The demand for sand as a building material has steadily increased all around the word due to increasing construction activities, as well as the scale and number of infrastructure projects. Scarcity of good quality natural river sand due to depletion of resources and restriction of river bed mining by constitutional bodies due to environmental conditions – has led to the wide scale adoption of Manufactured Sand (M Sand). M Sand is manufactured by the crushing of hard granite stone into cubical shaped particles with grounded edges and then washed and graded into a construction material. During application of M Sand – it is imperative to check that the composition of the particles adheres to specifications in order to ensure the durability and sustainability of the R.C.C structure throughout its service life.
Sand is defined as a loose granular substance, typically appearing as pale yellowish, brown, whitish or reddish, produced from the erosion of Siliceous and other rocks and is a major constituent of beaches, river beds, seabeds and deserts by sedimentation. Similarly, M. Sand or stone crushed sand may also be defined as a loose granular material, produced from the disintegration of rocks. M.Sand consists of particles smaller than gravel but coarser than silt and is used in mortar, glass, abrasives and foundry mould. As such sand is a naturally occurring granular sediment material composed of finally divided rock and mineral particles while M. Sand is a crushed rock material composed of finally divided rock and mineral.
With the world-wide decline in the availability of naturally occurring sands due to environmental pressures, the adoption of alternate, reliable materials such as M. Sand is increasing. Additionally, in countries like in India, constitutional bodies have imposed bans on river sand mining – leading to the further increase in the adoption of alternate materials.
Presently the use of M Sand in major construction projects around the world is steadily increasing as more construction technicians insist on its use. This increase in adoption of M Sand is attributed to the manufacturing process as it enables the consistent gradation of the particles while also reducing impurities to zero.
Deficiencies of River Sand
Civil engineers, architects, builders and contractors collectively believe and agree that presently available river sand is deficient in many respects. For instance, it contains high amounts of silt and fine particles that damage the quality and impact the life of a structure. Grading limits are also difficult to maintain within the required fitness modulus as the irregularity of the particle sizes of river sands greatly varies.
Additionally, river sand may contain other impurities like coal, lignite, bones, shells, mica, silt and other organic compounds – brought by the flow of river water – which makes the sand inferior for the use in cement concrete.
The composition of sand is highly variable depending on the local rock sources and erosion conditions. The most common constituent of sand is silicon dioxide abrasive particles (SiO2). Usually it is in the form of quartzite or decomposed sand stone in the form of siliceous rock. The fine aggregate rock sand or crushed stone sand should have less than 4.75 mm in size and fine aggregate below 600-micron, content usually 35% to 45% by mass of the total aggregate.
Indian standard IS 383 classifies in to Natural Sand which observed the Fine aggregate sand resulting from the natural disintegration due to erosion of rock, has been deposited by means of stream or glacial agencies as river sand. As such the so-called crushed stone sand or M. sand, is the fine aggregate sand obtained by crushing and processing natural hard stone.
The standard terminology used for sand is fine aggregate. The composition of sand is highly variable, depending on the local rocks, but the most common constituent of sand is Silica (silicon dioxide or SiO2). Fine aggregate is less than 4.75 mm or 4750 micron in size and the fine aggregate (F.A.) contents usually 35% to 45 % by mass or volume of total aggregate.
Deleterious Materials in Sand
Aggregate sand consists of naturally occurring, crushed or uncrushed stones, gravel and sand combined. These contents must be hard, strong, dense, durable, clear and free from veins and adherent coating. They should be free from injurious amounts of disintegrated pieces of alkali, vegetable matter and other deleterious substances. As far as possible the flaky and elongated pieces should be avoided. Aggregate sand should not contain any deleterious harmful materials such as coal, lignite, mica, muscovite, vermiculite, biotite, pyrites, shale or similar laminated material, clay, alkali, soft friable fragments, sea shells and organic impurities in such quantity which affect the strength and durability of the concrete.
The sand to be used should not contain any such material liable to attack the steel reinforcement. The maximum quantity of deleterious materials should not exceed the limits shown below in the table1.
However, engineers in charge of projects often relax some of the limits at his/her discretion resulting in the needed for further tests to achieve satisfactory performance.
The presence of mica (or muscovite, vermiculite, biotite) in the fine aggregate has been found to reduce considerably the durability and compressive strength of concrete. Further investigations are underway to observe the deleterious effects of mica.
General Sand, Requirements
- All the particles of the sand should have higher strength.
- Edges of the particles should be grounded with smooth surface texture.
- There should not be any organic impurities in the sand.
- In manufactured sand the permissible limit of micro fines below 75 microns should not be more than 15% but always kept below it.
- Particles size in general should remain within the 150 microns to 4750 Micron limits.
- Silt in crushed sand should not be more than 2% & other impurities should also not exceed the permissible limit.
- The sand particles must be abrasive in nature and no particle should be soluble in water.
Quality Tests of Sand
Manufactured sand should adhere to the standards of the BSI codes and must undergo the following quality tests
- Sieve analysis test of sizes of sand particles and percentage of total fine aggregate in required gradation.
- Optical microscopic study to check the particle shape grounded and surface texture – which should be smooth.
- Slump test by slump cone method to measure the cubical shape of the particle.
- Cube test for compressive strength.
- Test for silt and clay.
Grading proportion of Aggregate must be maintained
M Sand produced and processed by proper machines can be a better substitute of river sand. For this, the M Sand must be of proper gradation as per IS 383. The sand should have its particles from 150 microns to 4750 microns or 4.75 mm in a proper proportion as shown below in table 2. When the fine particles are in proper proportion then the sand will have fewer voids for the cement to occupy. Blow in table 2 four zones I, II, III & IV zone grading guiding proper distribution of particles are shown for the proper grading and distribution in M Sand.
It shall be described as fine aggregate, Grading Zones I, II, III, and IV. Where the grading falls outside the limits of any particular grading zone of sieves, other than IS sieve 600 microns by a total amount not exceeding 5 percent, then it shall be regarded as falling within the grading zone. This tolerance shall not be applied to the percentage of passing the IS sieve 600 microns or to the percentage passing any other sieve size on the coarse limit of grading zone ‘I’ or the finer limit of grading zone ‘IV’.
It is recommended that the fine aggregate confirming to grading zone IV should not be used in reinforced concrete unless tested for suitability of proposed mix proportion.
The percentage of passing the sand through sieve 600 microns will decide the grading zone of the sand. As grading zone I is a coarse sand and zone II, zone III and zone IV are fine sand shown in the above grading table.
Fineness Modulus (FM) of the Sand
Fineness Modulus (FM) is an index of fineness of an aggregate. FM is required for the preparation of mixed design as the sand gradation has largest effect on workability. Fine sand (Low FM) has much higher paste effect with good workability.
The Fineness modulus is obtained by adding the sum of the cumulative percentage of sand retained on each specified series of sieve, and divided by 100 as shown in the above table. As in table 3 the addition of cumulative retention percentage in zone I is 400 in first case and 271 in second case so these cumulative additions are divided by 100, obtaining the fineness modulus of grading zone I to be 4.00 and 2.71 respectively. Similarly, the FM of other zones are calculated as shown above in table 3.
Alternatives of river sand
- Manufactured crushed stone sand
- Silica sand
- Fly Ash / Bottom Ash / Pond Ash
- Sea sand
- Crushed waste glass sand
- Dunes sand of desert
Manufactured crushed stone sand
Manufactured sand is popularly known by several names such as crushed sand, green sand, Rock sand, Ultra Mod sand, Poabs sand, Robo sand, Barmac sand, Pozzolan sand etc. Indian standard IS 383-1970 reaffirmed 2007 named the manufacture sand as ‘crushed stone sand’.
Crushed stone sand is produced by first crushing the boulders in a primary crusher and then feeding the aggregates (small sized stone gravel) in a vertical shaft impactor (VSI) machine specially designed for sand making. The resulting product may further be crushed in secondary crusher to obtain gravel sand. Further the required gradation of the sand produced by screening the product and removing its unwanted fine below 75 microns either by washing the sand or in dry process by blowing the fines with a system of air blower mechanism.
Manufactured sand eliminates the silt fines by washing having gradation of IS 383 as desired with no any other impurities is a better alternate of river sand preferred by civil engineers and contractors.
Silica sand is a better alternate to river sand. It is the product of quartzite hard stone. It has balanced physical and chemical properties for construction uses. Silica sand can withstand any aggressive environmental and climatic conditions. It has enhanced durability, greater strength and overall economy.
Fineness modulus of fine aggregate is required for the mix design of concrete. Lower the fineness of sand, higher will be its workability. The grading zone of sand is defined by the percentage of sand passing through a 600-micron sieve.
Bundi silica sand, Rajasthan is a company that has developed a reputation in this field. Nearly a thousand tons of sand per day is distributed to valued projects in the Kota region of the State. Bundi silica sand is a washed sand free of silt, dust, clay aggregates and all other deficiencies.
The grading and fine modulus (FM) of the products are calculated below in the table as 2.79, 2.56 and 2.37 respectively shown below.
Other Silica Deposits
The other measure deposit of silica sand mine is Shivalica silica mine near Bayana, district Bhartpur Rajasthan producing construction grade silica sand. The gradation of the sand is best suitable for construction projects as required under IS 383 as fine aggregates grading zones. On analyses, it’s FM of distribution grading of particles observed 2.86 & 2.79 as zone of fine aggregate. Presently this mine is supplying nearly 800 tons per day to meet out the demand of nearby cities, Delhi- Faridabad, Noida, Mathura, Aligarh, BulandShahar. There are other deposits of silica sand at many places in India which are producing glass grade sand. The low-grade silica sand containing of higher percentage of iron, not suitable to glass & foundry products are processed for the M Sand grading and commercially used the over burden containing inferior Silica to meet out the demand of the country and to make the working eco-friendly.
The Stone grit crusher used for producing grit and ballast produce the screened fine sand below 4.75 mm containing fine dust and clay. It may be used alternate of river sand after processing. The micro fine sand and clay impurities are removed by putting a sand washing unit to utilize the screened waste sand, below4.75mm. At nearby Jaipur a propel Industries PLD product ‘Sand Washer’ unit is in operation to wash the grit crusher’s produced waste sand to remove clay & fines and dispatching the so produces M Sand daily nearly 1200 tones to meet out the demand of Jaipur and Delhi cities.
Fly Ash/Bottom Ash/pond Ash
These three types of ash namely Fly ash, bottom ash and pond ash are produced by thermal plants. Fly ash is collected by the mechanical or electrostatic precipitators from the flue gases of the power plants. The Bottom ash is collected from the bottom of the boilers of the plant. Pond ash is a by- product of thermal plants. It is considered as the waste product of the thermal plant. Its disposal is a big problem. It requires lot of disposal area. The fly ash and bottom ash are mixed together and transported in the form of slurry in a lagoon to store. This deposit is called pond ash. This ash can be used as an alternate of river sand. The strength of concrete increased with respect to the percentage of slag added by weight in the fine aggregate up to 40% of copper slag.
Sea sand if processed in proper ways may be proved a better substitute of river sand. Though it has many challenges to make it suitable for concrete. The sea sand contains higher percentage of chlorides which increase corrosion in steel. It’s higher contents of shales make the sand finer than river sand which decreases the strength of the concrete. However, if proper filtration and proper washing is done to remove chlorides and fines then the sand can be used effectively for construction Industry.
The sand taken from the off-shore area has lower salinity presence than the sand of beaches. After studies by the national building research organization sea sand has been found as a sustainable alternate to river sand. Countries such as UK, Netherland, India, Seychelles Island, Singapore and Japan are already using sea sand for construction. Japan and Great Britain produce two-thirds of the world’s marine aggregate. Offshore sand gravel mining has become a 200 million USD industry.
Crushed Waste Glass sand
Glass is made of silica sand. When the waste glass is crushed, it converts into its raw material silica sand. It is then graded by screening through the specified IS sieve. It has the same chemical composition of silicon dioxide SiO2… As described silica sand is a better alternate of River Sand.
Dune sand in desert
In desert areas sand dunes are formed due to weathering actions from air storms, and other naturally occurring phenomena. The weathering causes erosion of sand particles which is carried by the air and settles down into sand dunes. Further to filtration and processing this sand may be a sustainable alternate to river sand.
Creditability of manufactured Sand
Crushed stone sand or silica sand has the following advantages when used for construction:
- Greater Durability: Manufactured sand has balanced physical and chemical properties which can withstand any aggressive environmental and climatic conditions.
- Higher Strength: The superior shape of particle’s grounded edge, smooth surface texture and proper gradation leads to chemically stable parameters – providing greater durability and higher strength to the concrete.
- Greater Workability: The crusher dust is flaky and angular in shape which is troublesome to work with. There will be no plasticity in the mortar which makes it difficult even for masonry work. However, the product of VSI machines provides cubical shaped particles with grounded edge and superior gradation which gives good plasticity to mortar providing excellent workability.
- Economy: Uses of manufactured sand reduce cost. Since unlike river sand, it does not contain impurities and wastage will be nil. In the international construction scenario, no river sand is used at all. Additionally, the use of manufactured sand also ensures a significant reduction in the amount of cement used in concrete.
Manufactured sand proves to be the best alternative to river sand. Mining of river bed to get river sand will lead to environmental disaster. The natural beauty of the river destroyed, Ground water level, lowered, create water scarcity and put threat to the safety of bridges and dams. So the Government has also come forward to preserve the rivers by “banning mining of river bed”.
The aim of this article is to promote the use of manufactured sand by listing out the advantages and technical specifications; including guide lines to manufacture stone crushed sand or silica sand. This product must be made available in every district of every state to meet out the demand of the country. The grit crusher sand after processing to remove fines and clay by means of auto mechanical washing or by air blowing in close circuit will be a best suitable and economical M. Sand product alternate of River sand.
The thoughts and opinions expressed in the article are author’s own who is a retired ‘CEO’ of mines from Bundi Silica Group.
- Elavenil S. Nagabhushana Rao, Radhakrishan, R and Hariharan. K Journal of Current science, vol.7,No 1,pp19-24.
- Manufactured sand by Dr. Aswath M U, Professor and Head, Department of Civil Engineering Bangalore institute of Technology.
- Manufactured Sand, A Solution and Alternative to River Sand and in Concrete manufacturing — Dr. S. Elavenil, Professor in civil Engg., S.R.M. University Kattankulathur India, B. Vijaya, Assistant professor in civil Engg., M. G.R. Educational & Research Institute University, Chennai, India.
- COM, Thu., February 15,2018, the daily of Jammu and Kasmir.
Chand Chandna: Retired as CEO Mines from Bundi Silica Group of mines after working there for24years. Overallexperience as a general manager in the field for 50 years. Graduated in mining from Institution of Engineers. Did first class mine Managers’ certificate, Surveyors certificate and Chartered Engineer.Presented papers in various seminars and published more than 45 papers & innovative worksin different journals. Author of two published Books named: “Learners vision for Blasting & Mining Operations” and “Resonant of Mining Questions”. Received Lifetime Achievement Award from the Indian Mining & Engineering Journal for outstanding contribution in the field of Mining Engineering, Training & Development. Inventor of innovative Jackhammer Wet Drilling process and Dust extractor for Dry Jackhammer drilling to control silicosis. Prototypes for both inventions have been demoed in the field in multiple states and appreciated.