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Wirtgen widens Camps Bay Drive

Camps Bay Drive is a major scenic route within the City of Cape Town. The route requires widening to safely accommodate the high volumes of tourists and MyCiti bus traffic.

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After the rehabilitation project, Camps Bay Drive in Cape Town presents itself 1.4m broader and therefore much more secure to accommodate increasing traffic.

Image credit: Wirtgen

To minimise the impact on traffic, the design brief targeted construction outside the summer peak tourist season and required investigation into shortened construction periods. The key role was played by Wirtgen cold recycling technologies. In action: the mobile cold recycling mixing plant KMA 200.

The South African metropolis has large volumes of reclaimed asphalt (RA) stockpiled from numerous maintenance works undertaken around the city. This material has generally been used for hard stand areas and shoulder construction, to reuse this high-quality material, WorleyParsons was tasked to investigate a more efficient and sustainable use for this material. Therefore, the use of a foamed bitumen technology was investigated and the base layer on Camps Bay Drive was constructed using 100% RA as a foamed Bitumen Stabilise Base (BSM) base layer.

WIRTGEN KMA 200 MIXES HIGH QUALITY RECYCLING MATERIAL.

Originally, the project consisted of localised road widening to accommodate the proposed MyCiti buses however due to the large volume and sizes of the proposed buses, a geometric analysis resulted in the entire portion of the road being widened by 1.4m. The proposed pavement design involved a light rehabilitation with the widening area requiring full depth construction however during construction, numerous weak horizons were discovered along the road. The pavement design implemented for construction involved the following:

  • 50mm AE-2 asphalt surfacing
  • 200mm foamed BSM 1 base
  • 150mm G5 subbase, natural gravel
  • 150mm G7 selected subbase, pioneer rock layer
  • In-situ
  • 100% RA
  • 100% RA with 10% crusher dust
  • 100% RA with 25% G4 gravel material
  • Paving 100mm thick BSM layer and allowing for bulking of 30 to 40mm
  • Applying primary compacting using a 12-t tandem drum roller
  • Paving the second 100mm thick BSM layer on to the lower half of the layer
  • Applying primary compaction using a 12-t tandem drum roller
  • Applying final compaction using two pneumatic tire rollers (27t PTR) until compaction was achieved

The project was divided into three construction sections. Section 1 from Geneva Drive to Prima Avenue, Section 2 from Prima Avenue to Rontree Avenue and Section 3 from Rontree Avenue to Houghton Road.

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At the Ndabeni Roads and Stormwater Depot in Maitland, the Wirtgen cold recycling mixing plant KMA 200 quickly and reliably produced the BSM mix. 
Image credit: Wirtgen

To ensure more uniformity and better quality of the mix, a static mobile mixing plant was specified for production of the BSM.

PROPER RECIPE IS DECISIVE

Power Construction was appointed to carry out the construction of the works and Milling Techniks carried out the production of the BSM using its Wirtgen KMA 200.

During construction, the stockpiled RA was sent for technical testing at BSM Laboratories in Durban. The design was carried out on three design options using the two dedicated stockpiles of materials from two sources which were created for the project by the City. The design options included:

Based on the results obtained, the most cost-effective option to yield a BSM 1 is 100% RA mix design using 2.1% foamed bitumen and 1% cement.

The batching plant was set up at the Ndabeni Roads and Stormwater depot in Maitland. The depot provided sufficient space to establish the KMA 220 as well as allowing for the stockpiling of the unprocessed RA, screened RA and processed BSM. The specification called for crushing of the RA to remove the oversized fractions. An alternate proposal in the form of screening the material to minus 19mm in place of crushing the material by the contractor was accepted, provided the fines fraction (0.075mm) met the specification of 4%. This was monitored for the duration of the project with a fines fraction of between 3% and 4% recorded. The screened RA was processed using the KMA to form a BSM 1, which was stockpiled for up to seven days at the depot

To ensure an adequate quality of the BSM and consistency within the mixing process, Power Construction, Milling Techniks and WorleyParsons created a quality system tailored for the BSM production using the KMA. This was implemented to ensure the mix met the BSM 1 specification throughout the project. Once the BSM was produced, the material was either placed on site immediately or protected and stockpiled at the Ndabeni Depot.

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The proper recipe and professional BSM producing of the Wirtgen cold recycling mixing plant were the key factors for a successful project.

Image credit: Wirtgen

BSM QUALITY CHECK BEFORE PAVING IS MANDATORY

The BSM was paved using a heavy duty tracked paver from Power Construction in two 100mm thick layers in the same process.

The process used to get the required 100% Minimum Dry Density (MDD) compaction is as follows:

Before starting with paving and compaction, a testing of the BSM was undertaken by Soillab that established a testing rig in accordance with the TG2, 2009 specification. Acceptance control was carried out on the Indirect Tensile Strength (ITS) and MDD taken from the batching plant and site samples.

The three sections identified were constructed using similar techniques, however in Section 1 and 3, the BSM was opened to traffic immediately after construction and in some cases 24 hours after construction.


 

 

 

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