Transportation Engineering I Lab Notes

1. Objective

To determine the abrasion value of coarse aggregates using the Los Angeles Machine as per IS: 2386 (Part IV) – 1963. This test assesses the hardness of aggregates and their resistance to wear due to abrasion and attrition.

2. Apparatus

• Los Angeles Abrasion Machine
• Abrasive charge (Steel balls, approx. 48mm diameter, 390-445g each)
• IS Sieves (1.70 mm, and sizing sieves for grading)
• Balance (accuracy 1g or 0.1% of sample weight)

3. Theory & Scope

The Los Angeles (LA) abrasion test measures the degradation of mineral aggregates of standard gradings resulting from a combination of actions including abrasion or attrition, impact, and grinding in a rotating steel drum containing a specified number of steel spheres.

Significance: Road aggregates are subjected to abrasion effects by traffic wheels (pneumatic or iron-tired). Hardness (resistance to abrasion) is a critical property for wearing courses.

Standard Limits (IRC):

• For Bituminous Concrete/Surface Dressing: Max 30%
• For WBM Base Course/Bituminous Macadam: Max 40%
• For WBM Sub-base: Max 50%

4. Procedure

1. The sample was prepared by passing the aggregates through a 20 mm IS sieve and retaining them on a 10 mm IS sieve.
2. Clean aggregates were selected and 5000 g (5 kg) of the sample was weighed.
3. The weighed sample was placed into the cylinder of the Los Angeles Abrasion Machine.
4. An abrasive charge consisting of 11 steel balls was added to the machine along with the aggregates.
5. The machine cover was fixed efficiently, and the machine was rotated at a speed of 30 to 33 rpm for 15 min.
6. After the completion of revolutions, the machine was stopped, and the material was discharged into a tray.
7. The entire material was sieved through a 1.70 mm IS sieve to separate the fines.
8. The weight of the aggregate retained on the 1.70 mm sieve was measured and recorded.

5. Observations and Calculations

Parameter	Value
Grading Selected	B
Number of Steel Balls	11
Original Weight of Sample (W₁)	5000 g
Weight of Aggregate Retained (W₂)	3555 g (3.555 kg)
Loss of Weight (W₁ – W₂)	1445 g (1.445 kg)

6. Result

The Los Angeles Abrasion Value of the given aggregate sample is 28.9%.

7. Discussion and Conclusion

The obtained abrasion value is 28.9%.

Comparison with Standards: The value is below the strict limit of 30% specified for high-quality Bituminous Concrete and Surface Dressing.

Suitability: Since the value is less than 30%, the aggregate is considered hard and tough. It is suitable for all road construction purposes, including the topmost wearing courses (Bituminous Concrete) as well as base courses (WBM) and sub-bases.

Conclusion: The aggregate possesses excellent resistance to abrasion and is recommended for use in heavy traffic road pavements.

8. Precautions

• Sieving: Sieving through the 1.70 mm sieve must be thorough to ensure all fines are separated.
• Cleanliness: The sample must be clean and free from organic impurities.
• Machine Speed: The rotation speed of the drum must be strictly maintained between 30 and 33 rpm. Deviation in speed affects the impact dynamics of the steel balls.
• Abrasive Charge: The steel balls should be checked for wear; if they become too small or light, they should be replaced.

1. Objective

To determine the Aggregate Crushing Value (ACV) of coarse aggregates as per IS: 2386 (Part IV) – 1963. This test measures the resistance of an aggregate to crushing under a gradually applied compressive load.

2. Apparatus

• Steel cylinder (15.2 cm dia) with base plate and plunger
• Compression Testing Machine (CTM) capable of applying a load of 40 tonnes
• Tamping rod (16 mm dia, 45-60 cm long)
• IS Sieves (12.5 mm, 10 mm, and 2.36 mm)
• Balance (accuracy 1g)

3. Theory & Scope

The Aggregate Crushing Value gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load.

Significance: Aggregates in road pavements (especially top layers) must withstand the crushing effect of heavy traffic wheel loads and rollers. Weak aggregates crush into fines, leading to pavement failure.

Standard Limits:

• For Surface Course (Wearing Coat): Max 30%
• For Base Course (WBM): Max 45%

4. Procedure

1. The sample was prepared by passing the aggregates through a 12.5 mm sieve and retaining them on a 10 mm sieve.
2. The cylinder was filled in three equal layers, and each layer was tamped 25 times with the tamping rod.
3. The weight of the sample in the cylinder was recorded (W₁).
4. The plunger was inserted, and the assembly was placed in the Compression Testing Machine (CTM).
5. A load of 40 tonnes was applied gradually over a period of 10 minutes.
6. The crushed material was removed and sieved through a 2.36 mm IS sieve.
7. The fraction passing the 2.36 mm sieve was weighed (W₂).

5. Observations and Calculations

Description	Value (kg)
Weight of Measuring Cylinder	0.965
Weight of Measuring Cylinder + Aggregate	3.765
Weight of Aggregate (W₁)	2.800
Weight of Aggregate Retained on 2.36 mm Sieve	2.310
Weight of Aggregate Passing 2.36 mm Sieve (W₂)	0.490

6. Result

The Aggregate Crushing Value of the material is 17.5%.

7. Discussion and Conclusion

The Aggregate Crushing Value obtained was 17.5%. This value indicates that the aggregate possesses high resistance to crushing under gradually applied loads. Since the value is well below the maximum limit of 30% specified for wearing courses, the aggregate is classified as strong and is suitable for use in high-quality road construction, including surface courses and base courses.

8. Precautions

• Loading Rate: Apply the load of 40 tonnes uniformly over a period of 10 minutes to avoid sudden impact effects.
• Plunger Movement: Ensure the plunger moves freely inside the cylinder without friction against the walls.
• Tamping: Tamp each layer exactly 25 times to ensure uniform compaction of the sample.
• Sieving: Handle the crushed material carefully to prevent any loss of fines during transfer and sieving.

1. Objective

To estimate the Aggregate Impact Value (AIV) of the given sample as per IS: 2386 (Part IV) – 1963. This measures the toughness of the aggregates (resistance to sudden shock).

2. Apparatus

• Impact Testing Machine (Hammer weight 13.5-14 kg, Fall height 380 mm)
• Cylindrical measure (75 mm dia, 50 mm depth)
• Tamping rod (10 mm dia)
• IS Sieves (12.5 mm, 10 mm, 2.36 mm)
• Balance (accuracy 0.1g)

3. Theory & Scope

Toughness is the property of a material to resist impact. Moving vehicles cause sudden shock loads on road aggregates. The AIV test simulates this condition.

Significance: A critical test for wearing course aggregates where impact from traffic is high.

Standard Limits (IRC):

• For Wearing Course (Bituminous Surface): Max 30%
• For Base Course (WBM): Max 45%

4. Procedure

1. The test sample was prepared by passing clean aggregates through a 12.5 mm IS sieve and retaining them on a 10 mm IS sieve.
2. The cylindrical measure was filled in three layers, each tamped 25 times, and the net weight of the sample was determined (Weight A).
3. The sample was transferred to the impact machine cup, compacted with 25 strokes, and the cup was fixed firmly in position.
4. The hammer was allowed to fall freely from a height of 380 mm for 15 blows, with intervals of at least one second between blows.
5. The crushed aggregate was removed, sieved through a 2.36 mm IS sieve, and the fraction passing the sieve was weighed (Weight B).

5. Observations and Calculations

Description	Trial I (kg)	Trial II (kg)
Weight of can	1.970	1.970
Weight of can + aggregate	2.485	2.520
Weight of dry sample (W₁)	0.515	0.550
Weight of portion passing 2.36mm sieve (W₂)	0.100	0.125
Aggregate Impact Value ((W₂/W₁) × 100)	19.42%	22.73%

6. Result

The Average Aggregate Impact Value is 21.08%.

7. Discussion and Conclusion

The Aggregate Impact Value obtained for the tested sample is 21.08%. This value falls within the range of 20-30%, which classifies the aggregate as “Satisfactory”. According to IRC standards, aggregates used for wearing courses should not have an impact value exceeding 30%. Since the obtained value is within this limit, the aggregate is considered sufficiently tough for road surfacing applications, though it is not classified as “exceptionally strong.”

8. Precautions

• Machine Stability: The impact machine was placed on a rigid, level base (concrete block) to ensure the shock was fully transmitted to the aggregate and not absorbed by the floor.
• Verticality: The guide columns were checked to be perfectly vertical to ensure a frictionless free fall of the hammer.
• Blow Interval: The interval between blows was maintained at not less than 1 second.
• Hammer Safety: The hammer locking mechanism was checked to ensure it worked correctly to prevent accidental injury.