Natural river sand had been the principal constituent of all construction activities over centuries. But unscrupulous and ruthless excavation of river beds led to the fast depletion of this once abundant natural resource which actually took millions of years to attain its present form.
Excessive in-stream sand and gravel mining caused the dipping of water levels, degradation of rivers and river bank erosion. In many regions of the world, the extraction of sand and gravel is heavily taxed or banned completely to preserve remaining deposits.
Sand researchers world over were in continuous research to find an alternative for river sand, who zeroed in on manufactured sand or popularly known as M-sand.
Experts vouch that manufactured sand is not only a viable alternative to natural sand, but is superior in many ways. River sand is not graded properly and has excessive silt and organic impurities like coal, bones, shells, mica and silt and these can be detrimental to durability of steel and concrete, whereas manufactured sand has no silt or organic impurities.
Manufacturing of sand involves three stages, crushing of stones into aggregates by VSI, which is fed into a rotopactor to crush aggregate into sand in required grain sizes. Screening is done to eliminate dust particles and washing of sand eliminates very fine particles present within. The end product will satisfy all the requirements of IS:383 Zone II and can be used in concrete and construction.
Only, sand manufactured by VSI crusher and rotopactor is cubical and angular in shape. Sand made by other types of machines is found to be flaky and contain higher percentage of dust. Generally, manufactured sand is classified as Zone I, Zone II, Zone III and Zone IV (i.e. coarser to finer). There is sieve designation for each zone. Gradation is made in accord with the usage of the sand. There are testing sieves, consists of 4.75mm, 2.36mm, 1.183mm, 600microns, 300 microns and 150 microns.
Zone I sand is used for concreting while sands Zone II to IV are used for plastering. Tests have revealed that the characteristics of mortars and concrete using M-sand as fine aggregate are superior when compared to the natural sand as fine aggregate.
Pune-Mumbai expressway was completely built using manufactured sand. Runway of Thiruvananthapuram International airport, new flyover at Thakaraparambu and Palayam underpass at Thiruvananthapuram are also learnt to have constructed using M-sand.
Manufactured sand is a 100 per cent substitute for river sand, says Dr. Kuncheria P. Isaac, vice chancellor of Kerala Technical University. Two factors determine the quality of manufactured sand; size and shape. The sand particles should not be flaky and elongated as that may make the mix weak and affect the durability and strength of the concrete.
Rocks with more mica content are considered not suitable for manufacturing sand. The rocks present in our state are of the required quality, says Dr. Kuncheria. Over the years the availability of rocks also may get depleted and may get replaced by another material like gypsum, but as of now we have ample resources.
It would be difficult for a layman to distinguish manufactured sand as they are usually bluffed by masons or contractors with rock sand sprinkled with water. Rock sand is the residue dust formed during the stone crushing. Chances of developing early cracks and weakening are more as it is devoid of required grades and not undergone adequate cleaning.
Sand quality can be tested at the labs of any of the engineering colleges present across the State, says Dr. Kuncheria.
Mortars with M-sand exhibit better workability and water retention characteristics, confirms a study held at IIS, Bangalore. For 1:4 cement mortar, to achieve 100 per cent flow the water cement ratio required is about 0.88 using M-sand whereas 1.20 using river sand. Lower water-cement ratio results in better characteristics of mortars in hardened state.
Government should standardise the production of manufactured sand, says Joseph Jacob, director, POABS Group, pioneers in quality manufactured sand.
Listing of quality manufacturers and grading the system will ensure the quality of m-sand and reduce the supply of inferior quality product in the market.
It is also essential to create awareness on the use of M-sand for construction purpose and scarcity of river sand, says Joseph.
Manufactured sand is a 100 % substitute for river sand, says
Kuncheria P. Isaac, VC, Kerala Technical University.
