soundness

Deleterious Materials

Gradation

Soundness

Before After

Aggregate Gradation

– The distribution of particle sizes expressed as a percent of total weight.

– Determined by sieve analysis

Gradations

Mechanical Sieve

Individual Sieve Stack of Sieves

Mechanical Sieve

Stack in Mechanical

Shaker

Book Notes –Chapt. 2

GRADATION CURVE:

SPSW

GP

GW

Book Notes –Chapt. 2

SIEVE PANS : P.58

Gravel

Clay and Silt

Sand

* Uniformly graded- Few points of contact- Poor interlock (shape dependent)- High permeability

* Well graded- Good interlock- Low permeability

* Gap graded- Only limited sizes- Good interlock- Low permeability

Types of Gradations

Aggregate Size Definitions

Nominal Maximum Aggregate Size– one size larger than the first sieve

to retain more than 10% Maximum Aggregate Size

– one size larger than nominal maximum size

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100100999989897272656548483636222215159944

Questions - ?