On concrete pavements, road infrastructure deficit, challenges ahead (3)

Continued from yesterday
So, what is the matter with our roads? Will a shift from flexible to rigid pavements as put forward by the Honourable Minister fix all the problems? The 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.
Concluded

Dr. Ezeajughi, Civil Engineer, Geotechnical Engineering Consultant and COREN registered contributed this from his Brisbane, Australia office.