Atta Ajayabi et al. SBE0124

The REBUILD project’s response to the Environmental Audit Committee’s inquiry into the ‘Sustainability of the Built Environment’

 

Submission by Atta Ajayebi1,4, Han-Mei Chen2, Kan Zhou3, Peter Hopkinson1, Yong Wang2, Dennis Lam3

1Exeter Business School, University of Exeter, United Kingdom

2Department of Mechanical, Aerospace and Civil Engineering, School of Engineering, University of Manchester, United Kingdom

3School of Engineering, University of Bradford, United Kingdom

 

The response draws on research evidence from the EPSRC funded REBUILD project (Grant Ref: EP/P008917/, 2018-2021) which has the aim of creating new circular economy systems for regenerating building and construction products.

 

2. How can materials be employed to reduce the carbon impact of new buildings, including efficient heating and cooling, and which materials are most effective at reducing embodied carbon?

The existing stock of buildings in the UK contains a vast stock of construction products and materials, that are typically downcycled at the end of a buildings economic or service life. Such stocks provide a reservoir of building products and materials for the future. The challenge is that most buildings were not designed for adaptation, dis-assembly, or high value re-use. This is especially true for the most carbon intensive products – concrete, brick, steel (see Table 1) which comprise a large proportion of the embodied carbon of the majority of UK buildings. Table 2 highlights the status of reclaim  in the UK for these three major structural products and materials.

Table 1: Production of virgin construction materials- embodied carbon (kgCO2eq/kg product)

Dataset/ Product

Clay Bricks

Concrete

(25 Mpa)

Precast Concrete

Steel – hot or cold rolled

Reinforcement steel

Ecoinvent 3.0 (2019)

0.320

0.1031

-

2.210

2.468

GaBi  9.2 (2019)

0.244

-

-

-

-

ELCD (2011)

-

-

0.121

2.052

1.031

Industry Data 2.0 (2019)

-

-

 

2.23

1.926

 

Urban mining potential: If building product could be recovered directly and re-used cost-effectively, rather than recycled, it could reduce waste, move end of life structural building products and components up the waste hierarchy and offer both cost and multiple resource and environmental benefits.  Moreover, there is significant potential to reduce the carbon footprint of new build by incorporating reclaimed structural products into new build either directly or modified to match new construction techniques and other whole life considerations (see Figure 1). 

It should also be noted that the carbon reduction impact of reclaiming and reusing construction products could happen much sooner than the other carbon reduction strategies (e.g. carbon sequestration, low carbon new materials and materials that are designed for deconstruction). As the earlier carbon reduction actions will be more impactful on tackling climate change, it necessary to highlight this advantage of reusing products compared to the other strategies.

For instance bricks: In the UK approximately 1.9 billion bricks are manufactured each year from a total demand of 2.5 billion. Less than 5% of the 2.5 billion bricks demolished each year in the UK are reclaimed for reuse, the majority are crushed and much of this is used to form aggregate or else landfilled (Kay and Essex, 2008). A high proportion of these bricks could be re-used directly within buildings or other forms of construction requiring whole brick structural strength.

Table  2: End of Life status quo scenarios- typical UK/EU end of Life scenarios at the time of demolition: (Eurofer (2012), BRE (2012))

Materials

Bricks

Mortar

Concrete Block

Concrete

precast concrete

Reinforced Concrete

Reinforcing Steel

Steel Decking

Structural hollow sections

C

R

C

R

End

of Life

Reuse

10%

0

0

0

0

0

0

0

0

10%

7%

Recycling

80%

80%

90%

90%

90%

98%

90%

98%

98%

89%

93%

Landfill

10%

20%

10%

10%

10%

2%

10%

2%

25%

1%

0

 

For concrete and steel: whilst the direct maintenance and re-use of products has significant environmental benefits over recycling only a small percentage in the UK (approximately 3 Mt) are reclaimed for direct re-use, mostly for heritage products or easily demountable structures such as steel sections from portal frames (around 4% of all steel in buildings is re-used vs 92% recycled). Although structural steel elements are inherently reusable with minimal reprocessing, reclaiming structural steel elements from existing buildings pose significant technical challenges.

Concrete structural elements are difficult to reclaim (Durmisevic, 2010) hence there has been a greater focus on recycling rather than re-use. It is possible to reclaim RC structural elements from prefabricated concrete structures because the prefabricated elements were assembled together in the first cycle of construction. In addition to having a very low carbon footprint, re-use of concrete panels can reduce the cost of new construction by 20–30% (Huuhka et al., 2015). Figure 2 compares the potential energy and embodied carbon for recycling or reuse of concrete elements versus virgin production.

 

Fig. 1. Environmental impact comparison of the production (up to the factory gate) of a cubic meter of concrete building material of new, recycled, and re-used materials (Glias, 2013).

 

Barriers and challenges: Whilst reducing the need for virgin aggregate, the current demolition practice of crushing brick loses much of the embodied energy and carbon. The REBUILD project however has shown the technical feasibility of separation and the reclaimed bricks have almost identical mechanical properties as new bricks (Zhou et al., 2019). REBUILD analysis has shown that reclaiming activities consume as little as 0.65% of the total embodied energy of new brick manufacturing (Ecoinvent, 2019), as well as the potential to reclaim and reuse the bricks for further structural purposes with further environmental and economic benefits. In whole building carbon assessment reclaim and re-use will therefore produce a significant credit by avoiding use of new materials. Reuse is also a much higher credit than recycling (see below).

Table 3 compares the energy consumption and embodied carbon per new brick versus reclamation using sawing and punching techniques. Reclaiming steel members from composite steel-concrete structures is hampered by the difficulty of accessing shear connectors. REBUILD has demonstrated the technical feasibility to access and successfully cut the shear connectors without damage to the steel retaining almost identical mechanical properties as new steel.

Table 3:  Comparison of energy consumption and climate change inducing environmental emissions for brick manufacturing and reclamation

Brick type/Reclaiming method

Energy consumption

(MJ/bricka)

Emissions contributing to the embodied carbon (g CO2eq/bricka)

Manufacture of new bricks (total embodied)

9.2b

757 b

Saw-cutting reclaiming (electricity at site)

0.06

0.54 c

Punching reclaiming (electricity at site)

0.36

3.22 c

a: One brick is assumed to weigh 2.3 kg.

b: based on analysis of life cycle energy consumption and emissions, data obtained from Ecoinvent 3.4 for a typical clay brick of this size at the market and consequential allocation of life cycle processes- Cumulative Energy Demand and IPCC100a 2013 impact assessment methods applied respectively.

c: 2014 UK grid mix based on electricity fed into the low voltage transmission network, data obtained from Ecoinvent 3.4, ecoinvent (2019).

Benefits of increasing reclaim and re-use rate at scale: Our analysis of the whole life cycle (i.e. Life Cycle Assessment) of the construction materials have revealed the embodied carbon potential of reclaimed structural products. When comparing the scenario of 30% reuse of materials to the status quo of UK market, the results indicate that a total reduction of 13-31% in carbon emissions during the life cycle of the products. In addition, the results also show that reusing has significant benefits compared to recycling, where the carbon saving benefits can be potentially higher (up to 8 times). The potential reductions in the overall emissions of current UK demand scenario for construction materials is shown in table 4.

Table 4: Total life cycle embodied carbon of the materials based on two scenarios of 1) status quo and 2) 30% reuse

 

Clay Brick

Concrete Block

Concrete

precast concrete

Reinforced Concrete

Reinforcing Steel

Steel Decking

Structural hollow sections

1) Status Quo

0.15

0.10

0.13

0.19

0.14

0.91

1.18

1.17

2) 30% reuse scenario

0.12

0.07

0.09

0.13

0.10

0.65

0.93

1.02

Change (%)

-21.0%

-27.3%

-29.4%

-31.1%

-31.4%

-27.6%

-21.4%

-13.0%

 

4. What role can the planning system, permitted development and building regulations play in delivering a sustainable built environment? How can these policies incentivise developers to use low carbon materials and sustainable design?

The planning system could provide a major stimulus to structural product reclaim as part of a wider circular economy construction system. Scaling up reclaim and re-use will require storage of product and inventory as part of a supply-demand matching optimisation. This will require land and a change to permit procedures to avoid categorisation of product as ‘waste’. The planning system can also be a major enabler of data sharing – future demand, locations, demolition and release rates which would be fundamental building blocks of a large-scale urban mining and circular economy system. The planning system could also be more visionary and ambitious around these issues, for example see Amsterdam’s Roadmap https://www.metabolic.nl/projects/city-of-amsterdam-circular-building-tendering/

5. What methods account for embodied carbon in buildings and how can this be consistently applied across the sector?

The embodied carbon of buildings has been standardised by frameworks such as the EN 15804 that allows for stage-by-stage assessment of the embodied carbon construction projects. This notably includes end-of-life activities such as waste disposal, recycling, and reuse. Quantifying the embodied carbon of the current building stock as a potential source of future low carbon products is an essential requirement for future implementation of urban mining. Various stock-flow models have been developed, but none developed specifically to estimate product life cycle benefits and embodied carbon. The REBULD model (Ajayebi et al., 2020) produces quantitative and qualitative map of urban stocks that enables accounting for stocks and flows of materials at urban scale. Figure 2 demonstrates the scope of granular data of the model. Spatially explicit mapping of embodied carbon allows for integration of planning, end-of-life, storage, and matching local supply and demand of products.

Fig. 2. A snapshot of the REBUILD model indicating the built-in data of individual buildings.

 

 

6. Should the embodied carbon impact of alternative building materials take into account the carbon cost of manufacture and delivery to site, enabling customers to assess the relative impact of imported versus domestically sourced materials?

The embodied carbon of building materials and projects must take into account all life cycle stages including mining, manufacturing, transportation, storage and retailing. Similarly, the embodied carbon of end-of-life flows of materials should also be assessed as the benefits of reclaiming materials from local outflows may be greater than an imported comparable product. EPDs, LCA tools, and product labels enable architects, planners, and builders to measure and manage the embodied carbon of projects by considering all life cycle stages.

The REBUILD system model includes all stages of the post demolition construction value chain and the embodied carbon in both new and reclaimed materials and subsequently enables a comparative system assessment of carbon benefits of implementing a reuse oriented Circular Economy.

 

9. How should re-use and refurbishment of buildings be balanced with new developments?

The reclaiming, remanufacturing, and reuse and materials at the end-of-life of buildings can reduce the amount of construction waste as well as the need for new materials, which can significantly reduce the overall embodied carbon of the projects. As it was described in our response to Q2, the REBUILD team has estimated that an achievable reuse target of the three products of steel, concrete and bricks, can reduce the embodied carbon of the load bearing sections of buildings by up to 30%.

An understanding of the ‘equivalence’ of the embodied carbon of existing in-use buildings can help developers to manage building reuse and refurbishment while consider options such as refurbishment, deconstruction and reuse, and demolition and recycling.

 

10. What can the Government do to incentivise more repair, maintenance and retrofit of existing buildings?

National Policy and Strategy on Construction and Demolition Waste is largely focussed on recycling rather the reclaim and higher value re-use. Several specific future actions to promote reclaim and re-use include:

New Eurocodes and performance standards: EN Eurocodes for masonry, steel and concrete provide a common approach for the design and conformity of buildings and other civil engineering works and construction products meeting the construction products regulation for works that meet the CE marking as well as specification in public contracts. They provide assurance on key mechanical, structural and fire resistance properties. No such standards exist for reclaimed or re-used products. Reclaimed and -reused products will be affected by many factors including loads, weather exposure or possible damage during the lifetime of a building. This acts as a deterrent to potential clients and end users. As REBUILD has shown reclaimed steels, brick and concrete products have very similar structural properties to new product.

 

Landfill tax: The landfill tax for inert construction and demolition waste is considerably lower than for waste that contains biodegradable materials. Construction waste contains high embodied carbon. Adjusting the tax for inert construction waste to signal the embodied carbon would stimulate further efforts to reduce C&DW at source. This would stimulate contractors and markets to innovate to reduce residual waste to landfill including re-use.

Regulatory Regime: Unknown quantities of C&DW are currently contaminated with plastics, hazardous materials prior to disposal. The shift to Site Waste Plans as a voluntary mechanism makes it more difficult to monitor contamination and illegal dumping of C&DW. Re-introducing SWP and tightening the protocols and standards for C&DW contamination would support separation and recovery of materials as part of an overarching framework for component and material recovery from end-of-life demolition.

May 2021

References:

 

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