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Concrete > Aggregates > Flashcards

Aggregates Flashcards

1
Q

What does ASTM stand for

A

American Society of Testing & Materials

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2
Q

Aggregates sources?

A
  • Sand & Gravel (~900 mil. tons/yr)
  • Crushed stone (~1.2 bil. tons/yr)
  • Iron ore blast furnace & other slags
  • Manufactured (lightweight & heavy weight)
  • Reclaimed
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3
Q

Aggregate whight types?

A
  • Crushed stone or Manufactured mineral
    • Rock quarried/processed through crushing & screen
      plant to reduce and separate into diff. sizes.
    • Limestones & dolomites (~70%, hard-soft)
    • Granites (~15%, hard)
    • Sandstones (~2%, soft)
      *Normal weight
    • Gravels, sands, normal crushed stone, bulk specific
      gravity - 2.4 to 2.9, bulk density (of bulk unit weight) -
      95 to 105 pcf) most commonly used.
      *Light weight
    • Manufactured or natural, Bulk density less than 70
      (pcf), most commonly used in light weight concrete.
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4
Q

Why do we include aggregates in concrete?

A

Increase dimensional stability, elastic modulus, durability, workability and cost.

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5
Q

Course aggregate (CA) classification

A

3/16 in. (4.75 mm) to 2 in. (50mm). #4 on sieve

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6
Q

Fine aggregate (FA) classification

A

<4,75mm; >75 10^6m $200 sieve

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7
Q

Mass concrete

A

May contain aggregate 6 in. (150mm)

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8
Q

Density of natural mineral aggregates

A

Sand and gravel have bulk density of 95 - 105 pcf & produce normal weight concrete (NWC).

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9
Q

Density of lightweight aggregates

A

> 70 pcf

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10
Q

Density of Heavyweight aggregates

A

< 130 pcf

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11
Q

3 major groups of rocks

A

1) Natural Mineral aggregates
2) Synthetic agregates
3) Recycled aggregates

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12
Q

3 types of Natural mineral aggs.

A

1) Igneous - formed from cooling of magma
2) Sedimentary - deposition minerals cemented together
3) Metaphoric - Igneous or sedimentary that change due to physical and chemical conditions below earth’s surface

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13
Q

What are Synthetic aggs.

A

1)Thermally processed materials ( expanded clays and
shale)
2) Aggs. made from industrial by-products (blast furnace slag, fly ash

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14
Q

What are recycled aggs.

A

1) Made from municipal wastes and recycled concrete from demoed buildings

Problems) cost of crushing, grading, dust control, seperating undesirable constituents.

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15
Q

ASTM C294 agg. classification

A

Silica minerals (quartz, opal, chalcedony, tridymite, cristobalite) feldspars, micaceous minerals, carbonite minerals, sulphides, ferromagnesium minerals, zeolites, tron oxides, & clay minearsl

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16
Q

Agg. DENSITY characteristics

A

Controlled by porosity.

1) Apparent specific gravity: Density of material including internal pores
2) Bulk density: Dry rodded weight. weight of agg. that would fill a unit volume

17
Q

4 MOISTURE CONDITIONS of aggs.

A

Controlled by porosity.

1) Oven dry (OD)
2) Air dry (AD)
3) Saturated surface dry (ssd)
4) Wet

18
Q

Oven dried agg.

A

No moisture. Less optimal for concrete b/c it absorbs h2o from concrete mix.

19
Q

Air dried agg.

A

No surface moisture but some internal moisture. less optimal b/c it absorbs h2o from concrete mix.

20
Q

Saturated Surface drie agg.

A

All pores have moisture but there is no excess water. Optimal for concrete mix b/c it doesnt absorb or add h2o from mix.

21
Q

Wet agg.

A

Agg. has excess h2o which adds to the concrete mix. not optimal b/c it makes the mix to wet.

22
Q

What doe SOUNDNESS of agg. mean?

A

controlled by porosity. Agg. unsound when volume changes when introduced by alternate cycles of wetting and drying/freezing or thawing. ie. limestone cracks so use smaller aggs.

23
Q

3 Characteristics controlled by POROSITY?

A

1) Density
2) Moisture condition
3) soundness

24
Q

Max size of agg (MSA) requirements

A

1) MSA < 1/5 of the narrowest dimension of the form in which concrete is to be placed.
2) MSA < 3/4 of max clear distanve b/w re-bar.
3) MSA < 1/3 thickness of unreinforced slabs
* choose smallest of the 3

25
Q

What concrete properties are affected by agg. size?

A

water demand, cement content, microcracking (strength)

26
Q

What concrete properties are affected by agg. grading?

A

Paste content (cost economy) and workability

27
Q

Different types of agg. grading?

A

1) Single-sized (one size)
2) poorly-graded (2 sizes)
3) well-graded (spectrum of sizes) OPTIMAL

28
Q

Fineness Modulus (FM)

A
  • The higher the FM, the more coarse the agg.
  • index of fineness of an aggregate.
  • computed by adding cumulative % of agg. retained on each sieve and / the sum by 100 [smallest size sieve]
  • IE. FM 4.00 can = fourth sieve
29
Q

Grading specifications-PCC for paving by WSDOT

A

See agg. lecture pg. 15/15

30
Q

How does Shape and texture affect concrete?

A

Rough-textured and elongated agg. require more cement past for workability (increased price) and affects initial strength

31
Q

4 SHAPE types of agg.

A
  • Round - loose edges
  • Angular - well defined edges OPTIMAL
  • Elongated - length is larger than other 2 dimensions
  • Flat/flaky - thickness small relative to 2 other dimensions
32
Q

What is SPECIFIC GRAVITY of agg?

A

Ratio of agg weight to weight of an equal volume of water. AVG. = 2.4 - 3.0. smaller the lighter

33
Q

DRY-RODDED unit weight of agg (BULK UNIT WEIGHT)?

A

Weight required to fill a specific unit volume after it has been rodded to attain max packing. Not the same as Specific gravity b/c this disregards volume.

34
Q

Agg. deleterious for concrete

A
  • Substances causing chemical reaction
  • Substances which undergo disruptive expansion
  • Clay particles w flat/elongated shape
  • Weak/soft particles
35
Q

Reactive aggragates

A

Alkali agg. alkali hydroxides react w reactive silicates to form alkali silica gels which absorb water from surroundings through osmosis.

  • leads to internal stress > weakening tensile strength of concrete.
  • if not avoided, reduce alkali content to .6% or less
36
Q

Optimal agg. size/shape

A
  • Rough crushed surface w/ great contact area w cement = strong concrete.
  • larger sized agg. = weaker concrete.
  • Flat shaped agg. = weaker concrete ( traps moisture from rising).
37
Q

When to use larger agg?

A

In lean mixes for best strength

38
Q

When to use smaller agg?

A

In rich concrete mixes (see pg. 20 of agg)

Concrete (11 decks)

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