7 LAB TESTS ON AGGREGATE TO CHECK QUALITY FOR USE IN ROAD WORK

Aggregate plays an important role in pavement construction. Affects to a great extent the load transfer capacity of pavements. It is therefore essential that they should be thoroughly tested before being used for construction. Not only must the aggregates be strong and durable, they must also have the proper shape and size to make the pavement act monolithic. The aggregate is tested for strength, hardness, hardness, size and water absorption.

To determine the suitability of an aggregate for use in pavement construction, the following tests are carried out:

  1. crushing test
  2. abrasion test
  3. impact test
  4. soundness test
  5. size test
  6. Specific gravity and water absorption test
  7. bitumen adhesion test

1.crushing test

Figure-1 Crushing Test Setup
Figure-1 Crushing Test Setup

One model in which pavement materials can fail is crushing under compressive stress. is standardized by a test IS: 2386 Part-IV and is used to determine the crushing power of aggregates. The total crushing value provides a relative measure of the resistance to crushing under a gradually applied crushing load.

The test consists of subjecting a sample of aggregates in a standard mold to a compression test under standard load conditions (see Figure-1). The dried aggregates passing through a 12.5 mm sieve and a 10 mm sieve are filled in three layers to a cylindrical measure of 11.5 mm diameter and 18 cm height. Each layer is tamped 25 times with a standard tamping rod. The test sample is weighed and placed in the test cylinder in three layers, with each layer being re-tamped. The sample is subjected to a compressive load of 40 tonnes which is gradually applied at a rate of 4 tonnes per minute. Then the crushed aggregate is sieved through a 2.36 mm sieve and the weight of the material passing through (W 2) is expressed as a percentage of the total sample weight (W1) which is the total crushing value.

Total crushing value = (W1/W2)*100

a price less than 10 shows exceptional strong aggregate Whereas 35. at over would normally be considered weak aggregate,

Also read: Crushing Test Process Of Aggregate

Read also: Crushing Value Test Procedure of Aggregates

2.abrasion test

Fig-2 Los Angeles Abrasion Test Setup
Fig-2 Los Angeles Abrasion Test Setup

Abrasion test is performed to test the hardness property of the aggregates and to decide whether they are suitable for various pavement construction works. The Los Angeles abrasion test is preferred for meeting the hardness property and is standardized in India (IS: 2386 Part-IV,

The principle of the Los Angeles friction test is to find the percentage wear due to the relative rubbing action between the aggregate and the steel balls used as the abrasive charge.

The Los Angeles machine consists of circular drums of internal diameter 700 mm and length 520 mm that are mounted on a horizontal axis allowing it to be rotated (see Figure 2). An abrasive charge consisting of cast iron spherical balls of diameter 48 mm and weight 340–445 g is placed in a cylinder with aggregates. The number of abrasive areas varies according to the grading of the sample. The amount of aggregate used depends on the gradation and usually ranges from 5–10 kg. The cylinder is then closed and rotated at a speed of 30–33 rpm for a total of 500–1000 revolutions depending on the gradation of the set.

After the specified revolutions, the material is sieved through a 1.7 mm sieve and the passed fraction is expressed as a percentage of the total weight of the sample. This value is called the Los Angeles friction value.


maximum value of 40 percent allowed for WBM Base Course under Indian conditions. For bituminous concrete, the maximum value of 35 percent is specified.

Read also: Los Angeles Friction Value Testing Process of Aggregates

3.impact test

Figure-3 Impact Test Setup
Figure-3 Impact Test Setup

The overall impact test is performed to evaluate the resistance to impact of the aggregate. The aggregates passing through a 12.5 mm sieve and maintained on a 10 mm sieve are filled into a cylindrical steel cup with internal diameter 10.2 mm and depth 5 cm which is attached to the metal base of the impact testing machine. The material is filled in 3 layers where each layer is tamped for 25 blows (see Figure-3). A metal hammer weighing from 13.5 to 14 kg is arranged by vertical guides to be dropped with a free fall of 38.0 cm and the test specimen is subjected to 15 numbers of blows. The crushed aggregate is allowed to pass through a 2.36 mm IS sieve. and the impact value is measured as a percentage of the aggregate passing through the sieve (W 2) for the total weight of the sample (W1,

Total Impact Value = (W1/W2)*100

set to be used to wear of courseeffect value should not exceed 30 percent, For bituminous macadam maximum permissible value is 35 percent, For water-bound macadam The base course is the maximum permissible value as defined by the IRC 40 percent.

Also read: Impact Value Testing Procedure Of Aggregates

4.soundness test

The purpose of strength testing is to study the resistance of an aggregate to weathering action, by conducting rapid weathering test cycles. Porous aggregates subject to freezing and thawing are likely to decompose prematurely. To ascertain the durability of such aggregates, they are subjected to a rapid strength test as specified in IS: 2386 Part-V,

Aggregates of specified size are subjected to cycles of alternating wetting in a saturated solution of sodium sulfate or magnesium sulfate for 16–18 h and then dried in an oven at 105 to 110 °C.0c for a constant weight. Afterwards five chakras, the weight reduction of the aggregate is determined by filtering and weighing all small particles.

must lose weight not more than 12 percent when tested with sodium sulphate And 18 percent With magnesium sulfate Measure.

Also read: Strength Testing Procedures Of Aggregates

5.size test

Fig-4 Flaky Gauge
Fig-4 Flaky Gauge

The particle size of the total mass is determined by the percentage of flaky and long particles in it. Aggregates that are flaky or elongated are detrimental to the high work efficiency and stability of the mixtures.

flaky index is defined as the percentage of the total mass of the particles whose The least dimension is less than 0.6 times their average size, The flakiness gauge (fig-4) is used for this test. The testing process was standardized in India (IS: 2386 Part-I,

elongation index An aggregate is defined as the percentage of the mass of the particles whose The greatest dimension (length) is 1.8 times their average dimension, This test applies to aggregates larger than 6.3 mm. An elongation gauge (see Figure-5) is used for this test. This test is also specified (IS: 2386 Part-I) however there is no recognized limit for the elongation index.


Fig-5 Elongation Gauge
Fig-5 Elongation Gauge

Also read: Gross Resilience Index Value Testing Process

Also read: Total Elongation Index Value Testing Procedure

6.Specific gravity and water absorption

The specific gravity and water absorption of the aggregate are important properties that are essential for the design of concrete and bituminous mixtures. The specific gravity of a solid is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. Since aggregates can have water-permeable voids, two measures of the specific gravity of the aggregate are used:

  1. apparent specific gravity and
  2. Bulk specific gravity.

apparent specific gravity, YesApplication, is calculated based on the net volume of the aggregate, that is, the volume excluding water-permeable vacancies. Thus

YesApplication , [(MD/VN)]/w

Where,

MD is the dry mass of the aggregate,

vn The net volume of the aggregate excluding the amount of substance absorbed is,


W is the density of water.

bulk specific gravity, YesBulk, is calculated based on the total amount of aggregate including water permeable voids. Thus

YesBulk , [(MD/VB)]/w

Where,

vb is the total amount of aggregate including the amount of water absorbed.


water absorption: The difference between apparent and bulk specific gravities is nothing but the water permeable spaces of the aggregates. We dry the set and a . We can measure the volume of such vacancies by weighing in saturated surface dry condition, with all permeable vacancies filled with water. The difference between the above two is M. Iswoo,

Mwoo Weight of dry aggregate minus weight of aggregate The saturated surface is dry condition. Thus,

Water absorption = (mwoo/MD)*100

The specific gravity of aggregates commonly used in road construction ranges from about 2.5 to 2.9. Water absorption values ​​for aggregates typically used in road surfacing range from 0.1 to about 2.0 percent.

Read also: Specific gravity and water absorption test procedure of aggregates

7.bitumen adhesion test

Bitumen adheres well to all common types of road aggregates provided they are dry and free from dust. The bituminous construction has practically no adhesion problems in the absence of water.

Adhesion problems occur when the aggregate is wet and cold. This problem can be dealt with by drying out the moisture from the aggregate and raising the temperature of the mixture. In addition, the presence of water causes the binder to detach from the coated aggregate. This problem occurs when the bitumen mixture is permeable to water.

A number of laboratory tests are performed to arbitrarily determine the adhesion of bitumen binder to aggregate in the presence of water. The static immersion test is the one specified by the IRC and is fairly simple. Principle of Testing 40. is to immerse the aggregate completely coated with binder in water created on0C temperature for 24 hours.

IRC specified maximum stripping value of aggregate Not more than 5%.

List of IS Codes for Composite Testing

Testing for IS Coded Sets

net worth

Test Type

test method

crushing power crushing test IS: 2386 (Part 4)
hardness Los Angeles abrasion test IS: 2386 (Part 5)
toughness total impact test IS: 2386 (Part 4)
Tolerance soundness test IS: 2386 (Part 5)
shape factor size test IS: 2386 (Part 1)
specific gravity and porosity Specific gravity test and water absorption test IS: 2386 (Part 3)
Adhesion of bitumen Stripping value of aggregate IS: 6241-1971

Author

Dr. Tom V Matthews (IIT Bombay)


Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.