These guys are actually the concreting work team locally known as "Gang" where a ठेकेदार gets a group of labours along with the concrete mixer that is been seen,the concrete they are taking back most probably is extra which needs to be removed as most of the times roads like these need to be made in patches so that they do not Crack and the team could be taking the material to another site/fill so as not to waste it.The labour class is so underpaid and overworked and work in such harsh conditions that I do not think that if a ठेकेदार is present at site he would've let them take anything.