aggregates

• aggregate

  means a mass of crushed stone, gravel, sand, etc. preodominantly composed of individual particles, but in some cases including clays and silts.
• 150mm (6in)

  largest particle size in aggregates
• 5-10 mm (0.0002 to 0.0004 in)

  smallest particle size in aggregates
• coarse aggregates

  aggregate particles that are retained on 4.75 mm sieve (no.4)
• fine aggregates

  aggregate particles that pass a 4.75mm sieve (no.4)
• maximum aggregate size

  the smallest size through which 100% of the aggregates pass
• nominal maximum aggregate size

  the largest sieve that retains any of the aggregate, but generally not more than 10%
• natural sources for aggregates

  • gravels pits
  • river run deposits
  • rock quarries
• manufactured aggregates

  can use slag waste from iron and steel mills and expanded shale and clays to produce lightweight aggregates.
• heavyweight concrete

  used for radiation shields, can use steel slag and bearings for the aggregate
• styrofoam beads

  can be used as an aggregate in lightweight concrete used for insulation.
• natural lightweight aggregates

  • pumice
  • scoria
  • volcanic cinders
  • tuff
  • diatomite
• aggregates are used primarily as an underlying material for foundations and pavements as riprap for erosion control, and as ingredients in portland cement and asphalt concretes
• aggregate underlying materials, or base courses, can add stability to a structure, provide a drainage layer, and protect the structure from frost damage
• stability

  is a function of the interparticle friction between the aggregates and the amount of clay and silt "binder" material in the voids between the aggregates particles
• portland cement concrete

  60% to 75% of the volume and 79% to 85% of the weight are made up of aggregates
• asphalt concrete

  aggregates constitute 75% to 85% of the volume and 92% to 96% of the mass.
• particle shape and surface texture

  determine how the material will pack into a dense configuration and also determines the mobility of the stones within a mix
• two considerations in the shape of the material

  • angularity
  • flakiness
• texture of coarse aggregates

  the roughness of the aggregate surface plays an important role in the way the aggregate compacts and bonds with the binder material
• soundness and durability

  the ability of the aggregate to withstand weathering
• toughness, hardness, and abrasion resistance

  the ability of the aggregates to resist the damaging effect of loads is related to the hardness of the aggregate particles
• absorption

  the amount of water the aggregates absorb is important in the design of potland cement concrete, since moisture captured in the aggregate voids is not available to react with the cement or to improve the workability of the plastic concrete
• specific gravity

  the weight-volume characteristics of aggregates are not an important indicator of aggregate quality, but they are important for concrete mix design
• density

  the mass per unit volume, could be used for these calculations
• bulk unit weight and voids in aggregates

  needed for the proportioning of portland cement concrete mixtures.
• strength and modolus

  the strength of portland cement concrete and asphalt concrete cannot exceed that of the aggregates. it is difficult and rare to test the strength of aggregate particles
• tensile strength of aggregates

  0.7 to 16 mPa(100 to 2300 psi)
• compressive strength of aggregates

  35 to 350 mPA(5000 to 50,000 psi)
• gradation

  describes the particle size distribution of the aggregate.
• sieve analysis gradation

  evaluated by passing the aggregates through a series of sieve
• deleterious substance

  is any material that adversely affects the quality of portland cement or asphalt concrete made with aggregate
• alkali-aggregate reactivity

  some aggregates react with portland cement, harming the concrete structure. the most common reaction, particularly in humid and warm climates, is between the active silica constituents of an aggregate and the alkalis in cement