CONCRETE PAVEMENTS AND ROAD INFRASTRUCTURE DEFICIT
Federal roads will continue to fail until fundamental errors in design are corrected, argues Lambert Ezeajughi
Since the assumption of office by the Minister for Works David Nweze Umahi, the road construction industry has been abuzz with expectations of what is to come. The expectations are not unconnected with the unparalleled level of infrastructure development witnessed in his eight-year tenure as the governor of Ebonyi State and the enthusiasm with which he has embraced his new role as minister. His enthusiasm to get things done and done properly may have informed his highway inspection tours across the states. A step in the right direction Mr. Minister as the tours would have provided you with a firsthand knowledge of the dire conditions of the state of our road infrastructure. A sector of Nigerians in the road space myself inclusive have watched and followed the tours albeit remotely with a view to finding out what the minister’s stake will be on the level of decay in the sector and how he intends to bridge the huge road infrastructure deficit. Deficit driven by incessant premature failures despite the unending huge budgetary provisions that run into trillions, inflated contracts, never-ending contract scope creep, the associated variations, and consequent financial losses. Since the completion of the tours, his observations on the dearth of Nigerian road infrastructure may have informed his immediate actions and pronouncements in respect of contract scope creep and associated variations and more importantly the proposed shift from flexible (asphalt surfaced) to rigid (concrete) pavements. It is not in doubt that he may have leveraged on his experiences in Ebonyi State for the push for concrete (rigid) pavements. Welcome to Nigeria’s federal roads His Excellency.
Since your pronouncements on a potential shift from flexible to concrete roads, the discussions that trailed the Lokoja – Obajana – Kabba – Ilorin Road when concrete pavement was first proposed has been re-ignited. It is no doubt that the level and rate of collapse of our roads may have informed such push. It is obviously a good call to want to look at the possibility of a shift from the status quo (asphalt roads) with a view to mitigating serious failure challenges facing the Nigerian road asset. With monies running into trillions of Naira spent in the road sector, yet several sections of Nigerian ‘Highways’ are in dire straits. The footages from the minister’s tours makes one wonder which of the national highways is performing well. Some of the highways are only a figment of the true meaning of the word highway. Some of the highways have long been abandoned because they have been either overgrown by weeds or they have become littered with mosquito breeding ponds in the wet season or dust chambers in the dry season causing irrecoverable health hazards to the communities where they were once road corridors. Some of the highways have become borehole fields rather than potholes if I may paraphrase the minister. The rate at which our roads fail is unbelievable. A classic example is the several failed sections of the re-constructed old Enugu – Onitsha Road which failed just under three years after reconstruction. The reconstruction was meant to complement the abandoned Enugu – Onitsha Expressway but it never lasted two decent cycles of rainy season. At the rate of the documented failures and as showcased by the minister’s tours, this is nothing but a crisis. With your zeal His Excellency, the question in everyone’s mind is, can you re-invent the magic you left in your home State? Can federal roads witness sustained, long-term performance which has been at the core of a myriad of factors driving Nigeria’s road infrastructure deficit?
To tackle significant underperformance driving the huge deficit concerns in the road sector, we must use a different cookbook from what is currently being used. It is on this background that it is imperative that we must firstly articulate the issues and then find answers to the issues driving the never-ending causes of premature failures of our road assets. Should we succeed in finding the answers, this may throw a light on whether the push for a shift from flexible to rigid pavement alternative would be a panacea to the failure crisis and therefore has merit. Before casting my dragnet in search of answers, I deem it worthy to express my sincere thanks to the minister for the path so far taken in steering his ministry within the short time he mounted the saddle. Firstly, for the understanding and enthusiasm shown in identifying the likely causes of the unending crisis in the road infrastructure space and making pronouncements on potential alternative solutions. It is humbling and gut wrenching to witness roads fail woefully just few years after construction despite gulping funds that run into millions. Secondly, for seeing the problems and calling them by their names and shifting blames appropriately where they rightly belong rather than play the chameleon or hide under political correctness at the expense of haemorrhaging road sector. The directors and their staff in the Ministry and the contractors, home grown, or expatriates have not been left out in the minister’s search for answers. Thirdly, but by no means the last, the minister’s stand on contract scope creep and associated variations in prices. How can a contract initially awarded at 10 billion Naira end up at 100 billion and yet nothing tangible can be shown for the huge expense, but rather abandoned contracts. I will prefer to stay away from discussions on these matters as they are mostly outside my sphere of competency and the scope of this write up. These issues, however, do point to the fact that there are minefields on the path of running the Nigerian road sector. Sir, I can only wish you luck as you sojourn in your very demanding portfolio.
The first cab off the rank among the issues that may have been driving the under performance of the Nigerian road assets would be what Duro Onabule in his article on “before Buhari’s budget on roads” published in the Sun Newspapers of September 2015, referred to as lack of sincerity in the preparation and execution of the road budgets. Duro opined that if only ten percent of the sincerity with which the budgets were prepared existed and translated to implementation, that Nigeria would have been better off in terms of overall development. Over the years, budget preparation and implementation had become more of a ritual without any true meaning attached. To drive this home, a former works minister was questioned by a senator during screening regarding why a road in his constituency was abandoned for two years. The minister replied that when they got to the site, they discovered that there was water at the site, hence work had to stop. The question that comes to mind is, were there studies, concept, and detailed designs for the project? Else, how was the bill of engineering measurement (BEME) prepared if the water was not identified and the associated costs to mitigate its adverse effect on building a road through that terrain provided for? The BEME figures would have been the most realistic numbers to inform budgetary provisions.
Secondly and a major plank of this piece is on the issue of resilient road assets – flexible (asphalt) or rigid (concrete). It is not intended to make this write up a technical one where asphalt fatigue, stress distribution, stresses and strains, beam theory and pavement rutting will dominate the discourse. Rather, it is intended to present a simplistic view of pavement types and the likely killer diseases that have bedeviled the performance of our road assets. Having followed the discussions on flexible and concrete pavements in the print and social media since the minister mounted the saddle, it will be worthwhile to define what these pavement types are with a view to clearing some of the misconceptions and abstract discussions that had floated around since this issue became a hot potato or do I say a Nollywood classic. In simple terms, flexible pavements are built from aggregates (usually rock from quarry) placed (compacted) in sub layers (usually two to three sub layers) and finished off with a wearing course (usually asphalt, the black stuff we see on all our roads). All these component layers are supported on the natural ground or foundation soil (usually called the subgrade). The number and thicknesses of the sub layers are always variable depending on the class of road. The class is determined by the number of vehicles that would use the road while it is in service, hence highways, arterials, minor roads, etc. On the other hand, rigid or concrete pavements consist of a concrete slab founded on the natural ground (subgrade) with or without the multiple sub-layers common in flexible pavements. Generally, rigid (concrete) pavements have only one sub-layer. The essence of the sub-layers in both the flexible and rigid pavements, multiple or single is to minimise the stresses (load from vehicles, especially trucks, transmitted through the tyres) onto the natural ground.
Concrete pavement capitalises on the strength of concrete to minimise the stress transmitted to the natural ground, hence the reduction in the number of sub-layers. From this simple definition, it can be understood that whichever way we go, flexible or rigid (concrete), the bottom line is about minimising the stresses on the subgrade. At this point, it may be pertinent to ask – why do we need to guard against the stresses imposed on the subgrade (natural ground)? Once the subgrade is overstressed through multiple passes of cars and trucks, especially trucks with high axle loads, going through over time, the subgrade will become weak and lose its capacity to take up the stresses from wheel loads and consequently fail. These failures usually manifest as rutting which gradually progress to potholes and consequent loss of function of the road asset followed by abandonment where no rigorous maintenance scheme is put in place.
I may have to breach my earlier promise not to make this piece technical by bringing in an element of stress-strain of the natural ground (foundation soil on which flexible or rigid pavement are built on) now that I have been boxed into a corner for lack of a simplified social jargon to express stresses and strains. Most natural ground (subgrade) have their peak (maximum) strength at about 4 to 6 percent strain. As the moisture content of the natural ground increases due largely to fluctuations in the existing ground water levels, increased rainfall which in recent times is heightened by climate change for non-sceptics, the strain at which the peak strength of the subgrade (natural ground) is reached drops due to increased pore pressures developed in the inter spaces between the soil particles. In some soils such as intermediate to high plastic clays, the peak strength drops drastically under increased moisture. The impact of the drop in strength is that the natural ground (subgrade) which supports either flexible or concrete pavement loses its ability to support wheel load which it can previously support. In the worst case, it may lose up to 100 percent of its carrying capacity under fully saturated condition; a ‘boiling’ condition (effective stress = zero) where the generated pore pressure is equal to the vertical stress.
This explains why most failures occur during the rainy season. In the light of this simplified soil – structure interaction view, the prediction of the likely moisture levels (equilibrium moisture) of the subgrade (natural ground) over the life of a road asset is vital to their long-term performance or survival. Maintaining the equilibrium moisture of the subgrade borders on road drainage and must be properly understood by all road engineers. They must be properly and logically designed and implemented to ensure successful long-term performance outcomes for either flexible or rigid pavement alternatives.
Most of our networks being it highways or minor arterials are of the flexible pavement type. These road networks by whichever standards they have been designed are supposed to have the pavement (the sub layers described earlier) and the asphalt surfacing (the black stuff) having a design life ranging from 10 for minor roads to up to 20 to 40 years for highways. From a technical viewpoint, the 10 to 20- or 40-year life does not mean a collapse state but a time within which some major work may be required such as removing the asphalt surfacing and replacing it. With this in mind, some of the re-constructed sections of the old Enugu – Onitsha Road which one would expect to have been designed for a minimum of 20-year life, failed under three years. Likewise, sections of the Lagos-Ibadan-Sagamu-Benin expressway failed woefully under five years until the recent intervention. Several sections of the Ajaokuta – Abuja Highway, the Auchi – Abuja Highway, the East – West Road, the Odukpani section of the federal highway to Calabar, sections of the Enugu – Onitsha Highway, especially at Ugwuoba are nothing but treacherous. So, what is the matter with our roads? Will a shift from flexible to rigid pavements as put forward by the Minister fix all the problems? Honourable Minister, Sir, until the fundamental design issues mitigating the performance of these assets are addressed, they will wear the tag of underperformance till the end of times. To drive this fundamental design flaws home, the physiography of the Korton – Karfe section of the Lokoja – Abuja Highway is on a sag. A good design rooted in long-term performance would have opted for a grade-separated carriageway or a viaduct – stunted flyover if I may borrow your phrase or more economically a series of bank of culverts with the approach embankments designed to withstand inundation. The reference design which was constructed at Korton – Karfe is a carriageway at grade with virtually no flood immunity. Sir, no concrete pavement will survive Korton – Karfe if implemented at grade. To further buttress the issue of fundamental design flaws, the Odukpani and Ugwuoba sections of the federal highways are supported on high plastic clays that have significant shrink-swell issues. These clays are susceptible to significant loss of strength under excessive moisture levels (inundation). These said, a simple shift to concrete pavement under these conditions without addressing significant fundamental design flaws will be tantamount to the proverbial selling of a monkey and buying a baboon for replacement. At best, a change from flexible to rigid pavement without addressing the fundamental design issues raised on these sections of the highway will be palliative.
Another factor that goes against rigid pavements is cost. Concrete pavements have high initial capital expenditure (CAPEX) and generally low maintenance cost outlay when compared to flexible pavements, but this is only on the condition that they have been properly designed and constructed. The cookbook for concrete pavements is tenfold those of flexible pavements and the damage factor for concrete pavements is of the twelfth (12th) power for loading more than the design load. In view of these, a rigid pavement that has failed to account properly for the axle loading over the design life, account for equilibrium moistures and its impact on the short and long-term strength of the subgrade (natural ground) supporting them over variable moisture regimes arising from ephemeral or permanent groundwater, that has failed to account for soil-structure interaction and variable temperatures, is poorly designed and is bound to fail. Apart from cost, fixing concrete pavements are difficult and expensive because when they fail, they fail badly.
It will be preposterous to think that I can exhaust all the perceived issues from my perspective that have been the root causes of the poor performance of the Nigerian road assets on the pages of this write up which incidentally has turned into an epistle. But before I sign off, permit me to quickly highlight one more point from my long shopping list – the issue of what constitutes a failure or defect and who shoulders the responsibility (defect liability issues). The weighting on these issues become accentuated when funds for road assets are sourced from elsewhere with a view to having a return on investment. Based on my experience, in advanced societies, movements (displacements) on the road surface in the order of millimetres more than prescribed performance values cause a lot of angst between designers, contractors and asset owners with respect to who foots the bill for the repairs. In our situation where roads fail catastrophically within a relatively short time frame after construction, sorting out who should be responsible and managing the damage will be a big challenge. A road without in-built immunity against long-term performance is not worthy of investing any fund that hinges on a return on investment. His Excellency, Sir, the choices available to you are clear – maintain the status quo and grapple with rampant failures or make a fundamental shift in the way we have been designing, delivering, and managing our road assets with a view to stemming the tide of failure crisis rocking the Nigerian road assets. It is only in the light of the later that you can reasonably manage defect liability issues and hope on delivering some dividends on any money that could be sourced from fund managers for investment in our road sector. I guess that it will also be naïve of fund managers to release monies kept in their trust for financing road assets if guarantees of a return on investment cannot be made, unless if they want to play the Nigerian card.
The honourable minister, I did not know how daunting writing a highly technical subject in a social arena could be until I got into the middle of this write up. I hope that I have been able to communicate. If it were to be a technical forum, I would have brought in phase relationships, moisture variabilities, degree of saturation (DOS levels) and material behaviour as they relate to soil strength under cyclic wheel loads both for the pavement and natural subgrade material to drive home the issues of underperformance and consequent premature failure. Talking through flexible and rigid pavements would have been much easier using these concepts to drive home the import of stresses and strains as they relate to pavement performance. Sir, you are an accomplished engineer, an accomplished public servant and I hope that rolling out rigid pavements as a fix it all will not be your Achilles heels. I wish you well in the huge tasks ahead and encourage all and sundry to give the honourable minister a fair go.
Engr. Ezeajughi, Civil Engineer, Geotechnical Engineering Consultant and COREN registered writes from Brisbane
