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Craig Mason
Engineering Manager
Asked a question 2 years ago

Can we alter the concrete mix design at site?

Sir As per Is -383 1970, the % of wt retained on 12.5mm must be nil. But when i conducted a sieve analysis of 10mm aggregate, i found out that about 1700 grams were retained on 12.5mm. Now as per mix design the ratio of 10mm and 20mm is 35% and 65%. Sir tell me what to do in such situation when the results alter hugely from mix design.

Where am I?

In TheConstructor you can ask and answer questions and share your experience with others!

Now you can use the aggregate between sieve size 10mm retaining and passing from 12.5 mm.use locally available materials to reduce cost.

Still, the mix design does not change but gives the desired result.

Theodore Ray
Planning and development surveyor

Thank you sir for your reply.

Now sir i want to ask you how can it be possible that only those which pass 12.5mm sieve , be used for ready mix concrete. The sample that i collected for sieve analysis was from the dumping area close to the batching plant. Now this 10mm aggregate will be used for RMC.

 So now what can i do in this situation. As i have mention that the 10mm aggregate lot contains aggregate higher than 10mm size as per my sieve analysis observation. 

Now this 10mm aggregate(which contains higher % of aggregate greater than 10mm) will go into the schwing setter weigh batch mixer. 

SO how can i use only those which pass 12.5mm sieve and nothing else.

In that case, you need to sieve the 10mm aggregates and use only those which pass through 12.5mm sieve. You can not alter the mix design.

In other case, you need to redo the mix design based on locally available material and use the mix proportion accordingly.