Studies recently completed by JG Afrika, a leading South African firm of consulting engineers, have informed the design of the rehabilitation of a strategic road that connects Tin Can Island Port to major commercial centres in Lagos State, Nigeria.
The existing access road from Tin Can Island and the six-lane expressway that connects Apapa Wharf, one of Nigeria’s major commercial centres, to Oworonshoki was built as early as the 1970s and has since fallen into a serious state of disrepair.
This has contributed to the severe vehicle congestion comprising mainly trucks that use the road to travel between the port and Oworonshoki every day.
In addition to the profound negative impact that this has had on efficiencies at the port and the Nigerian government’s larger trade facilitation programme, the severe traffic has negatively affected many small businesses in Apapa and road safety levels, especially during the wet season.
The rehabilitation of the roads as part of a public-private partnership was first mooted by AG Dangote Construction, a subsidiary of local cement giant, Dangote Industries, and the proposal was favourably received by the Federal Ministry of Power Works and Housing.
Notably, JG Afrika proposed a continuously-reinforced concrete pavement (CRCP) design to better cope with the growing number of heavy commercial vehicles travelling between Apapa Wharf and Oworonshoki every day.
The design is similar to the technology deployed in the construction of South Africa’s Ben Schoeman highway.
It still stands out as a stellar example of CRP design in the country by providing the South African National Roads Agency Limited with a more cost-effective means of maintaining this heavily-trafficked route that connects Johannesburg and Tshwane in Gauteng.
This design has replaced the initial suggestion of using a conventional jointed concrete pavement that would ultimately develop slab tilting and stepping on the extremely soft subgrade material encountered along sections of the existing road from Apapa to Oworonshoki.
Dangote Industries can be credited for introducing concrete pavements to the West African country.
Meanwhile, its construction arm has also invested heavily into the equipment required to construct these pavements. These include a concrete paver to significantly accelerate construction times and a state-of-the-art road recycler that will be able to easily convert the base layers into a cement-treated base on site.
Dr. Emile Horak, a well-known pavement specialist who led the JG Afrika team that undertook the pavement evaluation, previously played an instrumental role in assisting the contractor introduce in-situ recycling equipment to the West African country.
“Using this technology, combined with the concrete paver, the contractor will be able to complete the extensive rehabilitation required in a significantly shorter period than is possible constructing a conventional asphalt pavement. This is a major advantage considering that the contractor will be working in an extremely built-up area. The onerous process of having to relocate people and structures, in addition to the inconvenience caused by prolonged construction activities, were among the chief reasons for the Nigerian authorities ultimately delaying the rehabilitation of the road over the years,” Dr. Horak says.
JG Afrika was appointed by the contractor to undertake the pavement evaluation in 2018, and these critical insights have been incorporated into the final rehabilitation design by Yolas Consulting, a Nigerian engineering consultancy working on behalf of AG Dangote Construction.
A detailed assessment of the condition of the road pavements and a geotechnical investigation of material used in the existing road were undertaken as part of the project. In addition, JG Afrika undertook an extensive investigation of all available construction materials to build the road and structures.
The studies identified high deflection on the road as a result of a very weak pavement structure, while very poor materials were also used in the construction of the existing road, especially for the foundation layers.
Testing undertaken on asphaltic concrete samples showed that all of the properties met the specification requirements and that the grading of the aggregates was within the specification envelope for wearing course.
However, unsuitable material was identified in the samples of sub-base and sub-grade layers that were collected from various locations along the road.
Meanwhile, a visual condition assessment undertaken by the team of engineers showed significant distresses and failures on most sections of the existing road infrastructure.
According to the study, it will be possible to source sufficient filling material from all of the borrow pit areas that were investigated, while suitable crushed rock aggregate for the base course can be obtained from the rock outcrops that were observed along Logos-Ibadan road.
The engineers also found the available aggregate, water and river sand to be of a suitable quality for the construction works. Should there be insufficient river sand, they have recommended supplementing supply with quarry dust.
JG Afrika also noted that adequate provision be made in the Detailed Design Report for drainage and sub-drainage improvement, especially in the swampy areas, in addition to the need to reinstate the shoulder of the entire road.
Dr. Horak says the concrete pavement design expertise of Ane’ Cromhout, pavement engineer with the JG Afrika team, formed the basis of the recommendations to use CRCP. These recommendations made by JG Afrika were well received by the contractor and he anticipates work to commence imminently on the rehabilitation of this critical road infrastructure.
“Dangote Construction deserves to be lauded for the innovative approach that it has taken to rehabilitating the many roads in the country that have fallen into a serious state of disrepair. This has added impetus to the Nigerian government’s already-heightened focus on repairing these strategic assets and building new roads to expand the national network,” he concludes.