Slag in concrete

Hi Summer, Blast furnace slag is a waste product of the iron-making process. It is a glassy granule that is ground up and used as a cement admixture. Slag contributes to compliance under MRc4 as post-industrial recycled content. It is most easily available in steel producing regions, though is often shipped around the country. Typical percentages are in the range of 35-50% of cement only (not total concrete), and slag can have the effect of lightening the final concrete, helping decrease the urban heat island effect when used for sidewalks. Hope that helps, Anne

Yep- that's the right method. I've found that most cement suppliers are starting to provide the back-up information, though a few extra calculations steps are typically needed. There's a great sample table in the LEED Reference guide as well.

Where is 'slag' documentented as recycled content under MR4 in the various LEED programs? SCM's included in the calculations if they are considered recycled content under the ISO 14021 guidelines. ISO 14021 indicates that to be considered recycled content the material must be "ready to use" as it is produced by the industrial process (i.e. - fly ash). Since slag must be further processed - ground - is should be considered a by-product and not recycled content if I interpret the standard correctly. In essence, slag would be similar to aggregate in it's processing even though it's a SCM and therefore not considered recycled content. I fully understand the advantages of using slag in a concrete mix but I am trying to understand the application in MR4 more clearly. I would appreciate it if anyone can point me to any documentation which explains this more clearly. Thanks.