Reducing the carbon footprint of concrete generally involves reducing the amount of calcium oxide in the cementitous materialsbyblending flyashand/or ground limestone into the cement or by replacing some of the cement with supplementary cementitious materials. This increasesthe ratio of SiO2+Al2O3+Fe2O3to CaO+MgO in the cementitious material.While reducing the CaOcontent of cementitious ma-terials is good for the environment, it may not be good for concrete exposed to de-icing salts plus repeatedcycles of freezing and thawing due to the effect of carbon-ation. Though carbonation can refine the pore structure when using only portland cement, it coarsens the pore structure when using high levels of cement replace-ment.This leads to increased scaling potential.A review of theeffects of different cementitious materials combinations on carbonationalong with an examina-tion offield performance ofconcrete exposed to deicing salt plus repeated cycles of freezing and thawingis used to developa relationship based on the ratio of SiO2+Al2O3+Fe2O3to CaO+MgOin order to determine when limitations on cement replacement, or additional protective measures may be needed when scaling is a concern