What goes into making cement? The obvious answer is: limestone, which makes up approximately 94-95 per cent of Ordinary Portland Cement. But cement is more accommodating: the Bureau of Indian Standards says flyash can comprise up to 35 per cent of cement, and blast furnace slag (bfs)
Links:
[1] http://admin.indiaenvironmentportal.org.in/opinion/slaggard-rules
[2] http://admin.indiaenvironmentportal.org.in/category/author/radhika-krishnan
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/down-earth
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cement-industry
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/legislation
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/fly-ash