PROPERTIES OF CONCRETE

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PROPERTIES OF CONCRETE
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ARTICLEEffects of aggregates on properties of
concrete
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• SUBMITTED TO
• Dr. Ayub Elahi
• SUBMITTED BY
• 2K9-SCET-02/CIVIL
• 2K9-SCET-26/CIVIL
• 2K9-SCET-07/CIVIL
• 2K9-SCET-52/CIVIL
• 2K9-SCET-54/CIVIL

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• Aggregates
•  Granular mineral material(such as sand, gravel,
  crushed stone) used with a bonding medium (such
  as cement or clay) to make concrete, plaster, or
  terrazzo mixture.
• Sum minerals are given below
• Minerals
• Silica (ex. Quartz)
• Silicates (ex. Clay)
• Carbonate (ex. Calcite, dolomite).

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Types of aggregates

• 1.Fine aggregates
• 2.Coarse aggregats

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Properties of aggregates and their effects on
concrete
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• Grading
• Grading is the distribution
  of particles
• among various sizes. Grading is usually expressed
  in terms of cumulative percentage passing each
  sieve.
• Coarse Aggregate Grading
• Usually more water and
  cement is required for small-size aggregate than
  for large sizes,due to an increase in total
  aggregate surface area.

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• Grading sieves

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• The optimum maximum size of coarse
• aggregate for higher strength depends on
• 1.Relative strength of the cement paste
• 2. Cement-aggregate bond
• 3.Strength of the aggregate particles

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• Effect of Size on concrete
• Variation in the size of Aggregates changes the
  water demand, cement content, micro-cracking
  (strength) in concrete. It also effects
  pumpability, and durability of concrete.

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Effect of Size on concrete

• The larger the maximum size of the coarse
  aggregate, the lower the water demand of the mix.
  The maximum size of aggregates is important
  parameters in any concrete mix. its affect
  relative proportions in mix, workability,
  economy, porosity and shrinkage of concrete etc

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Effect of Grading on concrete

• Grading of aggregates depends on the proportions
  of coarse and fine aggregate. If grading of
  aggregate is varied, it also changes cement paste
  content (cost economy), workability of the mix,
  density and porosity

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Maximumaggregate size, they affect

• Relative aggregate proportions
• Cement and water requirement
• Workability
• Pump ability
• Economy

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Fineness modulus

• is a measurement of the coarseness or fineness
  of a given aggregate. For a fine aggregate, FM is
  calculated from the cumulative percentages of
  aggregate retained on sieves No.4,8, 16, 30, 50,
  100, 3/8in., 3/4in., 1.5in., 3in., and 6in.,
  divided by 100. The Fineness Modulus should be
  between 2.3 and 3.1.

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Effect of Fineness on Density of Concrete

• After measuring the slump, several 150 mm cubes
  were filled. These were cured in water tank for
  28 days. After curing, each cube was weighed
  using electronic balance and density of concrete
  was calculated.

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Texture

• The surface texture of aggregate can be either
  smooth or rough

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Effects of Surface Texture

• The surface texture of aggregate can be either
  smooth or rough. A smooth surface can improve
  workability, yet a rougher surface generates a
  stronger bond between the paste and the aggregate
  creating a higher strength
• Rough-textured and elongated particles require
  more cement paste to produce workable concrete
  mixtures, thus increasing the cost

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• The 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. Most natural
  sands and gravel from riverbeds or seashores are
  smooth and rounded and are excellent aggregates.
  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.

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Absorption and Surface Moisture

• The absorption and surface moisture of
• aggregates should be determined using
• ASTM C 70, C127, C128, and C 566 so that
• the total water content of the concrete can be
• controlled and the batch weights determined
• The moisture conditions of aggregates are
• Oven dry
• Air dry
• Saturated surface dry (SSD)
• Damp or wet

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Effects of absorption Surface Moisture

• that using saturated coarse aggregate in the mix,
  always
• yields higher shrinkage strain than is dry
  aggregate. There about 10 increase in drying
  shrinkage for all mixes, except in uncrushed
  gravel.The increase for uncrushed gravel was
  about 3 and that could be resulted from the low
  water absorption (0.98) and smooth surfaces
  which make no difference between dry and
  saturated condition.

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Effects of absorption Surface Moisture

• Using dry aggregate causeds the water/cement
  ratio in the vicinity of the aggregate particles
  to be less than else where because aggregate
  absorbed water to reach saturated surface-dry
  condition

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Moisture conditions of aggregate
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• The reduction in water content would improve the
  bond between cement mortar and aggregate and
  reduce the interface zone porosity and
  microcracking (2), and consequently,increases the
  restraining action of
• aggregate against drying shrinkage.The same
  influence was observed with respect to the
  elasticity modulus,compressive, and splitting
  tensile strength of concrete. For porcilinite
  aggregate, the effect of moisture content was
  more obvious on elasticity modulus and splitting
  tensile

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Refrences

• www.ads google.com
• NEVILLE, A.M, 'Properties of concrete', IV
  edition, Pearson Education Pvt. Ltd. 2005.
• www.engg pedia .com
• http//books.google.com.pk/books?idTNzk-4WA6GoCl
  pgPA412otsEV2yFWPT9Adqeffects20of20fineness
  20modulous20on20concpgPA412vonepageqffal
  se
• Slides of lecture

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