Concrete Aggregates

1
Concrete Aggregates
2
Introduction

• Australian Standards
• Types
• Sources
• Properties

3
Australian Standards

• AS 1141 Methods for Sampling Testing
  Aggregates
• AS 2758 Aggregates and Rock for Engineering
  Purposes
• AS 3600 Concrete Structures

4
AS 1141 Sampling Testing

• 1141.3 Sampling of Aggregates
• 1141.4 Bulk Density
• 1141.5 6 Particle Density (R.D.) water
  absorption
• 1141.11 Particle size distribution (Grading)
• 1141.12 Material finer than 75?m
• 1141.13 Material finer than 2 ?m
• 1141.15 Flakiness index
• 1141.22 Wet/Dry strength variation
• 1141.34 Organic impurities other than sugar
• 1141.38 Potential Alkali reactivity

5
Types

• Lightweight (density lt 2100 kg/m3)
• Vermiculite, perlite,
• Sintered FA, foamed slag
• Normal-weight (gt 2100 kg/m3)
• Natural sand stone
• Heavyweight (gt 3000 kg/m3)
• Barytes
• magnetite

6
Sources of sand

• Stream beds
• Best source clean, rounded strong
• Dunes
• Wind action single sized fine grained
• Alluvial deposits
• Alluvial deposits may contain different types
• Marine deposits
• May contain high chloride content

7
Crushed Rocks

• Igneous rocks
• Formed from molten minerals
• Basalt, diorite, granite
• Sedimentary rocks
• Formed by cementation or compaction of deposits
• Limestone, sandstone, shale, chert
• Metamorphic rocks
• Formed by pressure and heat
• Quartzite, marble, slate

8
Manufactured Aggregates

• Manufactured slag
• Air-cooled slag, granulated slag, foamed slag
• Expanded clays and shales
• Heated to 12000C
• Sintered Fly Ash
• Mix fly ash with coal slurry, pelletise and
  sinter at 14000C

9
Properties

• Grading
• Particle shape surface texture
• Density
• Water absorption
• Abrasion resistance
• Soundness
• Strength
• Reactivity
• Impurities

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Grading (Particle size distribution)

• Water demand
• Bleeding
• Segregation
• Continuous grading better than gap grading
• Maximum size smallest sieve all passing
• Nominal size whole No. above which nearly all
  passes

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Particle shape surface texture
12
Density

• Particle Density (Relative Density)
• Used to calculate volumes in a mix
• Usually 2.60 to 3.2
• Bulk density
• Loose or compacted
• Used to determine voids for mix design

13
Water absorption

• Water absorbed by the minute pores
• Can affect the water/cement ratio
• High absorption high shrinkage
• High absorption higher creep

14
Abrasion resistance

• Ability to resist friction
• Weak aggregates
• Higher water demand
• Lower wear resistance
• Less durability under exposed conditions

15
Soundness

• Ability to withstand aggressive conditions
  (weather)
• Wetting and drying
• Freezing and thawing
• Tested to AS 1141.24

16
Strength

• This will influence the concrete strength if weak
• Most aggregates are strong enough gt 100 MPa
• Tested to AS 1141.22 10 fines test

17
Reactivity

• Alkali-aggregate reaction
• Alkalies (Na K) in cement with silica in sand
• Forms a gel that is expansive
• Pyrites (ferrous sulphide)
• Oxidises and stains
• Hard burnt lime
• Expands causes pop-out and cracks

18
Impurities

• Sugar
• Retards setting times
• Organic matter
• Retards and lowers strength
• Silt, clay dust
• Decreases bond, increases permeability
• Montmorillonite clay
• Volumetrically unstable (wet dry conditions)

19
Water

• Rule fit for drinking
• Test for suitability
• Setting time - 60min 90 min of control
• Strength not less than 90 of control at 7 28
  days
• pH greater than 5

20
Water

• Chlorides
• Accelerate setting times, ultimate strength can
  be less
• Affect durability by promoting corrosion of the
  reinforcing steel
• Maximum content 0.8 kg/m3 concrete

21
Water

• Sulphates
• Affect the setting times
• Reduce later-age strengths
• Can cause sulphate attack of the cement
• Maximum content in concrete 50 g/kg cement

22
Water

• Carbonates Bicarbonates
• Can accelerate setting times
• Can lower strengths
• Not common but if water source unknown - test

23
Water

• Acid
• Not often a problem, but industrial waste water
  need to be tested
• Alkalinity
• Recycled water from concrete plants - satisfactory