Life-cycle impacts of the use of industrial by-products in road and earth construction

Abstract

A two-stage study “Life cycle analysis of road construction and earthworks” was part of a more extensive Finnish research project “Assessment of the applicability of secondary products in earthworks”. In the first stage of this work a life-cycle impact assessment procedure for the comparison and evaluation of alternative road and earth constructions was developed. Additionally, a database containing the environmental burdens of the most significant construction materials and unit operations was constructed. In order to evaluate the applicability of the procedure, the use of coal ash, crushed concrete waste and granulated blast-furnace slag in road construction was evaluated in case studies. The use of these secondary products was also compared with the use of natural materials in corresponding applications. The aim of the second stage was to transfer the assembled data for utilisation as a practical model by creating an inventory analysis program to calculate and compare the life cycle impacts of the most common road constructions and foundation engineering methods. The data obtained in the first stage was also augmented to the extent necessary for this purpose. The results of case studies indicate that the production and transport of the materials used in road constructions produce the most significant environmental burdens. Production of the bitumen and cement, crushing of materials and transport of materials are the most energy consuming single life-cycle stages of the construction. A large part of the emissions to atmosphere originates from energy production. In the expert assessment, consumption of natural materials and leaching behaviour were also regarded as being of great significance.