Polymer Modified Bitumen advantages
The following are the Limitations of the bitumen binder.
- Higher tyre pressure in trucks, overloading, and stiffer tyre sidewall in trucks are the main cause of rutting.
- Under these conditions, a road constructed with conventional bitumen binder is not able to cope up the above traffic requirements
- Hence we need the bituminous binder with higher stiffness and adequate elasticity at high service temperature.
Fatigue Cracking :
- Increased ESAL ( increased truck traffic) and repeated type loads are the main cause of fatigue cracking. Hence to cope up with fatigue cracking we require the bitumen with the following properties.
- At intermediate service temperature, we need a bituminous binder with lower stiffness and higher elasticity after aging of bitumen,
Low temperature of Thermal Cracking
- The low temperature of thermal cracking occurs at very low service temperatures.
- Unmodified bitumen cannot cope with the range of extreme minimum and maximum pavement temperatures
- Need bituminous binder with low stiffness at low temperature and high stiffness at high temperature.
- Conventional bitumen binder becomes brittle at low temperatures.
- It becomes soft in Hot climatic conditions.
- It is a high temperature susceptible.
- Hence Bitumen produced by the traditional method can not meet all the requirements of increasing service demands.
It is apparent from studies that the properties of bitumen and bituminous mixes can be improved/ modified with the mixing of either plastomeric (plastic-based ) or elastomeric ( Elastic-based )polymers.
Meaning and Types of Polymers
- Polymers simply mean, A very large molecules made by a chemical reaction of many smaller molecules (monomers) by forming a long chain.
- Sequence and chemicals structure of monomers determines the physical properties of Polymers
- General types of Polymers are Elastomers and plastomers.
Properties and type of elastomers
- It can be stretched like a rubber band and recover into the original shape after releasing the applied force.
- It adds a little strength to the modified bitumen. However modified bitumen becomes stronger when applied to tensile stress.
- Examples of elastomers: a) Styrene- Butadiene-Styrene Block Copolymer SBS
- b) Styrene- Isoprene-Styrene Copolymer SIS
- c) Styrene-Butadiene SB
- d) Styrene-Butadiene Rubber SBR
Properties and type of plastomers
- It is a tough , rigid network type polymer.
- when mixed with bitumen, it imparts high initial strength to bitumen against applied heavy load but it may crack at high strain.
- example: a) Polyethylene PE
- b) Ethylene- Vinyl Acetate Copolymer EVA
- c) Ethylene-Methyl Acrylate Copolymer EMA
- d) Ethylene-Butyl Acryl late Copolymer EBA
- e) Ethylene Ter Polymer ETP
Properties improved by Polymer
- A sufficient increase in viscosity and prevents plastic deformations.
- An increase in flexibility and elasticity of binder at low temperature to delay the crack formation (mainly due to fatigue failure )
- It imparts high thermostability and improved aging resistance in the binder.
Requirements from polymer
- The polymer should Be compatible with bitumen. It should have a similar temperature viscosity relationship as bitumen.
- It should be able to resist degradation at mixing temperature.
- It should be cost-effective.
- it should not change the modified bitumen properties during storage.
- It should be compatible with conventional mixing and laying machinery.
Classification of polymer Modified bitumen
The polymer modified bitumen (PMB) shall be classified into five grades as given below:
- a) Grade PMB 64-10, having average maximum pavement temperature < 64°C and minimum pavement temperature > (–10) °C;
- b) Grade PMB 70-10, having average maximum pavement temperature < 70°C and minimum pavement temperature > (–10) °C;
- c) Grade PMB 76-10, having average maximum pavement temperature < 76°C and minimum pavement temperature > (–10) °C;
- d) Grade PMB 82-10, having average maximum pavement temperature < 82°C and minimum pavement temperature > (–10) °C; and
- e) Grade PMB 76-22, having average maximum pavement temperature < 76°C and minimum pavement temperature > (–22) °C.
- The selection criteria for PMB grade shall be based on the service conditions of pavement temperature range and traffic
Types of polymer modified bitumen
IS 15462: 2019 and IRC SP 53:2010, classify the polymer and rubber modified bitumen into the following four types.
- PMB(P) : Plastomeric thermoplastic-based
- PMB(E): Elastomeric thermoplastic-based
- NRMB : Natural rubber and SBR latex-based and
- CRMB: Crumb rubber / treated crumb rubber based