River sand is a widely used construction material all over the world, especially in the production of concrete, cement-sand mortar and concrete blocks. Various Government, Non Governmental Organisations and Research Institutes are striving to identify alternative materials to supplement river sand. There is a strong need for research on river sand substitutes for concrete production and cement sand mortar production. The research should aim to identify suitable river sand substitutes for practical applications in the local construction industry and also focus on formulating practical solutions for using river sand substitutes. The development of standards / specifications and incorporating in the BIS codes will reduce the pressure on using river sand. The standards and codal specifications will assist to select and use the alternatives by the various stake holders. Quality certification of the alternate aggregates and quality certification of the concrete manufacturing process plays a vital role in ensuring the durability of the concrete.
Researchers are in continuous search for the alternatives to sand. Fine aggregate is one of the important constituents of concrete. River sand is becoming a scarce material. Sand mining from rivers has become objectionably excessive. It has reached a stage where it is killing all our rivers day by day. So sand mining has to be discouraged so as to save the rivers. As natural sand deposits become depleted near some areas of metropolitan growth, the use of alternatives to sands as a replacement fine aggregate in concrete is receiving increased attention. The National Green Tribunal also imposed ban and restrictions on the sand mining.
Some of the Alternatives to River Sand are
– Manufactured Sand
– Fly Ash/ Bottom Ash/Pond Ash
– Copper Slag – Filtered Sand
– Sea Sand, Slag Sand
– Crushed Waste Glass
– Recycled Aggregate/C&D Waste Aggregate etc..
Manufactured sand is popularly known by several names such as Crushed sand, Rock sand, Green sand, UltraMod Sand, Robo sand, Poabs sand, Barmac sand, Pozzolan sand etc. IS 383-1970 (Reaffirmed 2007) recognizes manufacture sand as ‘Crushed Stone Sand’.
Crushed stone sand is produced by crushing boulders. Manufactured sand is produced by rock-on-rock or rock-on-metal Vertical Shaft Impactor (VSI) in which the process that produced alluvial deposits is closely simulated. Particle size reduction and achieving equidimensional shape is critical to get desired properties. If rock is crushed in compression lot of inherent properties exhibited by natural river sand are lost. If proper technique of manufacturing is not adopted aggregates are bound to become flaky and elongated. Improvements to sand by way of washing, grading and blending may have to be done before use at the consumer end. In case of manufactured sand all the processes mentioned above can be done at manufacturing plant itself and controls are much better in producing quality fine aggregates.
Fine aggregates manufactured sand proposed to be used shall be produced from a Vertical Shaft Impact (VSI) crushers and shall conform to the requirements of Zone-II (in most of the cases) as per IS 383-1970 (Reaffirmed in 2007) and particles finer than 75 µm shall not exceed 15 %. Special efforts on the part of M-sand manufacturers (such as washing of sand by water or dry washing by air) is required to restrict particles finer than 75 µm to 15%. The global trend is to utilize dry classification solutions to produce manufactured sand. The dry separation process separates fine and coarse particles. This allows a reduced percentage of super fines in manufactured sand, thereby meeting specifications and achieving quality products.
M-sand can also be used for making masonry mortar and shall conform to the requirements of IS 2116-1980 (Reaffirmed 1998) – “Specification of sand for Masonry mortars”.
Issues and General Requirements of Manufactured Sand
The Civil engineers, Architects, Builders, and Contractors agree that the river sand, which is available today, is deficient in many respects. It does content very high silt fine particles (as in case of Filter sand). Presence of other impurities such as coal, bones, shells, mica and silt etc makes it inferior for the use in cement concrete. The decay of these materials, due to weathering effect, shortens the life of the concrete.
Now-a-days, the Government have put ban on lifting sand from River bed. Transportation of sand damages the roads. Removing sand from river bed impact the environment, as water table goes deeper & ultimately dry.
1. All the sand particles should have higher crushing strength
2. The surface texture of the particles should be smooth
3. The edges of the particles should be grounded
4. The ratio of fines below 600 microns in sand should not be less than 30%
5. There should not be any organic impurities
6. Silt in sand should not be more than 2%, for crushed sand
7. In manufactured sand the permissible limit of fines below 75 microns shall not exceed 15%
Manufactured Sand Quality
Manufactured Sand should adhere to the highest standards and must undergo the following quality tests
1. Sieve analysis
2. Optical Microscopic Study to check the particle shape
3. Workability (slump test by slump cone method)
4. Cube test for compressive strength
5. Tests for Silt and clay
The artificial sand produced by proper machines can be a better substitute to river sand. The sand must be of proper gradation (it should have particles from 150 microns to 4.75 mm in proper proportion). When fine particles are in proper proportion, the sand will have fewer voids. The cement quantity required will be less. Such sand will be more economical. Demand for manufactured fine aggregates for making concrete is increasing day by day as river sand cannot meet the rising demand of construction sector. Natural river sand takes millions of years to form.
Technical Specifications for Sand as Per BIS:
The Indian Standard IS: 383; “Specification for Coarse and Fine Aggregates from Natural Sources for Concrete” covers the requirements for aggregates, crushed or uncrushed, derived from natural sources, such as river terraces and riverbeds, glacial deposits, rocks, boulders and gravels, for use in the production of concrete for normal structural purposes including mass concrete works.
Before choosing any alternative one should check the technical specifications as per the BIS codes. Sand is mainly used for the preparation of mortar and concrete. It is also required to manufacture the building blocks. The standard terminology used for sand is fine aggregate. We all know that sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand is silica (silicon dioxide, or Si O2), usually in the form of quartz. Fine Aggregate( Sand and/or crushed stone) are less than 4.75 mm in size and F.A. content usually 35% to 45% by mass or volume of total aggregate.
Aggregates shall comply with the requirements of IS 383. As far as possible, preference shall be given to natural aggregates. Other types of aggregates such as slag and crushed over burnt brick or tile, which may be found suitable with regard to strength, durability of concrete and freedom from harmful effects may be used for plain concrete members, but such aggregates should not contain more than 0.5 percent of sulphates as SO, and should not absorb more than 10 percent of their own mass of water.
IS:383 classifies sand in to; Natural Sand – Fine aggregate resulting from the natural disintegration of rock and which has been deposited by streams or glacial agencies, Crushed Stone Sand – Fine aggregate produced by crushing hard stone; and Crushed Gravel Sand – Fine aggregate produced by crushing natural gravel.
Quality of Aggregates
Aggregates shall consist of naturally occurring (crushed or uncrushed) stones, gravel and sand or combination thereof. They shall be hard, strong, dense, durable, clear and free from veins and adherent coating; and free from injurious amounts of disintegrated pieces, alkali, vegetable matter and other deleterious substances. As far as possible, flaky, scoriaceous and elongated pieces should be avoided.
Deleterious Materials -Aggregates shall not contain any harmful material such as pyrites, coal, lignite, mica, shale or similar laminated material, clay, alkali, soft fragments, sea shells and organic impurities in such quantity as to affect the strength or durability of the concrete.
Aggregates to be used for reinforced concrete shall not contain any material liable to attack the steel reinforcement. Aggregates which are chemically reactive with alkalies of cement are harmful as cracking of concrete may take place.
Limits of Deleterious Materials: The maximum quantity of deleterious materials shall not exceed the limits specified in Table 1 when tested in accordance with IS: 2386-1963. However, the engineer-in-charge at his discretion may relax some of the limits as a result of-some further tests and evidence of satisfactory performance of the aggregates.
Aggregate Crushing Value: The aggregate crushing value, when determined in accordance with IS: 2386 (Part IV)-1963 shall not exceed 45 percent for aggregate used for concrete other than for wearing surfaces, and 30 percent for concrete for wearing surfaces, such as runways, roads and pavements.
Aggregates Impact Value: As an alternative, the aggregate impact value may be determined in accordance with the method specified in IS: 2386 (Part IV)-1963. The aggregate impact value shall not exceed 45 percent by weight for aggregates used for concrete other than for wearing surfaces and 30 percent by weight for concrete for wearing surfaces, such as runways, roads and pavements.
Aggregate Abrasion Value: Unless otherwise agreed to between the purchaser and the supplier, the abrasion value of aggregates, when tested in accordance with the method specified in IS: 2386 (Part IV)-1963 using Los Angeles machine, shall not exceed the following values:
a) For aggregates to be used in concrete for wearing surfaces: 30 percent
b) For aggregates to be used in other concrete: 50 percent
Soundness of Aggregate: For concrete liable to be exposed, the action of frost, coarse and fine aggregates shall pass a sodium or magnesium sulphate accelerated soundness test specified in IS: 2386 (Part V)-1963, the limits being set by agreement between the purchaser and the supplier, except that aggregates failing in the accelerated soundness test may be used if they pass a specified freezing and thawing test satisfactory to the user. [Note: – As a general guide, it may be taken that the average loss of weight after 5 cycles shall not exceed the following:
a) For fine aggregate: 10 percent when tested with sodium sulphate (Na2 SO4), and 15 percent when tested with magnesium sulphate (Mg SO4)
b) For coarse aggregate 12 percent when tested with sodium sulphate (Na2 SO4), and 18 percent when tested with magnesium sulphate (Mg SO4)
NOTE 1 -The presence of mica in the fine aggregate has been found to reduce considerably the durability and compressive strength of concrete and further investigations are underway to determine the extent of the deleterious effect of mica. It is advisable, therefore, to investigate the mica content of fine aggregate and make suitable allowances for the possible reduction in the strength of concrete or mortar.
NOTE 2- The aggregate shall not contain harmful organic impurities [tested in accordance with IS: 2386 (Part II) – I963] in sufficient quantities to affect adversely the strength or durability of concrete. A fine aggregate which fails in the test organic impurities may be used, provided that, when tested for the effect of organic impurities on the strength of mortar, the relative strength at 7 and 28 days, reported accordance with 7 of IS : 2386 (Part VI )-1963 is not less than 95 percent.
Size and Grading of Aggregates
IS 383 defines Fine Aggregates as aggregate most of which passes 4.75-mm IS Sieve and contains only so much coarser material as permitted in cl.4.3. [Cl. 4.3 Fine Aggregates -The grading of fine aggregates, when determined as described in IS: 2386 (Part I)-1963 shall be within the limits given in Table 4 and shall be described as fine aggregates, Grading Zones I, II, III and IV. Where the grading falls outside the limits of any particular grading zone of sieves other than 600-micron IS Sieve by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone. This tolerance shall not be applied to percentage passing the 600-micron IS Sieve or to percentage passing any other sieve size on the coarse limit of Grading Zone I or the finer limit of Grading Zone IV.]
NOTE 1-For crushed stone sands, the permissible limit on 150-micron IS Sieve is increased to 20 percent. This does not affect the 5 percent allowance permitted in 4.3 applying to other sieve sizes.
NOTE 2 – Fine aggregate complying with the requirements of any grading zone in this table is suitable for concrete but the quality of concrete produced will depend upon a number of factors including proportions.
NOTE 3 – Where concrete of high strength and good durability is required, fine aggregate conforming to any one of the four grading zones may be used, but the concrete mix should be properly designed. As the fine aggregate grading becomes progressively finer, that is, from Grading Zones I to IV, the ratio of fine aggregate to coarse aggregate should be progressively reduced. The most suitable fine to coarse ratio to be used for any particular mix will, however, depend upon the actual grading, particle shape and surface texture of both fine and coarse aggregates.
NOTE 4- It is recommended that fine aggregate conforming to Grading Zone IV should not be used in reinforced concrete unless tests have been made to ascertain the suitability of proposed mix proportions.
The percentage passing 600µm sieve will decide the zone of the sand: Zone-I Coarse Sand; Zone-II; Zone-III and Zone-IV Fine Sand. Grading Limits can also be represented through a graph of sieve size on the x-axis and % passing on the Y-axis (Semi log sheet).
Fineness Modulus (FM): The result of aggregate sieve analysis is expressed by a number called Fineness Modulus. It is obtained by adding the sum of the cumulative percentages by mass of a sample aggregate retained on each of a specified series of sieves and dividing the sum by 100. The specified sieves are: 150 µm (No. 100), 300 µm (No. 50), 600 µm (No. 30), 1.18 mm (No. 16), 2.36 mm (No. 8), 4.75 mm (No. 4), 9.5 mm , 19.0 mm , 37.5 mm , 75 m , and 150 mm.
Fineness modulus = 283 ÷ 100 = 2.83
FM is an index of fineness of an aggregate. The fineness modulus of the fine aggregate is required for mix design since sand gradation has the largest effect on workability. Fine sand (low FM) has much higher effect paste requirements for good workability. It is computed by adding the cumulative percentages of aggregate retained on each of the specified series of sieves, and dividing the sum by 100 [smallest size sieve: No. 100 (150 µm)]. The higher the FM, the coarser is the aggregate.
Sampling and Testing
Sampling: The method of sampling shall be in accordance with IS: 2430-1969. The amount of material required for each test shall be as specified in the relevant method of test given in IS: 2386 (Part I)-1963 to IS: 2386 (Part VIII)-1963.
Testing: All tests shall be carried out as described in IS: 2386 (Part I)-1963 to IS: 2386 (Part VIII)-1963. Unless otherwise stated in the enquiry or order, duplicate tests shall be made in all cases and the results of both tests reported.
Information to be furnished by the Supplier:
Details of Information: When requested by the purchaser or his representative, the supplier shall provide the following particulars:
a) Source of supply, that is, precise location of source from where the materials were obtained
b) Trade group of principal rock type present
c) Physical characteristics
d) Presence of reactive minerals
e) Service history, if any. Subject to prior agreement, the supplier shall furnish such of the following additional information, when required by the purchaser:
f) Specific gravity, g) Bulk density, h) Moisture content
i) Absorption value
j) Aggregate crushing value or aggregate impact value
k) Abrasion value,
l) Flakiness-index, m) Elongation-index, n) 3 Presence of deleterious materials
o) k) Potential reactivity of aggregate
p) m) Soundness of aggregate
Manufactured sand has balanced physical and chemical properties that can withstand any aggressive environmental and climatic conditions as it has enhanced durability, greater strength and overall economy. Usage of manufactured sand can overcome the defects occurring in concrete such as honey combing, segregation, voids, capillary etc.
The superior shape, proper gradation of fines, smooth surface texture and consistency in production parameter of chemically stable sands provides greater durability and higher strength to concrete by overcoming deficiencies like segregation, bleeding, honey combing, voids and capillary.
The crusher dust is flaky and angular in shape which is trouble some in working. There is no plasticity in the mortar which makes it even difficult for the mason to work, whereas the cubical shape with grounded edge and superior gradation gives good plasticity to mortar providing excellent workability.
Offsets Construction Defects
Manufactured sand has optimum initial and final setting time as well as excellent fineness which will help to overcome the deficiencies of concrete such as segregation, bleeding, honeycombing, voids and capillary.
Usage of manufactured sand can drastically reduce the cost since like river sand, it does not contain impurities and wastage is NIL. In International Construction Scenario, no river sand is used at all, only sand is manufactured and used, which gives superior strength and its cubical shape ensures significant reduction in the cement used in the concrete
Manufactured sand is the only alternative to river sand. Dredging of river beds to get river sand will lead to environmental disaster like ground water depletion, water scarcity, threat to the safety of bridges, dams etc.
Beside with the Government contemplating ban on dredging of River beds to quarry river sand, as part of the growing concern for environment protection, manufacturing sand will be the only available option.
Keeping the demand in mind and all the technical specifications mentioned above, we need to use Manufactured Sand in all construction works. Many manufacturers are producing quality M Sand using latest technologies ensuring the quality as per BIS specifications at affordable costs compared to river sand. As natural sand deposits become depleted, the use of alternatives to sand as a replacement for fine aggregate such as Manufactured Sand is receiving increased attention.
Acknowledgement: The content of the paper is sourced from various organisations for knowledge dissemination. All logos and images are property of the respective owners listed in the references
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