Indlovu
/íⁿɮʱoːvu/
(noun, meaning Mighty Elephant in Xhosa; honorific title for Zulu kings)
The Indlovu Floor is a rib-stiffened discrete funicular shell prefabricated with an unreinforced lightweight biomass concrete mix containing wood fibres from invasive alien plant species. Alien-invasive plants threaten South Africa’s key freshwater supplies and trigger large-scale wildfires thereby posing significant threats to delicate ecosystems.
Introduction
The Indlovu Floor showcases two core principles – Strength through Geometry and Material Effectiveness. The floor was developed in partnership with nonCrete, the Block Research Group and the CSIR’s Circular Economy Fund.
The result is a structural system with the potential to impact current building practices in South Africa. It can create job opportunities for local communities through the clearing of invasive vegetation, material production and the construction itself. With the unemployment rate amongst youth at 45% in South Africa, the need for such labour intensive 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. The mix is fire resistant and has excellent thermal insulation properties.
Rib-stiffened funicular floors
Exploiting the characteristics of the two types of mixes, a hybrid floor system was developed which uses the stronger mix in a completely unreinforced and prefabricated rib-stiffened shell and the lighter mix as a filler that is cast in situ. The filler mix levels the floor to create a walkable surface and stiffens 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 options to millions of people in South Africa while also creating new job opportunities in the sustainable construction sector. Project beneficiaries become skilled in the clearing of AIPs, the preparation of biomass mixes, the casting and installation of the prefabricated floors and the in situ finishing of them.
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 the design 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 rib-stiffened vaulted floor sustained more than four times its design load with negligible deformations.
To prove that the Indlovu Floors could fulfil the stRuctural Resistance (R), intEgrity (E), and Insulation (I) criteria for real building applications, a 5m long by 3m wide floor was exposed to the standard fire curve (ISO-834) for a duration of two hours, reaching a maximum temperature of approximately 1 050°C at the two-hour mark, in a furnace of the Ignis Testing Facility which was enlarged specifically for this test.
The Indlovu Floors were tested in accordance to EN 1365-2:2014 and were subjected to a full service load, 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 evenly increased beyond the full Serviceability Limit State value, demonstrating that there is no loss of strength or load-carrying capacity at very high temperatures.
Credits
Structural Design
Material Development
nonCrete PTY – Stephen Lamb and Andrew Lord
Fabrication
Andrew Lord
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 – Helen Stuart and Rodney February
Fire tests
Ignis Fire Lab – 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