CFA piling (Continuous Flight Auger) is an advanced piling technique which relies on some fundamental properties of fresh concrete.
CFA piles are installed by rotating hollow continuous flight auger into the soil to a designed depth. A special concrete is pumped through the hollow stem, maintaining static head pressure, to fill the cavity created as the auger is slowly taken out. The reinforcement steel cage sinks through the freshly placed concrete to complete the pile construction.
Concrete for CFA must be soft and workable but most importantly stable. Segregated or sticky concrete could not allow the cage placement, causing huge delay and costly rectifications.
Hanson Technical Requirements
Hanson WA were developing a new mixture for CFA piling and they were facing some stability issues of the mix. The required spread was 650mm with a T500 under 5 seconds, slump retention 60 minutes, C40 strength class.
Sika proposed ViscoCrete-190 SC as the main water reducer in the mix. As a result, wetting time at the batching plant was drastically reduced and the stability of the mix improved all over the required slump life. The mix was overall more robust with no signs of segregation.
Laboratory and Field Trials
The new admixtures combination has been successfully trialled in the local Laboratory first (690 mm spread, 4 seconds T500, 48.5 MPa strength at 28 day). Hence, the mixture was adapted and tested in a full-scale trial at East Perth. The field test mirrored what had been achieved in the Laboratory.
The concrete was easily pumped along the hollow stem of the piling rig and the steel reinforcement cage introduced effortlessly. Our Costumer and the final user were happy with the robustness and the softness of the new recipe.
Karrinyup Shopping Centre:
The Karrinyup shopping centre in Western Australia, is being redeveloped by AMP Capital.
The builder selected is Multiplex, with a start date of late 2018, estimated for completion in 2021 with a total of 290 stores added to the complex. It will offer a premium entertainment and shopping precinct with a new cinema, various dining options and multiple parking facilities.
The redevelopment project aims at doubling the area of the mall from 59,874m² to 109,000m².
Hanson were contracted by GFWA to supply the piling concrete package that lasted over 14 months, with over 4,000m3 supplied across the project.
The requirements of mix performance were high, with the mix consistency being paramount. With the project requiring multiple contractors to work simultaneously the pours would be exposed to delays onsite with mix requiring the characteristics to hold slump over a longer period to extend the life and workability of the product.
Another major factor was the project was extended over a period of time to fit to the project timeline. This meant that the mix needed to be consistent over the changing seasons, allowing for high temperatures in the summer season and low winter temperatures.
By introducing the ViscoCrete- 190 SC into the mix it drastically increased the long term workability of the mix, the slump retained its targeted slump for an extended period and minimises the risk of segregation in the mix causing pump blockages and delays to pours.
As a result, less loads were rejected to being out of specification.