Concrete Mix Proportioning

Where  concrete is specified by its grade i.e. characteristic compressive  strength like MI5, then the proportions of cement, aggregate and water  shall be determined by designing the concrete mix. You  will require following details to commence the actual working of concrete mix design. 

• Specified minimum or characteristic strength of concrete 
• Durability requirement of concrete depending upon environmental conditions 
• Type, average compressive  strength and  standard deviation of cement 
• Work ability  desired in mm 
• Maximum  size of aggregates 
• Shape of aggregates 
• Fineness based on percentage passing boo micron sieve or zone of fine aggregates 
• Specific gravity of aggregarls. 

In  case of volumetric mix the designation is 1:2:4, 1:3:6 etc. 

• To determine the volume 50 kg of cement is generally taken  as equal to 0.035 cm. 
• If fine aggregate is moist, determine and provide  allowance for bulking 
• The gauge boxes should be of such dimension that 50 kg of cement forms  a unit. 
• The equivalent size of box for 50 kg cement will measure 40 x 35 x 25 cm internally.  Do not  allow any consolidation of aggregates in the gauge boxes by ramming or shaking. 
• In case of design mix, trial mixes should he run as early  as possible on commencement of work, so that by the time excavation is done, enough information is available from trial mixes.