Figure A.1 Share of construction, renovation and demolition waste sent to landfill in selected countries
European countries have low shares of landfilling and high shares of waste recovery.
Figure A.2 Emerging alternative cementitious binders
Alternatives to Portland cement are dominated by industrial by-products, but bio-based binders have high potential.
Figure A.3 Availability of alternative cementitious binders, by region and type, 2018
Most countries could generate sufficient secondary cementitious materials to substitute for Portland cement.
Cementitious binders are an essential precursor to both concrete and mortar, with cement acting as a glue for aggregates and water to form a brittle and typically strong building material. Cementitious binders typically comprise hydraulic cement and supplementary cementitious materials in different proportions. Hydraulic cements bind the aggregates through a chemical reaction that is triggered by the addition of water. The most common example of hydraulic cement is “ordinary Portland cement.”
Producing Portland cement involves three main steps: preparing the material (extraction, crushing, pre-homogenisation and raw meal grinding), producing the clinker (preheating, precalcining, clinker production in a rotary kiln at temperatures of 1,450 degrees Celsius), and grinding the clinker (mixing or blending the ground clinker with gypsum and other components to produce cement) (IEA 2018a).
In concrete mixtures, supplementary cementitious materials are used, together with ordinary Portland cement, as extenders to improve the properties of fresh and hardened concrete, or to reduce the carbon footprint of the cementitious binder (American Concrete Institute 2022). The properties of the finished cement depend on the ratio and selection of the blending materials, which can broadly be classified as primary versus secondary cementitious materials (Shah et al. 2022).
Primary cementitious materials include limestone, natural volcanic materials, and kaolinite and calcined clays (including calcined clay limestone or LC3) (Scrivener et al. 2018a), while secondary cementitious materials include industrial by-products such as coal fly ash and steel blast furnace slag. They also include bio-based ashes (mostly by-products from agriculture, such as rice husk or cassava peel, as well as from forestry) and end-of-life materials (mostly binder from construction and demolition wastes, but also pozzolans from recycled glass) (see Figure A.2).
The type of supplementary cementitious material that can be used depends on the local context (see Figure A.3), such as the plant capacity, the moisture content and burnability of the raw materials, the availability of blending materials, the reliability of supply chains, as well as national cement standards. However, a major impediment to widespread adoption of many alternative, “circular,” secondary cementitious materials, particularly the bio-based options, is the variable performance and lack of local certification.
Figure A.4 Steel material flows
More than half of the world’s steel is used in the construction of buildings and infrastructure.
Figure A.5 Global flows of aluminium, 2007
Aluminium is produced using primary mined materials and, to a lesser extent, scrap.
Figure A.6 Global material flow and end uses of glass
Global glass production is divided into container glass (for food and beverages) and flat glass.