New Perspectives for
Resource-Efficient and Recycling-Optimized Construction
The building industry is responsible for 40-50 per cent of resource
consumption, 35 per cent of CO2 emissions, and 50 per cent of waste generation
worldwide. It therefore carries the greatest responsibility, but at the same
time wields the greatest leverage over the development of a sustainable way of life. Through the development of building components made of functionally graded materials, the building industry can make a significant contribution to reducing resource consumption, energy use, emissions, and waste.
Functionally graded concrete blocks
© ILEK, Stuttgart/Germany
On the interior of functionally graded building components, material
properties are continuously and smoothly varied (graded) in all three dimensions,
allowing them to optimally fulfil local structural, thermal, and other
requirements. This gradation of material properties is achieved either by
varying the porosity of the material, or by varying the ratio of components in a mixture of materials.
The basic concept of functionally graded materials was developed by the
aerospace industry. But while research in this field remained focused on thin
surface layers, the Institute for Lightweight Structures and Conceptual Design
(ILEK) at the University of Stuttgart expanded the principle, beginning in 2006,
to much larger dimensions and to applications in the building industry.
Porosity of graded concrete - close-up
© ILEK, Stuttgart/Germany
50 Per Cent Material Savings
By grading the interior porosity of structural building components,
material properties can be precisely matched to the actual applied loads. Thus
it becomes possible to avoid unstressed (and therefore extraneous) material.
Nature offers many examples of this principle of optimization, such as the
graded interior structure of cancellous bone. Structural tests have shown that
employing this approach in concrete slabs can result in material savings of over
50%. Because this reduces the cement content by the same proportion, equally
significant savings in the embodied energy and CO2 emissions associated with
cement production can be achieved, in addition to the dramatic material and
weight savings.
Single-Material Multifunctional Building Components
In materials such as concrete, metal, glass, and plastic, many different
material properties can be widely varied through changes in porosity - including
strength, thermal conductivity, and air-tightness. This makes it possible, for
example, to design a wall consisting purely of one material - such as concrete -
which fulfils all of the requirements of a building envelope. This both
increases valuable usable floor space, and significantly improves the
recyclability of the building component - in comparison, a typical Exterior
Insulation and Finishing System (EIFS) consists of dozens of different materials,
permanently bonded together in such a way as to make separation and recycling
virtually impossible. Through the graded transition from a dense supporting
outer layer to a highly porous insulating inner layer (eg. Aerogel concrete),
purely mineral-based outer wall elements can be achieved which are only a
quarter of the wall thickness of comparably high-performance insulating
concretes.
Functionally graded wall slab
© ILEK, Stuttgart/Germany
Automated Manufacturing
The greatest challenge in the pursuit of functionally graded materials lay in
the development of an economical manufacturing process to achieve the desired
material property gradients. Porosification was achieved in concrete through the
use of porous lightweight aggregate and the additional introduction of entrained
air voids in the cement matrix. Three-dimensional gradation was achieved using
the patented simultaneous spray process developed at the ILEK, in which the
consistency of the spray is continuously varied, and depending on the position
of the spray nozzle, the appropriate concrete mix is applied. The automation of
this process allows concrete building components with varying porosity to be
quickly and economically manufactured. Further development of this technology is
the focus of ongoing research at the ILEK.
Smooth transitions between different materials (concept illustration) © ILEK, Stuttgart/Germany
Seamless Material Transitions
In addition to porosity gradation, material gradation also has great potential.
Seamless transitions from one material to another would make possible
high-performance and aesthetically fascinating alternatives to traditional
connection techniques such as screwed and glued joints, which often represent
weak points in structural systems due to load concentrations and thermal
expansion issues. Manufacturing processes for seamless transitions between wood,
aluminum, plastic, and fibre-reinforced composite materials are in the
experimental phase.
Material Design as a Function of Form
The development of functionally graded building technology is first and foremost
a significant contribution towards the realization of truly resource-efficient
architecture. But it also gives rise to new aesthetic possibilities, and in fact
redefines the traditional relationship between form and function: It allows the
material properties of a building component to be designed irrespective of its
outer shape - whether through changes in porosity, stiffness, or transitions
between materials. While in the past the predominant optimization technique was
to design form as a function of material, functionally graded building
components offer an entirely new approach: the design of material as a function
of form.
Research Institute
The research and development initiative into functionally graded materials is
being pursued at the Institute for Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart, under the direction of Prof. Dr. Dr. E.h. Werner Sobek. The concepts for the manufacture and application of functionally graded building components have been developed by Pascal Heinz over the course of his doctoral thesis, begun in 2006. An ongoing research project entitled "Manufacturing Processes and Applications for Functionally Graded Materials in Construction", begun in 2009, has subsequently made possible a thorough experimental program yielding valuable results and practical experience. This
research was carried out by Pascal Heinz and Michael Herrmann, and funded
through the "ZukunftBau" research initiative of the German Federal Office for
Building and Regional Planning (BBR). The further development of functionally
graded concrete technology and its applications, specifically in material- and
weight-optimized high rise floor slabs, will be the focus Michael Herrmann's
doctoral thesis.
The initial project also gave rise to multiple follow-up projects centred on
the application-specific development of functionally graded materials. A number of leading companies in the German and international concrete industries are involved in these projects.
Project Team / Further Information:
ILEK
Lightweight Structures and Conceptual Design
University of Stuttgart, Germany
Prof. Dr. Dr. E.h. Werner Sobek
Dipl.-Ing. Pascal Heinz - eMail:
pascal.heinz@ilek.uni-stuttgart.de
Dipl.-Ing. Michael Herrmann - eMail:
michael.herrmann@ilek.uni-stuttgart.de
web:
www.uni-stuttgart.de/ilek
german version 