Expanding a key commercial corridor, China Railway Seventh Group Botswana is upgrading one of Botswana’s most important road networks, with a Cat RM300 rotary mixer responsible for the cement stabilisation works.
REPRESENTING AN investment of around one billion pula, Botswana’s A1 national road between Tonota and Francistown is undergoing a major upgrade as this single-lane section is progressively transformed into a north- and southbound dual carriageway, crossing four existing river bridges along the way.
A strategically important transportation route for both Botswana and the Southern African region, the A1 passes through Francistown, the nation’s second largest city, heading northwards to end at the Zimbabwe border some 90 km distant. From there, commercial traffic continues on to destinations that include Zambia and the DRC.
The contract for the reconstruction of the Tonota to Francistown route, covering a distance of approximately 30 km, was awarded to China Railway Seventh Group Botswana (CRSG Botswana) in August 2012 by Botswana’s Ministry of Transport and Communications, Roads Department. The 30-month construction programme commenced in May 2013 following an initial six-month mobilisation period entailing the relocation of water, sewage, telecommunication and electrical services. The consulting engineers are Pula Consultants, based in Botswana.
In addition to the installation of three major in-situ box culverts to cater for the extended pavement width, new simply supported independent bridges are being constructed alongside the existing Tholodi, Shashe and Bodumatau Bridges (1.88 km, 4.13 km and 23.9 km respectively). Tati River Bridge (28.86 km) on the outskirts of Francistown is the exception. Here the structure is being widened equally on each side from the existing width of 10.63 m to the new deck width of 28.55 m, maintaining the current road centreline. All the original bridges were built some 37 years ago when this A1 section was first constructed. Tholodi’s new carriageway bridge will be a 36.15 m long, 3 x 12 m span structure; Shashe will feature a new 144.6 m long, 12 x 12 m span bridge; and Bodumatau a new 24.1 m long structure with 2 x 12 m spans. All three bridges will have an overall deck width of 11 m with a road width between parapets of 10.4 m on a 2.5% crossfall. Bridge deck cross-sections consist of precast, ordinarily reinforced inverted T-Type beams with in-situ concrete between and on top, providing an overall deck thickness of 710 mm. Tati River Bridge, measuring 108.45 m in length, will also employ precast beams for the deck widening.
General rehabilitation and maintenance of the existing bridges is also being undertaken, along with the construction of concrete New Jersey type parapets that will replace existing steel handrails. New and existing bridges will be surfaced with a 50 mm thick asphalt overlay. Running in parallel with the bridge programme are extensive roadworks along the Tonata to Francistown section. In addition to new roadbed preparation, construction of in-situ reworked and new cement stabilised lower and upper sub-base layers form a major portion of the contract.
CRSG’s scope of works also includes the widening of existing cuts and fills, benching into old fills or the construction of new cuts and fills, plus horizontal and vertical realignment of the existing road in order to improve design speed, which is generally 120 km/h along rural sections, and 80 to 60 km/h through built-up areas.
The existing Thapama Traffic Circle (29.7 km) within Francistown will also be remodelled as a grade separated intersection, together with the construction of two access roads. New construction, as well as reconstruction of the existing pavement is being carried out by a Cat RM300 rotary mixer, which forms the critical path of the road contracts programme. Sold and supported by Barloworld Equipment, the RM300 is working alongside CRSG Botswana’s predominately Cat earthmoving fleet, comprising graders, excavators and rollers. (Barloworld Equipment is the Cat dealer for Southern Africa.)
In addition to its RM300 deployed on the A1, CRSG Botswana also has a Cat RM500 deployed in Zambia, where the company is currently working on a range of construction projects. According to CRSG, both machines are providing excellent production results with high mechanical availability.
Weighing in at around 24 454 kg, the Cat RM300 features a gross power delivery of 261 kW via its Cat C11 engine.This compares with the Cat RM500, which has an operating weight of 28 145 kg and is driven by a Cat C15 ACERT engine generating a gross power output of 403 kW.
“The key difference between the RM300 and RM500 is their power delivery and application requirements,” explains Barloworld Equipment’s product manager, Johan Hartman. “The Cat RM300 has a single water pump system, while the larger Cat RM500 features a dual water and emulsion pump design for either cement or bitumen stabilisation requirements. However, the two models have the same cutting drum widths and depths (depending on the rotor option selected).”
In working the lower and upper sub-base layers, the RM300’s universal rotor – equipped with its 200 carbide-tipped bits arranged in a chevron pattern – comes into play in reworking dense in-situ materials, in the process providing high levels of material pulverization and gradation. A three-position mode switch enables the rotor depth to be controlled manually or automatically to a preset cutting depth to ensure that the engineering design is precisely met. Width of cut is 2 438 mm, while the maximum mixing depth is 457 mm (when equipped with the universal rotor).
A key feature on the Cat RM300 is the machine’s side-to-side shifting operator station. The cab slides fully to either side of the machine using hydraulic-assist. This means that the operator always has maximum visibility for optimal in-situ mixing efficiencies, helping to ensure that CRSG meets its daily production rates within designed depth, moisture and compaction density targets.
Wholly owned by China Railway Group Limited, CRSG has established a strong presence on the African continent, with subsidiaries formed in Botswana, Zambia, Mozambique, Tanzania, Uganda, Ethiopia, Senegal, and Sierra Leone. In 2013, China Railway Group Limited was ranked 34th out of the world’s Top 250 International Contractors according to US-based Engineering News-Record’s annual industry survey.
The Tonota to Francistown project is the second Botswana contract awarded to CRSG. The first, valued at around 193 million pula, was completed in 2011, entailing the upgrading of a 38 km gravel section between Ngoma and Kachikau to a bitumen double seal single lane riding surface, which was officially opened in December of that year.