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• Aggregates


  Used primarily to provide bulk to concrete to increase the density of resulting mix
• Aggregates provide about 75% of the body of the concrete and hence its influence is extremely important
• Classification of aggregates


  • Natural aggregate
  • Artificial aggregate
• Natural aggregate


  Generally obtained from natural deposits of sand and gravels or from quarries by cutting rocks
• Artificial aggregate


  The most widely used artificial aggregates are clean broken bricks and air cooled fresh blast furnace slag
• Types of aggregates


  • Fine aggregates
  • Coarse aggregates
• Fine aggregates


  Small-size filler materials in construction
• Definition of fine aggregates


  Particles that pass through a 4.75 mm sieve and retain on a 0.075 mm sieve
• Sources of fine aggregates

  • River sand or machine sand
  • Crushed stone sand
  • Crushed gravel sand
• Function of fine aggregates in concrete

  Fill the voids between the coarse aggregate
• Uses of fine aggregates

  • Mortar
  • Plaster
  • Concrete
  • Filling of road pavement layers
• Coarse aggregates


  Larger-size filler materials in construction
• Definition of coarse aggregates


  Particles that retain on a 4.75 mm sieve
• Materials used as coarse aggregates

  • Brick chips (broken bricks)
  • Stone chips (broken stones)
  • Gravels
  • Pebbles
  • Cinders
• Sources of coarse aggregates

  • Dolomite aggregates
  • Crushed gravel or stone
  • Natural disintegration of rock
• Function of coarse aggregates in concrete

  Act as inert filler material
• Uses of coarse aggregates

  • Concrete
  • Railway track ballast
• Shape and texture of aggregate


  • Affects the properties of fresh concrete more than hardened concrete
  • Concrete is more workable when smooth and rounded aggregate is used instead of rough angular or elongated aggregate
  • Crushed stone produces much more angular and elongated aggregates, which have a higher surface-to-volume ratio, better bond characteristics but require more cement paste to produce a workable mixture
• Surface texture of aggregate


  • Can be either smooth or rough
  • Smooth surface can improve workability
  • Rougher surface generates a stronger bond between the paste and the aggregate creating a higher strength
• Grading or size distribution of aggregate


  • An important characteristic because it determines the paste requirement for workable concrete
• Moisture content of aggregate


  • An important factor when developing the proper water/cementitious material ratio
  • All aggregates contain some moisture based on the porosity of the particles and the moisture condition of the storage area

  
• Specific gravity of aggregate


  • Easily calculated by determining the densities by the displacement of water
  • All aggregates contain some porosity, and the specific gravity value depends on whether these pores are included in the measurement
• Bulk density of aggregate


  • Measures the volume that the graded aggregate will occupy in concrete, including the solid aggregate particles and the voids between them
• Porosity of aggregate


  • Means the pores present in the material structure
  • Porous aggregates have more surface area with good bond strength
  • Porosity of aggregate must be between 0-20% for its use in construction
• Strength of concrete


  • Depends upon strength of aggregates
  • For same bulk aggregates, the aggregates having higher strength will produce higher strength concrete