Wirtgen KMA 200 mixes high quality recycling material
Originally, the project consisted of localized 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 1,4 m. 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:
50 mm AE-2 Asphalt Surfacing
200 mm Foamed BSM 1 Base
150 mm G5 Subbase, natural gravel
150 mm G7 Selected Subbase, pioneer rock layer
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.
In order 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 with Milling Techniks carrying out the production of the BSM using their 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:
100% Reclaimed Asphalt
100% Reclaimed Asphalt with 10 % crusher dust
100% Reclaimed Asphalt with 25 % G4 gravel material
Based on the results obtained, the most cost effective option to yield a BSM 1 was the 100% Reclaimed Asphalt mix design using 2.1 % foamed bitumen with 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 19 mm in place of crushing the material by the contractor was accepted provided the fines fraction (0.075 mm) 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 7 days at the depot
In order 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.