Flashcards
CIVL 320 Aggregates
Cards in this deck (29)
- 1Aggregate- granular, inert, inorganic rocks and minerals
- used in concrete, asphalt, pavement, structural fill materials, geotech filters anddrains, env water filters
- naturally occuring or synthetic
- fine and coarse
- lightweight, semi lightweight, normal and heavy weight
- different rock types (granite, basalt, limestone, sandstones etc) - 2Spec Gravityheavy weight: SG>3
normal: SG 2.5-3
Light weight: SG<2.3 - 3Structural lightweight agg- shale, clay, slate, slag
- can be used to produce lightweight concrete w densities 1350 to 1850 - 4Insulating lightweigh agg-pumice, scoria, perlite, vermiculite, diatomite
- earthfill matl and insulating concrete densities 250-1450 - 5Heavy weight agg- magnetite, hematite, iron, steel punchings or shot
- high density up to 6400
- used in radiation shielding - 6Classification by particle size-fine: natural sand or crushed stone, passes 5mm sieve (#4)
- coarse: natural gravel or crushed stone, retained on 5mm sieve (#4) - 7Interaction with water
- 8moisture in aggs- if MC > AC, agg is wet, will give up water to surrounding concrete
- MC < AC, agg is dry and will absorb moisture from surrounding concrete - 9Porosity- pores may be interconnected or discontinuous
- low porosity desireable
- inc porosity: dec bulk density, dec elastic modulus, dec strength, dec abrasion resistance, inc permeability, dec durability - 10Bulking of sand- menisci form between particles making repulsive forces
- in vol of unit mass
- dry and fully sat sand will occupy less vol than sand at 10% MC
- difficult to accurately volume batch sand accurately (need to measure by mass taking into account the MC) - 11Particle size and grading- size of a particle refers to the size of the smallest square opening through which particle will pass (Sieve)
- MSA: max size agg is smallest sieve through which entire agg sample passes - 12Particle Size Distribution
- 13Grading specs- many applications: concrete, shotcrete,stucco, masonry mortar, asphalt, road bases, filter sands, drainage systems
- max and min cumulative percentages of matl passing each sieve
- performance method: only very broad range of max/min given initially, once a gradation is proposed and tested then supplier must produce within very tight allowable deviation - 14Blend calc- combining 2 or more agg sources together to obtain desired gradation - trial and error w spreadsheet
- agg often produced and stockpiled in narrow grade bands - 15Max vs Nominal max- max size: smallest sieve that all of a particular agg must pass through
- nominal max size: standard sieve opening immediately smaller than the smallest through which all of the agg must pass
- nominal max size may retain 5% to 15% - 16Types of "grading"- continuous: agg contains all size fractions between max and min particle sizes
- open (uniform): only one size fraction is present
- gap: missing one or more size fractions - 17Types of grading(graphs)
- 18reduction of voids- want to minimize void spaces between agg particles
- need to modify amt of sand so that a workable concrete can be made
- max particle packing can be predicted using fuller eqn(Pi=100(di/D)^n) - 19Fineness Modulus of Sand (FM)- approx single # to describe gradation of sand
- defined as summation of total mass retained on all standard sieves greater than and including #100 sieve - 20Particle shape and surface teture- shape: angularity - relative sharpness of edges and corners, sphericity - how close to a sphere
- texture: smooth or rough
- round, smooth = better workability
- rough, angular= better cement - agg bond, more agg interlock - 21Strength and toughness- important parameters because: durability and resistance to weathering of asphalt and concrete, abrasion resistance, resistance to degradation during processing and handling, concrete strength but primarily for high strength concrete
- compressive/crushing strength (unconfined compressive strength) - canmeasure using directly on rock core samples
- strength and toughness are difficult to measure directyl ,use indirect methods based on impact and abrasion
- Micro Deval and LA abrasion tests (agg rotated in steel drum containing steel spheres and are abrased and crushed) - 22Bond between paste and agg- influences concrete strength
- bond is due to: mech interlocking, chem activity, electrostatic condition on surface, capillary action
- surface coatings may influence bond: clay, silt, gypsum, detrimental to bond - 23Surface Chemistry- hydrophobic (water repellant): basic in nature, positive surface charge
- hydrophilic(water attracting): acidic, negative surface charge (more easily wetted bywater than cement) - 24Durability- unstable volume changes (ex) chem rxns, water absorption)
- freeze thaw deterioration
- mech degradation/breakdown
- chem degradation - 25Harmful properties
- 26Alkali-agg reaction (AAR)- visual symptoms: expansion, network of cracks, closing up orspalling at joints, relative displacements between sections of structure
- caused by: rxn of certain types of silica in agg with alkalis in cement
- controling AAR: non reactive agg, SCM, minimize exposuretowater, limit alkali loading - 27Recycled concrete agg- rubble from demolished buildings and structures - rebar removed
- contains agg coated with cement mortar
- often used only as fill matl butnow starting to be used in new concrete
- accepted if RCA meets all tests for normal agg
- sustainable goals are met due to reduced landfill needs, reduced consumption of natural agg sources, reduced trucking costs - 28RCA contd- difficulties: high absorption makes difficult to mix concrete, unknown strength, sand sizes may have too much passing 75 um sieve, contamination, inc creep and shrinkage and lower E
- mix designs often include only partial replacemnt of agg with RCA
- 30% coarse agg replacement results in very minor change to concrete properties - 29RCA contdeffect on concrete properties:
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- Flashcards on CIVL 320 Aggregates, created by Maddi Everton on 13/11/2017.
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- Maddi Everton
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