Getting the right mix
BY IMRAN MIRZA
If you visit Jaipur during monsoon, one thing that you would unmistakably end up noticing is the quality of roads. Unlike Mumbai and most other metros — where the first few showers turn the roads into a sea of potholes of all shapes and sizes — the roads in Jaipur are smooth as a runway. So what has Jaipur done that other cities have been unable to do?
The Jaipur Development Authority (JDA) has been using a readymade, generic, cold bituminous patching mix technology during monsoon, since 2010. The agency has done patch repairs worth more than Rs1 crore with great success. The authority has to maintain over 6,000-km lane of roads and streets in and around Jaipur, which receives an annual rainfall of around 650mm. Witnessing the success of this technology, even the Rajasthan PWD has followed JDA’s lead and used the same cold mix all across Rajasthan during 2012 monsoon.
There is no standard readymade cold patching material available in India, which can be used during the rainy season when hot mix plants are usually shut down. It is difficult to design stockpile patching mixtures because the properties required in stockpiling and handling, and after the material is placed in the pothole are contradictory. Some of these contradictory requirements pertain to aggregate gradation, aggregate shape and binder viscosity.
So what is this generic, unpatented, readymade cold bituminous mix technology? While working in Pennsylvania, USA, as chief asphalt engineer, Professor Prithvi Singh Kandhal, developed a simple and effective cold bituminous mix for potholes during early 1980s. This cold patching mix is manufactured in a batch type hot mix plant using local aggregates. The mix can be placed without preparing the pothole such as drying, squaring the edges, cleaning, and tack coating. This mix can be used to fill potholes during the rainy season, even when they are wet. The ‘idiot proof’ mix, as Kandhal calls it, requires no preparation of the pothole.
In a nationwide US Strategic Highway Research Program (SHRP) field study, this mix was adjudged as number one in terms of its durability in potholes. About 78 per cent of the patches survived for over four years. It has been used in extreme cold and rainy weather in the US for over 30 years. This readymade cold mix can be made and stored for six months and can be made by any bituminous mix plant (portable or stationary) in India using local materials. The mix has been successfully tried on Jaipur streets and on the Jaipur-Agra Road with the help of the students and faculty of Malviya National Institute of Technology in Jaipur and IJM. It also has been tried successfully by the West Bengal PWD and IIT Guwahati.
Kandhal argues that this cold mix technology is as cost effective as hot mix. “Cost analyses have shown that the cost of repairing potholes with readymade cold mix is about the same as cost of repairing with hot mix because the latter is more labour, material (tack coat), and equipment (roller) intensive,” he points out. Contractors struggle with using hot mix technology during rainy season as the roads are wet, leaving the mix ineffective.
Potholes get larger and deeper during the three months of monsoon and, therefore, require much more hot mix, the cost of prompt repair of potholes with cold mix may be half of hot mix. “What is the cost of injuries and fatalities; vehicle repair costs; and user delays resulting from unfilled potholes?” questions Kandhal. “It is very hard to estimate these costs. If we are a civilised country, we simply cannot wait and repair potholes after monsoon ends as we have been doing for the last 65 years after independence,” he stresses.
The mix is also handy for contractors who are responsible for maintaining national highways, state highways or PMGSY roads during the concession or warranty period. If there are a few potholes, there is no need to arrange hot mix. The contractor can take some bags of this mix, a labourer and a hand rammer, in a car or a pickup, and get the potholes repaired, as and when required. There is no need to wait for a sizeable number of potholes to appear and then fix them, as is in the case of hot mix.
Contractors and engineers often cite the lack of Indian Roads Congress (IRC) or MoRTH specifications for readymade cold patching mix for not using this technology. “This is again a lame excuse,” says Kandhal. The specifications prepared for this mix have been adopted by the JDA and Rajasthan PWD. Moreover, many contractors are already using patented readymade cold mix made with foreign technology, and are paying a premium price for it.
Kandhal had submitted a draft of this cold mix to the Flexible Pavement Committee of IRC for approval more than two years ago, but there has been no progress on this front. Construction Week received no response from the IRC, despite repeated emails asking for the status of this paper. Kandhal’s attempts to get the Central Road Research Institute (CRRI) to test the mix in its labs have received no response, highlighting the callousness of these institutions towards matters of public interest.
JDA’s engineer, Sapan Mishra, shared his experience with the mix. “We tried it first on a few patches. It has worked really well for us. The road adjacent to the potholes has come off but the potholes haven’t appeared again.” Mishra advises that it’s important to get the recipe of the mix right. “The aggregates, gradation and bitumen should be used based on the local conditions,” says Mishra. Jaipur has taken the lead and has invited tenders to use repair roads using this cold mix. “The response has been good. We are receiving lower-priced bids than we did earlier,” Mishra revealed, indicating that contractors have realised the benefits of economies of scale.
“This proposed generic mix is less than half the price of those patented mixes. Why are they paying more when this mix can be made by a local contractor,” asks Kandhal. The 72-year-old professor is willing to offer voluntary technical assistance and knowhow to those who are willing to try the technology. “With the availability of this mix, there is no excuse to use 19th century technology for filling potholes. We have the specifications; cost analyses; success story of this mix in Jaipur — essentially, everything you need for calling tenders. Do we still have an excuse?” scoffs Kandhal.