May 24, 2011

Polymer Modified Bitumen to save Maintenance Cost

It is possible to construct roads which require overlay not before eight to 12 years. It can save our mountains and hills, huge quantity of fuel, plant and machinery and can earn carbon credits.

Innovative solutions and products are available in India which can enhance the service life of roads by 50 to 150 percent.

India can save up to Rs 40,000 crore per year if all roads, i.e., 65,569 kms of National Highways (NH), 130,000 kms of srate highways(SH) and 31,40,000 kms of other roads, are constructed using styrene butadiene styrene (SBS) polymer modified bitumen (PMB), instead of conventional bitumen, as binder.

SBS PMB can be used as binder for construction of "wearing course" or top layer of the road as well as "binder course" (bituminous layer under wearing course). Use of PMB increases the rut, creep and fatigue resistance of the pavement, enhancing its performance and service life.

Use of SBS PMB in 'wearing course' enhances its overlay period where as its use in the binder course can enhance the design life of the road or reduce thickness of pavement resulting saving in initial cost of road.

Bitumen is modified using crumb rubber- CRMB, natural rubber- NRMB, elastomeric thermoplastic polymers- PMB (elatomeric) and plastomeric thermoplastic polymers- PMB (plastomeric). SBS PMB is PMB (elastomeric) or PMB(E). Keeping the temperature extremities and type of traffic (overloading etc) in view SBS PMB is ideal for India. It can withstand wide fluctuations in temperature and traffic intensity/volumes.

Wearing course of a road costs around 10 percent of the cost of the road. Bitumen contributes around 50 percent to this cost. Use of SBS PMB costs around 25 to 50 percent more than convention bitumen, depending on the type of SBS PMB. Thus use of SBS PMB in wearing course, increases the cost of wearing course by 12.5 percent to 25 percent and that of the road by 1.25 to 2.5 percent. But the life of wearing course increases by 50 to 150 percent.

Period of overlay of a road, ordinarily being overlaid at five years, will increase to eight (or even 12) years if SBS PMB is used as binder in place of conventional bitumen.

There are guidelines and specifications on modified bitumen issued by BIS (IS 15462:2002), by IRC (SP 53 2002, 2010) and the ministry of surface transport and highways (MORT&H) specs 2001 clause 521.

Ironically, MORT&H directed use of modified bitumen for the overlay of all NH since 1999, but only CRMB from PSU refineries (outsourced to small local venders) has been used. However, overly period of most NH which were constructed using CRMB has not been changed by the babus of MORT&H. Surprising BS PMB has not been used in any NH so far. The reason for the apathy can be explained by the babus of MORT&H only. Either they do not understand the efficacy of SBS PMB and continue celebrating the ignorance or there are vested interests.

Cost bituminous concrete (BC) being around 10,000 per cum, thickness of BC around 50 mm, width of NH as 15 metre and SH as 7.5 metre and width of other roads as 3.75metre and wearing course of SDBC as 25mm, savings per year can be calculated for the all the roads of India. It is more than Rs 40,000 crore per year.

It addition it saves our hills (stone quarries), fuel, bitumen, plant and machinery, personnel and environment. The commuters gets better roads free of frequent repair and maintenance. Toll collection is higher.

Why do stakeholders not opt for SBS PMB, with so many positives, defies logic, but it is a fact. The answer lies in few contractors managing to get many projects. They want to reduce initial cost irrespective of long term benefits of SBS PMB. There are others who can get away without maintenance of road.

Source -
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