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‘Bad Road Example In Mombasa’ Is Section Between Kengeleni
And Ratna Square In The Kongowea Area

Coastweek -- The wear and tear on our roads are becoming more noticeable despite the fact that the Chinese came and showed our local contractors how to do roads properly, writes Teti Kamugunda.

The properly probably means the start up aesthetics where the road looks very well finished.

If one looks at the finish on most of the roads done by Chinese contractors one is left wondering what we used to accept in the past and who had set those standards.

One thing I am sure about is that the Colonial government was not to blame.

Most of the roads built in the pre-independence period continued to provide good service without all the obvious wear and tear we see more and more of today.

The first eyesore that one gets on the more recent roads is the furrowing or channelling of the road.

This is where the ruts develop on tarmac in the areas that the tyres of vehicles run most of the time.

These have developed on many of the recently done roads both in Mombasa and Nairobi and indeed across many roads in the country.

They ruts tend to be on the main highways in to and out of county headquarters where the roads are tarmacked.

The ruts are also conspicuous where there is an incline on the roads.

Here in Mombasa the most obvious example of this is when one comes off the Makupa causeway on to the island.

As one begins to climb up to the island one begins to feel the ruts especially in small saloon cars as the steering becomes problematic.

Soon one can actually see the deformed road surface, especially as one approaches the roundabout.

But why the rutting?

There are two main causes of rutting in roads.

The first and most fundamental one is the condition of the substrate.

This is an inherent quality of the design and construction of the road.

If the substrate is not properly designed taking into consideration the type of soil, the drainage requirements and the loading, the substrate will not be able to bear the load and will start sinking.

Substrate failure is almost terminal for the road and the corrective action would be to rebuild the road from the foundation.

This is the most expensive type of failure and can be seen in many parts of Kenya.

There are several sections of road between Miritini and Mazeras that perennially fail due to this fact.

They have bad design considering that the locations are prone to flooding, have underground seasonal rivers or are natural wetlands.

Sometimes it is not the design that was faulty.

What has tended to happen is that the road is designed assuming certain conditions and these could change significantly if, for example, the zoning laws are not adhered to yet the design assumed that the zoning laws would be followed.

By changing the environment around the road, it could be that the drainage of water is directed to an area that cannot cope with the additional loading so undermines the substrate.

The roads instead of being roads could become the drainage channel as there is nothing else that allows water to flow freely.

An example is the perennial flooding that happens on the road section between Kengeleni and Ratna Square in Kongowea area.

This section of road has been flooding for the last thirty years every time it rains purely because of the building up of the area and the channelling of all the drainage water onto the road.

The road itself has not been redesigned to accommodate the changes in the environment around the road and we continue to see degradation of that road every year.

We re-carpet and re-carpet but the same problem occurs year in year out.

We are not addressing the basis problem that is the accumulation of water which has seriously undermined the substrate of the road.

This leads to rutting of the road over time especially with higher traffic density and heavier trucks.

The second major cause of rutting is the quality of material used to apply the top layer.

The temperature of the road surface can get quite high especially when it is coloured black.

Atmospheric temperature highs in Kenya can reach the mid thirties (in degrees Centigrade).

When the atmospheric temperature is at this level, the road surface can be almost double that temperature so the bitumen that we use must be able to withstand that higher temperature at the load for which it was designed.

The most common bitumen standard used in Kenya – which is the drummed bitumen commonly called penetration 80/100 bitumen or also now known as VG-10 works best at atmospheric temperatures between minus ten and thirty degrees.

The next grade is penetration 60/70 or VG-20 and this works between zero and forty degrees centigrade.

The grade after which is penetration 50/60 or VG 30 works between ten and fifty degrees centigrade.  Kenya needs to make a change to the design standards of roads and move to at least VG 20 or preferable VG 30 as the standard.

This will ensure that the softening of the road surface will be minimised due to the action of loads and shear caused by tyres.

There are many roads in the country where rutting is as a result of this inappropriate standard of bitumen.

There is also the reality that on inclines the weight distribution shifts so that the axle load is actually higher than what the design takes into consideration.

So, in order to avoid rutting it is important that the design is done properly and the materials specified are correct for the conditions that obtain in Kenya.

As Kachumbari says, we need good roads and we must give the preferred outcomes a good chance.

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