Gebers told Dezeen, “We saw the spire collapse and thought we could propose a way to combine the old materials with new technology to help speed up the reconstruction and make a cathedral that is not simply a copy of the original, but rather a cathedral that would show its layered history proudly.”
Indeed, their copy of the statue utilized a mixture of limestone and ash — similar to the materials found in the wake of the fire. By using the debris left behind after the blaze, Geboers believes it will help preserve the building’s historical integrity.
Gebers even believes that his technique could be used to replace the stone vaults that were damaged in the fire.
Although it might sound technologically complex, Gebers even suggests that this process would be cheaper than having highly trained and skilled artisans cut new pieces of stone, and could be done within the five-year timeframe promised by French President Emmanuel Macron. 
H/T: Dezeen