River Sand or the Bajri we refer to the sand that is used in the Construction purposes. Today it is the most required material for the construction industry, is being widely used and utilized all over the world. The question arises is that from where does this BAJRI comes? The River sand is the Sand is deposited in river beds, so the sand which we are using is actually from the dry river or from the banks of the river. Presently in states like Maharashtra, Rajasthan, Uttar Pradesh and Karnataka sand supply are becoming a mafia because sand supplies are limited. River waters are now behind dams due to which the sand does not get continually replenished like before. Riverine habitats get destroyed as mechanical dredgers are used.
Have we ever thought of the consequences for this?
How does it impact our Environment – Instream mining can have other costly effects beyond the immediate mine sites. Many hectares of fertile streamside land are lost annually, as well as valuable timber resources and wildlife habitats in the riparian areas. Degraded stream habitats result in loss of fisheries productivity, biodiversity, and recreational potential. Severely degraded channels may lower land and aesthetic values.
All species require specific habitat conditions to ensure long-term survival. Native species in streams are uniquely adapted to the habitat conditions that existed before humans began large-scale alterations. These have caused major habitat disruptions that favoured some species over others and caused overall declines in biological diversity and productivity. In most streams and rivers, habitat quality is strongly linked to the stability of channel beds and banks. Unstable stream channels are inhospitable to most aquatic species.
Factors that increase or decrease sediment supply often destabilize beds and banks and result in dramatic channel readjustments. For example, human activities that accelerate stream bank erosion, such as riparian forest clearing or instream mining, cause stream banks to become net sources of sediment that often have severe consequences for aquatic species. Anthropogenic activities that artificially lower stream bed elevation cause bed instabilities that result in a net release of sediment in the local vicinity. Unstable sediments simplify and, therefore, degrade stream habitats for many aquatic species. Few species benefit from these effects.
The most important effects of instream sand mining on aquatic habitats are bed degradation and sedimentation, which can have substantial negative effects on aquatic life. The stability of sand-bed and gravel-bed streams depends on a delicate balance between streamflow, sediment supplied from the watershed, and channel form. Mining-induced changes in sediment supply and channel form disrupt channel and habitat development processes. Furthermore, the movement of unstable substrates results in downstream sedimentation of habitats. The affected distance depends on the intensity of mining, particles sizes, stream flows, and channel morphology.
The complete removal of vegetation and destruction of the soil profile destroys habitat both above and below the ground as well as within the aquatic ecosystem, resulting in the reduction in fauna populations.
Channel widening causes shallowing of the streambed, producing the braided flow or subsurface integral flow in riffle areas, hindering the movement of fishes between pools. Channel reaches become more uniformly shallow as deep pools fill with gravel and other sediments, reducing habitat complexity, riffle-pool structure, and numbers of large predatory fishes.
Apart from threatening bridges, sand mining transforms the riverbeds into large and deep pits; as a result, the groundwater table drops leaving the drinking water wells on the embankments of these rivers dry. Bed degradation from in-stream mining lowers the elevation of streamflow and the floodplain water table which in turn can eliminate water table-dependent woody vegetation in riparian areas, and decrease wetted periods in riparian wetlands. For locations close to the sea, saline water may intrude into the fresh water body.
The value of the construction industry grew at a staggering rate of 15.10 per cent annually even in the economic slowdown and has contributed to 7.5-8.5 per cent of the country’s GDP (at current prices) for the past eight years. Thus, it is becoming increasingly embarrassing for people like me who talk about greening the industry to have no practical answer to this very critical question. The bigger question is: does the scientific community have the answer? And the answer I found to my delight is: yes, they do.
So let us see what are the alternatives for Sand that we can consider for construction purposes :
Presently, worldwide, about 33 million tonnes of copper slag is generated annually with India contributing 6-6.5 million tonnes. Khalifa S Al Jabri of Oman in his findings published in internationally refereed journals such as Cement and Concrete Composites and Construction and Building Materials in 2006 recommends that 50 per cent copper slag can be used as a replacement for sand in order to obtain concrete with good strength and durability requirements. Back in India, a study carried out by the Central Road Research Institute (CRRI) has also shown that copper slag can be used as a partial replacement for sand as fine aggregate in concrete up to 40 per cent in pavement grade concrete without any loss of cohesiveness and the compressive and flexural strength of such concretes is about 20 per cent higher than that of conventional cement concrete of the same grade.
Granulated blast furnace slag
According to the report of the Working Group on Cement Industry for the 12th five-year plan, around 10 million tonnes of blast furnace slag is currently being generated in the country from the iron and steel industry. In of the studies about this states that the data obtained from his research shows that the compressive strength of cement mortar increases as the replacement level of granulated blast furnace slag (GBFS) increases. He further concludes that from the test results it is clear that GBFS sand can be used as an alternative to natural sand from the point of view of strength. Use of GBFS up to 75 per cent can be recommended of sand.
India is currently producing in excess of 100 million tonnes of coal ash. Out of the total ash produced in any thermal power plant, approximately 15 -20 per cent is bottom ash and the rest is fly ash. Fly ash has found many takers but bottom ash still continues to pollute the environment with no safe disposal mechanism on offer. In of the studies about this states that the mechanical properties of special concrete made with 30 per cent replacement of natural sand with washed bottom ash by weight has an optimum usage in concrete in order to get a favourable strength and good strength development pattern over the increment ages.
About 20 to 25 per cent of the total production in each crusher unit is left out as the waste material-quarry dust. In of the studies about this states that the ideal percentage of the replacement of sand with quarry dust is 55 per cent to 75 per cent in case of compressive strength. He further says that if combined with fly ash (another industrial waste), 100 per cent replacement of sand can be achieved. The use of fly ash in concrete is desirable because of benefits such as useful disposal of a byproduct, increased workability, reduction of cement consumption, increased sulfate resistance, increased resistance to alkali-silica reaction and decreased permeability. However, the use of fly ash leads to a reduction in the early strength of concrete. Therefore, the concurrent use of quarry dust and fly ash in concrete will lead to the benefits of using such materials being added and some of the undesirable effects being negated.
India ranks fourth in terms of total foundry production (7.8 million tonnes) according to the 42nd Census of World Casting Production of 2007. Foundry sand which is very high in silica is regularly discarded by the metal industry. Currently, there is no mechanism for its disposal, but international studies say that up to 30 per cent of foundry sand can be utilized for the economical and sustainable development of concrete.
Construction and demolition waste
There is no documented quantification of the amount of construction and demolition (C&D) waste being generated in India. Municipal Corporation of Delhi says it is collecting 4,000 tonnes of C&D waste daily from the city which amounts to almost 1.5 million tonnes of waste annually in the city of Delhi alone. Even if we discount all the waste which is illegally dumped around the city, 1.5 million of C&D waste if recycled can significantly substitute demand for natural sand by Delhi. Recycled sand and aggregate from C&D waste is said to have 10-15 per cent lesser strength, than normal concrete and can be safely used in non-structural applications like flooring and filling. Delhi already has a recycling unit in place and plans to open more to handle its disposal problem.
Benefits of Alternatives–
Size, shape, texture plays an important role in the workability of concrete. With more surface area of sand, the demand for cement and water increases to bond the sand with coarse aggregates.
The control over these physical properties of manufacturing sand makes the concrete require less amount of water and provide higher workable concrete. The less use of water also helps in increasing the strength of concrete, less effort for mixing and placement of concrete, and thus increases the productivity of construction activities at the site.
Construction defects during placement and post-concreting such as segregation, bleeding, honeycombing, voids and capillarity in concrete get reduced by the use of M-Sand as it has optimum initial and final setting time as well as excellent fineness.
As discussed above, since the usage of M-Sand has increased durability, higher strength, reduction in segregation, permeability, increased workability, decreased post-concrete defects, it proves to be economical as a construction material replacing river sand. It can also save the transportation cost of river sand in many cases.
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