About 3% of greenhouse gases come from cement production - restoration nowadays always involves concrete. Archaeologists, generally, have a pretty dim view of alignments so it is unlikely the stones will be replaced in their original intended positions. The story of stone sockets is that they are often vague and 'casual' - not empty stone-sized slots. Restoration can be likened to playing Bach on modern instruments (RIP R. Moog). The tradition of vernacular stonework - essential for a 'proper job' - is nearly extinct.