With river sand becoming scarce and being sold at a premium following the Madras High Court restrictions on sand mining in rivers Cauvery and Tamirabharani, the need to find an alternative concrete aggregate material to river sand in construction works has assumed greater importance now .
Engineers and specialists have come out with their own ideas to minimise the use of river sand and use recent innovations such as M-Sand (manufactured sand), robot silica or sand, stone crusher dust, treated and sieved silt removed from reservoirs as well as dams besides sand from other water bodies.
The most preferred alternative to river sand is the M-Sand got through processing the blue metal quarry dust. Fine and uniform granulation of quarry dust by floating it through pressurised water shower leading to reduction of impurities gives us M-Sand.
The production of robot silica or sand, got through another method of processing gravel and soil by cleansing the material of clay and other impurities, providing uniform granulation to the processed material, is at a nascent stage and might take some more years to gain wider acceptability.
But both M-Sand and robot sand, due to their processing, is dearer when compared to river sand during normal availability periods in regular markets. Industry watchers point out that the presence of more than 500 blue metal crushers in the Karur-Tirupur-Coimbatore-Salem belt would easily facilitate production of M-Sand in huge quantities to meet public requirements of the region.
However, structural engineers and reputed builders whom The Hindu spoke to showed thumbs down to use of M-Sand and robot sand in concrete applications citing test failures for load bearing strength and durability for any mixture classification.
Particularly for concrete roof only river sand must be used to achieve the general required compression strength of 28-30 Kilogram Newton per square mm, they say adding any admixture aggregate containing quarry dust and M-sand might just fail to pass muster.
Then there are experts who propound the guided exploitation of silt gathered at the dam and reservoir sites across the State and remaining uncleared for decades.
“The silt at the major dams could be dredged, suitably sieved and processed to find applications instead of river sand. Thereby the pressure on river sand might come down drastically while dams and reservoirs could regain their lost volume and farmers and public might get innumerable benefits. All that could happen if the State government studies the situation and directs removal of silt of all dams and reservoirs,’’ notes former PWD Special Chief Engineer A. Veerappan.
The State government and the PWD need not spend a single pie on the effort and contractors could be engaged for dredging the dam sites and clearing the silt which simultaneously increases their dead storage capacity, he observes.
There are hundreds of PWD tanks and ponds besides thousands of water bodies under the control of the panchayats across the State that have gradually got shrunk due to accumulation of silt over the years.
They could be desilted and while the top layer of the removed silt could used as manure in agricultural applications the bottom strata could be used for filling works, retired PWD Superintending Engineer S.Natarajan opines.
However, structural engineers and builders point out that sand gradation must conform to BIS 383 Table 15 and BIS 10232 standards apart from which the sieved sand must conform to Zone II classification for concrete works.
There should not be any deleterious material covering sand granule for more than three per cent, passing the 75 micron sieve analysis process, they pinpoint when speaking about alternatives to river sand in concrete and plaster applications, be it for private or public use.
Sieved silt collected from ponds as well as dam sites, and conforming to such standards, could be used instead of river sand for mortar and plastering applications only in select cases under specialised care, some others say.
Presence of over 500 blue metal crushers in the Karur-Tirupur-Coimbatore-Salem belt will facilitate production of
M-Sand in huge quantities: industry watchers