Some crucial information about concrete mix design
Mix Design refers to the method of choosing perfect materials of concrete and finding out their proportionate ratios with the purpose of developing concrete with minimum specific strength and stability as reasonable as possible.
To form concrete maintaining desired strength and properties, choosing of components and their quantity should be determined and it is defined as concrete mix design.
The site engineer should provide following information at the time of delivering material for mix design to the mix design laboratory :-
A) Grade of concrete (the characteristic strength)
B) Necessary workability regarding slump
C) Other properties (if necessary)
Retardation of initial set (to get rid of cold joints for longer leads or ready mix concrete)
Slump retention (for ready mix concrete)
Pumpability (for ready mix concrete)
Expedition of strength (in case of precast members or where initial deshuttering is required)
Flexural strength (generally necessary concrete pavements)
Determine whether condition of exposure to concrete is mild, moderately severe or very severe. Exact analysis of soil should be made to determine existence of sulphates & chlorides for any doubt.
The degree of control at construction site is based on the following factors :-
Batching ? Weigh batching/volume batching
Type of aggregates ? Whether the type of aggregate will be mix graded or 10 mm, 20 mm aggregates should be utilized independently.
Testing of concrete ? Whether casting & testing of concrete cubes should be performed at construction site on regular basis.
Source of aggregate ? Whether sources of sand and aggregate are standard or should be altered regularly.
Supervision ? Whether skilled staffs are there to superintendent concreting work and make require changes like rectification of moisture in sand and alteration in material properties.
Site laboratory ? Whether the site will contain required laboratory tools like sieves, weighing balance etc. for the verification of material properties.