Important Asphalt Related Issues in
“American roads are good not because
is rich, but America
is rich because American roads are good.” John F. Kennedy America
“Never doubt that a small group of citizens can change the world. Indeed, it is the only thing that ever has.” Margaret Mead
fail prematurely especially during monsoons? India
potholes and more potholes in
– how to repair them especially during monsoons? India
- Why the NHAI is burying bitumen worth hundreds of crores rupees under national highways?
we really getting viscosity graded (VG) paving bitumen in
we really getting quality modified paving bitumen in
- Do we need to add mineral filler in bituminous mixes? (Q and A)
tack coat over prime coat: fundamentally not necessary and is gross waste
’s resources! India
need for training in asphalt technology in
, where is the vision? India
1. Why roads in
If somebody asks the “aam aadmi” (common man) in India this question, the majority response would be: Indian highway engineers “intentionally” construct road in such a way so that it keeps on failing prematurely and they keep on getting “fat” budget for maintenance (pothole repair) and resurfacing year after year.
Whereas lack of quality control is a contributing factor, there is a major fundamental engineering problem which the Indian public does not know. Of some ten types of bituminous paving mixes used in
seven are open graded (water-trapping) mixes. Examples: Bituminous Macadam
(BM); Semi Dense Bituminous Concrete (SDBC); Dense Bituminous Macadam (DBM)
Grading 1; Premix Carpet (PMC); and Mixed Seal Surfacing (MSS). The Built-Up
Spray Grout (BUSG) is no different. The remaining three are dense graded (desirable)
mixes. Examples are: Dense Bituminous Macadam (DBM) Grading 2; Bituminous
Concrete (BC) Grading 1; and Bituminous Concrete (BC) Grading 2. India
The water-trapping mixes also happen to be initially cheaper than the dense graded mixes and therefore are used commonly. (It does not matter if they generally last for 1-2 years compared to dense graded mixes which may last for 7-8 years. In other words, they are very expensive based on life cycle costs.) Water is enemy number one of bitumen. That is why, water-trapping mixes fail prematurely especially during monsoons. All across
the deadly combination of BM and SDBC is being used brazenly. PMC is also used
Most developed countries in the world generally have three dense graded bituminous mixes in their specifications: one each for base course, binder course and wearing course. And they have good durable roads despite heavy rainfall sometimes throughout the year. It is simply amazing as to why Indian highway engineers need additional seven water-trapping, problematic bituminous mixes for road construction/resurfacing?
Obviously, some engineers are technically ignorant about the fundamental principle of highway engineering to keep the water away from bituminous mixes. Others keep on using these water-trapping bituminous mixes knowing fully well about their impending premature failure resulting in “fat” budgets for pothole repairs/resurfacing. This is despite the fact that two technical papers have been presented on this topic and discussed at the Indian Roads Congress (IRC) sessions after publication in IRC journals. These two papers give comprehensive, easy to read, technical, and economical justifications to ban the seven water-trapping mixes such as BM, SDBC and PMC. Interested Indian highway engineers can access and download these two IRC papers at the following links:
Kandhal, P.S., V.K. Sinha and A. Veeraragavan. A Critical Review of Bituminous Mixes Used in
. Journal of the Indian
Roads Congress, Volume 69-2, July-September 2008. India
Kandhal, P.S., A. Veeraragavan, and R.K. Jain. Guidelines for Long Lasting Bituminous Pavements. Journal of the Indian Roads Congress, Volume 71-3, 2010.
The following link to a technical note explains how the open graded Premix Carpet (PMC) is causing havoc on city streets and rural roads. It is only suitable for PMGSY roads outside village areas.
Unfortunately, the continuation of these seven water-trapping bituminous mixes in MORTH and IRC specifications gives them undesirable technical legitimacy and excuse for continual use by highway engineers across
Based on past experience and recent deliberations (2012) of the IRC Flexible Pavement Committee, there is not much hope either of these two actions would occur in the near future. Therefore, it is up to young, rational highway engineers of
to challenge the old-timers who apparently have hijacked and sealed the fate of
bituminous roads in India . India
[Note: Only the Jaipur Development Authority (JDA) which maintains some 6,000 km of roads has banned all 7 water-trapping bituminous mixes and has used only dense graded bituminous mixes since 2010. JDA uses DBM Grading 2 for base course; BC Grading 1 for binder course; and BC Grading 2 for wearing course in new construction as well as resurfacing. This has resulted in smooth and durable roads, which remain largely pothole free after bearing the brunt of the last three heavy monsoons. Example of the JDA needs to be replicated across urban and rural
if good roads are desirable.] India
2. Potholes, potholes and more potholes in
Unfortunately, it has become an annual ritual when during the monsoons the Indian media reports extensively about potholes on city streets and rural roads across
The coverage includes traffic jams and people dying or getting injured from
potholes. It appears highway engineers in India
are downright insensitive to do something about this yearly disgrace on their
Again, just ask “aam aadmi” (common man) about this, who would say highway engineers are purposely not filling potholes before and during the monsoon so that potholes grow in numbers, in size, and in depth and they would get a “fat” budget later for pothole patching with hot asphalt mix. The public has been brainwashed in believing potholes are a natural phenomenon during rains (as if water in the Indian monsoon has some chemical to dissolve the bituminous road!). Public is also told potholes cannot be fixed during the three months of monsoon because the hot mix plants are shut down and/or potholes are damp or wet. This is the situation after 65 years’ independence!
The above is happening despite the fact that an “idiot-proof”, unpatented, economical, and effective readymade cold pothole patching mix (called “Kandhal Mix” by the Jaipur Development Authority in their contract documents) is available and which is the real answer to the pothole problem across
There is no other better, generic, economical and widely field-proven product for
this purpose in India .
This mix which costs about Rs. 6 per kg can be manufactured by local
contractors using local materials. There are some patented cold mixes such as
Shelmac which cost about three times more but are still being used in India
sparingly due to high costs. Cost of patching potholes with the Kandhal mix
which can be used throughout the year is about the same as patching with hot
mix. This is because the latter is labour intensive (cutting and squaring the
pothole); material intensive (tack coat material); and equipment intensive
(roller required for compaction). Life of the Kandhal mix is equal or more than
that of the hot mix patch. India
A technical paper describing the so-called Kandhal mix was published by the Indian Roads Congress (IRC) and presented at the IRC session in 2008. This paper can be accessed at the following link:
Kandhal, P.S. A Simple and Effective Method of Repairing Potholes in
. Journal of the Indian
Roads Congress, Volume 69-3, October-December 2008. India
It is not known at this time (November 2013) as to when the IRC would approve this unpatented Kandhal Mix as a standard; it has been pending there for over three years. But this is not an excuse not to use it. The Jaipur Development Authority (JDA) is using it successfully for the last three years with contracts worth over one crore each year. What is needed is the WILL POWER of the highway engineers to implement this technology, proven both in the
and US , in
the interest of general public. All contract documents for inviting tenders
such as “G” Schedule, specifications and rate analyses are available with other
information on the performance of this mix at the following link: India
The National Highway Authority of India (NHAI) has been burying the existing bituminous roads indiscriminately under highway soil embankments. It is especially so on many six-laning highway projects where the road level is being raised by the NHAI to build numerous ramps for overpasses which require soil embankments. Using existing well established asphalt reclaiming and recycling technology, which is over 30 years old, the highly expensive existing bituminous road can be reclaimed and recycled into a new road to be constructed over the soil embankments (asphalt is 100% recyclable). The bitumen and stone in the existing bituminous road are worth crores of rupees. Bitumen is about Rs. 50,000 per ton (moreover, the country has to import more crude from which bitumen is distilled). Net savings of about one crore rupees can be made if one km of an existing 4-lane bituminous road is reclaimed and recycled rather than burying it. Unfortunately, NHAI is burying kilometres and kilometres of roads every year. No civilized country in the world buries its bituminous road; rather reclaims the costly bitumen and stone for recycling.
Although the NHAI has been “encouraging” the contractors through circulars for some years now, only a few NHAI contractors are reclaiming and recycling the bitumen (called “black gold” in the industry) and the stone; and are pocketing crores of rupees on a typical NHAI project. A vast majority of contractors is simply and brazenly burying this country’s “dharohar” (property) causing a great loss to the State Exchequer.
Three open letters have been sent to the Chairman of NHAI since November 2011 to make the reclaiming/recycling of the existing bituminous road mandatory to put a stop to this great loss to the State Exchequer, which is estimated to be hundreds of crores every year. However, the NHAI has not taken any action (they are still in the “encouraging” mode). Therefore, this national loss is continuing due to NHAI’s incompetence, indecisiveness and lack of accountability.
Copy of the third open letter to the NHAI Chairman can be accessed at the following link:
Asphalt milling and recycling is a well established technology as mentioned earlier and has been used for over 30 years across the world. Asphalt pavement guidelines prepared by Prof. Prithvi Kandhal and Dr. Rajib Mallick for the US Federal Highway Administration (FHWA) can be accessed at the following link:
4. Are we really getting viscosity graded (VG) paving bitumen in
It is very unfortunate that many Indian highway engineers still do not know that it is illegal and unethical to specify, produce, and use penetration graded paving bitumens such as 60/70 and 80/100.
The Bureau of Indian Standards (BIS) revised IS:73 Specification for Paving bitumen in July 2006. The revised specification IS:73:2006 outlawed the old (more than 100 year old) penetration grades such as 60/70 and 80/100 and adopted new viscosity grades (VG) such as VG-30 in lieu of 60/70 and VG-10 in lieu of 80/100. [Prof. Prithvi Singh Kandhal was instrumental in introducing the viscosity grading of paving bitumen in India in 2005 with the assistance of 10 Jan Path, New Delhi.]
The Ministry of Road Transport and Highways (MORTH) issued Circular No. RW/NH-33041/3/2001-S&R (R)-Vol. III on
04/08/2008 to all the state PWDs, NHAI etc.
reminding them to implement the new bitumen viscosity grades as soon as
possible. According to the circular, the user must substitute VG-30 in lieu of
60/70, substitute VG-10 in lieu of 80/100, and substitute VG-40 in lieu of
30/40 or 40/50 grades. Is that really hard to do? Just changing the
nomenclature in tender notices or project reports is not a rocket science!
If the user would like to know more about viscosity grades (VG), please read the following IRC paper; it can also be downloaded at the link provided.
Kandhal, P.S. An Overview of the Viscosity Grading System Adopted in
for Paving Bitumen. Indian Roads Congress, Indian Highways, April 2007 India
The BIS has further revised IS:73:2006 Specification for Paving Bitumen in April 2013. The revised IS:73-2013 has the following significant changes. Instead of specifying a penetration range for each VG grade, only minimum penetration values have now been specified. For example: minimum penetration of 80 for VG-10 and 45 for VG-30. Instead of specifying the minimum absolute viscosity at 60 C, viscosity range has been specified for each VG grade. For example: 800-1200 poises for VG-10 and 2400-3600 poises for VG-30. These revisions were warranted and justified as explained in the IRC paper above.
Progressive user agency (be it PWD, contractor, consultant, testing laboratory or university) must purchase the viscosity testing equipment as soon as possible to monitor the grade and quality of the VG bitumen supplied by the oil companies. Research study completed by IIT Madras for BIS in 2011 determined that a significant percentage of VG-30 bitumen samples obtained across India were actually either VG-20 or VG-10; that is, softer viscosity grades which may cause premature rutting/bleeding in the asphalt pavements. Therefore, the user agencies must test at least the absolute viscosity at 60 C to ensure right VG grade is being supplied to the project. Only the vacuum capillary viscometer (and not the
can be used for determining the absolute viscosity at 60 C. Brookfield
viscometer can be used to determine the kinematic viscosity at 135 C in
addition to kinematic capillary viscometer. Brookfield
Click at the following link to access Prof. Kandhal’s technical note on equipment details and testing procedure:
In recent years, traffic loads and tyre pressures have increased, which has created a situation for which modified bituminous binders are needed. In the past, the following two specifications have been used by the highway agencies for specifying modified binders.
- Indian Roads Congress Publication SP:53-1999, “Tentative Guidelines on Use of Polymer and Rubber Modified Bitumen in Road Construction”, December 1999.
- Bureau of Indian Standards. IS 15462:2004, “Polymer and Rubber Modified Bitumen – Specification, 2004.
Four types of modified binders are included in the preceding two publications: Polymer Modified Bitumen or PMB (elastomer), PMB (plastomer), Crumb Rubber Modified Bitumen (CRMB), and Natural Rubber Modified Bitumen (NRMB). Since these are different types of modified bitumen materials, separate specifications and criteria in form of four tables are included as is the practice across the world.
These four modified binders are described briefly below.
Elastomers: Elastomeric polymers have the ability to resist permanent deformation and cohesive failure in the bituminous mix by stretching and then recovering their shape when the deforming force is removed similar to a rubber band. Therefore, PMB (elastomer) is resistant to rutting as well as fatigue cracking.
Plastomers: Plastomeric polymers form a tough, rigid, three dimensional networks within the bitumen. These plastomers give high initial strength to the bitumen to resist heavy loads. However, plastomers may crack at high strains. Therefore, PMB (plastomer) is primarily resistant to rutting.
CRMB: Rubber from discarded tyres is ground to a particulate or crumb prior to adding it to bitumen to produce CRMB. CRMB is much more complex and least understood compared to PMBs with elastomers. Because of the complex and varying chemical composition of crumb rubber obtained from tread/side wall of truck and/or car tyres, its compatibility with bitumen is always questionable. That is why; CRMB has given mixed performance in the
The quality control requirements right from the production to the end use of CRMB are too cumbersome because of two issues: (a) crumb rubber tends to separate and settle down in the bitumen and (b) crumb rubber is prone to degradation (devulcanization and depolymerization) if it is maintained at high temperatures for more than 6-8 hours. These quality control requirements for CRMB, which are hardly followed in
are given in the following IRC paper which can be downloaded at the link
Kandhal, P.S., “Quality Control Requirements for Using Crumb Rubber Modified Bitumen (CRMB) in Bituminous mixtures”, Journal of the Indian Roads Congress, Volume 67-1, 2006.
NRMB: Natural rubber modified bitumen is manufactured by adding natural rubber (which is available in south
to bitumen. However, NRMB should be used with caution because like CRMB it has
degradation problems if kept at high temperature for too long. India
However, the Flexible Pavement Committee (FPC) of the Indian Roads Congress (IRC) pulled a surprise in 2010 by revising IRC:SP:53-1999. The revised IRC:SP:53-2010 contains a “unified” single specification table for all four types of modified binders, which is not technically possible unless the unified specification is performance based which it is not. It was like mixing apples with oranges. The elastic recovery requirement was arbitrarily lowered to accommodate the CRMB. This IRC:SP:53-2010 has the following problems:
(a) Lowering the requirements to the level where a weak modifier like crumb rubber can also qualify, would lower the performance standard for all modifiers;
(b) Suppliers of better and more expensive products will tend to downgrade the quality of their products so as to be more competitive price wise if that is the criterion for decision making; and
(c) Lowering the quality will come in the way of producing still better products thus having a negative effect on further R&D activities.
Therefore, the highway agencies (government and contractors) who believe in quality should NOT specify the revised IRC:SP:53-2010. They should only specify: Bureau of Indian Standards. IS 15462:2004, “Polymer and Rubber Modified Bitumen – Specification, 2004 which remains unchanged in terms of four separate tables. PMB (elastomer) only should be demanded in the specifications in clear terms.
Detailed information on all types of modified binders including their characteristics, specifications and recommended uses in highway construction are given in the following IRC paper which can also be downloaded at the given link.
Kandhal, P.S. and M.P. Dhir. Use of Modified Bituminous Binders in
Current Imperatives. Journal of the Indian Roads Congress, Volume 72-3,
October-December 2011. India
1. Polymer modified bitumen (PMB) with elastomers is most commonly used with success on major highways in the developed countries because elasticity in this PMB provides resistance to both rutting and fatigue cracking. Such PMBs are also relatively more stable and maintain their integrity better compared to PMBs with plastomers, CRMB, and NRMB (natural rubber modified bitumen). Superpave performance grades have been made successfully with these PMBs. PMBs with elastomers are therefore recommended for heavily trafficked roads in
2. Polymer modified bitumen with plastomers are hardly used in flexible pavements in the developed countries because although they provide higher strength initially, they are prone to cracking at high strains and do not rebound after deforming force is removed. Therefore, there is no need to have a specification in
for PMBs with plastomers to avoid its unnecessary and improper use, until
proper technical justification is provided. India
3. Natural rubber modified bitumen (NRMB) has limited use to support the local industry in southern
It should not be used on heavily trafficked roads where only PMBs with
elastomers should be used as mentioned earlier. However, NRMB should be used
with caution because like CRMB it has degradation problems if kept at high
temperature for too long. India
4. CRMB is much more complex and least understood compared to PMBs with elastomers. Because of the complex and varying chemical composition of crumb rubber, its compatibility with bitumen is always questionable and therefore it has given mixed field performance. Besides, it has potential settling and degradation problems as mentioned earlier. Therefore, CRMB is not recommended for use in
5. Use of any modified binder in bituminous mix on low volume rural roads such as PMGSY is detrimental to their durability. The current practice of using CRMB in such applications should be discontinued until proper technical justification is provided.
6. Do we need to add mineral filler in bituminous mixes? (Q and A)
It is not understood as to why some engineers in
are obsessed with adding some sort of mineral filler (such as portland cement)
when the baghouse fines (stone dust) are abundantly available and are as good
as those fillers. It is simply a waste of money. The India
has one of the best roads in the world, if stone dust works there, why not in US ?
Hydrated lime can be added if moisture susceptibility is a problem based on mix
design test such as AASHTO T 283 as specified in the IRC standards. India
There are many other issues related to mineral fillers including stone dust. Mr. Rajib Chattaraj, Executive Engineer P.W.D.
Bengal had asked Prof. Prithvi Singh Kandhal some interesting and
good questions about the use of mineral fillers in bituminous mixes in .
Those Questions and Answers (Q and A) should be of interest to the highway
community in India
and can be accessed and downloaded at the following link: India
Prof. Kandhal had the privilege of leading research on mineral aggregates and fillers (including baghouse fines) at the national level in the
latest Information Manual on Baghouse Fines currently in use in the US
was authored by him. Therefore, the responses to Mr. Chattaraj’s questions are
based on his opinions considering the latest research on this subject. US
7. Applying tack coat over prime coat: fundamentally not necessary and is gross waste of
Are you applying tack coat over prime coat? If so, it is fundamentally not necessary and it is a sheer waste of
About 57 crores of rupees are wasted each year by unnecessarily applying tack coat over prime coat. If this useless practice is stopped,
would also need to import less petroleum crude oil because bitumen in the
emulsion is obtained from crude oil. India
Detailed technical justifications for eliminating the need for tack coat over prime coat and the associated extent of wastage of taxpayers’ money and
resources can be accessed and downloaded at the following link: India
MORTH should immediately issue a corrigendum to the 2013 Orange Book “Specifications for Road and Bridge Works” eliminating the requirement of tack coat over prime coat. Time is of essence. In the meantime, project engineers must use common sense, show their guts, and eliminate this requirement from the project to realize savings in the interest of country.
8. Dire need for training in asphalt technology in
Just ask a typical highway engineer in
(a) Which paving grades of bitumen are used in
(b) How would you determine if part of the paving bitumen has been replaced with marble dust during transport from refinery to the project site? [Most engineers would not be able to answer. They do not know about the very simple bitumen solubility test to determine the presence and amount of insoluble like dust in the bitumen.]
The preceding two questions are about the paving bitumen only, which is the most important and most expensive ingredient in bituminous mixes (about Rs. 50,000 per ton). There are other areas such as aggregate; mix design; construction; maintenance; and recycling. Most highway engineers in
Unfortunately, no quality road construction can be expected if the highway engineers are technically ignorant. It is just common sense.
Now, who is responsible for this technical ignorance prevailing among most highway engineers in
Even a small percentage of Rs. 75,000 crores, say 0.1 percent or 75 crores spent per year on this training will go a long way to achieve quality road construction across