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Materials > Aggregates > Flashcards

Aggregates Flashcards

1
Q

Types of aggregate

A

Primary
Secondary
Recycled

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2
Q

Primary Aggregates

A

Hard Rock Quarry
Sand and Gravel Pits
Marine Dredged

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3
Q

Secondary and recycled Aggregates

A

Byproducts from other extraction
eg Silica sand from china clay extraction
Crushed concrete aggregates, can contain up to 10% contaminents
Recyled hardcore from demolistion waste
(Not permitted for high strength and exposure specification)

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4
Q

Specialist Aggregates

A

Leca - Expanded clay balls

MagnaDense - Magnetite/ Iron ore (Superior Strength, radiation protection)

Foamglass - Recycled glass/ silica (light, strong compressive, workable, insulative, capilary break)

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5
Q

Properties of aggregate

A

Size/ Grading
Shape
Surface texture
Mineral/ Chemical composition

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6
Q

What does PSA stand for?

A

Particle size Analysis

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7
Q

Describe a nest of sieves

A

a mixture of stainless steel sieves with varying mesh and aperture sizes stacked ontop of each other with a pan at the bottom

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8
Q

What are sieves for?

A

Measusring nominal sizes of aggregates

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9
Q

What is the mesh and aperture?

A

The mesh is the bottom of the sieve
the aperture is the nominally sized hole in the mesh.

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10
Q

What is the difference between EN and BS for apertures?

A

BS requires square apertures

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11
Q

What is the Overload limt?

A

The overload limit is the maximum allowable mass of material that can be left on the sieve.
This can be calculated from the sieve diameter (A) and aperture size (d)
Ad^0.5/200

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12
Q

What happens if the Overload limit is exceeded?

A

Test repeated with a smaller sample
An extra sieve placed above the failed limit.
Sieve above the failed sieve dont have to be tested again.

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13
Q

What are the gradings for Coarse and fine aggregate?

A

Course aggregate d>2.0mm D>4.0mm
Fine aggregate D<4.0mm d = 0

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14
Q

Grading aggregates

A

Gc D(%)/d(%) d(mm)/D(mm)
Outer goes together
inner goes together
eg Gc 90/15 4/40
means 90% @ 40mm and 15% at 4mm

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15
Q

Types of course aggregate?

A

Graded and Single sized
Graded - a mixture of large and smaller
single sized - Two sizes closer together

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16
Q

Shapes and forms of aggregate?

A

Rounded
Irregular
Angular
Flaky
Elongated

17
Q

Terms for aggregate angularity/roundness?

A

Very angular
Angular
Subangular
Subrounded
Rounded
Well Rounded

18
Q

Terms for aggregate form?

A

Cubic
Flat
Elongate

19
Q

Terms for aggregate surface texture?

A

Rough
Smooth

20
Q

What is SSA/ Specific Surface Area?

A

Its defined as the total surface area of a material per unit of mass
eg m2/kg

21
Q

What particals have a higher SSA?

A

Smaller particles
Flat particles
Angular Particles will have a slightly higher

22
Q

What is a problem / character of aggregates with a higher SSA?

A

Water demand is higher in a concrete mix and it requires more cement to coat the particles for a given mass

23
Q

How do we test hardness of Aggregates?

A

LA Abrasion test.
grade aggregate,
then put in drum mixer with steel balls for a set period of time.
Sieve new results, the smaller the loss of the original nominal grading the better.

24
Q

What test might lend itself to aggregates used on roads?

A

Polished stone value

25
Q

What chemicals can be problematic for concrete?

A

Chlorides - Will encourage corrosion of steel (Marine Aggregates)
Sulphates - can react with cement and water causing spalling
Alkali Aggregate Reaction - can occur with a highly alkali cement
Iron Pyrites and organics contaminants cause staining

26
Q

What is AAR or ASR?

A

Alkali-silica reaction (ASR) is the most common form of alkali-aggregate reaction.
It occurs when the alkaline pore fluid and siliceous minerals in some aggregates react to form a calcium alkali silicate gel. This gel absorbs water, producing a volume expansion which can disrupt the concrete.

27
Q

Types of moisture content in aggregates?

A

Oven Dry -pores dry
Air Dry - some pores partially filled
Saturated surface dry - all pores filled with water
Wet - Excess water/ thin film sourrounding surface area.

28
Q

How do we achieve oven dry samples?

A

By oven drying at 105c for 24 hrs

29
Q

What moisture content do we usually assume aggregate to be for concrete mixes?

A

SSD Saturated surface dry

30
Q

Moisture content (M) can be expressed in terms of the mass of water as either

A
  • MWW, % Wet Weight (strictly mass not weight), or
  • MDW, % oven Dry Weight
31
Q

What is bulk density? why is it useful?

A

It’s the mass of particles (aggregate) in a given volume
eg 1000kg/m3
if a driver could only carry 10ton and but has 20m3, they can only fill up half the truck.

32
Q

What is the usual specific gravity of aggregate?

A

2.6 to 2.7 t/m3 (Specific gravity = density of solid/ density of water)

33
Q

How do we calculate density?

A

density = mass/volume

34
Q

how do we determine the specific gravity?

A

With a voidmeter

Materials (11 decks)

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