Yes, M-Sand (crushed sand) can replace 100% river sand in a concrete mix proportion.
M-Sand are manufactured by latest technology (Vertical shaft impactor nachines). They give at par results in comparison to rivers sand concrete mixes, in both fresh and hardened state. Since quality control is maintained in the process of preparing manufactured sand, the sand obtained will better confirm to the Zone-II grading standards (required by IS code for concrete works) at all times. The don’t have any organic or silt materials.
On the other hand, River sand may have organic impurities and silt.
Availability of river sand throughout the year is not consistent but you can have consistent supply of M-Sand.
So we recommend using manufactured sand as a replacement of river sand depending on availability and cost effectiveness.
Please note you need to have different mix design for both river sand and M-sand. So although river sand can be completely replaced with M-sand, a proper mix proportion needs to be adopted taking into account the finess modulus of each of these sands.
For Example: If both these sands have same finess modulus, the proportion of fine aggregate will remain same in the concrete mix.
If the finess modulus of M-sand is more than finess modulus of River Sand (used in Mix design calculation), then the m-sand being used is courser. So the proportion of M-sand (fine aggregate) to be mixed in the concrete would be higher.