Test: Highway Materials and Maintenance

California Bearing Ratio (CBR)

• The California bearing ratio test is used to evaluate the suitability of subgrade and the material used in sub-base and base course.
• It is measured to indicate the relative strength of paving materials and not the absolute strength.
• CBR test is a strength test conducted on the soil by introducing surcharge load at the compaction rate of 1.25 mm per minute on a completely soaked soil sample passing through 20 mm sieve size.
• The test results have been correlated with the thickness of the various materials required for the flexible pavement.

δ = displacement in mm
P_δ = Load corresponding to ‘δ’ settlement
P_s = Load for standard crushed aggregate:
At 5 mm penetration Standard load Ps = 2055 kg  
At 2.5 mm penetration standard load Ps = 1370 kg 
Calculation:
Given data;
The sample height = 125 mm
The change in sample height = 0.125 mm
The expansion ratio of this soil is 

Petrol is not used directly in highway construction, but by-product like bitumen is used. Stone, dust and soil may be used in subgrade and base.

Angularity:
It is the absence of roundness. An aggregate particle, which is more rounded, is less angular and vice versa.
Angularity number:

• Angularity number of an aggregate is the amount (to the higher whole number) by which the percentage of voids in it after compacting in a prescribed manner exceeds 33.
• Where “33” is the percentage of the volume of voids in a perfectly rounded aggregate. And, “67” is the percentage of the volume of solids in a perfectly rounded aggregate when compacted in a specified manner.
• The value of angularity number generally lies between 0 & 11.

Determination of angularity number:
(a) From the solids

(b) From the voids

Where C = weight of the cylinder, W = weight of aggregate in the cylinder, G_s = specific gravity of aggregate

• The penetration test is carried out to know the hardness or softness of bitumen used in road construction by measuring the distance in tenths of a millimeter to which a standard needle will penetrate vertically into a sample of bitumen under the stipulated condition of temperature, time, and loading.
• The slump test is conducted to test the workability of concrete.
• The fineness test is checked to test the proper grinding of the cement which significantly influences the rate of hydration.
• It is carried out to test the hardness property of aggregates and to decide whether they are suitable for different pavement construction works.

Various tests conducted on bitumen for testing its various properties are as follows:

Marshal test is used for designing the bituminous concrete for pavement construction, Beckenham Beam Method is used to determine the deflection of the pavement slab.
Bitumen is classified on the basis of either its penetration value or its viscosity.
Classification based on the penetration value of bitumen:
The penetration test is carried out to know the hardness or softness of bitumen used in road construction by measuring the distance in tenths of a millimeter to which a standard needle will penetrate vertically into a sample of bitumen under the stipulated condition of temperature, time and loading.
A bitumen specified as of grade 80/100 means that the range of penetration value of the sample is between 80 to 100 (i.e. actual penetration would range between 8 mm to 10 mm).
∴ Hardest grade of bitumen among the following is 30/40, as penetration would be as less as 3 to 4 mm only.
Note: It can be stated that for a hot climate, lower penetration grades of bitumen are preferred, and for cold climates, higher penetration grades of bitumen are preferred.

If the HFL is more than the formation level of the road which is going to be provided, then it has to be built on embankment.

Flashpoint:

• It is the lowest temperature at which the application of a test flame causes the vapors of the binder to catch an instant fire in the form of a flash under specified test conditions.
• Two types of test apparatus may be used for conducting flash point tests on bitumen, namely the Pensky-Martens Closed Cup Tester and Open Cup Tester.
• Here, In the bitumen test, momentary flash was seen at a temperature of 200° Celsius. So, the flash point is 200° Celsius.
• If the bituminous binder is further heated to a temperature higher than the flash point, the binder material itself catches fire and continues to burn, the lowest temperature causing this condition is called the fire point.

Fire Point:

• It is the lowest temperature at which the application of test flame causes the binder material to ignite and burn at least for five seconds under specified test conditions.
• Here, bitumen burned for at least 5 seconds at a temperature of 240° Celsius. So, the fire point is 240° Celsius.

Important Points

• The fire point is always higher than the flash point of a material.
• Pensky-Martens open cup tester is used to determine the flash & fire point of the bituminous binders.

The embankment is the lowest layer and it is below the sub grade, base is above sub base, sub base is above the sub grade.

Cutback bitumen:
(i) Cutback bitumen is bitumen with less viscosity which, is achieved by the addition of volatile diluent. Hence, to increase the fluidity of the bitumen binder at low temperature the binder is blended with a volatile solvent.
(ii) The viscosity of the cutback bitumen and the rate at which hardness on the road depends on the characteristics and quantity of both bitumen and volatile oil used as diluent.
(iii) Cutback bitumen is available in three types:

• Rapid curing (RC) →  In this bitumen is fluxed with Naptha/gasoline, petroleum
• Medium curing (MC) →  In this bitumen is fluxed with Kerosene or high diesel oil
• Slow Curing (SC) → In this bitumen is fluxed with High boiling point gas oil

Additional Information
(i) MC and SC cutback are used for priming and viscosity increases as the grade increases like RC-0, RC-1, RC-2. 
(ii) RT-1 is lowest viscosity used for surface painting but RT-4 may be used for premix in macadam.
(iii) RT-5 is used for grouting which has highest viscosity.
(iv) MC-2 will be thicker than MC-1 but RC-5 and SC-5 will have same viscosity.

CBR number decreases with an increase in height, the soil requires the highest CBR and the pavement requires the lowest CBR.

Bitumen is obtained by burning the petroleum at high temperatures, it is mostly used in the construction of flexible pavements.