Determination of Aggregate Impact Value – Impact Test on Aggregates is done to carry out to:

• Determine the impact value of the road aggregates,
• Assess their suitability in road construction on the basis of impact value.

Aggregate Impact Value on Coarse Aggregates

Apparatus for Aggregate Impact Test

The apparatus as per IS: 2386 (Part IV) – 1963 consists of:
(i) 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.
(ii) A cylindrical steel cup of internal diameter 102 mm, depth 50 mm and minimum thickness 6.3 mm. .
(iii) 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.

(iv) A cylindrical metal measure having internal diameter 75 mm and depth 50 mm for measuring aggregates.
(v) Tamping rod 10 mm in diameter and 230 mm long, rounded at one end.
(vi) A balance of capacity not less than 500g, readable and accurate up to 0.1 g.

Theory of Aggregate Impact Test

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.

Procedure of Aggregate Impact Test

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.

(i) 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.
(ii) Pour the aggregates to fill about just 1/3 rd depth of measuring cylinder.
(iii) Compact the material by giving 25 gentle blows with the rounded end of the tamping rod.
(iv) Add two more layers in similar manner, so that cylinder is full.
(v) Strike off the surplus aggregates.
(vi) Determine the net weight of the aggregates to the nearest gram(W).
(vii) 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.
(viii) 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.
(ix) 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.
(x) 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.

Observations of Impact Test

Observations	Sample 1	Sample 2
Total weight of dry sample (W1 gm)
Weight of portion passing 2.36 mm sieve (W2 gm)
Aggregate Impact Value (percent) = W2 / W1 X 100

Mean =

Result of Impact Test

Aggregate Impact Value =

Recommended Aggregate Impact Test Values

Classification of aggregates using Aggregate Impact Value is as given below:

Aggregate Impact Value	Classification
<20%	Exceptionally Strong
10 – 20%	Strong
20-30%	Satisfactory for road surfacing
>35%	Weak for road surfacing

Specified limits of percent aggregate impact value for different types of road construction by Indian Roads Congress is given below.

Sl No	Type of pavement	Aggregate impact value not more than
1.	Wearing Course	30
a)	Bituminous surface dressing
b)	Penetration macadam
c)	Bituminous carpet concrete
d)	Cement concrete
2.	Bitumen bound macadam base course	35
3.	WBM base course with bitumen surfacing	40
4	Cement concrete base course	45

41. A first class brick when immersed in cold water for 24 hours should not absorb water more than
a) 15%
b) 20%
c) 22%
d) 25%
Ans: b

42. Crushing strength of a first class brick should not be less than
a) 3.5 N/mm2
b) 7.0 N/mm2
c) 10.5 N/mm2
d) 14.0 N/mm2
Ans: c

43. The main function of alumina in brick earth is
a) to impart plasticity
b) to make the brick durable
c) to prevent shrinkage
d) to make the brick impermeable
Ans: a

44. The percentage of alumina in a good brick earth lies between
a) 5 to 10%
b) 20 to 30%
c) 50 to 60%
d) 70 to 80%
Ans: b

45. Excess of alumina in brick earth makes the brick
a) impermeable
b) brittle and weak
c) to lose cohesion
d) to crack and warp on drying
Ans: d

46. The nominal size of the modular brick is
a) 190 mm x 90mmx 80 mm
b) 190 mm x 190 mm x 90 mm
c) 200 mm x 100 mm x 100 mm
d) 200 mm x 200 mm x 100 mm
Ans: c

47. Percentage of silica in a good brick earth lies between
a) 5 to 10%
b) 20 to 30%
c) 50 to 60%
d) 70 to 80%
Ans: c

48. Excess of silica in brick earth results in
a) cracking and warping of bricks
b) loss of cohesion
c) enhancing the impermeability of bricks
d) none of the above
Ans: b

49. Which of the following ingredients of the brick earth enables the brick to retain its shape ?
a) alumina
b) silica
c) iron
d) magnesia
Ans: b

50. Which of the following pairs gives a correct combination of the useful and harmful constituents respectively of a
good brick earth ?
a) lime stone and alumina
b) silica and alkalies
c) alumina and iron
d) alkalies and magnesium
Ans: b

51. The process of mixing clay, water and other ingredients to make brick is known as
a) kneading
b) moulding
c) pugging
d) drying
Ans: a

52. Advantage of a clamp compared to a kiln for burning bricks is that
a) it takes less time for burning
b) it gives more output of first class bricks
c) it has less initial cost
d) it is suitable when bricks are required in large numbers
Ans: c

53. The internal size of mould used in brick preparation is
a) equal to the size of a fully burnt brick
b) smaller than the size of a fully burnt brick
c) greater than the size of a fully burnt brick
d) none of the above
Ans: c

54. Pug mill is used for
a) preparation of clay
b) moulding of clay
c) drying of bricks
d) burning of bricks
Ans: a

55. Which of the following bricks are used for lining of furnaces ?
a) overburnt bricks
b) underburnt bricks
c) refractory bricks 
d) first class bricks
Ans: c

56. The frog of the brick in a brick masonry is generally kept on
a) bottom face
b) top face
c) shorter side
d) longer side
Ans: b

57. Number of bricks required for one cubic metre of brick masonry is
a) 400
b) 450
c) 500
d) 550
Ans: c

58. Glazing is used to make earthenware
a) hard
b) soft
c) porous
d) impervious
Ans: d

59. Quick lime is
a) calcium carbonate
b) calcium oxide
c) calcium hydroxide
d) none of the above
 Ans: b

60. Quick lime is
i) slow in setting
ii) rapid in slacking
iii) good in strength The correct answer is
a) only (i)
b) only (ii)
c) both (i) and (ii)
d) both (ii) and (iii)
Ans: c

21. Crushing strength of a good building stone should be more than
a) 50 MPa
b) 100 MPa
c) 150 MPa
d) 200 MPa
Ans: b

22. Specific gravity for most of the building stones lies between
a) 1.5 to 2.0
b) 2.0 to 2.5
c) 2.5 to 3.0
d) 3.0 to 3.5
Ans: c

23. Spalling hammer is used for
a) driving wooden headed chisels
b) rough dressing of stones
c) carving of stones
d) breaking small projection of stones
Ans: b

24. Cross cut saw is used for
a) cutting soft stones
b) cutting hard stones
c) cutting large blocks of stones
d) dressing stones
 Ans: b

25. Sapwood consists of
a) innermost annular rings around the pith
b) portion of timber between heartwood and cambium layer
c) thin layers below the bark
d) thin fibre which extends from the pith outwards and holds the annular rings together
Ans: b

26. Which of the following trees yields hard wood ?
a) deodar
b) chir
c) shishum
d) pine
Ans: c

27. The radial splits which are wider on the outside of the log and narrower towards the pith are known as
a) heart shakes
b) cupshakes
c) starshakes
d) rindgalls
Ans: c

28. In which of the following pairs both trees yield soft wood?
a) deodar and shishum
b) chir and sal
c) sal and teak
d) chir and deodar
Ans: d

29. Which of the following timbers is suitable for making sports goods ?
a) mulberry
b) mahogany
c) sal
d) deodar
Ans: a

30. Assertion A : Shishum is used for decorative woodwork.
Reason R : Shishum can be polished to an excellent finish.
Select your answer according to the coding system given below :
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true
Ans: a

31. The disease of dry rot in timber is caused by
a) lack of ventilation
b) alternate wet and dry conditions
c) complete submergence in water
d) none of the above
Ans: a

32. Plywood has the advantage of'
a) greater tensile strength in longer direction
b) greater tensile strength in shorter direction
c) same tensile strength in all directions
d) none of the above
Ans: c

33. In which of the following directions, the strength of timber is maximum ?
a) parallel to grains
b) 45° to grains
c) perpendicular to grains
d) same in all directions
Ans: a

34. The moisture content in a well seasoned timber is
a) 4% to 6%
b) 10% to 12%
c) 15% to 20%
d) 100%
Ans: b

35. The trunk of tree left after cutting all the branches is known as
a) log
b) batten
c) plank
d) baulk
Ans: a

36. The age of a tree can be known by examining
a) cambium layer
b) annular rings
c) medullary rays
d) heart wood
Ans: b

37. Plywood is made by bonding together thin layers of wood in such a way that the angle between grains of any layer to grains of adjacent layers is
a) 0°
b) 30°
c) 45°
d) 90°
 Ans: d

38. The plywood
a) has good strength along the panel only
b) can be spilt in the plane of the panel
c) has greater impact resistance to blows than ordinary wood
d) cannot be bent more easily than ordinary wood of same thickness
Ans: c

39. The practical limit of moisture content achieved in air drying of timber is
a) 5%
b) 15%
c) 25%
d) 35%
Ans: b

40. First class timber has an average life of
a) less than one year
b) 1 to 5 years
c) 5 to 10 years
d) more than 10 years
Ans: d

1. Gypsum is a
a) mechanically formed sedimentary rock
b) igneous rock
c) chemically precipitated sedimentary rock
d) metamorphic rock
Ans: c

2. Which of the following sedimentary rocks changes into quartzite by metamorphic action ?
a) sand stone
b) lime stone
c) shale
d) gypsum
Ans: a

3. Which of the following represents a metamorphic rock?
i) slate
ii) shale
iii) quartzite
The correct answer is
a) only (iii)
b) both (i) and (iii)
c) both (ii) and (iii)
d) all (i), (ii) and (iii)
Ans: b

4. Quartitze is a
a) silicious rock
b) argillaceous rock
c) calcareous rock
d) aqueous rock
Ans: a

5. Which of the following is a mineral ?
a) basalt
b) granite
c) quartz
d) syenite
Ans: c

6. Slate is formed by metamorphic action on
a) shale
b) lime stone
c) sand stone
d) granite
Ans: a

7. Sandstone is a
i) sedimentary rock
ii) aqueous rock
iii) silicious rock
The correct answer is
a) only (i)
b) both (i) and (ii)
c) both (i) and (iii)
d) all (i), (ii) and (iii)
Ans: d

8. Which of the following is a rock ?
a) quartz
b) mica
c) gypsum
d) none of the above
Ans: c

9. Based on the following rocks and minerals, select the correct statement, quartz, shale, basalt, granite, marble, gypsum, mica
a) basalt and marble are the only metamorphic rocks
b) there is no sedimentary rock
c) granite is the only igneous rock
d) quartz and mica are minerals
Ans: d

10. A heavy stone is suitable for
a) arches
b) rubble masonry
c) roads
d) retaining walls
Ans: d

11. The stone suitable for rubble masonry should be.
a) hard
b) tough
c) heavy
d) light
Ans: a

12. Which of the following metamorphic rocks has the most weather resisting characteristics?
a) marble
b) quartzite
c) slate
d) lime stone
Ans: b

13. A good building stone should not absorb water more than
a) 5%
b) 10%
c) 15%
d) 20%
Ans: a

14. Which of the following has more fire resisting characteristics ?
a) marble
b) lime stone
c) compact sand stone
d) granite
Ans: c

15. Jumper is a tool used for
a) testing of stones
b) quarrying of stones
c) dressing of stones
d) none of the above
Ans: b

16. The important test to be conducted on a stone used in docks and harbours is-
a) hardness test
b) workability test
c) weight test
d) toughness test
Ans: c

17. The predominant constituent which is responsible for strength in granite is
a) quartz
b) felspar
c) mica
d) none of the above
Ans: a

18. Granite is not suitable for ordinary building purpose because
a) it can not be polished
b) it is not a fire proof material
c) it is costly
d) it has less crushing strength
Ans: c

19. Which of the following stone is best suited for construction of piers and abutments of a railway bridge ?
a) granite
b) sand stone
c) lime stone
d) quartzite
Ans: a

20. The preparation of surface of stone to obtain plain edges or to obtain stones of required size and shape is known as
a) quarrying of stones
b) blasting of stones
c) seasoning of stones
d) dressing of stones
Ans: d