INTRODUCTION:
SCREENERS companies near Dehradun and elsewhere have set up highly sophisticated as well as, eco-friendly screening and washing plants for the production of uncrushed (Shingle) coarse aggregates and coarse sand direct from river bed. These plants are producing and supplying uncrushed (Shingle) aggregates of sizes 40 mm, 20 mm, 12.5 mm and river coarse sand, which complies to the specifications of
IS : 383-19702.
SCREENERS companies near Dehradun and elsewhere have set up highly sophisticated as well as, eco-friendly screening and washing plants for the production of uncrushed (Shingle) coarse aggregates and coarse sand direct from river bed. These plants are producing and supplying uncrushed (Shingle) aggregates of sizes 40 mm, 20 mm, 12.5 mm and river coarse sand, which complies to the specifications of
IS : 383-19702.
Our construction sites, particularly Govt. Departments hesitates in the use of uncrushed coarse aggregate as so far they are being supplied to them direct from river bed or by manual sieving without washing them with water. Thus neither they are clean nor properly graded. This draw back is not with the uncrushed aggregates produces and supplied from SCREENERS modern plants with regular quality control. In this booklet the readers will find that when quality uncrushed aggregates are available not only economically but locally, our construction sites particularly Govt. Departments should not hesitate in the use of uncrushed aggregates from the river bed and save our environment, as crusher generate pollution. Further in all the Civil Engineering Codes uncrushed aggregates from river bed has been specified to be used in our all Civil Engineering Construction.
WHY SCREENERS RIVER BED UNCRUSHED AGGREGATES ARE TO BE USED IN MAKING CONCRETE?
According to SP: 23-19821 page 13 clause 2.2.1.2 as long as aggregates conform to the requirements of IS: 383 -19702 and concrete of satisfactory quality can be produced at an economical cost using the, both gravel/shingle (i.e. uncrushed) or crushed natural aggregate can be used for general concrete construction. It should be remembered, however, that in practice the aggregate available locally or within an economical distance has to be used, and this can generally produce satisfactory concrete, given an intelligent approach and sufficient care3.
WHY SCREENERS RIVER BED UNCRUSHED AGGREGATES ARE TO BE USED IN MAKING CONCRETE?
According to SP: 23-19821 page 13 clause 2.2.1.2 as long as aggregates conform to the requirements of IS: 383 -19702 and concrete of satisfactory quality can be produced at an economical cost using the, both gravel/shingle (i.e. uncrushed) or crushed natural aggregate can be used for general concrete construction. It should be remembered, however, that in practice the aggregate available locally or within an economical distance has to be used, and this can generally produce satisfactory concrete, given an intelligent approach and sufficient care3.
CPWD Specifications 20024 also recommend river bed shingle (uncrushed aggregate) for making concrete. Both uncrushed and crushed aggregate may be used in making concrete. However, both the aggregates shall be free from flat particles of shale or similar laminated materials, powdered clay, silt, loam adherent coatings, alkali, vegetable, matter and other deleterious substances. The aggregate shall conform to IS : 3832.
As per IS : 383-19702, fine aggregate (natural river sand) and aggregate (uncrushed river gravel) both obtained from river bed may be used in making concrete. However, they should conform the specifications of this code.
Keeping the above points in mind also economy and pollution control as crushing plants generate considerable pollution SCREENERS companies have installed modern fully mechanized washing and screening plants near Dehradun and elsewhere. These plants screen and washed the river bed aggregate and supply them as per specifications of IS: 383-19702.
The aggregates in these plants, are produces in its natural form thus prevent pollution and save our environment. At SCREENERS latest technology has been adopted, so that all the aggregates supplied from these plants conform to latest I.S. Specifications in making quality concrete, which could not be obtained from the out dated crushing plants. Not only quality aggregates are supplied from these plants, but they are also cheaper than crushed aggregates as can be seen from the statement given in table-1.
Table-1: Comparative Statement of cost (November 2003 rates)
| Sizes | Crushed aggregate from crusher Net rate/cu.m (Rs.) | Sizes | River bed uncrushed aggregate from SCREENERS Net rate/cu.m (Rs.) |
DEHRADUN SITE
| |||
| 12.5 mm | 475/- | 12.5 mm | 318/- |
| 20 mm | 460/- | 20 mm | 300/- |
| 40 mm | 450/- | 40 mm | 265/- |
| Crusher Dust | 370/- | Coarse sand | 370/- |
HARIDWAR, ROORKEE, SAHARANPUR SITES
| |||
| 12.5 mm | 425/- | 12.5 mm | 350/- |
| 20 mm | 400/- | 20 mm | 335/- |
| 40 mm | 385/- | 40 mm | 320/- |
| Crusher Dust | 370/- | Coarse sand | 425/- |
Note:
1. As river sand is available at the above sites, crusher dust is not being used in the construction of buildings at these sites.
1. As river sand is available at the above sites, crusher dust is not being used in the construction of buildings at these sites.
2. From the above statement it could be seen that crushed aggregates are about 57% costlier than SCREENERS uncrushed river bed aggregates.
3. In the following pages the reader will find that the aggregates of SCREENERS are as per specifications of IS: 383-19702 as they are produced in the modern fully mechanized aggregate screening & washing plant. From these plants the aggregates are obtained clean, free from silt, as they are washed with clean potable water from own bore well and mechanically screened in proper grading as per the specifications of IS: 383-19702.
4. 12.5 mm and 10 mm aggregates obtained from crusher grading in most cases are not found according to I.S. Specifications. Therefore in making concrete in combination with 20 mm or 20 and 40 mm aggregates they have to combine in suitable proportions otherwise gap grading will be formed.
AGGREGATES:
About 73% to 80% of the volume of structural concrete is occupied by aggregate, the quality of aggregate and its grading is of considerable importance. The properties of aggregate affect concrete workability, stability, finishing characteristic in fresh state, strength, durability and structural performance in hardened state5.
About 73% to 80% of the volume of structural concrete is occupied by aggregate, the quality of aggregate and its grading is of considerable importance. The properties of aggregate affect concrete workability, stability, finishing characteristic in fresh state, strength, durability and structural performance in hardened state5.
IS :456-20006 specified that aggregates shall comply with requirements of IS: 383-19702. As far as possible preference shall be given to natural aggregates. Coarse and fine aggregate shall be batched separately. All-in- aggregate may be used only where specifically permitted by the engineer-in-charge. Except where it can be shown to the satisfaction of the engineer-in-charge that supply of properly graded aggregate of uniform quality can be maintained over a period of work, the grading of aggregate should be controlled by obtaining the coarse aggregate in different sizes and blending them in the right proportions. When required, the different sizes being stocked in separate stock-piles. The grading of coarse and fine aggregate should be checked as frequently as possible.
The aggregates shall be hard, strong, dense, durable and shall not contain any harmful materials. The aggregate mostly of which retained on 4.75 mm sieve classified as coarse aggregate (aggregates) and aggregate mostly of which passes of 4.75 mm sieve classified as fine aggregate (sand). The aggregates are obtained from crusher or from natural sources. River gravel/shingle (uncrushed aggregate) and river sand are the example of natural aggregates. Aggregates obtained from crusher is classified as crushed aggregate.
The aggregate particle should not be flat or elongated but roughly cubical in shape. Bond between aggregate and cement paste is an important factor in the strength of concrete. For good development of bond, it is necessary that the aggregate surface be clean and free from adhering clay particles. Generally, when bond is good, a crushed specimen of normal strength concrete should contain some aggregate particles broken right through, in addition to the more numerous ones pulled out from their sockets. An excess fractured particles, however, might suggest that the aggregate is too weak. Clearly, the compressive strength of concrete cannot significantly exceed that of the major part of the aggregate contained therein.
The nominal maximum size of aggregate should be as specified in IS: 456-20006 clause 5.3.3. As the size of aggregate increases the surface area reduces, thus with the same workability reduces the water demand and with the same water-cement ratio reduces the cement content. The maximum size of aggregate also influences the compressive strength of concrete in that, for a particular volume of aggregate, the compressive strength tends to increase with decrease in the size of coarse aggregate. This is due to the fact that smaller size aggregates present, large surface area for bonding with the mortar matrix, it also result from the fact that the stress concentrate in the mortar aggregate interfaces increases with increases in the maximum size of aggregate. For high strength concrete 20 mm or of less size of coarse aggregate is preferable.
Table-2 : The following factors influence the performance of concrete.
Sr. No.
|
Factors
|
Influence on concrete property
|
1
| Specific gravity/porosity | Strength/absorption |
2
| Chemical stability | Durability |
3
| Surface texture | Bond grip |
4
| Shape | Water demand (strength) |
5
| Gradiation or particle size distribution | Water demand (strength) cohesion, bleeding and segregation |
6
| Maximum size | Strength and water demand |
7
| Deleterious materials | Water demand (strength), bond, cohesion and durability |
AGGREGATE QUALITY:
Clay, dust, silt or mud in aggregates because of inadequate washing at the aggregate source will produce lower strength concrete.
Clay, dust, silt or mud in aggregates because of inadequate washing at the aggregate source will produce lower strength concrete.
1. Crusher aggregates are not washed, thus they may contain a percentage of crusher dust. This dust if present as a coating around the larger aggregate will result in drop in strength of concrete. Similarly dust portion of the aggregate will cause an increase in water demand and subsequent drop in concrete strengths. The dust coatings on aggregate can increase the shrinkage of concrete by up to 70percent6.
2. Angular shape and rough texture of crushed aggregate required more water for a given workability. The rounded and smooth surfaces of uncrushed aggregates from the river bed improved the workability and this is advantageous in terms of reduced water demand.
3. Due to sharp angular shape crushed aggregate required more sand in order to compensate for the lowering of workability and proper finishing.
4. Uncrushed aggregate (river shingle) is satisfactory as far as shape is concerned and having rough texture in the production of high performance concrete.
5. This be known that uncrushed (shingle/gravel) aggregates have been used for high strength concrete without any serious problem of poor bond. If the shingle/gravel is clean and well washed the chances of poor bond are considerably reduced.
BOND OF AGGREGATE:
The determination of the quality of bond of aggregate is rather difficult and no accepted tests exist3. Bond between aggregate and cement paste is an important factor in the strength of concrete, especially the flexural strength, but the nature of bond is not fully understood. Bond is due, in part, to the interlocking of the aggregate and the hydrated cement paste due to the roughness of the surface of the former. Crushed aggregate rough surface, results in a better bond due to mechanical interlocking. However, unwashed crushed aggregate surfaces are generally coated with crusher dust, therefore, the rough surface bond benefit of crushed aggregate is not fully utilized. On the other hand a wash, clean, well graded having with in limits flaky and elongated particles uncrushed aggregates locally available is better than crushed aggregate coated with crusher dust and transported from long distances to construction site.
The determination of the quality of bond of aggregate is rather difficult and no accepted tests exist3. Bond between aggregate and cement paste is an important factor in the strength of concrete, especially the flexural strength, but the nature of bond is not fully understood. Bond is due, in part, to the interlocking of the aggregate and the hydrated cement paste due to the roughness of the surface of the former. Crushed aggregate rough surface, results in a better bond due to mechanical interlocking. However, unwashed crushed aggregate surfaces are generally coated with crusher dust, therefore, the rough surface bond benefit of crushed aggregate is not fully utilized. On the other hand a wash, clean, well graded having with in limits flaky and elongated particles uncrushed aggregates locally available is better than crushed aggregate coated with crusher dust and transported from long distances to construction site.
In most of the concrete construction M-20, M-25 and M-30 grade of concrete used. For such low strength concrete there is no justification in the use of crushed aggregate, particularly, when quality uncrushed aggregates from river bed are locally available, that too 57% cheaper than crushed aggregate.
Uncrushed (river shingle) aggregates have been used for high strength concrete without any serious problem of poor bond. If the shingle/gravel is clean and well washed the chances of poor bond are considerable reduced. Thus the bond strength may not be a controlling factor in the strength of ordinary concrete which is being used almost in 80% concrete construction.
A large number of projects have been executed either with uncrushed (shingle/gravel) or with crushed aggregates. Similarly, it is true for natural or crushed sand. The Engineer has to understand that, if the product material i.e. Quartzite, Basalt, Granite is the same, there is absolutely no harm in using it either in a natural or crushed form so long as it is free from deleterious materials.
GRADING OF AGGREGATES:
Coarse and fine aggregate grading shall be as specified in IS:383-19702. In the production of concrete the coarse and fine aggregates are to be combine to give a desired grading. The grading of aggregate is a major factor in the workability of a concrete mix. Workability, in turn, affect the water and cement requirements, control segregation, has some effect on bleeding, and influences the placing and finishing of the concrete. These factors represent the important characteristics of fresh concrete and affect also its properties in the hardened state, strength, shrinkage and durability. It is important to use aggregate with grading such that a reasonable workability and minimum segregation are obtained. A workable mixture which could produce a strong and economical concrete will result in honeycombed, weak, not durable and variable end product if segregation takes place. The aggregate available locally or within an economic distance has to be used, and this can generally produce satisfactory concrete, given an intelligent approach and sufficient care.
Coarse and fine aggregate grading shall be as specified in IS:383-19702. In the production of concrete the coarse and fine aggregates are to be combine to give a desired grading. The grading of aggregate is a major factor in the workability of a concrete mix. Workability, in turn, affect the water and cement requirements, control segregation, has some effect on bleeding, and influences the placing and finishing of the concrete. These factors represent the important characteristics of fresh concrete and affect also its properties in the hardened state, strength, shrinkage and durability. It is important to use aggregate with grading such that a reasonable workability and minimum segregation are obtained. A workable mixture which could produce a strong and economical concrete will result in honeycombed, weak, not durable and variable end product if segregation takes place. The aggregate available locally or within an economic distance has to be used, and this can generally produce satisfactory concrete, given an intelligent approach and sufficient care.
In routine concreting work, continuously graded aggregate is to be used as gap graded aggregate showed a greater proneness to segregation. For this reason gap grading is recommended mainly for mixes of relatively low workability; such mixes respond well to vibration. Good control and, above all, care in handling, so as to avoid segregation are essential. Gap-graded aggregate concrete is difficult to pump because of the danger of segregation and is not suitable to slip form paving.
SHAPE & SURFACE TEXTURE OF AGGREGATES:
Aggregates both natural and crushed are available in all types of shape and surface texture, see table-3 & 4.
Table-3: Particle shape:
Aggregates both natural and crushed are available in all types of shape and surface texture, see table-3 & 4.
Table-3: Particle shape:
Classification
|
Description
|
Example
|
| Rounded | Fully water worn or completely shaped by attrition | River or seashore gravels; desert, seashore and windblown sands |
| Irregular or partly rounded | Naturally irregular, or partly shaped by attrition, and having rounded edges. | Pit sands and gravel land or dug flints; cuboid rock |
| Angular | Possessing well-defined edges formed at the intersection of roughly planner faces | Crushed rocks of all types |
| Flacky | Materials, usually angular, of which the thickness is small relative to the width and/or length. | Laminated rocks |
Table-4: Surface characteristics of aggregate
Group
|
Surface texture
|
Example
|
1
| Glassy | Black flint |
2
| Smooth | Chert, slate, marble, some rhyolite |
3
| Granular | Sandstone, ollites |
4
| Crystalline | Fine: Basalt, Trachyte, Keratophyre
Medium: Dolerite, Granophyre, Granulite, Microgranite, some Limestone, many Dolomites.
Coarser: Gabbro, Gneiss, Granite, Granoiorite, Syenite
|
5
| Honey combed and porous | Scoriae, pumice, trass |
SPECIFIC GRAVITY:
Specific gravity of the aggregate generally is indicative of its quality. A low specific gravity may indicate high porosity and therefore poor durability and low strength. It is very important that the aggregates have high specific gravity. The concrete density will greatly depend on the specific gravity. The range of specific gravity for aggregates is generally between 2.4 and 2.9.
Specific gravity of the aggregate generally is indicative of its quality. A low specific gravity may indicate high porosity and therefore poor durability and low strength. It is very important that the aggregates have high specific gravity. The concrete density will greatly depend on the specific gravity. The range of specific gravity for aggregates is generally between 2.4 and 2.9.
OTHER IMPURITIES:
(a) ORGANIC
Organic matter in fine aggregates (sand) is usually found due to presence of vegetable matter. Even a very small fraction of organic matter will delay or prevent the hardening of concrete.
(a) ORGANIC
Organic matter in fine aggregates (sand) is usually found due to presence of vegetable matter. Even a very small fraction of organic matter will delay or prevent the hardening of concrete.
(b) CHLORIDE
Chloride if present in fine aggregates will not be harmful to plain concrete or mortar, but will be harmful to the reinforcement or other steel embedments in concrete or mortar. Chlorides attack steel and their presence will accelerate rusting. Sand dredged from creeks contain considerable amount of Chlorides and therefore needs to be washed before use in reinforced concrete structures.
Chloride if present in fine aggregates will not be harmful to plain concrete or mortar, but will be harmful to the reinforcement or other steel embedments in concrete or mortar. Chlorides attack steel and their presence will accelerate rusting. Sand dredged from creeks contain considerable amount of Chlorides and therefore needs to be washed before use in reinforced concrete structures.
Chlorides may also be present in cement, water and concrete additives. The total chloride content for long span bridges and prestressed structures must be limited to 0.10% by weight of cement and for reinforced concrete structures it must be limited to 0.15% by weight of cement.
(c) ALKALI REACTIVITY
It is important to know if the aggregates proposed to be used are alkali reactive before venturing to use them in concrete. If the aggregates are in use for several years without any problem, then detailed testing for alkali reactivity is not necessary.
It is important to know if the aggregates proposed to be used are alkali reactive before venturing to use them in concrete. If the aggregates are in use for several years without any problem, then detailed testing for alkali reactivity is not necessary.
If historically it is established that the aggregates proposed to be used are alkali reactive then the presence of alkali oxides (Na2O + 0.658 K2O) in cement have to be carefully examined. Alkali oxides in cement should not be beyond permissible limits i.e. more than 0.6 percent. Alkali oxides released from the cement will react with reactive form of silica present in alkali reactive aggregates. The reaction results in formation of alkali silica gel and involves expansive forces which in turn cause cracking and disintegration of concrete. However, such reactions generally take place after a lapse of nearly 2 to 3 years.
TESTING OF AGGREGATES
As per CPWD Specifications-20024, as Mandatory Test the sand should be tested for organic impurities, silt content, particle size distribution, bulking, and aggregate should be tested for percentage of soft or deleterious materials, particle size distribution, estimation of organic impurities, surface moisture, determination of 10% fine value, specific gravity, bulk density, aggregate crushing strength and aggregate impact value.
As per CPWD Specifications-20024, as Mandatory Test the sand should be tested for organic impurities, silt content, particle size distribution, bulking, and aggregate should be tested for percentage of soft or deleterious materials, particle size distribution, estimation of organic impurities, surface moisture, determination of 10% fine value, specific gravity, bulk density, aggregate crushing strength and aggregate impact value.
SIMPLE FIELD TESTING OF AGGREGATE
1. TEST FOR ORGANIC IMPURITIES IN FINE AGGREGATE
The aggregate must be checked for organic impurities such as decayed vegetation, humus, coal dust, etc. Colour test is a reliable indicator of the presence of harmful organic matter in aggregates except in areas where there are deposits of lignite.
1. TEST FOR ORGANIC IMPURITIES IN FINE AGGREGATE
The aggregate must be checked for organic impurities such as decayed vegetation, humus, coal dust, etc. Colour test is a reliable indicator of the presence of harmful organic matter in aggregates except in areas where there are deposits of lignite.
Procedure
(a) Fill a 350 ml clear glass medicine bottle upto 75 ml mark with a 3% solution of caustic soda or sodium hydroxide. A 3% solution of caustic soda is made by dissolving 3 gm of sodium hydroxide (which can be purchased from any local laboratory chemicals shop) in 100 ml of clean water (preferably distilled water). The solution should be kept in glass bottle tightly closed with a rubber stopper. Handling sodium hydroxide with moist hands may result in serious burns. Care should be taken not to spill the solution for it is highly injurious to clothing, leather and other materials.
(b) The representative sand sample is next added gradually until the volume measured by the sandy layer is 125 ml. the volume is then made upto 200 ml by the addition of more of the solution. The bottle is then corked and shaken vigorously and allowed to stand for 24 hours.
(c) At the end of this period, the colour of the liquid will indicate whether the sand contains a dangerous amount of matter or not. A colourless liquid indicates a clean sand free from organic matter. A straw-coloured solution indicates some organic matter but not enough to be seriously objectionable. Darker colour means that the sand contains injurious amounts and should not be used unless it is washed and a re-test then shows that it is satisfactory.
(a) Fill a 350 ml clear glass medicine bottle upto 75 ml mark with a 3% solution of caustic soda or sodium hydroxide. A 3% solution of caustic soda is made by dissolving 3 gm of sodium hydroxide (which can be purchased from any local laboratory chemicals shop) in 100 ml of clean water (preferably distilled water). The solution should be kept in glass bottle tightly closed with a rubber stopper. Handling sodium hydroxide with moist hands may result in serious burns. Care should be taken not to spill the solution for it is highly injurious to clothing, leather and other materials.
(b) The representative sand sample is next added gradually until the volume measured by the sandy layer is 125 ml. the volume is then made upto 200 ml by the addition of more of the solution. The bottle is then corked and shaken vigorously and allowed to stand for 24 hours.
(c) At the end of this period, the colour of the liquid will indicate whether the sand contains a dangerous amount of matter or not. A colourless liquid indicates a clean sand free from organic matter. A straw-coloured solution indicates some organic matter but not enough to be seriously objectionable. Darker colour means that the sand contains injurious amounts and should not be used unless it is washed and a re-test then shows that it is satisfactory.
2. TEST FOR SILT CONTENT OF FINE AGGREGATE
It is important to use clean aggregate for concrete. If the aggregates are coated with dirt, silt or clay, it will result in a poor concrete because the dirt will prevent the cement from setting and also weaken the bond between the aggregates and the cement paste. Further owing to their fineness and therefore large surface area, increase the amount of water necessary to wet all the particles in the mix, this also resulted more shrinkage of concrete. As determine with the given field test, the sand shall not contain more than 8% of silt.
It is important to use clean aggregate for concrete. If the aggregates are coated with dirt, silt or clay, it will result in a poor concrete because the dirt will prevent the cement from setting and also weaken the bond between the aggregates and the cement paste. Further owing to their fineness and therefore large surface area, increase the amount of water necessary to wet all the particles in the mix, this also resulted more shrinkage of concrete. As determine with the given field test, the sand shall not contain more than 8% of silt.
Procedure
(a) Fill a measuring cylinder with a representative sand (fine aggregate) sample upto 100 ml mark and add clean water up to 150 ml. to perform this test, more correctly better dissolve a little salt in the water (1 tea spoon full to 250 ml is the right proportion).
(b) Shake the sample vigorously for one minute and the last few shakes being in a side wise direction to level off the sand.
(c) Allow the cylinder to stand for three hours during which time any silt present will settle in a layer on the top of the sand and its thickness can be read off on the cylinder itself. The sand shall not contain more than 8% of silt.
Note: In performing this test the sand sample should not dry.
Glass measuring cylinder capacity should be 200 ml.
(a) Fill a measuring cylinder with a representative sand (fine aggregate) sample upto 100 ml mark and add clean water up to 150 ml. to perform this test, more correctly better dissolve a little salt in the water (1 tea spoon full to 250 ml is the right proportion).
(b) Shake the sample vigorously for one minute and the last few shakes being in a side wise direction to level off the sand.
(c) Allow the cylinder to stand for three hours during which time any silt present will settle in a layer on the top of the sand and its thickness can be read off on the cylinder itself. The sand shall not contain more than 8% of silt.
Note: In performing this test the sand sample should not dry.
Glass measuring cylinder capacity should be 200 ml.
3. TEST FOR MOISTURE CONTENT OF CONCRETE AGGREGATE
The various stages in which the aggregate may exist are (a) over dry (b) air dry (c) saturated surface dry (d) damp or moist. On the construction site, the sand (fine aggregate) usually carry some free moisture. Total internal moisture content of an aggregate in the saturated surface dry condition may be termed as “Absorption Capacity” although it is some times referred to simply as the absorption. The amount of water required to bring an aggregate from the air dry condition to the saturated surface dry condition is termed as “effective absorption”. The absorption is determined by finding the weight of a surface dried sample after it has been soaked for 24 hours and again finding the weight after the sample has been dried, the difference in weights, expressed as a percentage of dry sample weight, is the absorption capacity.
Procedure
(a) Take about one kg of representative sample of sand (fine aggregate) in a suitable size tray. Fully immerse this sand sample in clean water for 24 hours.
(b) After 24 hours of immersion take about 500 gm of representative wet sand sample. Dry this sand in saturated surface dry (SSD) condition either in air or heating in a fry pan. Take the weight of SSD sand sample (weight A). again put this SSD sand sample in fry pan and dry it fully in gentle heat. After drying take its weight (weight B).
(c) Take about 500 gm representative site sand sample. Take its weight (weight C) and fully dry it in a fry pan. Take the dry weight (weight D).
The various stages in which the aggregate may exist are (a) over dry (b) air dry (c) saturated surface dry (d) damp or moist. On the construction site, the sand (fine aggregate) usually carry some free moisture. Total internal moisture content of an aggregate in the saturated surface dry condition may be termed as “Absorption Capacity” although it is some times referred to simply as the absorption. The amount of water required to bring an aggregate from the air dry condition to the saturated surface dry condition is termed as “effective absorption”. The absorption is determined by finding the weight of a surface dried sample after it has been soaked for 24 hours and again finding the weight after the sample has been dried, the difference in weights, expressed as a percentage of dry sample weight, is the absorption capacity.
Procedure
(a) Take about one kg of representative sample of sand (fine aggregate) in a suitable size tray. Fully immerse this sand sample in clean water for 24 hours.
(b) After 24 hours of immersion take about 500 gm of representative wet sand sample. Dry this sand in saturated surface dry (SSD) condition either in air or heating in a fry pan. Take the weight of SSD sand sample (weight A). again put this SSD sand sample in fry pan and dry it fully in gentle heat. After drying take its weight (weight B).
(c) Take about 500 gm representative site sand sample. Take its weight (weight C) and fully dry it in a fry pan. Take the dry weight (weight D).
Calculations:
(1) Water absorption (%) = (A – B)/B x 100
(2) Total moisture in site sand (%) = (C – D)/D x 100
(3) Surface moisture in site sand (%) = Total moisture in site sand % – Absorption of site sand %
(1) Water absorption (%) = (A – B)/B x 100
(2) Total moisture in site sand (%) = (C – D)/D x 100
(3) Surface moisture in site sand (%) = Total moisture in site sand % – Absorption of site sand %
If the result is in negative, it means the sample does not contain any surface moisture and in it balance absorbed water is to be added to make the site sand in SSD condition.
Note:
(a) For obtaining the SSD condition of sand, it should be gently heated in a fry pan, while stirring with a glass rod until the surface moisture disappears. This is apparent when the sand loses its shining wet appearance and becomes dull, or when it just attains a free running condition. The end point of aggregate SSD condition could be find by practice. If the sand is heated beyond the SSD condition some of the absorbed moisture will also dry and then the SSD weight of aggregate will not be correct, and the obtained absorption result will not be correct.
(b) The same procedure with appropriate changes in the size of the sample and dimension of the container may be applied to obtained moisture content of coarse aggregate.
Note:
(a) For obtaining the SSD condition of sand, it should be gently heated in a fry pan, while stirring with a glass rod until the surface moisture disappears. This is apparent when the sand loses its shining wet appearance and becomes dull, or when it just attains a free running condition. The end point of aggregate SSD condition could be find by practice. If the sand is heated beyond the SSD condition some of the absorbed moisture will also dry and then the SSD weight of aggregate will not be correct, and the obtained absorption result will not be correct.
(b) The same procedure with appropriate changes in the size of the sample and dimension of the container may be applied to obtained moisture content of coarse aggregate.
4. TEST FOR BULKING OF SAND
Dry and fully saturated sand does not bulk. As the sand become finer the bulking of the sand increases. The bulking of sand is caused by the film of moisture which tends to keep the particles of sand apart.
Dry and fully saturated sand does not bulk. As the sand become finer the bulking of the sand increases. The bulking of sand is caused by the film of moisture which tends to keep the particles of sand apart.
Procedure:
Method 1:
Put sufficient quantity of site sand loosely into a suitable container until it is about two-third full. Level off the top of the sand and push a steel rule vertically down through the sand at the middle to bottom, measure the height. Suppose this is ‘X” cm,
Method 1:
Put sufficient quantity of site sand loosely into a suitable container until it is about two-third full. Level off the top of the sand and push a steel rule vertically down through the sand at the middle to bottom, measure the height. Suppose this is ‘X” cm,
Empty the sand out of the container into another container where none of it is lost. Half fill the first container with clean water. Put back about half the sand and rod it with a steel rod, about 5 mm in diameter, so that its volume is reduced to a minimum. Then add the reminder sand and level the top surface of the fully saturated sand. Measure its depth at the middle with the steel rule suppose this is ‘Y’ cm.
The percentage of bulking of sand due to moisture shall be calculated from the formula:
Percentage bulking = (x/y – 1) x 100
Percentage bulking = (x/y – 1) x 100
Method 2:
In a 250 ml measuring cylinder, pour the damp site sand, consolidate it by staking until it reacts the 200 ml mark.
In a 250 ml measuring cylinder, pour the damp site sand, consolidate it by staking until it reacts the 200 ml mark.
Then fill the cylinder with the clean water and stir the sand well (the water shall be sufficient to submerge the sand completely). It will be seen that the sand surface is now below its original level. Suppose the surface is at the mark of ‘Y’ ml, the percentage of bulking of sand due to moisture shall be calculated from the formula.
Percentage bulking = (200/y – 1) x 100
5. TEST FOR SPECIFIC GRAVITY OF AGGREGATE
The specific gravity of a substance is the ratio of the unit weight of the substance to the unit weight of water. A representative aggregate sample is SSD condition is obtained by quartering and the following weights are used in the tests for the various sizes of aggregates.
The specific gravity of a substance is the ratio of the unit weight of the substance to the unit weight of water. A representative aggregate sample is SSD condition is obtained by quartering and the following weights are used in the tests for the various sizes of aggregates.
Less than 4.75 mm ………………………. 500 to 700 gm
4.75 mm to 10 mm ………………………. 1000 to 1500 gm
10 mm to 20 mm ………………………. 1500 to 2000 gm
20 mm to 40 mm ………………………. More than 2000 gm
4.75 mm to 10 mm ………………………. 1000 to 1500 gm
10 mm to 20 mm ………………………. 1500 to 2000 gm
20 mm to 40 mm ………………………. More than 2000 gm
Procedure:
(a) Take a suitable size jar, the top open side of which have flange, so that a glass plate may be put on it.
(b) The jar should be filled with clean water upto the flange and slide on it the glass plate. If there is any air bubble, which can be seen from top of glass plate, then the jar top should be filled with more water. There should not be any air bubble. Take the weight of jar fully filled with water and upon it glass plate (weight A)
(c) About half empty the jar fill it with known weight of SSD aggregate sample (weight B). as mentioned at (b) fill the jar upto the top and putt glass plate on it. There should not be any air bubble. Take its weight (weight C)
Specific Gravity on SSD basis = B/[ B – (C – A)]
(a) Take a suitable size jar, the top open side of which have flange, so that a glass plate may be put on it.
(b) The jar should be filled with clean water upto the flange and slide on it the glass plate. If there is any air bubble, which can be seen from top of glass plate, then the jar top should be filled with more water. There should not be any air bubble. Take the weight of jar fully filled with water and upon it glass plate (weight A)
(c) About half empty the jar fill it with known weight of SSD aggregate sample (weight B). as mentioned at (b) fill the jar upto the top and putt glass plate on it. There should not be any air bubble. Take its weight (weight C)
Specific Gravity on SSD basis = B/[ B – (C – A)]
6. TEST FOR BULK DENSITY OF AGGREGATE
Bulk density is the weight of a unit volume of aggregate, usually stated in kg per litre on room dry basis in estimating quantities of materials and in mix computation, when batching is done on a volumetric basis.
Bulk density is the weight of a unit volume of aggregate, usually stated in kg per litre on room dry basis in estimating quantities of materials and in mix computation, when batching is done on a volumetric basis.
Concrete materials proportion by weight can be converted to proportions by volume, by dividing with the bulk density of the materials available for use at site. The bulk density of cement may be taken 1.44 kg/lit.
For determination of bulk density the container size shall be as given below:
For determination of bulk density the container size shall be as given below:
Size of particle
|
Nominal capacity (litres)
|
Inside dia (mm)
|
Inside height (mm)
|
Thickness of metal (Min.) (mm)
|
| 4.75 mm and under |
3
|
150
|
170
|
3.15
|
| Over 4.75 mm to 40 mm |
15
|
250
|
300
|
4.00
|
| Over 40 mm |
30
|
350
|
310
|
5.00
|
Procedure:
(a) About 100 kg of aggregate sample should be dried in the room.
(b) Take the weight in kg of empty container + glass plate (weight A)
(c) The container is to be filled with loose sand or loose aggregate i.e. sand or aggregate should be dropped in the container from about 5 cm heights from top of container. Take the weight of container filled with sand or aggregate + glass plate (weight B).
(d) Empty the container, filled it with clean water upto the top ridge put glass plate. There shall not be any air bubble. Take its weight (weight C). all weight should be taken in kg.
Loose bulk density in kg/lit.
on the basis of room dry sand or aggregate= (B – A)/(C – A)
(a) About 100 kg of aggregate sample should be dried in the room.
(b) Take the weight in kg of empty container + glass plate (weight A)
(c) The container is to be filled with loose sand or loose aggregate i.e. sand or aggregate should be dropped in the container from about 5 cm heights from top of container. Take the weight of container filled with sand or aggregate + glass plate (weight B).
(d) Empty the container, filled it with clean water upto the top ridge put glass plate. There shall not be any air bubble. Take its weight (weight C). all weight should be taken in kg.
Loose bulk density in kg/lit.
on the basis of room dry sand or aggregate= (B – A)/(C – A)
and voids percentage = (Specific Gravity – Bulk Density)/Specific Gravity x 100
Table 5. Size of sample required for various tests (IS: 2386-1963)
| Test |
Minimum sample size
| |
To be available in the Lab (kg)
|
To be tested
(kg)
| |
| Sieve Analysis
Miximum size present in substantial proportions
| ||
| 63 mm |
100
|
50
|
| 50 mm |
100
|
35
|
| 40 mm |
50
|
15
|
| 25 mm |
50
|
5
|
| 20 mm |
25
|
2
|
| 12.5 mm |
12
|
1
|
| 10 mm |
6
|
0.5
|
| 6.3 mm |
3
|
0.2
|
| 4.75 mm |
2
|
0.2
|
| 2.36 mm |
2
|
0.1
|
| Determination of Materials Finer than 75 Micron: | ||
| Maximum size present in substantial proportions | ||
| 40 mm or above |
20
|
5
|
| 20 mm |
10
|
2.5
|
| 10 mm |
10
|
2.0
|
| 4.75 mm |
5
|
0.5
|
| Estimation of organic impurities |
5
|
0.5
|
Determination of Specific Gravity and Water Absorption Aggregate larger than
| ||
| 10 mm |
10
|
2
|
| 10 mm - 4.75 mm |
5
|
1
|
| Smaller than 4.75 |
3
|
0.5
|
| Determination of bulk density and voids: | ||
| Maximum size of aggregate | ||
| Over 40 mm |
150
|
60
|
| 40 mm – 4.75 mm |
100
|
30
|
| Less than 4.75 mm |
20
|
30
|
| Determination of Aggregate Crushing Value: |
30
|
7
|
| Determination of Aggregate Impact Value: |
5
|
1
|
| Determination of Aggregate Abrasion Value by use of the Deval Machine: |
30
|
6
|
| Determination of Aggregate Abrasion Value by use of Los Angles Machine: |
300
|
50
|
| Determination of Aggregate Soundness: | ||
| Coarse Aggregate |
60
|
10
|
| Fine Aggregate |
10
|
1
|
Table 6 : Maximum weight to be retained at the completion of sieving:
I.S. Sieve
|
Coarse Aggregate Max weight for
|
Fine Aggregate
| ||
45 cm dia sieve (Kg)
|
30 cm dia sieve (Kg)
|
I.S. Sieve
|
Max weight for 20 mm dia sieve (gm)
| |
| 50 mm |
10
|
4.5
|
2.36 mm
|
200
|
| 40 mm |
8
|
3.5
|
1.18 mm
|
100
|
| 31.5 or 25 mm |
6
|
2.5
| ||
| 20 mm |
4
|
2.0
|
600 micron
|
75
|
| 12.5 mm/16 mm |
3
|
1.5
|
300 micron
|
50
|
| 10 mm |
2
|
1.0
| ||
| 6.3 mm |
1.5
|
0.75
|
150 micron
|
40
|
| 4.75 mm |
1
|
0.50
|
75 micron
|
25
|
| 3.35 mm |
0.30
| |||
Table. 7: I.S. Sieves for Sieve Analysis of Aggregates for concrete:
| Type | Sieve designations |
| Square hole, perforate plate | 80 mm, 63 mm, 50 mm, 40 mm, 31.5 mm, 25 mm, 20 mm, 16 mm, 12.5 mm, 10 mm, 6.3 mm, 4.75 mm |
| Fine mesh wire cloth | 3.35 mm, 2.36 mm, 1.18 mm, 600 micron, 300 micron, 150 micron and 75 micron |
Table. 8 : Proforma of sieve analysis of aggregates:
| I.S. Sieve size | Weight retained | % weight retained | % weight passing | Cumulative % weight, rtd. | Remarks |
| 80 mm | |||||
| 63 mm | |||||
| 40 mm | |||||
| 20 mm | |||||
| 16 mm | |||||
| 12.5 mm | |||||
| 10 mm | |||||
| 4.75 mm | |||||
| 2.36 mm | |||||
| 1.18 mm | |||||
| 600 micron | |||||
| 300 micron | |||||
| 150 micron | |||||
| Residue(Pan) |
—–
|
—–
| |||
| Total |
—–
|
—–
|
Note:- Refer IS: 383-1970 table 2 and 3 for the sizes of sieves to be used in the sieving of particular maximum size of coarse aggregate. For sieving the sand take sieves of sizes 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 micron, 300 micron, 150 micron.
CRUSHER & AIR POLLUTION PROBLEM:
When the rocks and river bed boulders are crushed, dry surfaces are exposed and air borne dust can be created. An inventory of sources of dust emissions usually begins with the first crusher and continues with the conveyor transfer points to and including the succeeding crushers. Here the aggregate is more finely grounded, and dust emission become greater. As the process continues, dust emission are again prevalent from sources at conveyer transfer points and the final screens.
When the rocks and river bed boulders are crushed, dry surfaces are exposed and air borne dust can be created. An inventory of sources of dust emissions usually begins with the first crusher and continues with the conveyor transfer points to and including the succeeding crushers. Here the aggregate is more finely grounded, and dust emission become greater. As the process continues, dust emission are again prevalent from sources at conveyer transfer points and the final screens.
In the modern screening and washing plant in the production of uncrushed (gravel/shingle) aggregate from the river bed they are not crushed, thus no dust is formed. Further aggregates are washed to remove silt and clay like materials. Therefore, uncrushed (gravel/shingle) aggregates produces in these plant arrive at site in a moist condition, hence do not present a dust problem. Whereas the crushed aggregate leave crushing plant very dry and create considerable dust when handled. To prevent dust in handling it is not possible to wet each load of crushed aggregate thoroughly before it is dumped from the delivery truck. Attempts to spray the crushed aggregate as it is being dumped have had very limited effectiveness.
During crushing of aggregates particles less than 100 micron remain suspended in the air. The suspension of a particle in the air follows a certain trajectory depending on its size, density, shape and other physical properties. In air turbulence the dry crusher dust has long trajectories or suspension time and settling distance to the ground. If a crushing plant is not properly designed and operate without any efficient prevention system this “fugitive” dust may generate air pollution.
Air quality due to pollution should be monitored monthly. The ambient air quality standards as recommended by Central Pollution Control Board (CPCB) India are given in Table-9.
Table-9 : Ambient Air Quality (CPCB) Standards of India:
Category
|
Area
|
Concentration micrograms per meter cube
| |||
SPm
|
SO2
|
CO
|
NOx
| ||
A
| Industrial and mixed use |
500
|
120
|
5000
|
120
|
B
| Residential and Rural |
200
|
80
|
2000
|
80
|
C
| sensitive |
100
|
30
|
1000
|
30
|
Notes:-
1. SPm : Suspended Particle Matters
SO2 : Sulpher Dioxide
CO : Carbon Mono-oxide
NOx : Nitrogen Oxide
2. The concentrations for the above pollutants shall be 95% of the time within the limits prescribed.
3. Category ‘C’ Sensitive areas are: Hill Stations, Tourist Resorts, Sanctuaries, National Park, National Monuments etc.
4. The air quality levels should be determined by sampling and brought down within specified ambient air quality standards through use of various mitigation measures, modern pollution free equipment and advance construction technology, such as giving preference in using uncrushed (gravel/shingle) natural aggregate in the general civil engineering construction work in place of crushed aggregate obtained from crusher.
1. SPm : Suspended Particle Matters
SO2 : Sulpher Dioxide
CO : Carbon Mono-oxide
NOx : Nitrogen Oxide
2. The concentrations for the above pollutants shall be 95% of the time within the limits prescribed.
3. Category ‘C’ Sensitive areas are: Hill Stations, Tourist Resorts, Sanctuaries, National Park, National Monuments etc.
4. The air quality levels should be determined by sampling and brought down within specified ambient air quality standards through use of various mitigation measures, modern pollution free equipment and advance construction technology, such as giving preference in using uncrushed (gravel/shingle) natural aggregate in the general civil engineering construction work in place of crushed aggregate obtained from crusher.
PROPERTIES OF SCREENERS RIVER BED UNCRUSHED AGGREGATES
PHYSICAL CHARACTERISTIC OF SCREENERS UNCRUSHED RIVER BED AGGREGATES
PHYSICAL CHARACTERISTIC OF SCREENERS UNCRUSHED RIVER BED AGGREGATES
The aggregates samples are obtained from Dehradun and elsewhere screener pants which are located at river bank produces, river coarse sand, 12.5 mm, 20 mm and 40 mm sizes uncrushed (gravel/shingle) aggregates in its natural form
1. Trade group of aggregate : Quartzite
2. Particle shape of aggregate : Irregular
3. Surface texture of aggregate : Granular/Rough
4. AGGREGATES PHYSICAL PROPERTIES
2. Particle shape of aggregate : Irregular
3. Surface texture of aggregate : Granular/Rough
4. AGGREGATES PHYSICAL PROPERTIES
S. No.
|
Test
|
Sand
|
Aggregate mixed lot 40 mm-4.75 mm average test value
|
Requirements as per IS:383-1970
|
| 1 | Aggregate crushing Value (%) | — | 23.5 | Shall not exceed 45% for aggregate used for concrete other than for wearing surfaces and 30% for concrete for wearing surfaces, such as runways, roads and pavement. |
| 2 | Aggregate Impact Test (%) | — | 20.4 | Shall not exceed 45% by weight for aggregate used for concrete other than for wearing surfaces and 30% for concrete by weight for wearing surfaces, such as runways, roads and pavement. |
| 3 | Soundness Average loss of weight (%) after 5 cycles with Magnesium Sulphate (MgSO4) | 9.5 | 11.2 | Average loss of weight after 5 cycles shall not exceed 15% for sand and 18% for coarse Aggregate. |
5. AGGREGATES OTHER PHYSICAL PROPERTIES:
S. No.
|
Test
|
Sand
|
12.5 mm Agg.
|
20 mm Agg.
|
40mm Agg.
|
Permissible limit
|
| 1 | Specific gravity | 2.65 | 2.64 | 2.65 | 2.65 | — |
| 2 | Bulk density (kg/lit) | 1.77 | 1.45 | 1.40 | 1.39 | — |
| 3 | Water absorption (%) | 0.8 | 0.6 | 0.5 | 0.5 | — |
| 4 | Flakiness Index (%) | — | 16.0 | 18.0 | 17.0 | See note |
| 5 | Elongation Index (%) | — | 8.0 | 9.0 | 11.0 | See note |
Note:-
The mass of flaky particles expressed as a percentage of the mass of the sample is called the flakiness index. Elongation index is similarly defined. Some particles are both flaky and elongated, and are therefore, counted in both categories.
The mass of flaky particles expressed as a percentage of the mass of the sample is called the flakiness index. Elongation index is similarly defined. Some particles are both flaky and elongated, and are therefore, counted in both categories.
Elongated and flaky particles, having a high ratio of surface are to volume, lower the workability of the mix and can also affect adversely the durability of concrete since they tend to be oriented in one plane with water and air voids underneath. As per BIS SP: 23-82 page 15 clause 2.2.2.2 a flakiness index not greater then 25% is suggested for coarse aggregate.
The presence of elongated particles in excess of 15% of the mass of coarse aggregate is generally considered undesirable. Ref. A.M. Naville, Properties of Concrete page 115-116.
6. BULKING OF SAND:
Moisture percent
|
Percent Bulking
|
1
|
6
|
2
|
12
|
3
|
15
|
4
|
17
|
5
|
18
|
6
|
18
|
8
|
16
|
10
|
12
|
12
|
8
|
15
|
2
|
17
|
–
|
7. DELETERIOUS MATERIALS IN SAND:
s. No.
|
Test Items
|
Results Obtained
|
Requirements as per
IS:383-1970
|
| 1 | Coal & lignite (percent by wt.) |
Nil
|
1.0 (Max.)
|
| 2 | Clay lumps (percent by wt.) |
Nil
|
1.0 (Max.)
|
| 3 | Materials finer than 75 micron I.S. Sieve (percent by wt.) |
0.3
|
3.0 (Max.)
|
| 4 | Soft fragments (percent by wt.) |
—
|
Test not required
|
| 5 | Shale (percent by wt.) |
Nil
|
1.0 (Max.)
|
| 6 | Total deleterious materials (percent by wt.) |
0.3
|
5.0 (Max.)
|
8. DELETERIOUS MATERIALS IN AGGREGATE:
S. No.
|
Test Item
|
Results obtained
|
Requirement as per IS:383-1970
| ||
12.5mm
|
20mm
|
40mm
| |||
| 1 | Coal & lignite (percent by wt.) |
Nil
|
Nil
|
Nil
|
1.0 (Max.)
|
| 2 | Clay lumps (percent by wt.) |
Nil
|
Nil
|
Nil
|
1.0 (Max.)
|
| 3 | Materials finer than 75 micron I.S. Sieve (percent by wt.) |
Nil
|
Nil
|
Nil
|
3.0 (Max.)
|
| 4 | Soft fragments (percent by wt.) | 1.2 | 1.0 | 1.0 |
3.0 (Max.)
|
| 5 | Shale (percent by wt.) | — | — | — |
Test not required
|
| 6 | Total deleterious materials (percent by wt.) | 1.2 | 1.0 | 1.0 |
5.0 (Max.)
|
9. SIEVE ANALYSIS OF SCREENERS AGGREGATES
Sieve size
|
Percentage passing
| |||
River coarse sand
|
River bed uncrushed aggregate 12.5 mm
|
River bed uncrushed aggregate
20 mm
|
River bed uncrushed aggregate
40 mm
| |
| 40 mm |
X
|
X
|
100
|
100
|
| 20 mm |
X
|
100
|
96
|
14
|
| 12.5 mm |
X
|
91
|
X
|
X
|
| 10 mm |
100
|
60
|
28
|
—
|
| 4.75 mm |
91
|
—
|
—
| |
| 2.36 mm |
74
| |||
| 1.18 mm |
55
| |||
| 600 micron |
38
| |||
| 300 micron |
20
| |||
| 150 micron |
5
| |||
| GRADING: |
As per IS:383-1970 sand is of Zone-II
|
As per IS:383-1970 12.5 mm graded aggregate
|
As per IS:383-1970 20 mm graded aggregate
|
As per IS:383-1970 40 mm single graded aggregate
|
Note:
1. The grading of aggregates and sand are suitable for Design Mix as well as Nominal Mix Concrete.
2. The best sand for concrete is that which passes 36 to 40% on 600 micron sieve, as this sand for a given workability will required less water. See the durability of concrete benefits with less water elsewhere is this report.
3. For pumped concrete sand should be 15-30% passing on 300 micron sieve and 4-8% passing on 150 micron sieve. Accordingly SCREENERS sand is also suitable for pumped concrete.
4. If sand passes on 150 micron sieve 7% or more, the concrete will be sticky and for a given workability need more water which reduces the concrete durability.
1. The grading of aggregates and sand are suitable for Design Mix as well as Nominal Mix Concrete.
2. The best sand for concrete is that which passes 36 to 40% on 600 micron sieve, as this sand for a given workability will required less water. See the durability of concrete benefits with less water elsewhere is this report.
3. For pumped concrete sand should be 15-30% passing on 300 micron sieve and 4-8% passing on 150 micron sieve. Accordingly SCREENERS sand is also suitable for pumped concrete.
4. If sand passes on 150 micron sieve 7% or more, the concrete will be sticky and for a given workability need more water which reduces the concrete durability.
10. CONCRETE MIX DESIGN WITH SCREENERS COARSE UNCRUSHED AGGREGATE & COARSE SAND:
(1) In all the Design Mixes the materials are Ordinary Portland Cement (OPC)-43 Grade, potable tape water, SCREENERS 20 mm graded uncrushed (gravel/shingle) aggregate and sand of Zone-II. For SCREENERS sand and aggregates grading refer sieve analysis report.
(2) All the Mix Designs carried out as per guide lines given in IS:456-2000.
(3) The minimum cement content and maximum free water-cement ratio in all the mixes are taken as mentioned in IS: 456-2000 Table-5, which is also reproduced in the revised CPWD Specifications-2002.
(4) As per IS: 456-2000 for reinforced concrete work the minimum grade of concrete shall be not less than M-20.
(A) M-15 Grade of Concrete: Slump 30 mm + 5 mm, Exposure-Moderate Target Strength = 22.4 N/mm2 at 28- day age.
Quantity of materials per cum of concrete on the basis of saturated and surface dry aggregates.
Water = 150 kg/m3
Cement = 250 kg/m3
Sand = 760 kg/m3
Aggregate = 1240 kg/m3
Mix ratio by weight on the basis of SSD Aggregates
Cement : Sand : Aggregate
1 : 3.04 : 4.96 W/C Ratio = 0.6
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 2.49 : 5.13 Free W/C Ratio = 0.6
Note: M-15 Grade of concrete is for plain cement concrete (PPC)
(1) In all the Design Mixes the materials are Ordinary Portland Cement (OPC)-43 Grade, potable tape water, SCREENERS 20 mm graded uncrushed (gravel/shingle) aggregate and sand of Zone-II. For SCREENERS sand and aggregates grading refer sieve analysis report.
(2) All the Mix Designs carried out as per guide lines given in IS:456-2000.
(3) The minimum cement content and maximum free water-cement ratio in all the mixes are taken as mentioned in IS: 456-2000 Table-5, which is also reproduced in the revised CPWD Specifications-2002.
(4) As per IS: 456-2000 for reinforced concrete work the minimum grade of concrete shall be not less than M-20.
(A) M-15 Grade of Concrete: Slump 30 mm + 5 mm, Exposure-Moderate Target Strength = 22.4 N/mm2 at 28- day age.
Quantity of materials per cum of concrete on the basis of saturated and surface dry aggregates.
Water = 150 kg/m3
Cement = 250 kg/m3
Sand = 760 kg/m3
Aggregate = 1240 kg/m3
Mix ratio by weight on the basis of SSD Aggregates
Cement : Sand : Aggregate
1 : 3.04 : 4.96 W/C Ratio = 0.6
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 2.49 : 5.13 Free W/C Ratio = 0.6
Note: M-15 Grade of concrete is for plain cement concrete (PPC)
(B) M-20 GRADE OF CONCRETE
Slump 40-60 mm, exposure-mild target strength = 28.3 N/mm2 at 28-days age
Quantity of materials per cum of concrete on the basis of saturated and surface dry Aggregates.
Water = 170 kg/m3
Cement = 320 kg/m3
Sand = 756 kg/m3
Aggregate = 1134 kg/m3
Mix ratio by weight on the basis of saturated and surface dry Aggregates
Cement : Sand : Aggregate
1 : 2.36 : 3.54 W/C Ratio = 0.53
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 1.93 : 3.66 Free W/C Ratio = 0.53
Slump 40-60 mm, exposure-mild target strength = 28.3 N/mm2 at 28-days age
Quantity of materials per cum of concrete on the basis of saturated and surface dry Aggregates.
Water = 170 kg/m3
Cement = 320 kg/m3
Sand = 756 kg/m3
Aggregate = 1134 kg/m3
Mix ratio by weight on the basis of saturated and surface dry Aggregates
Cement : Sand : Aggregate
1 : 2.36 : 3.54 W/C Ratio = 0.53
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 1.93 : 3.66 Free W/C Ratio = 0.53
(C) M-25 GRADE OF CONCRETE
Slump 40-60 mm, exposure-moderate target strength = 33.3 N/mm2 at 28-days age
Quantity of materials per cum of concrete on the basis of saturated and surface dry Aggregates.
Water = 174 kg/m3
Cement = 370 kg/m3
Sand = 716 kg/m3
Aggregate = 1120 kg/m3
Mix ratio by weight on the basis of SSD Aggregates
Cement : Sand : Aggregate
1 : 1.94 : 3.03 W/C Ratio = 0.47
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 1.59 : 3.14 Free W/C Ratio = 0.47
Slump 40-60 mm, exposure-moderate target strength = 33.3 N/mm2 at 28-days age
Quantity of materials per cum of concrete on the basis of saturated and surface dry Aggregates.
Water = 174 kg/m3
Cement = 370 kg/m3
Sand = 716 kg/m3
Aggregate = 1120 kg/m3
Mix ratio by weight on the basis of SSD Aggregates
Cement : Sand : Aggregate
1 : 1.94 : 3.03 W/C Ratio = 0.47
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 1.59 : 3.14 Free W/C Ratio = 0.47
(D) M-30 GRADE OF CONCRETE
Slump 40-60 mm, exposure-severe target strength = 39.9 N/mm2 at 28-days age
Quantity of materials per cum of concrete on the basis of saturated and surface dry Aggregates.
Water = 178 kg/m3
Cement = 414 kg/m3
Sand = 679 kg/m3
Aggregate = 1109 kg/m3
Mix ratio by weight on the basis of saturated and surface dry Aggregates
Cement : Sand : Aggregate
1 : 1.64 : 2.68 W/C Ratio = 0.43
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 1.34 : 2.77 Free W/C Ratio = 0.43
Slump 40-60 mm, exposure-severe target strength = 39.9 N/mm2 at 28-days age
Quantity of materials per cum of concrete on the basis of saturated and surface dry Aggregates.
Water = 178 kg/m3
Cement = 414 kg/m3
Sand = 679 kg/m3
Aggregate = 1109 kg/m3
Mix ratio by weight on the basis of saturated and surface dry Aggregates
Cement : Sand : Aggregate
1 : 1.64 : 2.68 W/C Ratio = 0.43
Mix ratio by volume on the basis of room dry Aggregates
Cement : Sand : Aggregate
1 : 1.34 : 2.77 Free W/C Ratio = 0.43
11. TEST REPORT OF 15 CM CONCRETE CUBES FROM THE MIXES BEING REPORTED:
S. No.
|
Mix No.
|
Grade of Concrete
|
Age (day)
|
Compressive strength (N/mm2)
|
1
|
A
|
M-15
|
7
|
14.5
|
2
|
7
|
14.0
| ||
3
|
7
|
13.5
| ||
4
|
28
|
22.5
| ||
5
|
28
|
23.0
| ||
6
|
28
|
22.5
| ||
1
|
B
|
M-20
|
7
|
19.0
|
2
|
7
|
20.0
| ||
3
|
7
|
20.2
| ||
4
|
28
|
29.0
| ||
5
|
28
|
30.3
| ||
6
|
28
|
29.5
| ||
1
|
C
|
M-25
|
7
|
24.0
|
2
|
7
|
23.3
| ||
3
|
7
|
25.0
| ||
4
|
28
|
34.0
| ||
5
|
28
|
34.5
| ||
6
|
28
|
34.5
| ||
1
|
D
|
M-30
|
7
|
27.5
|
2
|
7
|
28.0
| ||
3
|
7
|
27.0
| ||
4
|
28
|
41.5
| ||
5
|
28
|
42.0
| ||
6
|
28
|
41.0
|
12. COMPARASION OF CONCRETE MADE WITH CRUSHED AND UNCRUSHED AGGREGATES AND RIVER SAND IN BOTH THE CASES.
M-20 Grade of Concrete: Slump 40-60 mm, exposure-Mild Target Strength = 28.3 N/mm2 at 28 days age.
M-20 Grade of Concrete: Slump 40-60 mm, exposure-Mild Target Strength = 28.3 N/mm2 at 28 days age.
Description/Materials per cum.
|
Mix with Screeners uncrushed Aggregates
|
Mix with Hardwar crushed aggregate. In both the cases river sand of same grading of Zone-II
|
| Free water kg/m3 |
170
|
192
|
| OPC 43 grade kg/m3 |
320
|
349
|
| River sand |
756
|
720
|
| 20 mm graded aggregate |
1134
|
1089
|
| W/C Ratio |
0.53
|
0.55
|
| Sp. Gr. Of Combined Aggregates on SSD bars |
2.65
|
2.65
|
| Density kg/m3 |
2380
|
2350
|
| Slump mm |
50
|
50
|
| Av. 7 day compressive strength N/mm2 |
19.7
|
20.0
|
| Av. 28-day compressive strength N/mm2 |
29.6
|
30.5
|
From the above test results, it can be seen that concrete made with uncrushed aggregate will be more impermeable, dense, better finished and durable concrete, as it has 22 kg/m3 less water. Due to reduction in water the uncrushed aggregate concrete will also have reduce shrinkage. The cement saving in this concrete is 29 kg/m3. Taking into consideration the cost of uncrushed aggregate the overall reduction in cost of concrete made with uncrushed aggregate comes to about Rs. 177/- per m3.
13. NOMINAL MIXES
As per IS: 456-2000 clause 9.3 page 23 and also revised CPWD Specifications-2002 clause 4.2.3.2 page 47 nominal mix concrete may be used for concrete of M-20 or lower grade. However, nominal mix concrete is likely to involve a higher cement content.
As per IS: 456-2000 clause 9.3 page 23 and also revised CPWD Specifications-2002 clause 4.2.3.2 page 47 nominal mix concrete may be used for concrete of M-20 or lower grade. However, nominal mix concrete is likely to involve a higher cement content.
As screeners sand is of Zone-II and aggregate is 20 mm graded, the following nominal mixes by volume may be taken:
Cement : Sand : 20 mm aggregate
For M-15 Grade 1:2:4
For M-20 Grade 1:1.5:3
Note: If the mix is found harsh sand quantity has to be increased and aggregate is to be reduced with the same volume such as 1:2.5:3.5 in place of 1:2:4
For M-15 Grade 1:2:4
For M-20 Grade 1:1.5:3
Note: If the mix is found harsh sand quantity has to be increased and aggregate is to be reduced with the same volume such as 1:2.5:3.5 in place of 1:2:4
While taking aggregates by volume the bulking of sand is to be taken into consideration as per moisture of site sand. Free water cement ratio is to be maintained as per concrete required strength and exposure condition.
CONCLUSION:
1. In the production of crushed aggregate, the crushing plant generate dust. This ‘fugitive’ dust, if releases in the atmosphere untreated may pose pollution problem. Whereas, this pollution problem is not with the production of uncrushed (gravel/shingle) aggregate which is produces in the modern fully mechanized screening & washing plant.
1. In the production of crushed aggregate, the crushing plant generate dust. This ‘fugitive’ dust, if releases in the atmosphere untreated may pose pollution problem. Whereas, this pollution problem is not with the production of uncrushed (gravel/shingle) aggregate which is produces in the modern fully mechanized screening & washing plant.
2. In all the codes for civil engineering construction uncrushed (gravel/shingle) aggregates are specified in the production of concrete.
3. The construction sites, particularly the Govt. departments hesitates in the use of uncrushed coarse aggregate as so far they are being supplied to them direct from the river bed or by manual sieving without washing them with water. Thus neither they are clean nor properly graded. This draw back is not with the uncrushed aggregates produces and supplied from screeners modern fully mechanized automatic screening & washing plant with regular quality control. Screeners produces from river bed and supply in its natural form uncrushed (gravel/shingle) coarse aggregates of sizes 40mm, 20mm, 12.5mm and river clean coarse sand of the same source of river. All the aggregates are produces and supplied as per the specifications of IS: 383-1970.
4. Crushed coarse aggregates are about 57% costlier than screeners uncrushed river bed coarse aggregates. Crushed aggregates are transported from long distances which increases road congestion and poses pollution problems on the road as they are loaded and transported in dry state. Screeners uncrushed aggregates are locally available and transported in wet condition thus no dust generated during production, handling and in its transport.
5. During travel of gravels in river its sizes are reduces naturally without any micro cracking in the aggregates body or any crack and loose fragments attached in it. Infact this is not so with crushed aggregate as in mechanical crushing there are chances of attached crack and week fragments in the aggregate which may affect the strength of concrete.
6. Unwashed crushed aggregate surfaces are generally coated with crusher dust, therefore, the rough surface bond benefit of crushed aggregate is not fully utilized. On the other hand a wash, clean, well graded having within limit flaky and elongated particles uncrushed (gravel/shingle) aggregates locally available is better than crushed aggregate coated with crusher dust and transported from long distances to construction site.
7. In most of the concrete construction M-20, M-25 and M-30 grade of concrete is used. For such low strength concrete there is no justification at all in the use of crushed aggregate, particularly, when as per I.S. Specifications uncrushed aggregates from river bed are locally available, that too 57% cheaper than crushed aggregates.
8. Angular shape of crushed aggregate required more water for a given workability. Thus more cement will be required for a given water-cement ratio. More water-cement paste means less durability of concrete. Naturally formed surfaces of uncrushed aggregates from river bed improved the workability and this is advantageous in terms of reduced water demand which produces more dense, impermeable and durable concrete.
9. SCREENERS have set up quality control laboratory at its plant site. The builders including Govt. Departments may take the benefits of its free technical services in the DESIGN OF CONCRETE MIXES as per their site requirements. Generally for a construction site a Concrete Mix Design is carried out from a particular batch of aggregates. During construction in most cases the aggregates are changed and such Mix Design report has no value. In fact this is not so with SCREENERS uncrushed aggregates and river clean coarse sand as all sizes of aggregate and river sand are available throughout the year, even during the rainy seasons and supplied in consistent quality. Therefore, a CONCRETE MIX DESIGN developed with SCREENERS uncrushed coarse aggregates and river sand remain for the entire a construction work. The same benefits are also for nominal mixes.
10. To prevent pollution and save construction cost in all tender specifications for general concrete construction uncrushed (gravel/shingle) aggregates and river sand be specified. As screeners produces uncrushed (gravel/shingle) of sizes 40 mm, 20 mm, 12.5mm and river coarse sand from one source of river as per specifications of IS: 383-1970 these plants uncrushed aggregates and river sand be specified in the tender documents, without any hesitation.
REFERENCES:
1. SP-1982- Hand Book on Concrete Mixes (Based on Indian Standard) BIS, New Delhi.
2. IS: 383-1970- Specification for Coarse and fine aggregates from natural sources for concrete (second revision) BIS, New Delhi.
3. A.M. Neville- Properties of Concrete, 4th Edition.
4. Revised CPWD Specification 2002 for Cement Mortar Cement Concrete and RCC Work (In pursuance to IS: 456-2000)
5. Kishore Kaushal- Combining Fine and Coarse Aggregates, CE&CR, June 2004, pp 46-50.
6. IS: 456-2000- Plain and Reinforced Concrete, Code of Practice (Fourth Revision), BIS, New Delhi.
7. Dr. S.K. Kaushik, Dr. C.B. Kukreja, Professor V.K. Gupta and Kaushal Kishore- Material Testing Laboratory Manual, Standard Publishers Distributors, 1705-B, Nai Sarak, Delhi-110 006.
8. Kishore Kaushal- Concrete Mix Design based on IS: 456-2000, Civil Engineering & Construction Review march, 2001, pp 46-55.
9. IS: 2386- Method of Test for Aggregate for Concrete BIS, New Delhi.
(Part-I) - Particle size and shape
(Part-II) - Estimation of Deleterious Materials and Organic
Impurities.
(Part-III) - Specific Gravity, Density, Viods, Absorption and
Bulking.
(Part-IV) - Mechanical Properties.
(Part-V) - Soundness.
10. Kishore Kaushal- Manual of Concrete, Mix Design based on IS: 456-2000. Standard Publisheras Distributors, 1705-B, Nai Sarak, Delhi-110 006.
1. SP-1982- Hand Book on Concrete Mixes (Based on Indian Standard) BIS, New Delhi.
2. IS: 383-1970- Specification for Coarse and fine aggregates from natural sources for concrete (second revision) BIS, New Delhi.
3. A.M. Neville- Properties of Concrete, 4th Edition.
4. Revised CPWD Specification 2002 for Cement Mortar Cement Concrete and RCC Work (In pursuance to IS: 456-2000)
5. Kishore Kaushal- Combining Fine and Coarse Aggregates, CE&CR, June 2004, pp 46-50.
6. IS: 456-2000- Plain and Reinforced Concrete, Code of Practice (Fourth Revision), BIS, New Delhi.
7. Dr. S.K. Kaushik, Dr. C.B. Kukreja, Professor V.K. Gupta and Kaushal Kishore- Material Testing Laboratory Manual, Standard Publishers Distributors, 1705-B, Nai Sarak, Delhi-110 006.
8. Kishore Kaushal- Concrete Mix Design based on IS: 456-2000, Civil Engineering & Construction Review march, 2001, pp 46-55.
9. IS: 2386- Method of Test for Aggregate for Concrete BIS, New Delhi.
(Part-I) - Particle size and shape
(Part-II) - Estimation of Deleterious Materials and Organic
Impurities.
(Part-III) - Specific Gravity, Density, Viods, Absorption and
Bulking.
(Part-IV) - Mechanical Properties.
(Part-V) - Soundness.
10. Kishore Kaushal- Manual of Concrete, Mix Design based on IS: 456-2000. Standard Publisheras Distributors, 1705-B, Nai Sarak, Delhi-110 006.
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