Pavement Characteristics

Pavement Characteristics,

1. Friction 
2. Skid and Slip
3. Break Efficiency 
4. Unevenness Index 

Friction:

• Longitudinal Friction 
• Lateral Friction 

Longitudinal Friction :

Longitudinal frictions acts in the opposite direction of movement of vehicle. Longitudinal friction is mainly depends on, 

• Roughness of surface 
• Speed of the vehicle 
• Area of Contact 

Smooth tyre or warn out tyre offers higher friction factor than new tyre in dry pavement due to large area of contact. In wet condition coefficient of friction generated is less due to lubricant action.

As per the IRC recommendation the value of longitudinal friction is between 0.35 to 0.40.

Lateral Friction : 

Lateral friction comes in picture only when there is force in lateral direction. On horizontal curve while negotiating, the centrifugal force generated which is resisted by lateral friction.

As per the IRC recommendation the value of lateral friction is 0.15.

Skid and Slip:

Skid and slip is mainly depends on the tyre and pavement characteristics and it is differentiates by using rotational movement and translation movement of type.

1. when the translation movement of wheel is greater than the rotational movement, the condition is termed as skid, most of time skid is generated after the application of break.
2. when the rotational movement of wheel is greater than translation movement, the condition is termed as slip, most of time slip of wheel occurs when the value of friction factor is less i.e. wet condition.

Break Efficiency :

Break efficiency called 100 % if suddenly after  the application of break wheel completely jammed and rotational movement of wheel is zero. In this distance travelled by vehicle after application of break is only transnational distance called as pure skid. If break efficiency is less than 100 % then the distance travelled by vehicle is total of transnational and rotational movement, and in that case coefficient of friction generated will be less than maximum value.

Unevenness Index :

Uneven surface increases riding discomfort, fuel consumption, wear and tear of tyres and other parts and accident. The pavement surface conditions are commonly measured by using an instrument called as " Bump Integrator". unevenness index is nothing but the cumulative measure of vertical undulations of the pavement surface recorded per unit horizontal length of the road. 

Fifth wheel Bump Integrator

IRC Recommendations ,

Sr. No.	Pavement Type	Unevenness Index (Cm/km)	Riding Quality
1	Old Pavement	Below 95	Excellent
2		95 – 119	Good
3		120 – 144	Fair
4		144 – 240	Poor
5		Above 240	Very Poor
6	New Pavement	Below 120	Good
7		120 – 145	Fair
8		Above 145	Poor

Sr. No.	Unevenness Index (Cm/km)	Type of pavement	Remark
1	Below 150	Good	No need to Repair
2	151 – 250	Satisfactory
3	251 – 320	Bad	Should be Repair
4	Above 321	Uncomfortable	Construct New Road