Life cycle cost analysis of lightweight green concrete utilizing recycled plastic aggregates

The increasing quantities of plastic waste worldwide is an imminent problem with sever environmental impacts. Recent research was able to develop methodologies to recycle plastic waste and use it as a replacement to natural aggregates in concrete. This not only reduces the amount of unprocessed plastic waste, but also minimizes the need for natural aggregates; thus, which in turn reduces the environmental impacts of overexploiting aggregate quarries. The goal of this research is to assess the life cycle cost implications of utilizing green recycled plastic lightweight aggregates (PLA) - specifically those formed of linear low-density polyethylene (LLDPE) - in concrete structures. To this end, the authors considered a concrete structure with multiple variable design parameters, and conducted structural design using conventional concrete and concrete with recycled plastic in an alternating way; with a total of 24 different scenarios. Then lifecycle cost analysis was conducted on these scenarios using construction cost, operation and maintenance, and end of life cost. Finally, a sensitivity analysis was performed to quantify how the structural parameters and cost of key elements impact the cost effectiveness of the LLDPE-based PLA. The findings indicated that using LLDPE-based in concrete structures leads to savings in concrete and steel quantities up to 7.23% and 7.18% respectively depending on the structural configuration of the building. This leads to savings in life cycle costs up to 5.9% depending on the structural configuration and the discount rate. Also, the study revealed that structures with slab spans of around 4 and 5 m benefit the most from the use of LLDPE-based PLA; while those with smaller slab spans of 3 m benefit the least, and sometimes do not benefit at all - financially speaking. The outcomes of this research quantitatively validates the use of green recycled plastic aggregates as a substitute to the conventional aggregates in order to save the limited natural resources. Furthermore, the paper will contribute to the upcoming paradigm shift of utilizing recycled plastic in concrete and using concrete in general as a waste recycling system rather than just a building material; thus, minimizing the environmental impacts of both the concrete and plastic industries as well as helping developers reduce their life cycle costs.