Suitability of EPDs for Supporting Life Cycle and Comparative Analysis of Concrete Mixtures.

The use of environmental product declarations (EPDs) of concrete and other construction materials is gaining momentum. EPDs should enable an informed selection of products with a lower environmental footprint; hence, the issue of EPD comparability is highly relevant. In this paper, we identified and discussed the present shortcomings and future opportunities that can promote a meaningful EPD comparison for concrete products. Based on the published EPDs, we suggest a more comprehensive water consumption accounting, as the batching water is commonly underestimated. A set of performance metrics required to be specified for concrete are proposed to be included in the product category rules. An effort to develop a procedure for the regular calibration of existing tools with identical calculation databases and methods can produce outcomes that differ by 1-19%. The incorporation of prescriptive and consistently implemented life cycle inventory can minimize the calculation noise. The incorporation of uncertainty and variability as well as a supply-chain-specific EPD creation can help move toward a robust comparison based on the existing data in EPDs.

Material Stock and Embodied Greenhouse Gas Emissions of Global and Urban Road Pavement.

Roads play a key role in movements of goods and people but require large amounts of materials emitting greenhouse gases to be produced. This study assesses the global road material stock and the emissions associated with materials' production. Our bottom-up approach combines georeferenced paved road segments with road length statistics and archetypical geometric characteristics of roads. We estimate road material stock to be of 254 Gt. If we were to build these roads anew, raw material production would emit 8.4 GtCO2-eq. Per capita stocks range from 0.2 t/cap in Chad to 283 t/cap in Iceland, with a median of 20.6 t/cap. If the average per capita stock in Africa was to reach the current European level, 166 Gt of road materials, equivalent to the road material stock in North America and in East and South Asia, would be consumed. At the urban scale, road material stock increases with the urban area, population density, and GDP per capita, emphasizing the need for containing urban expansion. Our study highlights the challenges in estimating road material stock and serves as a basis for further research into infrastructure resource management.

Mitigating life cycle GHG emissions of roads to be built through 2030: Case study of a Chinese province.

The expansion of road networks in emerging economies such as China causes significant greenhouse gas (GHG) emissions. This development is conflicting with China's commitment to achieve carbon neutrality. Thus, there is a need to better understand life cycle emissions of road infrastructure and opportunities to mitigate these emissions. Existing impact studies of roads in developing countries do not address recycled materials, improved pavement maintenance, or pavement-vehicle interaction and electric vehicle (EV) adoption. Combining firsthand information from Chinese road construction engineers with publicly available data, this paper estimates a comprehensive account of GHG emissions of the road pavement network to be constructed in the next ten years in the Shandong province in Northern China. Further, we estimate the potential of GHG emission reductions achievable under three scenario sets: maintenance optimization, alternative pavement material replacement, and EV adoption. Results show that the life cycle GHG emissions of highways and Class 1-4 roads to be constructed in the next 10 years amount to 147 Mt CO2-eq. Considering the use phase in our model reveals that it is the dominant stage in terms of emissions, largely due to pavement-vehicle interaction. Vehicle electrification can only moderately mitigate these emissions. Other stages, such as materials production and road maintenance and rehabilitation, contribute substantially to GHG emissions as well, highlighting the importance of optimizing the management of these stages. Surprisingly, longer, not shorter maintenance intervals, yield significant emission reductions. Another counter-intuitive finding is that thicker and more material-intensive pavement surfaces cause lower emissions overall. Taken together, optimal maintenance and rehabilitation schedules, alternative material use, and vehicle electrification provide GHG reduction potentials of 11%, 4%-16% and 2%-6%, respectively.

The role of performance metrics in comparative LCA of concrete mixtures incorporating solid wastes: A critical review and guideline proposal.

Research and practice on concrete incorporating solid wastes have found many advocates in recent years. Despite significant advancements, the connecting link between the performance of concrete incorporating solid wastes and its environmental impacts is not fully captured. The current review article aims to address the dependency between concrete performance and the potential environmental impacts of concrete made with solid wastes. A systematic review of previous life cycle assessment (LCA) publications was performed with a focus on outlining the importance of including mechanical and durability properties of such type of concrete in obtaining robust LCA results. The data on four types of solid wastes, including construction and demolition waste, municipal solid waste incineration, tire rubber, and polyethylene terephthalate, were reviewed. Research gaps and future opportunities were discussed to advance the knowledge of concrete incorporating these solid wastes. Finally, recommendations were proposed to provide a guideline for construction materials stakeholders to develop a robust comparative LCA of the concrete, particularly that made with solid wastes.

The role of concrete in life cycle greenhouse gas emissions of US buildings and pavements.

Concrete is a critical component of deep decarbonization efforts because of both the scale of the industry and because of how its use impacts the building, transportation, and industrial sectors. We use a bottom-up model of current and future building and pavement stocks and construction in the United States to contextualize the role of concrete in greenhouse gas (GHG) reductions strategies under projected and ambitious scenarios, including embodied and use phases of the structures' life cycle. We show that projected improvements in the building sector result in a reduction of 49% of GHG emissions in 2050 relative to 2016 levels, whereas ambitious improvements result in a 57% reduction in 2050, which is 22.5 Gt cumulative saving. The pavements sector shows a larger difference between the two scenarios with a 14% reduction of GHG emissions for projected improvements and a 65% reduction under the ambitious scenario, which is ∼1.35 Gt. This reduction occurs despite the fact that concrete usage in 2050 in the ambitious scenario is over three times that of the projected scenario because of the ways in which concrete lowers use phase emissions. Over 70% of future emissions from new construction are from the use phase.

Urban-Scale Evaluation of Cool Pavement Impacts on the Urban Heat Island Effect and Climate Change.

We implemented a context-sensitive and prospective framework to assess the global warming potential (GWP) impacts of cool pavement strategies on specific roads for different cities. The approach incorporates several interconnections among different elements of the built environment, such as buildings and urban road segments, as well as the transportation fleet, using specific building and pavement information from an urban area. We show that increasing pavement albedo lowers urban air temperatures but can adversely affect the building energy demand in the areas with high incident radiation exposure. The heating energy savings and the radiative forcing effect improve the GWP savings in cold and humid climate conditions. The total GWP savings intensity is sensitive to the city morphology and road traffic. The probabilistic results show that cool pavement strategies can offset 1.0-3.0% and 0.7-6.0% of the total GHG emissions of the U.S. cities Boston and Phoenix, respectively, for a 50-year analysis period. The worldwide range of savings can be as large as 5.0-44.7 Gt of CO2 eq. A paradigm shift in pavement strategy selection is required in most neighborhoods.

Removing Shadows from Consequential LCA through a Time-Dependent Modeling Approach: Policy-Making in the Road Pavement Sector.

Lack of dynamic accounting in consequential life cycle assessment (CLCA) can keep policy-makers from having an accurate analysis of emission flows over time. In this study, we propose a dynamic CLCA framework to assess the environmental consequences of pavements. Dynamic changes in the demand vector and technosphere matrices were computed using relevant time horizons of affected supply technologies and incorporating time-dependent parameters. A Monte Carlo simulation was then conducted to propagate the variability, model uncertainty, and parameter uncertainty sources of LCI to the damage results. The results show that simplifying pavement CLCA framework through neglecting real-time changes results in notable diversions in the damage results. The environmental benefits of substituting asphalt with concrete are underestimated by 7, 17, and 77% for climate change, human health and resources categories, respectively. A divergence of 114% was also observed in ecosystem quality when using the static framework. Moreover, the lack of accounting for a temporal profile for GHG emissions using static characterization factors leads to a divergence of the GWP benefits of substituting asphalt with concrete of 473 t CO2eq (105%). The uncertainty results show 41-71% contribution of the variance in the damage categories is caused by the variability sources and is primarily attributed to monthly temperature accounting and service life.