On-line quality assessment and certification of recycled aggregates from demolition waste based on a chemical imaging approach

The environmental constraints, more and more limiting demolition waste (DW) disposal, especially in urban regions, and the corresponding decrease of steady supplies of good quality natural aggregates, joint to the need of ample supplies of concrete aggregates for the construction industry, make End-Of-Life (EOL) concrete recycling strongly increased in these last years. The aggregates recovery from DW represents a challenging perspective and more and more efforts have been thus addressed to perform a better DW characterization in order to improve its reuse. This paper discusses the possibility offered by an on-line utilization of chemical imaging based procedures finalized to evaluate the quality of aggregates particles (i.e. composition) as resulting from specialized comminution-classification actions implemented within the European C2CA project. More in details, hyperspectral imaging (HSI) based sensing system, working in the near infrared range (1000-1700 nm), was adopted to develop non-destructive, rapid and low cost analytical strategies finalized to detect the degree of liberation of concrete aggregates from mortar paste. Different chemometric techniques were applied in order to analyze acquired hyperspectral images: principal component analysis (PCA) for data exploration and partial least square-discriminant analysis (PLS-DA) to build classification models. Results indicate the ability of this approach to significantly distinguish liberated recycled aggregates, mortar and aggregate/mortar mixture.