One of the reasons why construction projects have slowed down in recent months is the inadequate supply of sand. This, plus the accompanying hike in the price of sand has hit builders really hard. With only 60 per cent of the required sand available, the work force on construction sites has also reduced to 30-40 per cent. The government has also imposed a ban on sand mining because indiscriminate mining poses a major environmental threat and is ravaging our rivers. The only solution to prevent illegal sand mining and reduce the demand for sand is to explore alternate material.
M-Sand
Manufactured Sand or M-Sand is the immediate substitute for river sand available today. It is obtained by crushing hard rock such as granite. Unless manufactured correctly, the aggregate could become flaky and elongated, which results in the concrete becoming harsh and difficult to work with. The presence of clay and silt should be avoided, as it delays the setting of cement. M-Sand is produced in large quantities in the Karur-Tirupur-Coimbatore-Salem belt, where there are several blue metal crushers. However, M-Sand is more expensive than river sand.
Copper slag
Copper slag is a by-product in the manufacture of copper, and about 24.6 million tonnes of slag are generated from the copper industry globally. Adding copper slag makes concrete substantially more workable due to the low water absorption and glassy surface of copper slag. It possesses mechanical and chemical characteristics that make the material well-qualified for use in concrete as a partial replacement for sand. The recommended replacement ratio is 40 per cent of copper slag.
GBFS
Granulated blast furnace slag or GBFS is a by-product obtained during the manufacture of iron in blast furnaces in integrated steel plants. This can be effectively used to replace river sand. Many developed countries have been using it as a sand substitute in concrete constructions. It does not contain chlorides, organic impurities, silt, clay or other material that could affect the quality or durability of concrete. It can be utilised partially as an alternative for natural sand in mortar applications.
Use of GBFS up to 50 per cent is recommended. The Karnataka State Pollution Control Board (KSPCB) is spearheading a campaign along with infrastructure industries, technologists and engineers to utilise the millions of tonnes of unused GBFS as a least-cost replacement for natural sand.
Pond ash
Pond ash is a by-product of thermal power plants. It contains a significant amount of relatively coarse particles. Unused fly ash and bottom ash (residue collected at the bottom of the furnace) are mixed in slurry form and deposited in ponds, creating pond ash.
Sea sand
Use of sea sand requires careful filtering and washing, as untreated sea sand contains high levels of chloride salts that will corrode steel reinforcements and result in distressed buildings. It also contains a high percentage of shale and is finer than river sand. Properly washed and treated sea sand can be used to good effect.
Filtered sand
Filtered sand is prepared by excavating the earth and washing it with water from a nearby source, poured with force from a pipe. The silt slurry is allowed to flow down and the separated top layer called filter sand is stacked. This filter sand is sticky and very different from river sand. Buildings constructed using such 'filtered sand' may last for 8-10 years only.
As its use increases, many monitoring authorities are raising concerns over the material.
Powdered glass
Sheet glass waste is generated in large volumes and using it in concrete construction is advantageous, as the production cost of concrete will go down. Coloured sheet glass is packed as waste and used in land filling. The optimum replacement level is 10 per cent.
The writer is Professor & Head, Department of Civil Engineering, SRM University, Ramapuram Campus. Mail her at hod.civil@rmp.srmuniv.ac.in
