Aggregates Flashcards
What does ASTM stand for
American Society of Testing & Materials
Aggregates sources?
- Sand & Gravel (~900 mil. tons/yr)
- Crushed stone (~1.2 bil. tons/yr)
- Iron ore blast furnace & other slags
- Manufactured (lightweight & heavy weight)
- Reclaimed
Aggregate whight types?
- 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.
- Rock quarried/processed through crushing & screen
Why do we include aggregates in concrete?
Increase dimensional stability, elastic modulus, durability, workability and cost.
Course aggregate (CA) classification
3/16 in. (4.75 mm) to 2 in. (50mm). #4 on sieve
Fine aggregate (FA) classification
<4,75mm; >75 10^6m $200 sieve
Mass concrete
May contain aggregate 6 in. (150mm)
Density of natural mineral aggregates
Sand and gravel have bulk density of 95 - 105 pcf & produce normal weight concrete (NWC).
Density of lightweight aggregates
> 70 pcf
Density of Heavyweight aggregates
< 130 pcf
3 major groups of rocks
1) Natural Mineral aggregates
2) Synthetic agregates
3) Recycled aggregates
3 types of Natural mineral aggs.
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
What are Synthetic aggs.
1)Thermally processed materials ( expanded clays and
shale)
2) Aggs. made from industrial by-products (blast furnace slag, fly ash
What are recycled aggs.
1) Made from municipal wastes and recycled concrete from demoed buildings
Problems) cost of crushing, grading, dust control, seperating undesirable constituents.
ASTM C294 agg. classification
Silica minerals (quartz, opal, chalcedony, tridymite, cristobalite) feldspars, micaceous minerals, carbonite minerals, sulphides, ferromagnesium minerals, zeolites, tron oxides, & clay minearsl
Agg. DENSITY characteristics
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
4 MOISTURE CONDITIONS of aggs.
Controlled by porosity.
1) Oven dry (OD)
2) Air dry (AD)
3) Saturated surface dry (ssd)
4) Wet
Oven dried agg.
No moisture. Less optimal for concrete b/c it absorbs h2o from concrete mix.
Air dried agg.
No surface moisture but some internal moisture. less optimal b/c it absorbs h2o from concrete mix.
Saturated Surface drie agg.
All pores have moisture but there is no excess water. Optimal for concrete mix b/c it doesnt absorb or add h2o from mix.
Wet agg.
Agg. has excess h2o which adds to the concrete mix. not optimal b/c it makes the mix to wet.
What doe SOUNDNESS of agg. mean?
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.
3 Characteristics controlled by POROSITY?
1) Density
2) Moisture condition
3) soundness
Max size of agg (MSA) requirements
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
What concrete properties are affected by agg. size?
water demand, cement content, microcracking (strength)
What concrete properties are affected by agg. grading?
Paste content (cost economy) and workability
Different types of agg. grading?
1) Single-sized (one size)
2) poorly-graded (2 sizes)
3) well-graded (spectrum of sizes) OPTIMAL
Fineness Modulus (FM)
- 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
Grading specifications-PCC for paving by WSDOT
See agg. lecture pg. 15/15
How does Shape and texture affect concrete?
Rough-textured and elongated agg. require more cement past for workability (increased price) and affects initial strength
4 SHAPE types of agg.
- 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
What is SPECIFIC GRAVITY of agg?
Ratio of agg weight to weight of an equal volume of water. AVG. = 2.4 - 3.0. smaller the lighter
DRY-RODDED unit weight of agg (BULK UNIT WEIGHT)?
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.
Agg. deleterious for concrete
- Substances causing chemical reaction
- Substances which undergo disruptive expansion
- Clay particles w flat/elongated shape
- Weak/soft particles
Reactive aggragates
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
Optimal agg. size/shape
- 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).
When to use larger agg?
In lean mixes for best strength
When to use smaller agg?
In rich concrete mixes (see pg. 20 of agg)
