As innovative new building materials are created to meet sustainable building practices, a means of evaluating their durability is needed. A BRANZ project is on the case, developing a framework to do just this.
ONLY A FEW metallic materials and coatings with recognised durability can be used as acceptable building solutions. These include aluminium, copper, stainless steel and zinc. Recently, the sustainability of the production processes for some of these materials, such as hot-dip galvanised coatings, has been questioned. Alternative materials are therefore needed to sustain future building.
More sustainable materials emerging
Technological advances have led to the development of new or innovative materials comprising ceramics or composites or utilising nanotechnologies. For example, innovative coatings have been manufactured with micro-capsules capable of regulating micro-environments or having the ability to self-repair. These coatings may provide better protection than conventional coatings, which rely solely on barrier or galvanic effects.
If the new or innovative materials demonstrate appropriate durability, they have the potential to deliver environmental, life-cycle cost and performance benefits to buildings.
Assessing durability is difficult
Before the industry will embrace new or innovative materials, their potential risks must be analysed and minimised.
Durability assessment of new or innovative materials is challenging since the materials are unique in terms of composition, micro-structure, processing, functional design or in-service condition adaptability. Criteria and schemes need to be developed to assess the durability of these materials to inform the industry and establish confidence in their use in the building sector.
Framework for developing durability assurance
BRANZ has a new project, A durability evaluation framework for innovative building materials, to help facilitate durability assessment. It aims to produce knowledge and tools that bridge the gap between increasing demands and current capabilities for durability assessment of new or innovative materials. The project is designed with two interconnected parts:
- Part one involves developing an over-arching strategy to guide the establishment of generalised procedures for durability assessment (Figure 1).
- The second part will apply top-down and bottom-up approaches (Figure 2) to refine durability requirements and to develop test schemes that support phases 3–5 of the strategy.
Start with durability assessment strategy
The project will compile relevant information to describe the objective, method and structure of the phased durability assessment strategy. It will also answer questions frequently asked by manufacturers or suppliers of new or innovative materials:
- What should the durability assessment include?
- How can the results be interpreted for in-service durability?
Core components identified to technically support this strategy include (see Figure 1):
- Phase 1: Materials – a generic database of new or innovative building materials and a database of material specification
- Phase 4: Evaluation – a compilation of durability indicators and acceptance criteria appropriate for new or innovative materials
- Phase 5: Interpretation – a database of expected service lives of typical building materials and service life prediction methods, models or tools.
Refining durability requirements
Building materials need to be investigated in the context of the building system they form a part of, rather than as single components in isolation. Correspondingly, the top-down approach will be used to interpret durability at various levels to produce an integrated hierarchy of requirements. These include (see the right-hand side of Figure 2):
- Building Code – durability requirement (5, 15 or 50 years)
- building system – behaviour requirement under in-service conditions
- building component – functional requirement within overall behaviour of the building system
- building material – constitutional requirement such as dimension, geometry and physicochemical property.
This hierarchy indicates that the basic characteristics of a material are fundamental to its durability when used on a building.
Bottom-up approach to guide assessment
The properties of building materials need to be characterised to establish a baseline for durability assessment with a bottom-up approach. This is highlighted by the bottom tetrahedron of Figure 2 showing that any change in composition, micro-structure or processing of a material can impact on its property, performance and eventually durability.
For example, new zinc coatings with magnesium perform better than conventional zinc coatings. The root cause is that magnesium addition changes the coating structure, leading to beneficial composition and structure changes in the corrosion product layer.
Durability assessment needs to go beyond the test-and-see type characterisation. This project will also collect information about the actions, interactions and responses to explore mechanisms behind degradation and failure of new or innovative materials.
The science from one level will be used to inform the next. By using the material-structure-environment paradigm (middle and top tetrahedrons of Figure 2), it will be possible to quantitatively assess materials performance and durability in an integrated, whole-systems context.
Test schemes to be developed
Using the top-down and bottom-up principles, three test schemes will be designed and
developed as part of this project to support Phase 3: Methodology of the strategy in Figure 1:
- A scheme for characterisation of fundamental material properties using advanced techniques such as electron microscopy, X-ray diffraction and spectroscopy.
- A multi-stage scheme for investigation of metal-moisture-chemical interactions.
- An accelerated field exposure scheme for assessment of material-atmospheric environment (salt and solar irradiation) interactions.
These tests aim to answer the questions asked by organisations assessing durability of new or innovative materials:
- How can the assessment and tests required be done?
- Are current methods and techniques appropriate for the assessment and tests?
Building Code compliance
The BRANZ project will inform manufacturers, suppliers or evaluators in selecting and integrating relevant core components and test schemes to build a variety of functional modules for property, performance and durability evaluation. This will then contribute towards a dynamic assessment process for specific new or innovative materials or material groups to achieve Building Code compliance.
Ultimately, this research aims to provide industry with confidence in the appropriate use of new or innovative materials for building and construction.
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