Experts advocate composite pavement for durable road construction

In view of persistent road failures in Nigeria, experts, after an exhaustive discussion last week, settled for composite pavement-admixture of the well known asphalt and concrete pavements as the reliable panacea to capable of arresting the menace.

The event was the “CED Forum/Award 2016” ceremony, held at the Sheraton Hotel, Ikeja, with the theme: “Concrete Road in Nigeria: Durability, Acceptability and the Economic Benefit to a Developing Nation.”

The Guest Speaker, Dr Isa Usman Emoabino, an engineer, in his lecture, noted that the primary structural difference between a rigid and flexible pavement is the manner in which each type of pavement distributes traffic loads over the sub grade.

Explaining the concepts, Emoabino noted that rigid pavement has a very high stiffness and distributes loads over a relatively wide area of sub-grade, where a major portion of the structural capacity is contributed by the concrete slab itself.

“For a flexible pavement (asphalt), the load carrying capacity is derived from the load-distributing characteristics of a layered system.

“A flexible pavement structure is typically composed of several layers of material with better quality materials on top where the intensity of stress from traffic loads is high and lower quality materials at the bottom where the stress intensity is low.

“Flexible pavements can be analysed as a multi-layer system under loading. A typical flexible pavement structure consists of the surface course and underlying base and sub-base courses. Each of these layers contributes to structural support and drainage.

“When hot mix asphalt is used as the surface course, it is the stiffest (as measured by resilient modulus) and may contribute the most (depending upon thickness) to pavement strength,” he stated.

The Speaker listed the advantages of Asphalt (Bitumen) as being economical, as it is still less costly compared to concrete. It also takes less time to build an asphalt road than a concrete road. Asphalt dries faster, freshly laid asphalt can carry load immediately.

Asphalt is recyclable, it can be used again and again by melting it; it is also easy for maintenance; and repairing just a part of the asphalt road is easily possible. Asphalt roads can be relayed over the old layer, and they provide better traction and skid resistance for vehicles and tends to help keep roads free from ice and snow.

However, its disadvantages are that in the context of durability, heavy rain and other extreme weather conditions damage the asphalt road, and they need frequent repairs.

“Excess axle load causes deflection and deformation on the road including weather pollution. Melting asphalt produces lots of harmful greenhouse gases. Asphalt is a costly petroleum product,” said Emoabino.

Conversely, rigid pavement structure is composed of a hydraulic cement concrete surface course, underlying base and sub-base courses.

According to him, the surface course (concrete slab) is the stiffest layer and provides the majority of strength.

“The base or sub-base layers are orders of magnitude less stiff than the concrete surface but still make important contributions to pavement drainage and frost protection and provide a working platform for construction equipment.

“Rigid pavements are substantially ‘stiffer’ than flexible pavements due to the high modulus of elasticity of the concrete material, resulting in very low deflections under loading”.

The rigid pavements can have reinforcing steel, which is generally used to handle thermal stresses to reduce or eliminate joints and maintain tight crack widths.

The construction of a rigid pavement is a fairly complex process which involves; proper preparation of the sub grade and sub-base, placing reinforcing bars or dowels appropriately, Careful choice and handling of aggregates.

“Development of concrete mix design adequate for the projected axle load, production and transport of the concrete, placing, finishing, curing and joint sawing the concrete.

“Concrete roads are durable and safe; Less prone to wear and tear; Low maintenance requirements; Long-term performance (40years) of rigid pavement. Although, all depends on proper pavement design, materials selection and good construction practices.

However, it was noted that it’s affordability for a developing Nation where numerous infrastructure needs seek the attention of inadequate funds.

Chairman, Estate Surveyor and Valuer Registration Board in Nigeria (ESVRABON), Elder Williams Odudu, while lending support for concrete road, noted that the initial construction cost of the concrete road is generally higher compared to asphalt paving.

Maintenance Problem is to be considered. “In case the concrete road breaks, the whole concrete slab needs to be replaced leading to higher costs. Also, safety features must be considered. In rainy season vehicles tend to slip or slide on concrete road due to rain. So could be prone to more road accidents.

“Notwithstanding the above, for economic benefit on Nigeria roads, composite pavement structure should be considered.

“Composite Pavement is an overlay of asphalt on concrete road. The asphalt overlay may have been placed as the final stage of initial construction, or as part of a rehabilitation or safety treatment. “Composite pavement behaviour under traffic loading is essentially the same as rigid pavement.

“Concrete roads are highly durable, less fuel use and environmentally friendly as compared to asphalt roads. However Concrete construction cost far exceed Asphalt Construction Costs for same road type”.

At the end of the discussion, virtually all the speakers believed that composite pavement that combine the advantages of concrete for high load carrying capacity and asphalt for safety will be more sustainable for a developing nation (especially for Nigeria where maintenance budget is always low or sometimes zero.

Recognising the importance of CED Forum Award of Excellence, the Managing Director/CEO, Century 21 System Communication, Mr. Kenneth Olusola Stephenson, said he applauded the team at CED Forum Award and CED Magazine for taking the initiative to organize and champion the development awards.

“Our winners today, especially as we celebrate 20th edition of the platform, embody this mindset. They come from the built environment with good character and a spirit of service; professionals and organizations that put the nation and the customer at the center of every operation; engineering and construction in continuous pursuit of operational excellence so as to be best-in-class globally; and in academic pursuit.

“Also of note is that most of the winners have distinguished themselves in the sectors where many companies are grappling with the challenges of our tight labour market and the attendant recession

“They are all leaders in their own right, but let me take just one of the winners as an example, Dr. Ogbonnaya Onu, an engineer. Today he is the Nigeria’s Minister of Science and Technology where he has promised a new way of doing things with innovation as the centerpiece.

Other awardees include Messrs Iro vester Engineering Limited, Alfa Centuari Pumps Limited. Automated geotechnin Limited, Bow dynamics systems Limited, Global Sterling Products Limited, Natony Limited and Tegas Engineering Company Limited. Others are Mrs Funmi Akingbohun, Messrs Adewale Ikotun, Sam Nwosu, Dele Olaiya and Associates, SPA Dredging Company Limited and Skyes Energiprojekt Limited.