There are several materials that can act as partial substitutes to Portland cement, which can lead to GHG and cost reductions. The material substitution measures discussed here include the supplementary cementitious materials (SCM) called fly ash and granulated blast furnace slag (slag). Both of these materials can act as substitutions for Portland cement and are already well known in the marketplace. Substitution rates for these materials can range as high as 50-70%. In addition, using recycled concrete as a substitute for virgin aggregate is also considered in this section as a GHG reduction measure, although the GHG savings are considerably less than cement substitution. The reductions achieved using SCM can be substantial. For example, a 50% slag substitution will result in a 40% reduction of GHG impact of a standard 4000 psi mix. The figure below shows the GHG reductions that can be achieved with varying levels of cement substitution.