Specifying Sustainable Concrete Understanding the role of constituent materials 2 SPECIFYING SUSTAINABLE CONCRETE BREEAM ‘Outstanding’ and 2014 Stirling Prize short listed London School of Economics utilised 50% GGBS in the cement to contribute to its About this publication sustainability strategy. © VIEW. Concrete’s flexibility offers many opportunities for designers to influence the environmental, economic and social credentials of their projects, including performance credentials such as fire, durability, acoustics and adaptability. This publication is intended to assist designers in optimising the sustainable credentials of concrete through specification. This guide focuses on concrete, its constituent materials and how the variation of specification can influence the sustainability performance of concrete. Sustainable credentials with the greatest scope for influence through specification include: the performance of fresh and hardened concrete (e.g. strength gain, durability); embodied CO2 (ECO2); CO2 associated with transportation; responsible sourcing and use of recycled or secondary materials. Aspects of sustainability, outside the scope of this document, are addressed in other Concrete Centre guidance. Readers should refer to www.concretecentre.com/ publications for titles including: Concrete and BREEAM, Material Efficiency, Concrete and Fire Safety, and Thermal Mass Explained. Contents Introduction 3 Key guidance 3 Responsible sourcing of materials 4 Aggregates 6 Cements and combinations 10 Water 15 Admixtures 16 Cover image: Reinforcement 18 White Collar Factory, London is a BREEAM ‘Outstanding’ 17-storey office building that has Specification of Concrete to BS 8500 20 extensive exposed concrete throughout. This provides the thermal mass that’s intrinsic Specification examples 21 to its passive cooling strategy. For more on this project, see page 9. References 22 Image © Timothy Soar SPECIFYING SUSTAINABLE CONCRETE 3 Introduction Key guidance Concrete’s role in delivering a sustainable built Guidance that balances the desire to specify concrete environment through the performance benefits with low environmental impact, whilst ensuring of durability, robustness, fire resistance, thermal other performance parameters are optimised, can mass, acoustic performance and flood resilience – be summarised as follows: together with a reduced need for applied finishes – is ¢ Specify the strength required from producers with Product Conformity increasingly recognised and utilised by design teams in Certification. the delivery of the most sustainable projects. ¢ Consider specifying strength at 56 days rather than the conventional 28 days, where appropriate. Concrete is a versatile and natural material and designers can use it efficiently to deliver structure and other functions of integrated designs. ¢ Specify the largest maximum aggregate size conducive to achieving In addition, concrete and its constituents have strong sustainability placing and full compaction. credentials; for example, they are local to the UK and many have been ¢ Permit the use of recycled or secondary aggregates but do not certificated to the highest, most demanding responsible sourcing over specify. standards. These factors are resulting in designers choosing concrete on ¢ Specify concrete with a wider range of cement types/combinations sustainability grounds alone. selected from Table 1 from BS 8500-2: 2015. Sustainability is optimising economic, social and environmental issues. Many ¢ Embodied CO2 (ECO2) of concrete should not be considered or assessment tools and methodologies have been developed to provide specified in isolation of other factors such as strength gain. measures and comparison tools. The shortcoming of generalised tools is ¢ Permit the use of admixtures. Admixtures can be used to enhance that - by definition - they are general, and specific geographical or project sustainability credentials and reduce the ECO2 of concrete, as well as constraints may not be accounted for. modifying its physical properties. ¢ Specify BES 6001 responsibly-sourced concrete and reinforcement A challenge for all assessments is weighting the different factors which often to gain credits under BREEAM. have different units of measurement; for example, how does one compare ¢ The specification of recycled and secondary aggregates is often biodiversity, health and safety and transportation CO2 emissions? Therefore it is accepted good practice for designers to not simply follow a tick box mentality not the most sustainable option, although it may gain most points. in their use of assessment tools but to understand the factors and take a holistic BS 8500 allows producers to use up to 20% of recycled aggregates in and whole-life view of sustainability when considering their project. many concretes. ¢ The BRE Green Guide does not recognise the availability or otherwise The European standard for concrete BS EN 206 [1] and its UK of recycled product when incentivising the use of recycled content. complementary Standard, BS 8500 [2] do not contain any provisions for Recycled aggregates should only be specified when they are locally specifying sustainability. This document aims to provide guidance over available, otherwise transportation impacts exceed the intended and above concrete standards, to enable the project team to balance the benefits. Using this assessment methodology, this should be discussed desire to specify concrete with low environmental impacts whilst ensuring with the client or project code assessor to prevent unfair penalisation. that its other performance parameters are optimised. These performance ¢ Use of cementitious additions can reduce the embodied CO parameters can affect overall environmental impacts, as well as other 2 (ECO ) of concrete and influence its visual appearance. When sustainability issues. 2 aesthetics are critical, specify the cement/combination to achieve colour consistency. 4 SPECIFYING SUSTAINABLE CONCRETE Responsible sourcing of materials The concrete industry was the first industry to link its sustainable construction strategy [3] to independent- certification scheme, BES 6001, and set targets for concrete and concrete products to be certified. BES 6001 provides a common benchmark for all construction products to demonstrate their responsible sourcing credentials. The full listing of products certified to BES 6001 is available at www.greenbooklive.com. shown on each product BES 6001 certificate available at BES 6001– Framework Standard www.greenbooklive.com and is often higher than the generic score for the Responsible Sourcing of allocated to BES 6001 in BREEAM. The majority of certified concrete production attracts a RSCS score of 7 – currently the highest value for any Construction Products scheme. The BRE responsible sourcing standard, BES 6001[4] first launched in The 2020 target for BES 6001 certification is 95% and the aspiration of the October 2008, provides a benchmark to compare responsible sourcing concrete industry is to achieve 100%. performance for all construction products on an equal basis. The aim of BES 6001 was to integrate all of the activities associated Figure 1: The activities of the supply chain covered by the responsible with responsible sourcing, from the point at which a material is mined sourcing standard BES 6001 or harvested in its raw state through to manufacture and processing; together with a delivery mechanism using certified management systems. Supply chain The responsible sourcing standard encompasses social, economic and environmental dimensions and addresses aspects such as stakeholder engagement, labour practices and the management of supply chains TransportDelivery upstream of the manufacturer. Materials sourcing Product manufacture Energy management In 2014, BES 6001 was revised to significantly increase the minimum level of requirements to demonstrate compliance and to further encourage Life cycle thinking the adoption of best practice in the management of sustainable Ecotoxicity development. Figure 1 shows activities in the supply chain which are addressed by this standard. Traceability Accreditation to BES 6001 enables products to gain credits under Legal compliance assessment schemes, including BREEAM and CEEQUAL (the assessment and awards scheme for improving sustainability in civil engineering and public Health and safety management realm projects). Environmental management Management, measurement Production certified to BES 6001 and reporting of: • Greenhouse gas emissions responsible sourcing standard • Water usage, waste management • Employee training and skills Providing evidence of the responsible sourcing of building products and • Local community engagement • Transport and delivery impacts materials continues to be crucial with the need to demonstrate compliance with a recognised responsible sourcing scheme, certified by a third Resource use management party. Concrete industry indicators report the proportion of concrete and constituent materials production that are currently certified to BES 6001. Quality management During 2017, certification of concrete products to BES 6001 reached 92% Ethical trading and employee rights of production tonnage [3]. Over 90% of this certified tonnage achieved a performance rating of ‘Very Good’ or ‘Excellent’. Of key interest to construction being rated to BREEAM assessment schemes, is a rating of responsible sourcing used in calculating credits. This is now demonstrated THE CONCRETE INDUSTRY HAS COMMITTED TO by the Responsible Sourcing