Repairing Potholes During Rainy Season

Readymade Kandhal Pothole Patching Mix was adopted as Indian Roads Congress (IRC) Standard Specification IRC: 116-2014 for Readymade Bituminous Pothole Patching Mix Using Cut-Back Bitumen. All concerned highway engineers in India should play a role in repairing potholes not only during the rainy season but also throughout the year using the amazing Indian technology. This would prevent accidents from potholes resulting in numerous deaths and serious injuries.
Prof. Prithvi Singh Kandhal

Development of potholes on Indian roads and streets after the onset of monsoons is a common phenomenon. Every year, there is a public outcry and newspapers are full of pictures showing potholed roads and pavements. Potholes killed 3,597 people in 2017, claiming about 10 lives daily! Besides inconvenience to motoring public and pedestrians, potholes also cause user delays, which cost money in terms of their time; extra fuel consumption when vehicles have to stop or go slowly; excessive wear and tear of vehicles with frequent repairs; and increased air pollution caused by vehicle emission due to slow or stopped traffic.

Unfortunately, a vast majority of our highway engineers either do not repair the potholes at all or fill them temporarily with dirt and/or stones, which wash away during the next rain. They wrongly believe that potholes cannot be repaired permanently during the rainy season. They are unaware that a pothole patching mix is available in India, which can be used not only during the rainy season but also throughout the year.

This readymade patching mix meets the Indian Roads Congress IRC:116-2014, “Specifications for Readymade Pothole Patching Mix Using Cut-Back Bitumen” and has the following attributes:
  • Most economical to produce and apply
  • More or less permanent (over 5 years’ service life)
  • A readymade cold mix with storage life of at least 6 months
  • Placed in 50kg bags for ease of handling and transportation
  • Application: potholes need not be dry; no spraying of bitumen needed; compaction with a handheld rammer by a labourer; road can be opened to traffic right away. No other material or machinery needed.
  • Not patented; anybody can make it using local materials
  • Pothole patching is possible during a lull in rain showers (just sweep the excess water out of the potholes)
  • Pothole patching is possible during extreme cold winter and hot summer conditions.
Indian Roads Congress IRC:116-2014 was drafted by the author based on a pothole patching mix he developed in the USA while working as Chief Asphalt Road Engineer of the Pennsylvania Department of Transportation (Figure 1). The mix was adjudged as the best pothole patching mix in a 4-year US nationwide field research (documented in US Transportation Research Board Journals). It has had excellent field performance when used by the Rajasthan PWD and the Jaipur Development Authority. That is why the IRC adopted it.

Different cold patching mixes being tried in the field in the USA

Development of Readymade Pothole Patching Mix Formulation
The characteristics discussed below appeared desirable for development of a satisfactory and economical stockpile patching mixture:

Finer and Predominantly One-sized Gradation. A gradation consisting of 100% passing the 9.5 mm or 4.75 mm sieve has the following advantages:
  • Mix is pliable and workable.
  • Due to increased surface area, more bituminous binder can be incorporated into the mix to improve its durability.
  • Mix remains pliable for a prolonged period of time and continues to densify easily under traffic and will continue to adapt to the changing geometry of the pothole. This characteristic enhances its chances of survival.
Clean Aggregate. It is very important to keep the dust content (material passing the 0.075 mm sieve) in the mixture as low as possible to impart tackiness. This would significantly improve the adhesive and cohesive properties of the mixture.

Adequate Binder Content. It has been determined that at least 4.5% residual bituminous binder (total binder minus diluent) is required in a stockpile patching mixture made from an aggregate whose water absorption is 1.0% or less. If the aggregate absorbs water in excess of 1.0%, the residual binder content should be increased by a similar amount.

Proper Type and Amount of Anti stripping Agent. The anti stripping agent is an important part of the formulation of the stockpile mixture. A mixture should retain its coating in the stockpile under adverse weather conditions, during handling, and in the pothole after placement. It has to survive in conditions that led to the creation of the pothole in the first place (such as poor base, inadequate drainage, and deteriorated adjacent pavement).

Salient features of IRC: 116-2014 Specifications for Readymade Pothole Patching Mix Using Cut-Back Bitumen
Production: The stockpile patching mix must be produced using a conventional batch type hot mix plant, which is operated at relatively low temperatures. [Drum mix plant can be used in India if there is no flame in the drum when volatile cutback is introduced for mixing.] Small portable hot mix plants have also been used in India (Figure 2). Again, under no circumstances MC bitumen containing kerosene should be added when there is a flame present in the drum.

Repair of pothole on NH 11 (Jaipur Agra Road) – mix being placed in the pothole

Bituminous Materials: Since it is a cold mix, medium curing cutback bitumen (containing kerosene as diluent) conforming to IS: 217 Specification for Cutback Bitumen should be used as a binder. MC-800 grade cutback bitumen should be used in India’s hot climate. MC-250 grade cutback bitumen should be used when the patching mix is intended to be used in extremely cold regions in North or in high altitude places. Unfortunately, no pure emulsified bitumen is available, which is as effective as medium curing cutbacks.

Composition of Mixture. The patching mix should conform to the gradation given in Table 1.

Table 1. Gradation of Stockpile Patching Mix
Sieve size in mm Percent passing
9.5 100
4.75 40 – 100
2.36 10 – 40
1.18 0 - 10
0.075 0 – 2
It should be noted again that the material passing 0.075 mm sieve is restricted to 2% maximum (based on washed gradation). This is essential for the quality and durability of the patching mix.

Preparation of Mixture. As mentioned earlier, the stockpile patching mix should be produced in a conventional hot mix plant. The temperature of aggregate and bituminous material should comply with those shown in Table 2.

Table 2. Temperature Ranges for Producing Stockpile Patching Mix
Bituminous material Aggregate temperature, C Bitumen temperature, C
MC-250 25 – 65 55 -80
MC-800 25 – 65 75 - 95
Performance History in India
This generic cold patching mix was produced on a limited scale in Rajasthan during the 2008 monsoons. Potholes on NH 11 (Jaipur-Agra Road) and some main streets of Jaipur were patched successfully with this mix. The residual bitumen content in the patching mix was 4.5%.

Figure 3 shows the repair of a pothole on NH 11 (Jaipur-Agra Road). Figure 3(a) shows the mix being placed in a pothole; Figure 3(b) shows completed patch; and Figure 3(c) shows the same patch after subjected to traffic on NH 11 and after rains.

Faced with severe pothole problem during 2010 monsoon, the Jaipur Development Authority (JDA) experimented with this mix in October 2010. JDA has to maintain some 6000 km lane of roads and streets in Jaipur. Satisfied with its excellent performance even in very adverse circumstances, JDA has been inviting tenders for “Kandhal Readymade Pothole Patching Mix” since 2011 (about one crore rupees worth per year). This generic mix supplied by the local contractors in a 50-kg plastic lined bags (Figure 4) to the JDA has a shelf life of at least 6 months and therefore it is used throughout the year.

Kandhal mix supplied in 50-kg plastic lined bag

This readymade pothole patching mix does not require any preparation of the pothole such as squaring and applying tack coat; the mix is simply taken out of the 50-kg bag, leveled, hit with a hand rammer by ordinary laborer (no roller), some light sand or grass/leaves is sprinkled on surface to prevent pick up by vehicle tyres, and opened to traffic right away. If there is water in the pothole, simply sweep off the extra water. The patch will outlast the adjacent road area.

Figures 5(a) and 5 (b) show as to how a pothole on Raj Bhawan Road in Civil Lines, Jaipur was simply cleaned, filled with this readymade patching mix, and hit with hand rammer. Photograph in Figure 5 (c) taken after several months of rain and traffic shows that the patch was still there but the hot mix asphalt road surrounding the patch had eroded.

A pothole on Raj Bhawan Road in Civil Lines, Jaipur being cleaned for repair

Rajasthan PWD followed JDA and used this generic patching mix successfully in 2012 on state roads and national highways. Finally, the Jaipur Development Authority’s “Readymade Kandhal Pothole Patching Mix” was adopted as Indian Roads Congress (IRC) Standard Specification IRC: 116-2014 for “Readymade Bituminous Pothole Patching Mix Using Cut-Back Bitumen” (42).

Cost Analyses
Cost analyses have shown that the cost of this unpatented, generic pothole patching mix is about one-third the cost of many patented readymade mixes available in India.

Cost analyses have also shown that the cost of repairing potholes with readymade cold mix is less than the cost of repairing with hot mix asphalt because the latter is more labour intensive (squaring the pothole), material intensive (binder for tack coat), and equipment intensive (need for roller). Moreover, hot mix cannot be used during rainy season any way.

This mix is also very handy for contractors who are responsible for maintaining national highways, state highways or rural roads during the concession or warranty or defect liability period. If there are a few potholes there is no need to arrange hot mix; take some bags of this readymade cold mix and a labourer (with a hand rammer) in a car or pickup and get the potholes repaired.

About the author
Prof. Prithvi Singh Kandhal
Prof. Prithvi Singh Kandhal is Associate Director Emeritus of the National Center for Asphalt Technology (NCAT) based at Auburn University, Alabama, U.S.A. NCAT is the largest asphalt (bitumen) road technology center in the world. Prior to joining NCAT in 1988, Prof. Kandhal served as Chief Asphalt Road Engineer of the Pennsylvania Department of Transportation for 17 years. He was the chairman and president of many national and international prestigious organizations in asphalt road technology.

He has drafted many standards for the Indian Roads Congress and the Bureau of Indian Standards. He was also instrumental in single-handedly introducing viscosity grading of bitumen in India in lieu of penetration grading in 2005. “A Simple Guide for Producing and Placing Readymade, Cold, Pothole Patching Mix in Accordance with Indian Roads Congress Specification IRC:116-2014” prepared by him, gives all the nuts and bolts of producing and placing this mix. It can be downloaded for free at https://www.scribd.com/document/388136056.

In April 2012, he received the ‘Lifetime Achievement Award in Asphalt Road Technology’ from the International Association of Asphalt Paving Technologists during their annual banquet held in Austin, Texas, USA.
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