Cementitious materials limitations for concrete exposed to deicing salt plus repeated cycles of freezing and thawing

Abstract

Reducing the carbon footprint of concrete generally involves reducing the amount of calcium oxide in the cementitous materials by blending flyash and/or ground limestone into the cement or by replacing some of the cement with supplementary cementitious materials. This increases the ratio of SiO2+Al2O3+Fe2O3 to CaO+MgO in the cementitious material. While reducing the CaO content of cementitious materials is good for the environment, it may not be good for concrete exposed to deicing salts plus repeated cycles of freezing and thawing due to the effect of carbonation. Though carbonation can refine the pore structure when using only portland cement, it coarsens the pore structure when using high levels of cement replacement. This leads to increased scaling potential. A review of the effects of different cementitious materials combinations on carbonation along with an examination of field performance of concrete exposed to deicing salt plus repeated cycles of freezing and thawing is used to develop a relationship based on the ratio of SiO2+Al2O3+Fe2O3 to CaO+MgO in order to determine when limitations on cement replacement, or additional protective measures may be needed when scaling is a concern.