L1

L1

1. Principles of Concrete Mix Design

   • Process of selecting the most appropriate materials and their relative proportions in order to achieve specified properties as economically as possible.

2. These properties are normally:

   • Compressive Strength
     • Material strength properties from same batch follow normal distribution
       • always possibility that random very low value may arise
         • Characteristic strength -is the strength below which not more than a certain percentage of test sample values may fall (in the case of Eurocodes the value is 5%).
           • Variability is measured by standard deviation Typical differences of 5 N/mm2 can occur for the same nominal mix proportions through “natural” variability.
   • Workability
     • Required workability depends on:
       • type of construction
       • techniques of transporting
       • placing and compacting being used
     • Workability test usually specified in terms of slump test, also used for indicative acceptance testing
       • neither test is precise, so design method uses range of Workability (e.g. 30-60mm slump)