| Road and bridge construction, reconstruction and extension projects have been rapidly growing with the accelerated process of urbanization in China. However, various environmental impacts associated with these construction projects could not be neglected. On one hand, due to its characteristics (high energy consumption and use of natural resources), it is a sector which contributes highly to global warming. On the other hand, generation of high volumes of construction waste and extensive use of natural aggregates in concrete production are directly linked to the significant environmental impacts. As a result, utilization of old road or bridge construction materials, especially aggregates, as direct replacement of the natural aggregates would have a broad margin for environmental improvement, which might play an important role in lowering the environmental burden caused by road and bridge constructions, improving the utilization of natural resources and achieving China’s energy conservation and emission reduction targets. Though some previous studies explored the applicability of demolition waste as recycled construction materials in China, there is still a lack of quantitative evaluation system or tool to assess the reduction effects of this process. Therefore, a more holistic and quantified assessment is needed for evaluation of the environmental benefits of using recycled construction materialsIn this study, a life-cycle based energy conservation and greenhouse gas (GHG) emissions reduction system for assessing the utilization of recycled construction materials (especially aggregates) was developed, and case study of the Shanghai Middle Ring Link was provided as a proof of the system’s effectiveness and practicability. Through literature review and site investigation, energy saving and GHG emissions reduction effect of the recycled aggregates in road and bridge reconstruction and extension were evaluated. The results were:(1) From the view of the aggregate’life-cycle system, the energy consumption of using natural aggregates was 214146.538 kJ per functional unit, the GHG emssions was 16.029 kg CO2e per functional unit; while the energy consumption of using recycled aggregates was 143710.416 kJ per functional unit, the GHG emssions was 11.416 kg CO2e per functional unit. Compared with natural aggregates, utilization of recycled aggregates would have a reduction of energy consumption and GHG emissions, approximately 33% and 29%, respectively; from the view of the case-study project, the energy consumptions were 942436.556 kJ per functional unit and 872000.434 kJ per functional unit, respectively, and the GHG emssions were 206.866 kg CO2e per functional unit and 202.210 kg CO2e per functional unit, respectively, which meaned the total reconstruction projects would reduce about 7.47% of the energy consumption and about 2.25% of the GHG emissions. Compared the aggregate system, the energy conservation and emission reduction effects of the project system decreased. This might be due to huge energy use of the cement production during the project.(2) The influential elements that affect the energy consumption and GHG emissions of the system were identified, such as waste disposal method, mode of transportation and distance. It was found that the combination of different waste disposal methods and rational site selection would greatly contribute to the reduction of energy consumption.(3) A primary analysis of overall environmental benefits of the recycling aggregates from old road and bridge construction was conducted. Considering both environmental and economic value, a saving of 117.66 yuan per ton was estimated by using recycled aggregates. Moreover, the reduction of other pollutants caused by electricity and oil use were calculated. For instance, recycling one tonne waste concrete would reduce industrial wastewater 810.782 g, COD 0.921 g and industrial waste gas 0.350 m3.Finally, other applications of recycled construction materials were introduced along with both advantages and disadvantages.This paper presents a process based calculation of environmental impacts associated with recycled road and bridge construction waste (especially aggregates) from reconstruction and extension projects. Quantitative and comparative life cycle assessment results on road construction waste are essential first steps towards making informed decisions towards more sustainable practices in low-carbon cities and eco-friendly roads construction in China. |
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