Various Strands of Mix Designing, Significance & Specific Principles

Mix Proportioning & Strands of Mix Design

Mix Proportioning

Concrete Mix Proportioning is the science of deciding relative proportions of ingredients of concrete, to achieve the desired properties in the most economical way.

Strands Of Proportioning

Absolute Volume Methods

Weight Methods

Various Methods of Concrete Mix Design

1.American Concrete Institute Committee 211 Method

  • Absolute Volume Method
  • Reliable
  • Entrapped Air Considered
  • Higher w/c Ratio
  • Higher Fines content hence better Workability

2.Bureau of Indian Standards Recommended Method IS 10262-2009

  • Coarse Aggregate calculation sequence follows ACI Method
  • Provision for Use of Chemical & Mineral Admixtures
  • Lower Fines hence more voids

3.Road note No. 4 (Grading Curve) Method

  • High Cement Content, Obsolete
  • Cannot be used for Gap Graded Aggregates

5.Trial and Adjustment Method

6.Department Of Environment (DOE – British) Method

  1. Fineness modulus Method
  2. Maximum density Method
  3. Indian Road Congress, IRC 44 Method
  4. USBR (United States Bureau of Reclamation) Mix design practice

Significance

Its an art rather than a science

Attaining predefined requirements

  • Workability of fresh concrete
  • Placing
  • Compacting
  • Finishing
  • Strength of hardened concrete at a specified age

Durability under specific exposure conditions

  • Freeze thaw cycles
  • Sulphate water
  • Natural agents

Satisfying the performance requirements at the lowest possible cost

  • w/c ratio
  • a/c ratio
  • Fa/Ca ratio
  • Substitution of cement using pozzolanic or cementitious materials

Specific Principles 

Specific Principles

Workability

Workability embodies consistency and cohesiveness

Strength

Structural Safety – Minimum Required Strength to be attained. The strength of a material is defined as the ability to resist stress without failure

Properties of concrete, such as

  • Elastic modulus,
  • Water tightness or impermeability, and
  • Resistance to weathering agents including aggressive waters,are believed to be dependent on strength

Durability

  • Exposure Conditions
    • Durability ignored for Normal Exposure
  • Strength- Index of general Durability
  • Service life of Concrete

Objectives of Mix Proportioning

Quality concrete

  • Better strength
  • Better imperviousness and durability
  • Dense and homogeneous concrete

Economy

  • Economy in cement consumption
  • Best use of available materials

 

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