M-sand or manufactured sand is a purpose made fine aggregate produced by crushing a suitable stone, ex- granite, basalt, quartz, or lime stone. M-sand manufactured as per the standards would have characteristics similar to the river sand and in certain parameters, exceed the basic properties required for fine aggregates.
In the manufacturing process, the stone boulders are crushed using a combination of a primary Jaw and a secondary cone crusher, the resulting material is then passed through a vibratory screen to separate stones larger than 30 mm, which is again, re-processed through the secondary cone crusher. The stones which are 30mm and below are fed into a VSI crusher for further reduction in size up to 4.75mm and below, the said material is passed through a vibratory screen with sieve size of 4.75 mm in a continuous loop to produce M-sand, the larger particles are fed back into the VSI crushers.
Due to the rock on rock configuration of the VSI crusher each individual particle attains a cuboidal structure which imparts a smooth texture similar, to the weathered river sand particles giving a very good workability, to the resultant m-sand, cement and coarse aggregate mixture.
Crusher dust cannot be called as M-sand, as the particles are flaky and does not adhere to the requirements of fine aggregates, as per the ISI 383 standards. It is a sub-standard material and cannot replace river sand or manufactured sand (M-sand).
With rampant and un-checked sand mining, there is a severe depletion of sand from the river bed, which has serious environmental consequence on the long term. Government, Local NGO’s and environmental protection agencies have strongly protested against this illegal mining.
Use of Manufactured sand in place of river sand is the only way to prevent further depletion, in fact river sand mining is banned in the state of Goa and Kerala. This trend is seen all over the world, it’s only a matter of time before the government of India bans sand mining across the country.
Summary of results on concrete
Two commonly used grades of concretes M20 and M30 were examined for their characteristics in fresh and hardened state. The results can be summarised as follows.
- IS456 code specifies a minimum slump of 50 mm for medium workability.M20 and M30 grade concrete mixes meet this requirement when M-sand is used as fine aggregate.
- Compressive strength of concrete (M20 and M30) with sand is marginally higher(6-9%) when compared to the concrete with river sand.
- Flexure strength of M-sand concrete is 12-15% higher than that of river and concrete.
- Pull out bond test indicates marginally higher bond strength for M-sand concrete when compared with the bond strength of river sand concrete.
- The stress-strain behaviour of M-sand and river sand concretes are similar.The secant modulus(at 30% of compressive strength) of the M20 grade concrete with M-sand and river sand is nearly equal at 24,000 MPa.
Summary of results on mortars
The results of the tests on mortars and masonry using river sand and M-sand as fine aggregate can be summarised as follows.
- Grading limits of M-sand falls within the grading Zone-II sand,grading limits specified by IS 383 code.
- Shapes of the M-sand particles resemble the shape of river sand particles.
- Bulk density and specific gravity of M-sand are comparable to those of river sand.
- Mortars with M-sand show better workability and require lower water-cement ratio to achieve a specific flow value when compared to mortars with river sand.
- M-sand mortars show higher water retentivity values.
- Compressive strength of mortar with M-sand is higher than that of the mortar with river sand for mortar flow in the range of 85-100%.
- Flexure bond strength of masonry using M-sand mortar is significantly higher when compared with the mortar using river sand.
- M-sand mortar shows higher compressive strength and modulus for masonry when compared with the values for masonry using river sand.