CMT

• Properties of aggregates

  • Specific weight
  • Water absorption
  • Abrasion
  • Density
  • Uniformity
• Aggregates generally occupy 70 to 80% of the volume of concrete and therefore have a significant effect on its properties
• Strength of concrete and mix design are independent of the composition of aggregate, but durability may be affected
• Classification of aggregates based on specific gravity

  • Heavyweight
  • Normal-weight
  • Lightweight
• Classification of aggregates based on grain size

  • Fine aggregates (>0.07mm & passing through 4.75mm)
  • Coarse aggregate (retained on 4.75 mm sieve & <80mm)
• Fine aggregates


  Sand, silt and clay. Crushed stone and crushed gravel might also fall under this category. Used to improve workability of a concrete mix
• Coarse aggregates


  Natural stone or gravel that has not been crushed or processed. Reduce the amount of water needed for a concrete mix, which may also reduce workability but improve its innate strength
• Classification of aggregates based on density

  • Lightweight
  • Standard
  • High density
• Lightweight aggregates


  More porous than their heavier counterparts, used in green construction, concrete blocks and pavements, insulation and fireproofing
• High density aggregates


  Used to form heavyweight concrete for high strength, durable concrete structures like building foundations or pipework ballasting
• Classification of aggregates based on geographical origin

  • Natural
  • Processed
• Natural aggregates


  Taken from natural sources, such as riverbeds, quarries and mines. Sand, gravel, stone and rock are the most common
• Processed aggregates


  Also called 'artificial aggregates' or 'by-product' aggregates, taken from industrial or engineering waste. Common examples include industrial slag and burnt clay
• Classification of aggregates based on shape

  • Rounded
  • Irregular
  • Angular
  • Flaky
  • Elongated
  • Flaky and elongated
• Rounded aggregates


  Natural aggregates smoothed by weathering, erosion and attrition. Rocks, stone, sand and gravel found in riverbeds. Improve workability
• Irregular aggregates


  Shaped by attrition but not fully rounded. Consist of small stones and gravel, offer reduced workability compared to rounded aggregates
• Angular aggregates


  Crushed rock and stone, used for higher strength concrete. Workability is low, but can be offset by filling voids with rounded or smaller aggregates
• Flaky aggregates


  Thin in comparison to length and width, increase surface area in a concrete mix
• Elongated aggregates


  Longer than they are thick or wide, also add more surface area to a mix - meaning more cement paste is needed
• Flaky and elongated aggregates


  A mix of the previous two, the least efficient form of aggregate with regards to workability
• Specific Gravity is defined as the ratio of Weight of Aggregate to the Weight of equal Volume of water
• Specific gravity of aggregates normally used in construction ranges from about 2.5 to 3.0 with an average value of about 2.68
• Material having higher Specific Gravity is generally considered as having higher strength
• Water absorption of aggregate


  A measure of porosity, considered as a measure of resistance to frost action and weathering
• Abrasion test


  Carried out to test the hardness property of aggregates, to find the percentage wear due to relative rubbing action between the aggregate and steel balls used as abrasive charge
• Particle shape and surface texture influence the properties of freshly mixed concrete more than the properties of hardened concrete
• Particle shape classifications

  • Angular
  • Subangular
  • Subrounded
  • Rounded
• Angular and rough-textured aggregates


  Produced by crushing rocks, have sharp corners and rough texture. Generally produce bulk materials with higher stability than rounded, smooth-textured aggregates
• Rounded aggregates


  Aggregates that have become completely rounded through weathering and transportation in water. Easier to work into place than angular aggregates
• Particle shape of coarse aggregates

  • Angular
  • Rounded
  • Flaky
  • Elongated
  • Flaky and elongated
• Flat particle


  Ratio of the "middle" dimension to the smallest dimension exceeds 3 to 1
• Elongated particle


  Ratio of the longest dimension to the middle dimension exceeds 3 to 1
• Flat and elongated particle


  Ratio of the largest dimension to the smallest dimension exceeds 5 to 1
• Texture of coarse aggregates

  • Glassy
  • Smooth
  • Granular
  • Crystalline
  • Honeycombed and Porous
• True slump


  The general mass of the concrete drops evenly without any disintegration
• Shear slump


  One side of the concrete shears or falls from the main portion, indicating lack of cohesion
• Collapse slump


  The concrete completely collapses, indicating the mix is too wet
• Zero slump


  The concrete maintains the shape of the mold, indicating the mix is too stiff with almost no workability
• Materials Testing


  Measurement of the characteristics and behavior of materials to be used in specifying the suitability of materials to various applications (e.g. construction)
• Materials Testing


  Examination of material properties with respect to design and use of end product