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Extrusion dies, in which melted raw materials are forced continuously into a profile to produce various plastic products, are often empirically designed leading to overweight and waste in materials, energy and emissions. Lightweight design method has been applied to reduce weight and increase material efficiency of extrusion dies at design stage. However, the research work was often focused on weight reduction with function requirements as the design constricts. Environmental impacts (EIs) over the entire life cycle of dies are not considered, as a result, it may result in environmental burdens being shifted from design stage to other stages of life cycle of products. Aiming at it, a new lightweight design method is proposed to integrate life cycle assessment (LCA) with shape optimization. The optimization mathematic models for the proposed method are developed, in which the EIs of extrusion dies are modeled as a function of shape variables and processing parameters. An example of extrusion dies for plastic pipe was presented to illustrate the effectiveness of the proposed method. The results showed that 13% weight reduction whist achieving reduction in EIs over the life cycle of dies in comparison with 18% weight reduction yet 29% increase in EIs at manufacturing stage and resultant increase in EIs over the life cycle using conventional lightweight design method in which EIs are not taken into account. It indicated that the proposed lightweight method could have great potentials to reduce weight and prevent environmental burdens shift problem.

Concrete waste can be recycled to produce an aggregate product; referred to as recycled concrete aggregate (RCA). While RCA is mainly used as a road base filler material, it has the potential to replace natural coarse aggregate (NA) in structural concrete. In determining the environmental performance of the resultant concrete product from this substitution, referred to as recycled aggregate concrete (RAC) against its counterpart, natural aggregate concrete (NAC), it is important to consider the effects of the entire life cycle including the upstream processes associated with each. This paper evaluates “cradle-to-gate” embodied energy (EE) of RAC received at a construction site, in comparison to NAC, using the input-output-based hybrid approach, using an Australian context. The paper constructs a model to evaluate EE of RAC and analyses the incremental energy of RAC as opposed to NAC, to identify what contribute to the difference out of four primary factors discussed in previous research. It was found that the EE of RAC is marginally different to that of NAC by +2.1 to −1.1%, and the variation was subject to the magnitude and direction of the four factors considered. The mix composition, primarily the binder composition, was found to have the highest contribution to the difference, significantly standing out from the direct energy difference between RCA and NA, difference of sourcing distance between RCA and NA and the difference of direct manufacturing energy between RAC and NAC.

Over the past three decades, life cycle assessment (LCA) has been increasingly employed to evaluate the environmental impacts of products and buildings. However, the reliability of LCA is frequently weakened by the practice of arbitrary omission of processes and materials and the problem of insufficient data, both leading to inconsistencies in the LCA results. This study proposes an Index of Completeness (IoC) to account for the completeness of an LCA study for a variety of impact categories. An IoC calculation tool is developed to cover the entire life cycle of buildings, including stages of product, construction, use and end-of-life as well as the benefits from recycling and reuse. The IoC helps to identify and remove the inconsistencies in LCA and to enhance its comparability. Residential building projects are tested as case studies. It is found that the IoCs of most impact categories are as high as 98%–99%, whereas of the category of human toxicity the IoC is 85%, mainly due to the fact that plywood formwork was not included in the original model. Sensitivity analysis reveals that dataset changes in an LCA model can not only affect the impact assessment results, but also possibly have influence on the completeness of the LCA model. The LCA practitioners are suggested to combine the newly developed IoCs with the standard four phases of LCA when applying to complex products. Future research should focus on case studies implementing the IoC calculation tool, inclusion of more impact categories in the IoC model, and continuing development to include other complex products.

Buildings are responsible for more than 40% of global energy usage and as much as 33% of global greenhouse gas emissions in both developed and developing countries. However, the study of carbon emissions over a building's life cycle based on Ecotect and building information modeling in developing areas of Nanjing has yet to be conducted. Therefore, the results and recommendations of this paper represent a contribution to the literature on this topic. The scientific value of this paper is that Ecotect and building information modeling can be helpful in simplifying the estimation of carbon emissions over a building's life cycle because they can provide a majority of the information and calculation tools necessary for performing an life cycle assessment (LCA), which may alleviate the problem of insufficient information when executing an LCA of a building. A sensitivity analysis was performed by changing several parameters to identify the parameters that have the largest impacts on the performance a building. A comparison of the life cycle carbon emissions for each stage showed that the operational stage is the largest contributor to carbon emissions. Approximately 85.4% of the total carbon emissions were generated during operation. The construction stage accounted for 12.6% of the total carbon emissions. Approximately 2% of the total carbon emissions occurred during the demolition stage. Compared to the total carbon emissions over the entire life cycle of the building, carbon sequestration by vegetation was minimal. Thus, these findings indicate that governments can achieve the greatest reductions in carbon emissions by targeting the operational phase of buildings. However, the opportunity for addressing non-operational phases should not be ignored because the average carbon emissions per working area per year of non-operational stages are far greater than those of the use phase.

Quantitative environmental life cycle assessment of products can be a useful tool in product-oriented environmental management. With this methodology the environmental impacts of the product during its entire life cycle are attributed quantitatively to the functioning of the product as far as possible. Currently, the scientific basis of methods for assessing the environmental impacts of products is not yet adequate. Methods are divergent, yield conflicting results and contain considerable gaps. In two successive articles an overview of the similarities and differences between these methods, as developed in different countries, is given. To enable fruitful discussions on methods used, and to make life cycle assessment (LCA) an acceptable tool for product-oriented environmental management, a general methodological framework is proposed. In this first article a general introduction to LCA is given, a general methodological framework is proposed and two components of the methodological framework, the goal definition and the inventory, are discussed in more detail.