Used or surplus materials were perceived as waste and of no value once they had served their design life.
This is referred to as a linear economy; where raw materials are extracted, manufactured into building component and then disposed of when their intended use comes to an end. Often, these components are in great working order and can still perform their intended use for years to come.
There is a growing understanding of a circular economy, where a component follows the same manufacturing stages as a linear economy component, except it is repurposed for another application, close-loop recycled to form a newer version of itself in another form or open-loop recycled to form part of a newer version of a new component.
Materials and components no longer required for their current use, should be seen as opportunities rather than waste. Opportunity to repurpose a component for another use.