Bm And More Bm - It Is Unbelievable!

BM and more BM – It is unbelievable! The Ministry of Road Transport and Highways (MORTH) has just revised their Specifications for Roads and Bridges (the so-called orange book). The draft revised specification has been posted on the Indian Roads Congress (IRC) web site at www.irc.org.in presumably for inviting comments within a short time period. First of all, I would like to commend Shri V. K. Sinha, Director General Roads (who has just retired) and Shri R. P. Indoria, Secretary General IRC for expediting the revision of the whole orange book after its urgency was pointed out in my letter dated 27 January 2009 to you all; it was titled, “When will be the orange book revised?”. I had the privilege of submitting detailed draft revision to Section 500 related to bituminous pavements (copy also sent to you on 18 May 2009) on request of MORTH and IRC. While many revisions suggested by me have been incorporated, I was very disappointed with the following two items, which need to be addressed before the orange book is published. •

BM and more BM

A paper titled, “A Critical Review of Bituminous Mixes Used in India” authored by myself, Shri V. K. Sinha, Director General MORTH, and Prof. A. Veeraragavan, IIT Madras was published in the Journal of Indian Roads Congress,Volume 69-2, JulySeptember 2008 and was presented at the IRC session in Kolkata in November last year. (A copy of this paper with Q and A is attached for your ready reference.) A very strong technical case was made in that paper to delete the Bituminous Macadam (BM) altogether from the orange book considering permeability, structural strength, use as PCC, cost considerations, traffic conditions, and general statements. It was concluded with technical justifications that dense graded DBM should be used in lieu of open graded, undrained BM especially to obtain long lasting pavements. Not only the BM (see Clause 506) has been retained in the revised draft specification, another “Lean Bituminous Macadam” (LBM) has been added (see Clause 504) to make things even worse. It appears the engineers with old mindset who had the final “say” in the revision of Section 500 have sentimental attachment to open graded, porous BM to the detriment of our roads in India. Unfortunately, engineering principles and not sentiments govern the performance of our roads as I also wrote to Hon. Kamal Nath, Minister MORTH. Among several reasons given in the attached IRC paper, the use of BM defies the following two fundamental principles of pavement engineering and drainage (hydraulics): 1. Do not provide a porous course within a pavement unless it is a drainage course with a direct, positive outlet for water. This fundamental principle is being violated when the highly porous (pervious) BM is used (even if it is used for PCC) without any direct, positive drainage outlet. This creates a “bath tub” within the pavement resulting in potential for stripping (water damage due to loss of bitumen coating from the aggregate surface) in BM as well as in DBM overlying it. The highway engineers with old mindset do not mind creating perennial “bath tub” (that too at the bottom of our pavements) for which the future generation of our highway engineers will not excuse us. Just imagine what they have to do if the BM starts to deteriorate and fall apart from

stripping under the DBM and BC. We are supposed to give them long lasting bituminous pavement which use dense mixes only. Not only the BM has been retained in the revised specifications, a “lean” BM with 2.5% bitumen content has also been added now to make things worse. The thinner bitumen coating in the “lean” BM is likely to strip more easily rendering the BM into rubble of bare stones. I have observed numerous premature pavement failures resulting from stripping in many countries of the world. It is not a good sight when we see bare or poorly coated aggregate particles resulting from stripping. I wish I could show all those disaster slides but there is no forum in India to share these experiences. 2. Water flows from the less pervious GSB to highly porous BM. This is the law of hydraulics on which the 2-layer drainage system is already functioning in the US (discussed in the attached IRC paper). The revised BM Specification Clause 506 states, “Since the bituminous macadam is an open-graded mixture, there is a potential that it may trap water or moisture vapour within the pavement system. Therefore, adjacent layer should have proper drainage quality to prevent moisture-induced damage to the BM.” By adjacent layer they obviously mean the GSB. What the highway engineers with old mindset do not realize that the water in saturated GSB will flow into more porous (pervious) BM layer and not vice versa according to the principles of hydraulics, no matter what they write in the specifications. Instead of providing a point-by-point rebuttal of fundamental reasons cited in the IRC paper to delete the BM (which they owe to the country), the advocates of BM say it acts as a “crack relief layer”, it is “good” and “cheap” for India. Even if it does act as a crack relief layer (largely based on their gut feeling) pavement engineers would not like a bituminous course which is likely to act as a “bath tub” within the pavement and its own integrity is at risk due to stripping (water is a known enemy of bitumen). Going into the 21st Century, we are extremely proud of our space technology such as Chandrayaan and we should be. However, we are going back to the 19th Century in terms of bitumen technology due to some engineers with old mindset. If we had a reasonably good reputation of building durable bituminous roads in India, please add not one but two more BMs by all means. Unfortunately, we do not. Using BM without providing direct, positive outlet for water is against the concept of long lasting pavements, which is being adopted by developed countries. Providing pavement edge drains or extending the BM all the way to the embankment edge (similar to GSB) to drain it directly will be too expensive which even the developed countries have difficulty affording it. • No suitable substitute for SDBC Although the “semi dense” SDBC has been deleted from the revised orange book, it should have been replaced with a new dense 9.5 mm nominal mix (proposed as BC Grading 3 in the attached IRC paper) for use in 25-mm thin application and in urban areas. It should be done now. The 12.5 mm mix (BC Grading 2) now proposed for a 25-mm thin application also is not technically suitable because it cannot be compacted well to provide an impervious surface. This is because it does not satisfy the minimum desirable ratio of lift thickness and nominal size of about 3 to obtain

optimum compaction. I cannot imagine what is the problem in including the 9.5-mm mix, which is widely used in the US even on many interstate highways. Finally, I am beginning to believe that it is a battle between the “ego” of the engineers with old mindset and fundamental principles of pavement engineering and drainage (hydraulics). If you believe in the latter which is necessary for long lasting pavements in India, it is time to speak up and write to the Secretary General of IRC to delete both BMs and also include a 9.5 mm mix in lieu of SDBC for thin applications. Please email to [email protected] as soon as possible. Time is of essence. Caution is advised for BOT or PPP contractors who have to maintain their highway for 15-20 years. If you use BM within your pavement as PCC and/or base course, keep in mind there is a potential for premature failure of the highway, which will cost too much in its rehabilitation since it is deep down. If you have any questions on the two items, please feel free to contact me via e-mail. Sincerely, Prof. Prithvi Singh Kandhal Jaipur [email protected] 5 September 2009