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Civil Engineering MaterialsSAB 2112

Physical & Mechanical Properties of Aggregates

Dr Mohamad Syazli Fathi

Department of Civil EngineeringRAZAK School of Engineering & Advanced Technology

UTM International Campus

August 18, 2010

CONTENT SCHEDULE – 1st Meeting

1. Introduction, cement manufacturing process, types of cement chemical composition of OPCcement, chemical composition of OPC

2. Hydration of cement, testing of cement, types of aggregates, physical and mechanical characteristics of aggregates

3. Size distribution and testing of aggregates, water in concrete types of chemical admixturesconcrete, types of chemical admixtures

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CONTENT SCHEDULE – 2nd Meeting

1. Types of pozzolanic admixtures, water-cement ratio and its effect in concreteand its effect in concrete

2. Workability, test of fresh concrete, segregation and bleeding in concrete

3. Concrete on site - method of production, concrete strength and grade

4 C i d d i l H d d4. Concrete proportions - standard, nominal; Hardened concrete tests- destructive and non-destructive tests

Aggregate

Aggregate: Aggregate: • the inert filler materials, such as sand or stone, used in making concrete• added up to 80% by volume in ordinary concrete to provide bulk

CharacteristicCharacteristic

- Must clean & durable & Free from organic impurities & dust (WHY?)- it may prevent the cement paste from coating the aggregate properly- preventing bonding- reduce strength of the concrete

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Aggregate Quality

• Aggregate should not contain materials• Aggregate should not contain materials which are likely to– Decompose/change in volume (eg coal, clay)– React with cement paste (eg certain siliceous

compounds (ASR))

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– Affect appearance of concrete (eg salt, pyrites)

Aggregate Cleanliness

• Should be free from dust clay etcShould be free from dust, clay, etc• Sea dredged aggregate may be contaminated with

chlorides• Excessive washing is costly and may wash away fines• Shape will affect workability and durability• Grading - involves seiving to find out the proportions of

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Grading involves seiving to find out the proportions of different sized aggregate (eg continuously-graded, gap-graded etc)

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Aggregates

• Gravels, crushed rock, and sands, etc, which are mixed with cement and water to make concrete.

• Will influence all aspects of the concrete, eg– Durability– Structural performance– Cost

• Two main categories

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– Fine < 5mm– Coarse > 5mm

Types of Natural AggregatesFine Aggregates

• natural sand crushed rock crushed gravel that pass 5mm BS Sieve Dry• vary in character depending on their location, method of extraction & grading.• “Sharp” sand has angular grains – used mainly for concrete• “Soft” sand has smaller rounded grains – used for mortars & renderings• Soft sand has smaller rounded grains – used for mortars & renderings

Coarse Aggregate• materials that retained on a 5mm sieve when dry.• 10mm for small section work with a lot of close reinforcement• 20mm for general work• 100 – 150 mm for large reinforced pours

All in Aggregategg g• mixture of coarse & fine aggregate either as extracted / delivered• not allowed for structural purposes

Graded Aggregates• natural agg. consist of different size of stones randomly mixed.

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Source: http://training.ce.washington.edu/wsdot/modules/03_materials/03-2_body.htm

Other Types of Aggregates

• (may be naturally occurring or industrial ( y y gproducts)

1. Normal density aggregates (most widely used)2. Lightweight aggregates (eg pumice, expanded clay

- “Leca”, PFA - “Lytag”, Expanded Slag - “Pellite”)3. High density aggregate (eg, lead)

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4. Fibres (eg asbestos, wood, steel, glass, polymers)

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Concrete =Concrete =

• 25-40% cement

(absolute volume of cement = 7-15% ; water = 14-21%)

• Up to 8% air (depending on top size of coarse aggregate)

1. BS EN 1097-8 describes the test method for mechanical and physical properties of aggregates.

BS EN 1097-8:2009 Tests for mechanical and physical properties of aggregates. Determination of the polished stone value

Contents of BS EN 1097-8:Foreword 1 Scope2 Normative references 3 Definitions 4 Principle 5 Sampling

2. This part of the BS EN 1097 series of standards concentrates on determining the polished stone value (PSV) of a coarse aggregate used in road surfacing.

3. PSV is a measure of the resistance of coarse aggregate to the polishing action of vehicle tyres under conditions similar to those occurring on the surface of a road.

4. For other purposes, in particular factory production control, other methods may be used provided that an appropriate

ki l ti hi ith th f th d h b

6 Materials 7 Apparatus 8 Preparation of test specimens 9 Conditioning of the rubber-tyred wheel10 Accelerated polishing of specimens 11 Friction test procedure 12 Calculation and expression of results 13 Test report

working relationship with the reference method has been established.

5. This standard also describes an optional method for the determination of the aggregate abrasion value (AAV). The AAV method should be used when particular types of skid resistant aggregates (typically those with a PSV of 60 or greater) which can be susceptible to abrasion under traffic, are required.

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Physical Properties of Aggregates:

1.Unit Weight and Voids

2. Specific Gravity

3. Particle Shape and Surface Texture

4. Shrinkage of Aggregates

5. Absorption and Surface Moisture

6. Resistance to Freezing and Thawing

Unit Weight(unit mass or bulk density)

The weight of the aggregate required to fill a g gg g qcontainer of a specified unit volume.

• Volume is occupied by both the aggregates and the voids between the aggregate particles.

• Depends on size distribution and shape of particles and how densely the

t i k daggregate is packed

• Loose bulk density

• Rodded or compact bulk density

Normal-weight concrete… bulk density of aggregate is approximately 75-110 lb per cubic foot.

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Weight Examples of Aggregates Used

Uses for the Concrete

ultra-lightweight vermiculite, ceramic can be sawed or nailed,

also used for its insulating propertiesinsulating properties

lightweight expanded clay, shale or slate, crushed brick

used primarily for making lightweight concrete for

structures, also used for its insulating properties

l i h

crushed limestone, sand, river gravel, used for normal concretenormal weight

g ,crushed recycled

concrete

used for normal concrete projects

heavyweight steel or iron shot; steel or iron pellets

used for making high density concrete for

shielding against nuclear radiation

Voids• Void content affects mortar requirements in mix design;

water and mortar requirement tend to increase as aggregate void content increasesvoid content increases.

• Void content between aggregate particles increases with increasing aggregate angularity.

• Void contents range from 30-45% for coarse aggregates to about 40-50% for fine aggregates.gg g gg g

• Total volume of voids can be reduced by using a collection of aggregate sizes.

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The cement paste requirement for concrete is proportional to the void content of the combined aggregate.

Specific Gravity (Relative density)

Absolute: the ratio of the weight of the solid to the weight of an equal volume of water (both at a stated temperature)

• refers to volume of the material excluding all pores

Apparent: ratio of the weight of the aggregate (dried in an oven at 212- 230ºF for 24 hours) to the weight of water occupying a volume equal to that of the solid including the impermeable pores

l f lid i l d i bl (b t t

Used for calculating yield of concrete or the quantity of aggregate required for a given volume of concrete.

• volume of solid includes impermeable pores (but not capillary pores)

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Particle Shape and Surface Texture

A t h ld b l ti l f f fl t d l t d ti l

• Rough textured, angular, elongated particles require more water to produce workable concrete than do

smooth, rounded, compact aggregates.

• Aggregates should be relatively free of flat and elongated particles (limit to 15% by weight of total aggregate).

• Important for coarse and crushed fine aggregate -

these require an increase in qmixing water and may affect

the strength of the concrete, if cement water ratio is not

maintained.

Particle Shape and Surface Texture

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Shrinkage of Aggregates:

fine grained sandstones, Large Shrinkage =slate, basalt, trap rock, clay-containing

Low Shrinkage = quartz, limestone, granite, feldspar

What happens if pp

abnormal aggregate

shrinkage occurs?

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1. Excessive cracking

2. Large deflection of reinforced beams and slabs

3. Some spalling (chipping or crumbling) If more than 0.08 percent shrinkage occurs, the aggregate is considered

undesirable.

Absorption and Surface Moisture

If water content of the concrete mixture is not kept constant, the compressive strength, workability, and

h i illother properties will vary from batch to batch.

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1. Oven dry-fully

Moisture Conditions of Aggregates

fully absorbent

2. Air dry- dry at the particle surface but

i icontaining some interior moisture3. Saturated surface dry (SSD) –neither absorbing water nor contributing water to the concrete mixture

4. Wet or moist- containing an excess of moisture on the surface

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Absorption Capacity: maximum amount of water aggregate can absorbAbsorption Capacity: maximum amount of water aggregate can absorb

• Absorption Capacity (%) = [(WSSD – WOD)/WOD] X 100

Surface Moisture: water on surface of aggregate particles

• Surface Moisture (%) = [(WWET – WSSD)/WSSD] X 100WET SSD SSD

Moisture Content: of an aggregate in any state

•Moisture Content (%) = [(WAGG – WOD)/WOD] X 100

Resistance to Freezing and Thawing

• Important for exterior concrete (for cold countries).

• Affected by an aggregate's high porosity, absorption, permeability and pore structure.

• If aggregates or concrete absorbs so much water that when the water freezes and expands the concrete cannot accommodate the build up of internal pressure, pop–outs may occur.

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Aggregate Gradation

Measurement• Gradation is usually measured by a sieve analysisGradation is usually measured by a sieve analysis.• In a sieve analysis, a sample of dry aggregate of known weight is separated

through a series of sieves with progressively smaller openings. Once separated, the weight of particles retained on each sieve is measured and compared to the total sample weight.

• Particle size distribution is then expressed as a percent retained by weight on each sieve size. Results are usually expressed in tabular or graphical format.

• The typical graph uses the percentage of aggregate by weight passing a certain• The typical graph uses the percentage of aggregate by weight passing a certain sieve size on the y-axis and the sieve size raised to the nth power (n = 0.45 is typically used) as the x-axis units. The maximum density appears as a straight line from zero to the maximum aggregate size (the exact location of this line is somewhat debatable, but the location shown in the next Figure is generally accepted).

* Uniformly graded

Types of Gradations

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

* Well graded- Good interlock

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- Low permeability* Gap graded

- Only limited sizes- Good interlock- Low permeability

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Aggregate Gradation

• Use 0.45 Power Gradation Chart• Blend Size Definitions

– maximum size– nominal maximum size

• Gradation Limits

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– control points– restricted zone

Typical Aggregate Gradations

Source: http://www.asphaltwa.com/wapa_web/modules/03_materials/03_aggregate.htm

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Aggregate GradationTypical Gradations (see Figure)1. Dense or well-graded.

– Refers to a gradation that is near maximum density.

2. Gap graded.p g– Refers to a gradation that contains only a small percentage of aggregate particles in the

mid-size range. The curve is flat in the mid-size range. These mixes can be prone to segregation during placement.

3. Open graded.– Refers to a gradation that contains only a small percentage of aggregate particles in the

small range. This results in more air voids because there are not enough small particles to fill in the voids between the larger particles. The curve is flat and near-zero in the small-isize range.

4. Uniformly graded.– Refers to a gradation that contains most of the particles in a very narrow size range. In

essence, all the particles are the same size. The curve is steep and only occupies the narrow size range specified.

Other Gradation Terms1. Fine aggregate (sometimes just referred to as "fines").

– natural or crushed sand passing the No. 10 sieve and mineral particles passing the No. 200 sieve.

2. Coarse aggregate.– as hard, durable particles or fragments of stone, gravel or slag retained on the No. 10 , p g , g g

sieve. Usually coarse aggregate has a toughness and abrasion resistance requirement.3. Fine gradation.

– A gradation that, when plotted on the 0.45 power gradation graph, falls mostly above the 0.45 power maximum density line. The term generally applies to dense graded aggregate.

4. Coarse gradation.– A gradation that, when plotted on the 0.45 power gradation graph, falls mostly below

the 0.45 power maximum density line. The term generally applies to dense graded aggregate.

5. Mineral filler.– as a finely divided mineral product at least 65 percent of which will pass through a No.

200 sieve. Pulverized limestone is the most commonly manufactured mineral filler, although other stone dust, silica, hydrated lime, portland cement and certain natural deposits of finely divided mineral matter are also used (Asphalt Institute, 1962).

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Mechanical Properties of Aggregates

There are many tests which are conducted to check the quality of aggregates. (Aggregates are very important component of concrete, so the quality really matters when it comes to aggregates).

Various test which are done on aggregates are listed below.1. Sieve Analysisy2. Water Absorption 3. Aggregate Impact Value4. Aggregate Abrasion Value5. Aggregate Crushing Value

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Questions - ?

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