Indlovu
/íⁿɮʱoːvu/
(noun, meaning Mighty Elephant in Xhosa; honorific title for Zulu kings)
The Indlovu Floor is a rib-stiffened discrete funicular floor prefabricated with an unreinforced lightweight biomass concrete mix containing wood fibres from an invasive alien plant species that have “clogged” some of South Africa’s key freshwater supplies, posing a serious threat to delicate ecosystems.
Introduction
The Indlovu Floor is a pure application of two of BRG’s core principles, Strength through Geometry and Material Effectiveness. The floor was developed through a collaboration with nonCrete (the Cape Town-based company behind the development of a low-carbon, biomass concrete mix) in the context of their “Alien to Biomass Housing” project, co-funded by CSIR’s Circular Economy Fund and by WWF’s Nedbank Green Trust.
The result is a structural system with the potential to revolutionise current building practices in South Africa, while also creating job opportunities for the local communities involved in the clearing of the vegetation, the material production and the construction itself. With the unemployment rate amongst youth at 45% in South Africa, the need for such opportunities that at the same time address the housing crisis has never been greater.
Lightweight biomass concrete
Despite covering only 10% of South Africa, the Cape region provides more than 50% of the country’s water. Unfortunately, many of its water-catchment systems and rivers have been infested by water-thirsty alien invasive plants (AIPs) that severely affect water supplies. In an attempt to address this problem, nonCrete developed a process where the AIPs are cut down and shredded into wood chips and bound into two different types of mixes: a structural mix that is 55% lighter than conventional concrete, and a non-structural mix that is even 65% lighter.
Using large amounts of locally available and intrinsically renewable biomass, the use of other scarce resources like sand and conventional aggregates is drastically reduced. Furthermore, the carbon absorbed by these fast-growing AIPs is permanently locked into the building, in a process called carbon sequestration. Last but not least, the mix also showcases excellent thermal insulation properties, which in the case of floors come to an advantage in terms of fire resistance.
Rib-stiffened funicular floors
Exploiting the characteristics of the two types of mixes, we developed a hybrid floor system that uses the stronger mix in a completely unreinforced and prefabricated rib-stiffened shell, and the lighter mix as a filler that is applied in situ to build a walkable surface and to stiffen the structure against asymmetrical loads. The resulting structural section experiences mostly compressive stresses of a very low magnitude – an ideal application for the nonCrete biomass mix!
Fabrication
The broader aim of the project is to contribute to the provision of much needed safe, affordable, sustainable and dignified housing to millions of people in South Africa while also providing these communities with new job opportunities: project beneficiaries are currently being trained to process the invasive plants, prepare the biomass mixes, cast and install the prefabricated floors and then finish them in situ with the non-structural mix. Conscious of the local constraints but also of the underlying opportunities, the design team identified offsite modular prefabrication as the best strategy to ensure a cost-effective, speedy and quality-assured delivery of the structural skeleton of the floor, combined with a more conventional finishing strategy on site.
Load and fire testing
To verify the validity of our assumptions and structural analysis, a series of load tests were carried out in the presence of third party checkers on 5m long and 1m wide sections of the floor, both empty and filled, applying distributed, asymmetrical and point loads. The stiff floor sustained more than four times its design load with negligible deformations.
To prove that the Indlovu Floors could fulfill the REI criteria for real building applications, a 5m long by 3m wide floor was exposed to a fire of 1200°C for a duration of 2 hours, following an ISO-standard fire curve, in a furnace of the Ignis Testing Facility that was enlarged specifically for the test.
The floor performed even better than expected, showing neither signs of structural distress nor material spalling, confirming its higher insulating property than normal concrete. Even more remarkably, the floor continued to sustain the full design load during the entire cooling phase, after which the load was even increased beyond the full Serviceability Limit State value, demonstrating that there is no loss of strength or load-carrying capacity at very high temperatures.
Outlook
Having sustained the most rigorous third party verifications, Indlovu Floors are now on a fast-track towards full Building Accreditation, ready to be deployed on a number of pilot projects across the region.
Credits
Structural Design
Block Research Group
Material Development
nonCrete PTY (Stephen Lamb and Andrew Lord)
Fabrication
The One Nil Construction Team – led by Grabeth Nduna and supported by Peter Mafuwe and mSotho Mojalefa Thelingoana
Funding support
The CSIR Circular Economy Demonstration Fund – led by Prof Linda Godfrey and supported by Dr Coralie van Reenen and Thabang Molefi
WWF Water Source Partnerships South Africa – in particular Helen Stuart and Rodney February
Fire tests
Ignis Fire Lab (in particular Ryno van Wyk, Dirk Streicher, Pieter Grabe)
Prof Richard Walls – Fire Engineering Department of Stellenbosch University
Verification of test results
Ian Upton – Martin and Associates
Additional material development
Emeritus Prof Julian Cooke
Supporting project documentation
Leigh Meinert
Mignon Hardie