Discussion

The previous sections introduced a range of alternative materials, design strategies and business models listed in Table 10 overleaf. The list includes some options that were not previously detailed due to the limited potential scale of their application in the UK. This includes niche construction methods using alternative materials such as earth (Pacheco-Torgal & Jalali, 2012); tyres (Peacock et al., 2010) and bamboo (van der Lugt et al., 2006). Each option is presented alongside a summary of suitable applications and a qualitative assessment of the immediacy and magnitude of associated carbon savings. Any carbon savings achieved from implementation of these options depends upon the particular material and project parameters, assumptions about the benefits of carbon sequestration and so forth. Thus the table should be viewed as a rough guide only.

Table 10: Summary of options for reducing the use of carbon-intensive materials in the UK construction sector

Potential applications Carbon savings

Residential Retail Offices Education Infrastructure Other Substructure Superstructure Immediacy Magnitude

Alternative biotic materials

Timber (traditional forms, SIPs, Brettstapel, CLT, glulam, timber-steel hybrid construction) Straw-bale (infill, load-bearing or composite panels e.g. Modcell®)

Biocomposites

Earth (rammed earth, unfired brick, cob, wattle and daub, adobe)

Hemp (hempcrete and hemp-lime blocks and panels)

Limecrete

Bamboo (laminated or unprocessed) Cardboard (tubing or panels)

Other alternative materials Geopolymer cements Geopolymer composites Completely recyclable concrete Self-healing materials

Plastic (FRP, ETFE) Tyres

Concrete and masonry units incorporating supplementary cementitious materials or aggregate substitutes such as:

Industrial wastes (GGBS, fly ash, silica fume, pulp and paper mill residuals, coarse steel slag, copper slag, cotton waste, sewage sludge ash etc.)

Consumer wastes (plastics, glass, ceramics, tyres, textiles)

Agricultural wastes (rice husks, corn cobs, vegetable fibres, nut shells etc.)

Construction and demolition waste Alternative business models Component leasing

Other product service systems

Potential applications Carbon savings

Residential Retail Offices Education Infrastructure Other Substructure Superstructure Immediacy Magnitude

Design strategies

Use of structurally optimised components (carpet/roll-out reinforcement; variable depth members etc.)

Design for high utilisation ratios of standard components

Design for longevity Design for deconstruction

Adaptable design in new buildings Adaptive reuse of existing structures

Key

Carbon savings incurred immediately (e.g. through absolute reduction in material use or direct displacement of more carbon-intensive material)

Carbon savings incurred in long term (e.g. over decades through reduced maintainence or reduced demand for new components or structures) Immediacy of carbon savings

Substantial carbon savings

(e.g. provides zero or very low carbon alternative to conventional approach)

Minimal carbon savings (e.g. provides <5% reduction compared

with conventional approach) Magnitude of carbon savings

The highlighted options in the review draw upon a diverse range of materials and approaches but share many common barriers to uptake. These barriers are explored in detail in the next chapter. The following discussion is structured around three key questions arising from the review. What are the critical research gaps?

Over what timeframe can these options contribute significant carbon reduction?

What combination of options may be required to meet sector and national carbon reduction targets?

4.6.1 What are the critical research gaps?

It is clear from the body of evidence reviewed that past research has suffered from a number of shortcomings. The academic research on low carbon materials focusses too much on developing new materials and not enough on ensuring current materials are used efficiently. This is reflected in the distribution of publications encountered in the literature review, far more of which focus on material innovation – particularly in concrete and masonry – and few of which focus upon the real material efficiency of current building designs. Similarly, though there is a wealth of detailed studies on the physical performance of materials, there is a corresponding lack of detail in determining their associated environmental impacts. Few studies provide detailed consideration of potential supply chains for low carbon materials and there appears to be an insufficient focus upon the realistic potential for commercialisation of novel materials. Similarly, there are few detailed studies addressing the barriers to greater adoption amongst construction practitioners, clients and building users. Future research should seek to address these shortcomings and strike a balance between developing innovative materials, exploring factors preventing best practice in industry, and preparation of more practical guidance documents.

4.6.2 Over what timeframe can these options contribute significant carbon reductions?

For many options it is difficult to determine a realistic timeframe for adoption and the potential scale of associated carbon reductions. However, some general points can be made.

Though authors have argued that DfD is “the most important green design strategy for achieving material sustainability” (Kestner & Webster, 2010), it is unlikely to yield sizeable carbon emission reductions in the timescale required to avert dangerous levels of climate change. The design life of buildings is typically greater than the 35 years or so in which significant reductions in carbon emissions must be achieved. The buildings reaching end of life in the intervening period will predominantly have been designed with little regard for deconstruction. This is not to suggest that innovations in material recovery and reuse cannot yield

carbon reductions through displacement of virgin materials in the interim period.

The assertion is simply that DfD is unlikely to make a major contribution towards fast approaching carbon reduction targets, though widespread adoption of DfD principles should yield substantial reductions in the longer term.

Similarly, a number of the material innovations, particularly alternative cements, self-healing and completely recyclable concretes, may take many years to achieve commercial production, let alone harvest the carbon benefits associated with increased durability. In the meantime more immediate responses, such as encouraging careful attention to concrete mix design, with adjustment to key parameters and the appropriate use of admixtures, could yield significant reductions in embodied emissions (Purnell & Black, 2012; Purnell, 2013; Minson & Berrie, 2013).

Many of the more advanced materials mentioned in the review will play a key role in ensuring the viability of construction in the restricted carbon space beyond 2050.

However, the majority of options that are already commercially available generally exhibit a smaller range of applications and potential carbon reductions.

4.6.3 What combination of options may be required to meet sector and national carbon reduction targets?

Allwood has contended that to achieve Construction 2025 targets the sector should seek to use “half as much material for twice as long” (Allwood, 2015).

However, it is doubtful that either of these goals is imminently achievable. Whilst the demonstrated scope for material efficiency through design is significant, there is no evidence to suggest it amounts to halving material use. Even the best examples produced to date have only shown potential reductions of around a third of certain materials used for some elements of particular structure types. Meanwhile the prospect of doubling structure lifetimes poses a serious risk to investors and goes against the current trend of shorter lifetimes and faster turnover of stock. It is likely that achieving carbon reductions of the order required will necessitate a broader combination of the options described, including significantly increased use of alternative materials.

Critics of alternative, particularly biotic, materials frequently suggest that concerns surrounding durability should prevent specification. However, to this author’s knowledge there is no published evidence suggesting that the real building service life achieved in practice, as opposed to the design life, is any longer for more durable materials such as steel. Research has repeatedly suggested that the common reasons for building demolition are almost entirely unrelated to material durability.

Given the uncertain scope for uptake of each of the described options, the most dangerous fallacy is that any individual option could prove sufficient in itself.

As Paul Ekins is fond of saying with reference to the selection of energy technologies:

“you can pick any option you like, so long as it is all of them”. A similar approach will likely be required in construction if carbon reduction targets are to be achieved.