Expert: Babak Esmailzadeh Hakimi - 1/16/2012

Question
I am using sieved saw dust as sand replacement in concrete. i got 8N/mm^2 as 7 day strength for M25(1:1:2) concrete grade.Can you suggest ways to increase its strength ? Is there any technique we can use to get a more effective concrete?

Answer
Dear Sharmila

Concrete admixture is very serious even for moderate range of strength. Saw dust cant replace sand in concrete and sand cant replace gravel. I suggest this formula to be tested ( this is not very accurate  but a guide)   :

600-800 kg gravel with maximum size of 1/2-3/4 inch
1100- 1300 kg sand  
300 kg cement type 1 or 2
250-300 lit water

In the case you would have 28 days strength less than what you expected you can add some more cement to your admixture.

Please give me information about your tests. Looking foreward to hear from you.

Best Regards
Babak Esmailzadeh Hakimi