Concrete containing the High Density aggregate MagnaDense is widely used in projects where space is limited or there is a requirement for additional weight to overcome civil engineering challenges.
Naturally, concrete producers may have concerns about mixing heavyweight concrete for the first time. We asked ready mix producers, ad-mixture experts and installers for their perspective on working with MagnaDense concrete compared to standard density.
Production of MagnaDense high density concrete
Contrary to popular belief, you can produce MagnaDense high density concrete using standard plant and equipment. The main difference is the rate of production. You generally slow this down to allow the plant to cope with the additional weight. Extra loads on electric motors, belts and overhead storage bins need to be considered from an engineering and safety perspective.
Mark Wood, Area Production Manager – Concrete & Asphalt at Breedon Group commented “it is important that plant assessments are carried out prior to using MagnaDense as it allows you to identify any weaknesses in the operation when producing heavy weight concrete. What is key to production is having the skills and confidence to produce it.”
When production began on the recent Subsea Protection Systems project, Mark quickly realised that the weigh-bin doors required modification. He, therefore, installed stronger hydraulics to ensure the doors closed under the additional weight.
As with standard concrete, MagnaDense high density concrete can be produced using a mobile plant on site. This type of plant is particularly useful for remote projects.
The importance of mix design
A good mix design will produce a homogeneous, cohesive concrete with little bleed and segregation. And therefore, allows for suitable placing by either skip or pump. “The use of modern admixtures allows you to produce the concrete with a longer open life,” says Jack Sindhu, Technical Manager for Capital Concrete. “This will enable the concrete to maintain workability for a longer period of time avoiding water addition, which can be detrimental to the density, strength and finish of the concrete”.
In many ways, MagnaDense heavyweight concrete performs the same as standard density concrete. You can specify the mix design to achieve extended setting times. Consequently, allowing the concrete to transport over longer distances and potential delays on site. We can help you to design the concrete to be self-compacting or traditional slump and strength and higher earlier strengths can be achieved.
The use of admixtures
As with standard concrete, you can utilise admixtures to optimise the properties of MagnaDense concrete, depending on the project. Although there are many factors that would need to be taken into consideration, three aspects of an admixture’s performance, in particular, are critical for MagnaDense high density concrete.
“The water and air contents are significant factors in obtaining the required density, and you must select any admixture to minimise these” explains Ian Ellis, Technical Services Manager – Admixture Systems UK & Ireland for BASF. “The third important factor that people often forget, which tends to be a direct result of minimising the concrete water & air contents, is the concrete rheology, commonly referred to as ‘stickiness’. There are admixtures available which can optimise of all three of these factors and thus enable the production of an easy to place user-friendly MagnaDense high density concrete.”
Due to the additional weight of MagnaDense concrete, you can transport less material per load, meaning additional haulage may be required. “It takes drivers a little time to get used to travelling with MagnaDense concrete,” says Jack. “Due to the weight of the concrete, the result is a higher centre of gravity in the truck’s drum mixer and the driver must ensure they adjust their driving style and speed of the drum to accommodate this.”
You can place MagnaDense concrete with the same equipment as standard concrete, using the same pumps and skips. However, you need to take some considerations into account. Andrew Turner, Special Projects Manager for Camfaud Concrete Pumps expressed “The concrete mix design, pumping system and personnel are all key to successful placement of MagnaDense concrete.”
When pumping MagnaDense heavyweight concrete, a modern, well-maintained pump with sufficient power and pressure capacity and compatible pipeline & couplings are most important. “If the critical success factors are met, there should be no reduction in the pumping rate or increase in pumping pressures,” says Andrew.
Our customers place MagnaDense concrete from a boom or manually handle pipeline and vibrate the concrete normally. Be aware that pressure on the formwork can increase due to the density, so this should be taken into account.
Addressing the issue of cost
As a general rule, when compared to standard concrete, high density concrete is more expensive per cubic metre. The saving comes from the overall project costs including:
- where space is at a premium – you can build additional rooms or the overall footprint reduced;
- where there are civil engineering challenges e.g. the need for movement of existing infrastructure. You can use MagnaDense Concrete to stabilise existing infrastructure negating the need for expensive groundworks;
- Other construction costs e.g. reducing the piling requirements or reducing the size of a bridge counterweight cast in steel.
The importance of service
Many projects are subject to changes in timescales and demands, leading to short lead times. Due to our strategic local stocks, LKAB Minerals can supply MagnaDense exactly when you require this. “LKAB is always spot on with deliveries, sometimes with short lead times,” says Andy Green, Breedon Group’s East Anglia Area Sales Manager for Readymix Concrete and Asphalt. “We always receive MagnaDense on time, in full and at the right specifications.”
Over the years, our customers use MagnaDense concrete extensively on various projects, from hospitals and nuclear facilities to bridges and tunnels. Our commercial team have many years of experience in developing mix designs alongside engineers, concrete producers and admixture companies to develop the optimal concrete for a particular project.
Read more about some of our recent projects by clicking the links below:
- Shaft Infill Project, Essex
- Samuel Beckett Bridge, Dublin
- Wirral Dock Bridge, UK
- St Pauli Elbe Tunnel, Germany
- European Spallation Source, Sweden
- Dolphin Mooring Quay, UK
- ITER Research Facility, France
Education through free webinars
We continue to offer a series of webinars, focussing on Civil Engineering challenges and MagnaDense High Density Concrete. Find out more about our most recent webinars below:
- High-Density Concrete & ballast in bridge constructions
- Gypsol Anhydrite Screed; a sustainable flooring solution
- Ground stabilisation with high-density concrete
- High-Density Concrete for Radiation Shielding
- Gypsol Anhydrite Screed; placing floor coverings
- The efficient use of GGBS in concrete
- Properties and installation of high density concrete
- Sustainability in LKAB
We continue to plan more webinars. Please keep an eye on our website or social media for more updates.