Analysis on environmental and economic benefits of steel slag asphalt mixture on a life cycle basis
In order to comparatively analyze the environmental and economic benefits of steel slag asphalt mixture and promote the resource utilization of steel slag in the construction of road engineering,life cycle analysis method was used on the basis of activity data collected from an expressway engineering project in Hunan Province and quota data.The energy consumption and carbon emission were quantified respectively for steel slag asphalt mixtures and conventional asphalt mixtures AC-13C、AC-20C.The environmental benefit of steel slag replacing different natural aggregates(basalt and limestone)for the surface and intermediate layers of asphalt pavement were comparatively analyzed.The carbon fixation potential of steel slag was discussed under laboratory conditions,based on spontaneous carbonation reaction of alkaline-earth minerals in steel slag.In addition,the cost-effectiveness analysis method was applied to compare the construction and maintenance cost of steel slag asphalt mixture and conventional asphalt mixture.Then,the influence of transportation distance of steel slag on construction cost was investigated to propose the maximum economic transportation distance for steel slag.The results show that the carbon emission of 1 000 m3 steel slag asphalt mixtures AC-13C、AC-20C are 157.11 and 148.22 tonnes respectively throughout the whole construction process,which reduces 12.20%and increases 3.08%respectively compared with conventional asphalt mixture.The carbon emission of steel slag asphalt mixtures AC-13C、AC-20C are respectively 80.25 and 73.50 tonnes at the stage of production and transportation of raw material,accounting for 51.08%and 49.60%of the whole construction process.The theoretical maximum carbon fixation varies from 0.33 to 0.48 tonnes CO2 per tonne of steel slag,and thus the potential of carbon fixation is considerable.The results of economic analysis suggest that the construction cost and maintenance annual cost of the surface layer of steel slag asphalt mixture AC-13C is 42.0 and 8.8 yuan/m2 every year,which reduces 6.8 and 3.6 yuan/m2 every year,with the comparation of conventional basalt asphalt mixture.Nevertheless,the construction cost of the intermediate layer of steel slag asphalt mixture AC-20C is 57.6 yuan/m2 every year,which is slightly higher than that of conventional limestone asphalt mixture(54.0 yuan/m2 every year).The transportation distance of steel slag has a strong influence on environmental and economic benefits.There are no benefits in the aspect of carbon emission and construction cost when the transportation distance of steel slag is over 171.8 and 225.0 km.Therefore,it is suggested that steel slag is used near the production site,and meanwhile applied in the surface layer to replace basalt,so as to maximize its environmental and economic benefits.16 tabs,7 figs,47 refs.