Highway materials & Construction

HIGHWAY MATERIAL & CONSTRUCTION

 

 

Index:

A. Highway Material

• Test for road aggregate 
• Test for bitumen 
• Marshall mix design 

B. Symptoms and cause of defects 

C. Pavement construction 

I will be discussing all the above topic clearly one by one so stay calm and enjoy the article. 

 Test on road aggregate 

1. Crushing Test ( For strength)

Specification :

• Size of aggregate :10 to 12 mm
• No. of layers : 3
• Rate of loading : 4 ton/min
• Time of loading :10min
• Sieve size for sieving crushed aggregate : 2.36mm

Now, Aggregate Crushing value (ACV) : W2/W1 *100

W2= Weight of aggregate passing 2.36 mm sieve

W1= Total Weight of aggregate

As per IRC,

• ACV should not be greater than 30% for surface course
• ACV should be greater than 45% for base course 

2. Impact test (For toughness)

 

Specification :

• Size of aggregate :10 to 12mm
• Height of fall: 38cm
• Weight of hammer : 13.5 - 14.5kg
• No. Of blows: 15
• Sieve size: 2.36mm

Aggregate Impact Value (AIV) : W2/W1 *100

W2: Weight of aggregate passing 2.36 mm sieve

W1: Total Weight of aggregate

As per IRC, 

• AIV should not be greater than 30% for surface course
• AIV should not be greater than 35% for  Base course

3. Abrasion Test (for wear and tear) :

Specification :

• Rate of rotation : 33 rpm
• No. Of revolution :500
• Sieve size :1.7mm

Abrasion value (AV)= w2/w1 *100

w2: weight of aggregate passing 1.7mm sieve

w1: Total weight of aggregate 

As per IRC,

• AV should not be greater than 30% for surface course
• AV should not be greater than 50% for base course. 

Co-efficient of Hardness= 20 - 1/3 *Loss of weight in gram. 

4. Soundness Test(Durability & weathering):

• Aggregate of specified size are subjected to cycles of alternate wetting in saturated solution of either sodium sulphate or magnesium sulphate at a certain temperature and then drying in air at 105°C.
• Each cycle involves between 16-18 hrs of submergence in sulphate solution followed by 4 more hours of drying. 
• Loss in weight should not be greater than 12% for sodium sulphate and 18% for magnesium sulphate. 

5. Shape test :

There are many shapes of aggregate :

• Angular
• Rounded
• Flaky
• Elongated 
• Flaky & elongated 
• Flat particles 

Flakiness index:

• Size of aggregate >6.3mm
• Flakiness index of aggregate is the percentage by weight of aggregate particles of least dimension of which is less than 0.6 of mean dimension. 

Flakiness Index (FI) = w2/w1 *100

w2= weight of flaky particle

w1=weight of total aggregate 

As per IRC, 

• FI should not be greater than 25% for bituminous concrete
• FI should not be greater than 15% for WBM

Elongation index :

• Size of aggregate >6.3mm
• Elongation index of aggregate is the percentage by weight of aggregate particles of greatest dimension of which is greater than 1.8 of mean dimension. 

EI= w2/w1 *100

As per IRC, 

• EI should not be greater than 15%

Angularity number (AN) :

AN=(67-100w/c*Ga)

W= weight of aggregate to fill the cylinder 

C= weight of water to fill the cylinder 

Ga= specific gravity of aggregate 

• AN =(67-%Solid volume)
• 67% represents volume of solids of rounded aggregate in well compacted state which would have 33% void. 
• Acceptable range for construction : 0-11
• Angularity number measures void excess of 33%
• It shows degree of packing 
• For Rounded aggregate AN=0
• For angular aggregate AN is not equal to 0.

6. Water Absorption Test :

• Water absorption should not be more than 0.6% of weight of aggregate. 

7. Specific gravity Test:

• It measures the quality of strength of materials. 
• Specific gravity of solids lies between 2.6 to 2.9

                       BITUMEN

1. BITUMEN 

• Manufactured by fractional distillation of crude oil. 
• Solube in cs2 and ccl4
• More resistant to water
• Free carbon content is less
• Less temperature susceptibility 

Grading by VG (viscocity grading) :

1. VG-40:(3200 poise) : Used in high stress area/toll plaza/truck terminal
2. VG-30:(2400 poise): Used for paving applications
3. VG-20:(1600 poise): Used for paving applications in cold climate.
4. VG-10:(800 poise) : Used for spraying applications.

2. TAR

• Manufactured by destructive distillation of coal or wood.
• Soluble in toluene
• Less resistant to water 
• Free carbon content is more
• More temperature susceptibility 

Grading by RT(Road Tar) :

1. RT-1: Used for surface dressing in very cold weather conditions 
2. RT-2: Used for surface dressing under normal climate conditions 
3. RT-3: Used for surface dressing & renewable coat 
4. RT-4: Used for premix Tar mecadam. 
5. RT-5: Used for grouting 

3. Asphalt 

• Asphalt is produced in a plant (hot mix plant) that heats, dries, and mixes aggregate, bitumen and sand into a composite mix.

4.Cutback Bitumen

• Cutback bitumen is obtained by blending bitumen binder with suitable volatile diluents or solvents in the required proportion to reduce its viscosity to the desired range. 

Grading by RC:

• RC(Rapid curing)
• MC(Medium curing) 
• SC(Slow curing)

It is used for :

• Colder region
• Tack coat without heat
• Bituminous mixes
• Soil bitumen stabilisation 

5. Bituminous Emulsion :

• A bituminous emulsion is a liquid product in which a substantial amount of bitumen is suspended in a finely divided condition in an aqueous medium and stabilized by means of one or more suitable material.
• Types of Bituminous Emulsion :

1. Anionic Bituminous emulsion 
2. Cationic Bituminous emulsion (used in India)

Grading system :

• Rapid setting type(RS-1/RS-2)(Generally used for repairing works) 
• Medium setting type(MS)
• Slow setting type(SS-1/SS-2)

  Test For Bitumen

1. Penetration test :

• It represents the softness or hardness of bitumen by measuring the depth in 0.1 mm to which a standard needle carrying a weight of 100g penetrates in 5 sec at temperature 25°C.
• Grade of bitumen is decided on the basis of Penetration test. 
• If grade of bitumen is 80/100 then Penetration values lies between 8 to 10mm.
• If grade of bitumen is A-30 then bitumen is manufactured from Assam petroleum. 
• If grade of bitumen is S-30 then  bitumen is manufactured from other than Assam petroleum. 

2. Viscosity test

• It measures resistance to flow. 
• It is the time taken in sec by 50 ml of bitumen to flow beaker through a standard orifice under standard test conditions. 
• It is measured by "saybolt furol".
• Standard temperature for this test is 25° and 50°.
• Viscosity of tar is measured by "tar viscometer ".

3. Float test 

• It is used to measure consistency of material for which penetration & viscosity test can not be conducted. 
• Time required by water to inject through bitumen is called Float value. 
• Higher the float value stiffer the bitumen.

4. Ductility test 

• It is the distance in cm  to which a standard briquette of size 10mm  x  10mm can be stretched before the thread breaks at a standard temperature of 27°C.
• Min ductility for grade 45 & above is 75cm.

5. Softening point test

• Softening point is the temperature at which the substance attains a particular degree of softening under standard test condition. 
• This test is also known as ring & ball test. 
• Softening point of various bitumen grade used in paving jobs varies between 35°to 70°C.

6. Flash & Fire point test

• Flash Point : It is the temperature at which bitumen vapours take fire. 
• Flash point of bitumen is 175°C.
• FIRE POINT: It is the lowest temperature at which material gets ignited. 
• It is measured by "Pensky Martin".

 Marshall Mix Design

• The mix design determines the optimum Bitumen Content for evaluation of performance of bituminous mix.
• Desirable properties :

1. Stability 
2. Flow value
3. Unit value 
4. Air void 
5. VFB(Void Filled with Bitumen) 
6. VMA(Void in Mineral Aggregate)

• Marshall stability and flow value determined experimentally and all other properties calculated theoretically.