Life cycle assessment of hot mix asphalt and zeolite-based warm mix asphalt with reclaimed asphalt pavement

A comprehensive life cycle assessment of asphalt pavements was conducted including hot mix asphalt (HMA), warm mix asphalt (WMA) with the addition of synthetic zeolites, and asphalt mixes with reclaimed asphalt pavement (RAP). The environmental impacts associated with energy consumption and air emissions were assessed, as well as other environmental impacts resulting from the extraction and processing of minerals, binders and chemical additives; asphalt production; transportation of materials; asphalt paving; road traffic on the pavement; land use; dismantling of the pavement at the end-of-life and its landfill disposal or recycling. Monte Carlo simulations were also conducted to take into account the variability of critical input parameters. Taking into account the entire life cycle, the impacts of zeolite-based WMA pavements were almost equal to the impacts of HMA pavements with the same RAP content. The reduction in the impacts of WMA resulting from the lowering of the manufacturing temperature was offset by the greater impacts of the materials used, especially the impacts of the synthetic zeolites. Moreover, by comparing asphalt mixes with different RAP contents, it was shown that the impacts of asphalt mixes were significantly reduced when RAP was added. All endpoint impacts as well as climate change, fossil depletion and total cumulative energy demand were decreased by 13–14% by adding 15% RAP. A key advantage of WMA is the potentially greater use of RAP. Thus, the decrease in the impacts achieved by adding large amounts of RAP to WMA could turn these asphalt mixes into a good alternative to HMA in environmental terms.     

Life cycle climate impacts of the US concrete pavement network

Life cycle assessment (LCA) offers a comprehensive approach to evaluate and improve the environmental impacts of pavements. First, a general pavement LCA methodology is created that describes the concepts necessary to conduct a comprehensive pavement LCA. Second, the methodology is applied to the life cycle of concrete pavements to quantify current emissions across the road network. System boundaries are drawn to include all phases of the pavement life cycle – materials production, construction, use, maintenance, and end of life. Greenhouse gas emissions are quantified for twelve functional units, which evaluate average conditions for each major roadway classification in the United States. The results present the relative contribution of each component in the life cycle, the annual emissions occurring during the 40-year analysis period, and the sensitivity of these results to model parameters. It is found for all roads that the majority of emissions occur in year one – from cradle-to-gate materials production, and pavement construction – primarily due to cement production. The results are most sensitive to traffic volume, and then to parameters affecting the cement production. Based on emissions and their sensitivity, the LCA results suggest three broad reduction approaches: reducing embodied emissions, reducing use phase emissions, and reducing end-of-life emissions.     

Hybrid life cycle assessment for asphalt mixtures with high RAP content

With the pavement industry adopting sustainable practices to align itself with the global notion of habitable environments, there has been growing use of life-cycle assessment (LCA). A hybrid LCA was used to analyze the environmental footprint of using a reclaimed asphalt pavement (RAP) content in asphalt binder mixtures. The analysis took into consideration the material, construction, and maintenance and rehabilitation phases of the pavement life cycle. The results showed significant reductions in energy consumption and greenhouse gas (GHG) emissions with an increase in RAP content. The contribution of the construction phase to the GHGs and energy consumption throughout pavement life cycle is minimal. Feedstock energy, though not consequential when comparing asphalt mixtures only, has a significant impact on total energy. Based on LCA analysis performed for various performance scenarios, breakeven performance levels were identified for mixtures with RAP. The study highlighted the importance of achieving equivalent field performance for mixtures with RAP and virgin mixtures.     

A GIS analysis of suitability for construction aggregate recycling sites using regional transportation network and population density features

Aggregate is used in road and building construction to provide bulk, strength, support, and wear resistance. Reclaimed asphalt pavement (RAP) and reclaimed Portland cement concrete (RPCC) are abundant and available sources of recycled aggregate. In this paper, current aggregate production operations in Virginia, Maryland, and the District of Columbia are used to develop spatial association models for the recycled aggregate industry with regional transportation network and population density features.The cost of construction aggregate to the end user is strongly influenced by the cost of transporting processed aggregate from the production site to the construction site. More than 60% of operations recycling aggregate in the mid-Atlantic study area are located within 4.8 km (3 miles) of an interstate highway. Transportation corridors provide both sites of likely road construction where aggregate is used and an efficient means to move both materials and on-site processing equipment back and forth from various work sites to the recycling operations.Urban and developing areas provide a high market demand for aggregate and a ready source of construction debris that may be processed into recycled aggregate. Most aggregate recycling operators in the study area are sited in counties with population densities exceeding 77 people/km² (200 people/mile²). No aggregate recycling operations are sited in counties with less than 19 people/km² (50 people/mile²), reflecting the lack of sufficient long-term sources of construction debris to be used as an aggregate source, as well as the lack of a sufficient market demand for aggregate in most rural areas to locate a recycling operation there or justify the required investment in the equipment to process and produce recycled aggregate.Weights of evidence analyses (WofE), measuring correlation on an area-normalized basis, and weighted logistic regression (WLR), are used to model the distribution of RAP and RPCC operations relative to transportation network and population distribution data. The models can be used on a regional scale to quickly map the relative site suitability for a RAP or RPCC aggregate recycling operation in a particular area based on transportation network and population parameters. The results can be used to identify general areas to be further evaluated on a site-specific basis using more detailed marketplace information. As transportation or population features change due to planning or actual development, the models can be easily revised to reflect these changes.     

Energy consumption comparison for different asphalt pavements rehabilitation techniques used in Chile

In developing countries without the availability of reliable pavement management systems, recycling techniques may offer the best alternative for pavement structural rehabilitation. However, for many government officials and contractors there is a clear understanding of the technical advantages of recycling but not a clear perspective of cost saving. Since cost is a relative value among different regions of any country the following work makes an energy analysis of the construction process of the three different rehabilitation techniques available in Chile. Three different structural pavement rehabilitation alternatives were studied and compared using an energy consumption methodology:

• •Asphalt overlay;
• •Reconstruction;
• •Cold in place recycling with foamed asphalt.

The methodology considers different project scenarios by combining expected traffic and soil support values. For each rehabilitation technique and scenario, the construction processes were analyzed and the design layers were transformed to equivalent energy units (MJ/m²).Results show that cold in place recycling utilizes the lowest amount of energy compared with reconstruction or an asphalt overlay in all the scenarios studied, producing more differences when rehabilitating roads for less trafficked roads. The study also concludes that aggregate haulage distance is the most sensitive factor on total energy consumption when comparing the three alternatives.     

Use of system dynamics for proper conservation and recycling of aggregates for sustainable road construction

A significant amount of mineral aggregates are used in constructing, rehabilitating and maintaining roads. As local (nearby) quarries get exhausted, aggregates need to be hauled from sources that are at ever-greater distances. Hence, over time the cost of trucking as well as the amount of emissions generated by trucking increases with a decrease of local natural aggregate stocks. The objectives of this study are to construct and utilize a system dynamics model of the depletion of a stock of natural aggregates due to pavement construction and maintenance, and determine the effect of using local and nonlocal aggregates, recycling and project cancellation (slowing growth) on the paving of roads. Long-term simulations are carried out with available aggregate stock, trucking distance and cost data. The quality of roads and a sustainability score, based on engineering, economic and environmental factors (emissions) are evaluated for different scenarios. An optimal combination of the use of local and nonlocal recycled aggregates, recycling and project cancellation is recommended. The proposed system dynamics model could be utilized by agencies to plan for the proper utilization of aggregate resources for road development and maintenance/rehabilitation projects.     

Photochemical model evaluation of the surface ozone impact of a power plant in a heavily industrialized area of southwestern Spain

The characterization and evaluation of the impact that an industry is likely to have on the surrounding ozone levels is one of many problems confronting air quality managers and should be taken into consideration when authorizing its installation. The correct management of an environment, in terms of monitoring existing industries and planning new activities, requires adequate knowledge of the processes sustained by the industrial emissions therein.This paper explores the improvements in air quality management arising from taking into account the uncertainties involved in the photochemical modeling of the impact of an industry on surface ozone levels.For this, we evaluate the impact on ozone levels of a power plant located in an industrial area of southwestern Spain (Huelva). The evaluation takes into account the effects of both emissions' uncertainty and the non-linear chemistry between ozone and its precursors, thus providing a probable range of increase over the normative values (hourly and 8-hourly maximums) defined in the European Directive. The proposed methodology is easily applicable by air quality managers.Advanced modeling techniques were used for the power plant assessment, MM5 atmospheric modeling system, and air quality model CAMx. The results from meteorology and ozone forecasts have shown acceptable agreement with the observations.The spatial distribution of the impact is found to be strongly determined by mesoscale meteorological processes, which are reinforced by the local orography; there is also a marked temporal evolution. The industrial plume is observed to induce a decrease (or maintenance) of the ozone levels near the emission source (0–10 km), and an increase in the ozone concentrations farther away (with maximums between 10 and 50 km). In fact, in the meteorological episodes with a predominance of local breeze circulations, impacts have been detected at distances of more than 100 km from the emission source.Sensitivity of the power plant impact to variations in ozone precursor emissions is described, and the scenarios and the points in the domain presenting higher sensitivity and registering larger impacts are also identified. The results show that the largest impacts take place in emission scenarios where the NO_x has been reduced with respect to the base case scenario. In contrast, in scenarios where the VOC emissions are reduced with respect to the base case scenario, the impact is smaller or remains unchanged. This is important in areas like the study case, where there is a high percentage of biogenic VOC emissions and the industrial areas are close to natural protected areas and agricultural fields.     

Study on recycled asphalt concrete for use in surface course in airport pavement

This research investigated the possibility of using recycled asphalt concrete as surface course in airport pavement. The basic properties of recycled asphalt binder after short- and long-term aging were firstly tested and compared with those of the virgin asphalt. Then, a series of laboratory tests were performed to evaluate the performance of recycled asphalt concrete (containing 40% and 70% RAP), in which the HMA mixture without RAP was used as a control. Furthermore, an experimental pavement consisting of three sections (corresponding to 0%, 40% and 70% RAP content) was constructed to verify the laboratory test results. These results indicated that the recycled asphalt could achieve the similar properties against long-term aging as virgin asphalt. Recycled asphalt concrete containing 40% RAP could be used as surface course in airport pavement as it exhibited similar performance as control mixture both from the laboratory and experimental pavement test results. On the contrary, recycled asphalt concrete containing 70% RAP was not recommended as its fatigue property was much poorer compared with that of virgin asphalt mixture.     

Evaluation of life cycle inventory data for recycling systems

This paper reviews databases on material recycling (primary as well as secondary production) used in life cycle assessments (LCA) of waste management systems. A total of 366 datasets, from 1980 to 2010 and covering 14 materials, were collected from databases and reports. Totals for CO₂-equivalent emissions were compared to illustrate variations in the data. It was hypothesised that emissions from material production and the recycling industry had decreased over time due to increasing regulation, energy costs and process optimisation, but the reported datasets did not reveal such a general trend. Data representing the same processes varied considerably between databases, and proper background information was hard to obtain, which in turn made it difficult to explain the large differences observed. Those differences between the highest and lowest estimated CO₂ emissions (equivalents) from the primary production of newsprint, HDPE and glass were 238%, 443% and 452%, respectively. For steel and aluminium the differences were 1761% and 235%, respectively. There is a severe lack of data for some recycled materials; for example, only one dataset existed for secondary cardboard. The study shows that the choice of dataset used to represent the environmental load of a material recycling process and credited emissions from the avoided production of virgin materials is crucial for the outcome of an LCA on waste management. Great care and a high degree of transparency are mandatory, but advice on which datasets to use could not be determined from the study. However, from the gathered data, recycling in general showed lower emission of CO₂ per kg material than primary production, so the recycling of materials (considered in this study) is thus beneficial in most cases.     

Life cycle inventory of recycling portable nickel–cadmium batteries

In this study, the environmental impact of recycling portable nickel–cadmium (NiCd) batteries in Sweden is evaluated. A life cycle assessment approach was used to identify life cycle activities with significant impact, the influence of different recycling rates and different time boundaries for emissions of landfilled metals. Excluding the user phase of the battery, 65% of the primary energy is used in the manufacture of batteries while 32% is used in the production of raw materials. Metal emissions from batteries to water originate (96–98%) from landfilling and incineration. The transportation distance for the collection of batteries has no significant influence on energy use and emissions. Batteries manufactured with recycled nickel and cadmium instead of virgin metals have 16% lower primary energy use. Recycled cadmium and nickel metal require 46 and 75% less primary energy, respectively, compared with extraction and refining of virgin metal. Considering an infinite time perspective, the potential metal emissions are 300–400 times greater than during the initial 100 years. From an environmental perspective, the optimum recycling rate for NiCd batteries tends to be close to 100%. It may be difficult to introduce effective incitements to increase the battery collection rate. Cadmium should be used in products that are likely to be collected at the end of their life, otherwise collection and subsequent safe storage in concentrated form seems to offer the best solution to avoid dissipative losses.     

Multivariate data analysis applied in Hot-Mix asphalt plants

A multivariate data analysis was used with environmental data obtained from Hot-Mix asphalt (HMA) plants. The main objectives of the study were to describe and interpret the real “phenomena” that exist on HMA plants; also, to search for the best mixing conditions, i.e. production with less energy consumption and less emissions. Another important objective was to identify means to allow HMA plants to be designed and operated in better ways. Along the study, an approach of the manufacturing process is presented, allowing for an overall comprehension of the plant's operation.There is not only one parameter to be controlled and checked when HMA are being produced. In this context, a multivariate data analysis was carried out, and the main control parameters considered for prediction and regression analysis were Hot-Mix asphalt formula, fuel type, burner flow rate, fuel consumption, negative pressure of the drum, air temperature, moisture of aggregates, asphalt temperature and rate of production.“Global warming emissions”, “organic emissions”, and “energy consumption” were chosen as models of regression. Globally, plants powered by natural gas emit half the amount of CO₂, nine times less NO_x and eighteen times less CO than plants with fuel oil. Considering NO_x and CO₂ emissions, small plants are preferable over big plants. For organic emissions, if the asphalt temperature increases, TOC emissions are increased; however, if the rate of production increases, TOC emissions are decreased. Previously supposed as an important parameter, moisture of aggregates had no great importance in the statistical analysis. Likewise, the formula of HMA produced also had no great importance, despite many types of formulas studied.The main conclusions in regards to the means with which Hot-Mix asphalt plants can be designed and operated in better ways were: the manufacturing of hyper-mobile and small HMA plants as opposed to stationary large plants, and the use of burners with natural gas instead of fuel oil in all cases. The production of HMA plants, aiming at a cleaner production, means to operate asphalt plants always considering timespan in the long term. This encompasses undertaking daily, weekly and yearly analyses. Therefore, it is necessary to produce with low rate of production and low bitumen temperature, and to maintain a regular production in order to avoid peaks of production and unnecessary starts and stops. It is also interesting to increase the culture of heated stocks.Finally, this study shows that would be an advantage to use multivariate data analysis and then to estimate with very good accuracy emissions and energy consumption in HMA plants using current parameters of control.     

Evaluation of recycling efforts of aircraft companies in Wichita

The number of manufactured aircraft has been continuously increasing worldwide because of the high demand for airline transportation. During manufacturing, many advanced materials and devices are used to build various sizes and shapes of aircraft. However, most of these materials and devices require considerable energy and labor to produce, so reusing these at any life stage of the aircraft offers many economic and environmental benefits, and is considered lucrative and environmentally responsible. Several recyclable materials—composites, metals and alloys, wires, wood, paper, plastics, electronics, and avionics—emerge as waste streams during the manufacturing of aircraft. Many aircraft companies have been recycling these materials to remanufacture aircraft parts or other products for more sustainable production. In the present study, we evaluated the recycling efforts of local aircraft companies in Wichita, KS. These efforts were considered in terms of recycling efficiency/rate and environmental benefits. These included cradle-to-gate (CTG) life-cycle inventory analysis of the materials, carbon dioxide emissions, virgin material replacement with recycled materials, and natural resources usage. Our findings show that there exists a significant potential for contributions to sustainability as well as environmental and health benefits in the region from recycling by aircraft manufacturing plants.     

Determining contamination level of heavy metals in road dust from busy traffic areas with different characteristics

This study identified the levels and sources of heavy metal contamination in road dust from busy traffic areas in a typical industrial city in Korea. This study compared the total concentrations, as determined by aqua regia digestions and atomic absorption spectroscopy, of cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn) and nickel (Ni) in the road dust from areas with different characteristics such as traffic rotaries, downtown areas, circulation roads, and asphalt and concrete highways. The contamination levels of the heavy metals in the road dust were evaluated using the contamination factor and the degree of contamination. The contamination levels of the heavy metals in the road dust were highly dependent on traffic volume and atmospheric dispersion from traffic rotaries. Industrial emissions and the frequency of brake use and vehicles coming to a complete stop were additional factors that affected the contamination levels in downtown areas. The concrete highway had higher contamination levels of the heavy metals than the asphalt highway. Vehicle speed was also a strong contributing factor to the degree of contamination of heavy metals in the road dust from the circulation roads and highways.     

Modelling and analysis of international recycling between developed and developing countries

To deal with the complexity of recycling, a wide variety of models have been developed, each serving a specific purpose. Despite the current trend increasing international trade in recycling-related material flows, the international dimension of physical and economic relationships in recycling is often ignored in current models and analyses. This paper develops a formal model of an international material-product chain (MPC) that represents the mechanism behind international recycling. The attention is focused on the case of a developed and a developing country that exchange material commodities, final products and recyclable waste. Among others, the model demonstrates that taking into account environmental externalities results in higher levels of recycling. Moreover, we show that international recycling is mainly driven by regional differences in the quantity and quality of factor endowments and economic efficiency of recycling. Given that industrialised countries are relatively well endowed with recyclable waste, the recovery rate usually exceeds the utilisation rate. In developing countries, an opposite pattern is observed.     

Abundances and flux estimates of volatile organic compounds from a dairy cowshed in Germany

Animal husbandry and manure treatment have been specifically documented as significant sources of methane, ammonia, nitrous oxide, and particulate matter. Although volatile organic compounds (VOCs) are also produced, much less information exists concerning their impact. We report on chemical ionization mass spectrometry and photo-acoustic spectroscopy measurements of mixing ratios of VOCs over a 2-wk measurement period in a large cowshed at the Federal Agricultural Research Centre (FAL) in Mariensee, Germany. The high time resolution of these measurements enables insight into the sources of the emissions in a typical livestock management setting. During feeding hours and solid manure removal, large mixing ratio spikes of several VOCs were observed and correlated with simultaneous methane, carbon dioxide, and ammonia level enhancements. The subsequent decay of cowshed concentration due to passive cowshed ventilation was used to model emission rates, which were dominated by ethanol and acetic acid, followed by methanol. Correlations of VOC mixing ratios with methane or ammonia were also used to calculate cowshed emission factors and to estimate potential nationwide VOC emissions from dairy cows. The results ranged from around 0.1 Gg carbon per year (1 Gg = 10(9) g) for nonanal and dimethylsulfide, several Gg carbon per year for volatile fatty acids and methanol, to over 10 Gg carbon per year of emitted ethanol. While some estimates were not consistent between the two extrapolation methods, the results indicate that animal husbandry VOC emissions are dominated by oxygenated compounds and may be a nationally but not globally significant emission to the atmosphere.     

On modelling the global copper mining rates,market supply,copper price and the end of copper reserves

The world supply and turnover of copper was modelled using simple empirical estimates and a COPPER systems dynamics model developed for this study. The model combines mining, trade markets, price mechanisms, population dynamics, use in society and waste as well as recycling, into a whole world system. The degree of sustainability and resource time horizon was estimated using four different methods including (1) burn-off rates, (2) peak discovery early warning, (3) Hubbert's production model, and (4) COPPER, a system dynamics model. The ultimately recoverable reserves (URR) have been estimated using different sources that converge around 2800 million tonne, where about 800 million tonne have already been mined, and 2000 million tonne remain. The different methods independently suggest peak copper mine production in the near future. The model was run for a longer period to cover all systems dynamics and delays. The peak production estimates are in a narrow window in time, from 2031 to 2042, with the best model estimate in 2034, or 21 years from the date of writing. In a longer perspective, taking into account price and recycling, the supply of copper to society is estimated to run out sometime after 2400. The outputs from all models put focus on the importance of copper recycling so that society can become more sustainable with respect to copper supply.     

An overview of waste materials recycling in the Sultanate of Oman

Various wastes and by-product materials are generated in the Sultanate of Oman including reclaimed asphalt pavement (RAP) aggregate, demolition concrete, cement by-pass dust (CBPD), copper slag, petroleum-contaminated soils (PCS), discarded tires, incinerator ash, and others. Recycling of such materials in construction is not practiced. Research data are also minimal into the potential use of selected materials in construction applications. This paper will present the results of several laboratory studies conducted into the use of PCS in asphalt concrete mixtures; on the use of CBPD in soil stabilization and flowable fill mixtures; on the utilization of copper slag and CBPD as cementitious materials; on the use of incinerator ash in cement mortars; and on the use of RAP aggregate in road bases and sub-bases. Laboratory data generally indicate that it is feasible to partially reuse some of these materials in construction provided that economic incentives and environmental concerns are taken into consideration.     

Engineering properties of asphalt concrete made with recycled glass

Taiwan is an island nation with high population density: 23 million people living in a total land area of 30 000 sq. km. The island has transformed from an agricultural society to an industrial one in the past three decades. Coming with the transformation is a cumulated waste problem. Taiwan produces nearly 5 million tons of waste each year, of which 10% is of glass materials. Bureau of Highway Department funded a research program to investigate ways of recycling the glass waste. This report presents information on the program and laboratory/field test data. Materials used in the test program included 85/100 asphalt, Type II modified asphalt, and treated glass waste. Four glass contents: 0, 5, 10, and 15%, in terms of the total aggregate weight, were used in the mixture designs for casting series of 10 cm diameter by 6.35 cm disk specimens. Tests including Marshall stability value, dry/wet moisture damage, skid resistance, light reflection, water permeability, and compaction were carried out in accordance with the ASTM and AASHTO procedures. The test results reveal that glass waste is a viable material for asphalt concrete that has been widely used in pavement that offers profound engineering and economic advantages.     

Effectiveness of a Coral-Derived Surfacing Material for Reducing Sediment Production on Unpaved Roads, Schoffield Barracks, Oahu, Hawaii

This study evaluated the effectiveness of two application rates of a coral-derived surfacing material for both traffic and nontraffic road conditions using simulated rainfall (110–120 mm h⁻¹ for 30–90 min) on 0.75-m (wide) × 5.0-m (long) plots of similar slope (roughly 0.1 m m⁻¹). The coral is a locally available material that has been applied to unpaved roads surfaces on Schoffield Barracks, Oahu, Hawaii (USA), where this experiment was conducted. The simulations show that compared with a bare control plot, the coral-based surface application rates of 80 and 160 kg m⁻² (equivalent to only 10- and 20-mm thicknesses) reduced road sediment production by 75% and 95%, respectively, for nontraffic conditions. However, after two passes of the research vehicle during wet conditions, sediment production rates for the two coral treatments were not significantly different from those on the bare road plots. The overall effectiveness of the coral-derived surfacing material is unsatisfactory, primarily because the on-road surface thickness associated with the application rates tested was too small. These rates were selected to bracket those applied to training roads in the study area. Furthermore, the composition of the coral-based material does not facilitate the development of a sealed, erosion-resistant surface. When applied at the low rates tested, the coral material breaks down under normal traffic conditions, thereby losing its ability to counter shearing forces exerted by overland flow on long hillslopes where erosion measures are most needed. These simulations, combined with observations on roads in the study area, indicate that this material is not an appropriate road surfacing material for the site—at least for the low application rates examined. These results are preliminary; extended testing of higher applications rates at the hillslope scale under natural climate and traffic conditions is needed to better judge the effectiveness of this material over time.     

Assessing the potential of yield improvements, through process scrap reduction, for energy and CO2 abatement in the steel and aluminium sectors

Targets to cut 2050 CO₂ emissions in the steel and aluminium sectors by 50%, whilst demand is expected to double, cannot be met by energy efficiency measures alone, so options that reduce total demand for liquid metal production must also be considered. Such reductions could occur through reduced demand for final goods (for instance by life extension), reduced demand for material use in each product (for instance by lightweight design) or reduced demand for material to make existing products. The last option, improving the yield of manufacturing processes from liquid metal to final product, is attractive in being invisible to the final customer, but has had little attention to date. Accordingly this paper aims to provide an estimate of the potential to make existing products with less liquid metal production.Yield ratios have been measured for five case study products, through a series of detailed factory visits, along each supply chain. The results of these studies, presented on graphs of cumulative energy against yield, demonstrate how the embodied energy in final products may be up to 15 times greater than the energy required to make liquid metal, due to yield losses. A top-down evaluation of the global flows of steel and aluminium showed that 26% of liquid steel and 41% of liquid aluminium produced does not make it into final products, but is diverted as process scrap and recycled. Reducing scrap substitutes production by recycling and could reduce total energy use by 17% and 6% and total CO₂ emissions by 16% and 7% for the steel and aluminium industries respectively, using forming and fabrication energy values from the case studies. The abatement potential of process scrap elimination is similar in magnitude to worldwide implementation of best available standards of energy efficiency and demonstrates how decreasing the recycled content may sometimes result in emission reductions.Evidence from the case studies suggests that whilst most companies are aware of their own yield ratios, few, if any, are fully aware of cumulative losses along their whole supply chain. Addressing yield losses requires this awareness to motivate collaborative approaches to improvement.