Aggregate - coarse aggregates, testing & limits

classification and tests

1. UNIT-1 TRADITIONAL BUILDING MATERIALS “AGGREGATE”

2. INTRODUCTION Filler with binding material Derived from rocks Form body of concrete Reduce shrinkage and effect economy Occupy 70 -80 % of volume and have considerable influence on properties of concrete. Important to obtain good quality of aggregates. Not chemically inert Chemically active by exhibiting chemical bond at interface of aggregates and cement paste. securing volumetric stability and durability .

3. CLASSIFICATION Broadly aggregates are classified into two categories:- Fine aggregate (>0.07mm & passing through 4.75mm) Coarse aggregate(retained on 4.75 mm sieve & <80mm)

4. COARSE AGGREGATE

5. CLASSIFICATION On the basis of geological origin:- Natural Artificial On the basis of size:- All-in-aggregate Graded aggregate On the basis of shape:- Angular aggregate Flaky aggregate On the basis of unit weight:- Normal Heavy Light

6. GEOLOGICAL ORIGIN NATURAL AGGREGATE:- obtained by crushing rocks. Also by weathering action/natural agencies of rocks. Most widely used are igneous rocks. ARTIFICIAL AGGREGATE:- (not used for R.C.C works) Broken bricks (brick bats suitable for mass concreting e.g. foundations) Blast furnace slag (precast concrete products, fire resistant but responsible for corrosion due to sulphur content) Synthetic aggregates (thermally processed materials such as expanded clay and shale) (light weight concrete)

7. SIZE All-in-aggregate:- Different fractions of fine and coarse sizes. They are not recommended for quality concrete. Graded aggregate:- Aggregate most of which passes through a particular size of sieve are known as graded aggregate. e.g.: a graded aggregate of nominal size 20mm means an aggregate of which passes IS sieve 20 mm.

8. SHAPE Elongated aggregate:- Length is 1.8 times or nine fifths of its mean dimension. Flaky aggregate:- Least lateral dimension should be less than 0.6 times or three fifths of the mean dimension. Orient in one plane with water and air voids underneath. Adversely effect durability and are restricted to maximum of 15 %.

9. UNIT WEIGHT AGGREGATE SPECIFIC G R A VITY UNIT WEIGHT (kN/m3) BULK DENSITY (kN/m3) EXAMPLE normal-weight 2.5-2.7 23-26 15.20-16.80 sand heavy-weight 2.8-2.9 25-29 >20.80 Scrap iron light-weight 12 <11.20 dolomite

10. SURFACE TEXTURE (SMOOTHNESS & ROUGHNESS) CLASSIFICATION EXAMPLES Glassy Black flint Smooth Gravel, Marble Granular Sandstone Rough Basalt Crystalline Granite Honeycombed & Porous Brick, slag

11. GOOD QUALITIES OF AN IDEAL AGGREGATE: An ideal aggregate used for the manufacturing of concrete and mortar, should meet the following requirements. It should consist of natural stones, gravels and sand or in various combinations of these materials. It should be hard, strong and durable. It should be dense, clear and free from any coating. It should be free from injurious vegetable matters. It should not contain flaky (angular) and elongated pieces. It sh o ul d no t c o n t a in a n y m a t eri a l liable t o a t t ac k steel reinforcement in case of reinforced concrete.

12. CHARACTERISTICS OF AGGREGATES: Important characteristics of aggregates which influence the properties of resulting concrete mix are discussed as under : Aggregate containing the constituents which generally react with alkalies in cement cause excessive expansion, cracking of concrete mix, should never be used. Suitability of aggregates should be judged either by studying its service history or by laboratory tests.

13. The size and shape of the aggregate particles mainly influence the quantity of cement required in a concrete mix and ultimately economy of the concrete. For the preparation of economical concrete, one should use largest coarse aggregates feasible for the structure. Type of structure Max. size of aggregate 1. Mass concrete work 40 mm i.e. dams, retaining walls, piers and abutments, etc. 2. R.C.C work i.e. beams, 20 mm columns, etc 3. Flooring 10 mm

14. PROPERTIES STRENGTH PARTICLE SHAPE SPECIFIC GRAVITY BULK DENSITY VOIDS POROSITY MOISTURE CONTENT

15. STRENGTH Should be equal to that of concrete. Rocks commonly used as aggregates have a higher compressive strength. Tests conducted for evaluation of strength are crushing, impact and ten % fines test. Crushing test is more reliable. Toughness by impact test. Hardness by abrasion test.

16. SHAPE & TEXTURE Shape influences the properties of fresh concrete more than hardened concrete. Round & irregular aggregates are highly workable but yield low strength. Flaky aggregates require more cement paste, produce maximum voids. Angular shape is best. Shape and texture governs water requirement.

17. SPECIFIC GRAVITY SG lies between 2.6 – 3.5 for natural aggregates. Influences strength and absorption of concrete. Low SG high porosity and therefore poor durability and low strength. Density greatly depends upon specific gravity.

18. BULK DENSITY & VOIDS Depends upon particle size , grading and moisture content. A higher bulk density of coarse aggregate is an indication of fewer voids to be filled by sand and cement. If the voids are more in the concrete , the strength will be low.

19. POROSITY The entrapped air bubbles in the rocks during their formation lead to minute holes called as pores or cavities. The porosity of rocks is less than 20%. T h e concrete becomes permeable and effects bond. The porous aggregate absorbs more moisture, resulting in loss of workability.

20. MOISTURE CONTENT A high moisture content increases the W/C ratio to an appreciable extent. The surface moisture expressed as a % of the weight of the saturated surface dry aggregate is known as moisture content.

21. DELETERIOUS MATERIALS & ORGANIC IMPURITIES Organic matters, clay, shale, coal, iron pyrites, etc., may have harmful or chemical effects on the aggregates. Affects the properties of concrete and are undesirable. Salts cause efflorescence. Sulphides cause surface staining.

22. ALKALI AGGREGATE REACTION Inert material till 1940. Extensive expansion and complete disruption and disintegration of the concrete is known as alkali aggregate reaction or concrete cancer. The trouble is due to reaction between silica in aggregate and alkalis in cement. A reactive aggregate , if in finely ground state will inhibit the action. Reaction between cement and aggregate can be of two types:- alkalis with either silicas or carbonates in the aggregate. Reaction with silicas is common.

23. The AAR takes place only in presence of water or water vapour . The water forms strong caustic solute with alkalis of cement. This caustic liquid attacks reactive silica to form alkali silica gel (AAR GEL) of unlimited swelling type.

24. Concept clarity

25. Pics of Alkali Aggregate Reaction

26. Factors affecting Alkali Aggregate Reaction Reactive type of aggregates [REACTIVE SILICA] , have been found to have serious effects IF PRESENT IN SMALL QUANTITIES BUT NOT if it constitutes the whole of aggregate. High alkali content of cement . If there is very small amount of alkalis in cement and very reactive silica it is not a problem, however the increase in alkali content [> 0.6 %] of cement posses issues of AAR. Availability of Moisture Content . AAR occurs ONLY in the presence of moisture, which is the reason why AAR is NOT observed in the interior mass of concrete . Temperature Conditions should be favourable, generally in the range of 10 to 38 C .

27. Control of Alkali Aggregate reaction By selecting non – reactive aggregate. By using Low Alkali Cement. By controlling Moisture Content. By using Puzzolonas [REACTIVE SILICA] The aggregates are found to be reactive when they contain silica in a particular proportion and fineness . When fly-ash or surkhi or dust is added this optimum condition of silica being in particular proportion and fineness is disturbed and the aggregates become passive. By adding air-entraining agents. Alkali silica gel which imparts pressure over the set cement gel, can be negated with the addition of air entraining agents which absorb the osmotic pressure.

28. SOUNDNESS Soundness is defined as the ability of aggregate to resist changes in volume as a result of changes in physical conditions. The conditions like freezing, thawing, temperature changes, alternate wetting and drying. Porous and weak aggregates undergo excessive volume changes under these conditions.

29. THERMAL PROPERTIES The coefficient of thermal expansion of concrete increase with that of coarse aggregate. Any difference in the coefficients of coarse aggregate and cement paste may break the bond between the two.

30. FINENESS MODULUS (F.M ) It is a numerical index of fineness, giving some idea about the mean size of the particles in aggregates. The sum of cumulative percentage of residues retained on each of the Indian standard sieves ( 80mm, 40mm, 20mm,10mm, 4.75mm, 2.36m , 1.18mm , 600 microns, 300 microns and 150 microns each succeeding sieve has half the aperture of the previous one), divided by the 100,is known as “ Fineness modulus ” of the aggregates.

31. The fineness modulus of an aggregate is roughly proportional to the average size of particles of the aggregates. The F.M. varies between 2 to 3.2 for fine aggregate, between 5.5 to 8 for coarse aggregate and between 3.5 to 6.5 for all in aggregate. The objective of finding F.M. is to grade the given aggregate for the required strength and workability of concrete mix with minimum cement. Higher the F.M. aggregate result in harsh concrete mixes and lower F.M. results in uneconomical concrete mixes.

32. TESTS ON AGGREGATE PARTICLE SIZE FLAKINESS &ELONGATION INDEX MOISTURE CONTENT SPECIFIC GRAVITY AND WATER ABSORPTION TEN PERCENT FINE VALUE AGGREGATE CRUSHING VALUE AGGREGATE IMPACT VALUE AGGREGATE ABRASION VALUE

33. PARTICLE SIZE 35 Sieve analysis is also called as Particle size value. In determination of the proportions of the particles with in certain ranges in an aggregate by separation on various sieves of different size openings, may be defined as sieve analysis. FINENESS MODULUS = cumulative % of agg retained on each sieve /100

34. 36

35. FLAKINESS & ELONGATION INDEX Large number of flaky particles more voids more mortar to fill voids uneconomy effects durability. Aggregates may break down easily under heavy loads. Also called shape test. I.S. 2836 part-1

36. TEST Apparatus required:- Aggregate sample Digital balance Elongation gauge & Thickness gauge Test sieves of sizes – 63mm, 50mm, 40mm, 31.5mm, 25mm, 20mm, 16mm, 12.5mm and 10mm & 6.3 mm.

37. ELONGATION GUAGE

38. THICKNESS GAUGE

39. PROCEDURE Take the aggregate sample which contains minimum 200 pieces of any fraction. Sieve the sample through mentioned sieves i.e., from 63mm to 6.3mm sieves. The aggregate retained on 63mm and passed through 6.3mm should not be considered. The aggregate passed through 63mm and retained on 6.3mm and its above sieves is taken along with sieves. Now we have specified size range for every particle. Now weigh aggregate retained on different sieve and note down the total weight as “W1 ”

40. RESPECTIVE SLOTS IN GAUGES

41. For determining F.I., the aggregate retained on sieves are separated. Now each aggregate is passed through the corresponding slot in the thickness gauge. F.I. = (W1/W2) X 100 Where, W1 is weight of aggregate passing through the slot of thickness gauge. W2 is the total weight of sample.

42. For determining E.I ., the aggregate retained on sieves are separated. Then each aggregate piece is passed through the corresponding slot of length gauge. E.I. = (W1/W2) x 100 Where, W1 is weight of aggregate retained on length gauge. W2 is total weight of aggregate.

43. MOISTURE CONTENT A sample of 2 kg of aggregate is used for conducting the test. The sample should be throughly washed to remove finer particles, dust etc., & then placed in wire basket and immersed in distilled water at room temperature for a period of 24 hrs. Then the aggregates are removed & gently surface dried with a dry cloth and weighed.

44. The aggregates are then placed in an oven at a temperature of 100 to 110 degree C for 24 hrs. After 24 hrs , aggregates are removed and cooled in air tight container and weighed. Water Absorption = (W1/W2) x 100 Where, W1 is weight in gm of the surface dry aggregate. W2 is weight in gm of oven dried aggregate. Water absorption shall not exceed 2%.

45. Sp.Gr. is used in certain computations for concrete mix design or control work, such as, absolute volume of aggregate in concrete. It is not a measure of the quality of aggregate. S p . G r .= Weight of Agg. (W A ) Weight of an equal volume of water (V A *ρ w ) = W A V A *ρ w = ρ A ρ w Density of Agg. SPECIFIC GRAVITY Density of Water

46. AGGREGATE IMPACT VALUE TEST The aggregate impact value gives a relative measure of the resistance of an aggregate to sudden shock or impact. The property of a material to resist impact is known as toughness. Due to movement of vehicles on the road the aggregates are subjected to impact resulting in their breaking down into smaller pieces . The aggregates should therefore have sufficient toughness to resist their disintegration due to impact. This characteristic is measured by impact value test . The aggregate impact value is a measure of resistance to sudden impact or shock, which may differ from its resistance to gradually applied compressive load.

47. APARATUS The apparatus as per IS: 2386 (Part IV) – 1963 consists of : A testing machine weighing 45 to 60 kg and having a metal base with a painted lower surface of not less than 30 cm in diameter. It is supported on level and plane concrete floor of minimum 45 cm thickness. The machine should also have provisions for fixing its base . A cylindrical steel cup of internal diameter 102 mm, depth 50 mm and minimum thickness 6.3 mm . A metal hammer or tup weighing 13.5 to 14.0 kg the lower end being cylindrical in shape, 50 mm long, 100.0 mm in diameter, with a 2 mm chamfer at the lower edge and case hardened. The hammer should slide freely between vertical guides and be concentric with the cup. Free fall of hammer should be within 380±5 mm . A cylindrical metal measure having internal diameter 75 mm and depth 50 mm for measuring aggregates . Tamping rod 10 mm in diameter and 230 mm long, rounded at one end. A balance of capacity not less than 500g, readable and accurate up to 0.1g.

48. PROCEDURE The test sample consists of aggregates sized 10.0 mm 12.5 mm. Aggregates may be dried by heating at 100-110° C for a period of 4 hours and cooled . Sieve the material through 12.5 mm and 10.0mm IS sieves. The aggregates passing through 12.5mm sieve and retained on 10.0mm sieve comprises the test material. Pour the aggregates to fill about just 1/3 rd depth of measuring cylinder. Compact the material by giving 25 gentle blows with the rounded end of the tamping rod. Add two more layers in similar manner, so that cylinder is full. S trike off the surplus aggregates. Determine the net weight of the aggregates to the nearest gram(W). Bring the impact machine to rest without wedging or packing up on the level plate, block or floor, so that it is rigid and the hammer guide columns are vertical. Fix the cup firmly in position on the base of machine and place whole of the test sample in it and compact by giving 25 gentle strokes with tamping rod. Raise the hammer until its lower face is 380 mm above the surface of aggregate sample in the cup and allow it to fall freely on the aggregate sample. Give 15 such blows at an interval of not less than one second between successive falls.

49. Remove the crushed aggregate from the cup and sieve it through 2.36 mm IS sieves until no further significant amount passes in one minute. Weigh the fraction passing the sieve to an accuracy of 1 gm. Also, weigh the fraction retained in the sieve. Compute the aggregate impact value. The mean of two observations, rounded to nearest whole number is reported as the Aggregate Impact Value. Aggregate impact value = (W2/W1) x 100 Where, W1 is total weight of dry sample W2 is weight of portion passing through 2.36 mm sieve. Recommended Aggregate Impact Test Values Aggregate Impact Value Classification <20% Exceptionally Strong 10 – 20% Strong 20-30% Satisfactory for road surfacing >35% Weak for road surfacing

50. AGGREGATE CRUSHING VALUE I.S. 2386-PART 4 Aggregate crushing value test on coarse aggregates gives a relative measure of the resistance of an aggregate crushing under gradually applied compressive load . Coarse aggregate crushing value is the percentage by weight of the crushed material obtained when test aggregates are subjected to a specified load under standardized conditions. Aggregate crushing value is a numerical index of the strength of the aggregate and it is used in construction of roads and pavements .

51. APARATUS A steel cylinder 15 cm diameter with plunger and base plate. A straight metal tamping rod 16mm diameter and 45 to 60cm long rounded at one end. A balance of capacity 3 kg readable and accurate to one gram. IS sieves of sizes 12.5mm, 10mm and 2.36mm A compression testing machine. Cylindrical metal measure of sufficient rigidity to retain its from under rough usage and of 11.5cm diameter and 18cm height. Dial gauge

52. PROCEDURE Coarse aggregate passing 12.5mm IS sieve and retained on a10mm IS sieve are selected and heated at 100 to 110°C for 4 hours and cooled to room temperature . Put the cylinder in position on the base plate and weigh it  (W) . Put the sample in 3 layers, each layer being subjected to 25 strokes using the tamping rod. Care being taken in the case of weak materials not to break the particles and weigh it  (W1) . Level the surface of aggregate carefully and insert the plunger so that it rests horizontally on the surface. Care being taken to ensure that the plunger does not jam in the cylinder. Place the cylinder with plunger on the loading platform of the compression testing machine. Apply load at a uniform rate so that a total load of 40T is applied in 10 minutes.

53. Release the load and remove the material from the cylinder. Sieve the material with 2.36mm IS sieve, care being taken to avoid loss of fines. Weigh the fraction passing through the IS sieve (W2). Calculation of Aggregate Crushing Value The ratio of weight of fines formed to the weight of total sample in each test shall be expressed as a percentage, the result being recorded to the first decimal place. Aggregate crushing value = (W2 x 100) / ( W1-W) W2 =Weight of fraction passing through the appropriate sieve W1-W =Weight of surface dry sample . The aggregate crushing value shall not exceed 30%

54. TEN PERCENT FINES TEST The ten percent fines value gives a measure of the resistance of an aggregate to crushing, that is applicable to all aggregates. The sample for test consists of surface dry aggregates passing through a 12.5 mm sieve and retained on 10 mm sieve. T est sample is dried in oven for a period of four hours at a temperature of 100 to 110 C.  

55. PROCEDURE The cylindrical measure is filled by the test sample of aggregate in three layers of approximately equal depth, each layer being tamped 25 times. The test sample in the cylinder with the plunger in position is placed in the compression testing machine. The load is applied at a uniform rate so as to cause a total penetration of the plunger of about 20mm for normal crushed aggregates in 10 minutes. For rounded or partially rounded aggregates, the load required to cause a total penetration of 15mm is applied where as for honeycombed aggregates a penetration of 24mm is applied in 10 minutes.

56. After the maximum specified load is reached, the load is released and the aggregate from the cylinder is sieved from 2.36mm IS sieve. The fines passing 2.36mm.IS sieve is weighed and expressed as a percentage of by weight of the test sample. Normally this % will fall within the range 7.5 to 12.5. Load required for 10% fines = 14x / (y + 4) x  = load in tones y  = mean percentage fines from two tests at x tone load.

57. AGGREGATE ABRASION VALUE The abrasion value of coarse aggregate may be determined by either Deval machine or Los Angeles machine. The aggregate abrasion value gives a relative measure of resistance of an aggregate to wear when it is rotated in a cylinder along with some abrasive charge. The percentage wear of the aggregates due to rubbing with steel balls is determined and is known as Los Angeles Abrasion Value. ABRASIVE CHARGE:- cast iron spheres or steel balls approximately 48 mm in diameter and weighing between 390 to 445 gm.

58. 64

59. PROCEDURE The test sample consists of clean aggregates dried in oven at 105° – 110°C. The sample should conform to any of the gradings shown in table 1. Select the grading to be used in the test such that it conforms to the grading to be used in construction, to the maximum extent possible. Take 5 kg of sample for gradings A, B, C & D and 10 kg for gradings E, F & G. Choose the abrasive charge as per Table 2 depending on grading of aggregates. Place the aggregates and abrasive charge on the cylinder and fix the cover.

60. Rotate the machine at a speed of 30 to 33 revolutions per minute. The number of revolutions is 500 for gradings A, B, C & D and 1000 for gradings E, F & G. The machine should be balanced and driven such that there is uniform peripheral speed. The machine is stopped after the desired number of revolutions and material is discharged to a tray. The entire stone dust is sieved on 1.70 mm IS sieve. The material coarser than 1.7mm size is washed, dried in oven at 105 – 110 degree C & weighed correct to one gram.

61. Sieve size (square hole) Weight of test sample in gm Passing (mm) Retained on (mm) A B C D E F G 80 63 2500* 63 50 2500* 50 40 5000* 5000* 40 25 1250 5000* 5000* 25 20 1250 5000* 20 12.5 1250 2500 12.5 10 1250 2500 10 6.3 2500 6.3 4.75 2500 4.75 2.36 5000

62. Grading No of Steel balls Weight of charge in gm. A 12 5000 ± 25 B 11 4584 ±25 C 8 3330 ± 20 D 6 2500 ± 15 E 12 5000 ± 25 F 12 5000 ± 25 G 12 5000 ± 25

63. Original weight of aggregate sample = W 1  g Weight of aggregate sample retained = W 2  g Weight passing 1.7mm IS sieve = W 1  – W 2  g Abrasion Value = (W 1  – W 2  ) / W 1  X 100 Maximum abrasion value ranges between 30 % to 60 % for various pavement types.