An additive formulation for reduction or prevention of microbially induced corrosion in concrete, cementitious material (such as mortar or grout), or a combination thereof. The additive formulation comprises a Quat Silane and a fungicide, wherein the ratio of the Quat Silane to the fungicide in the formulation is in a range of about 10:1 to about 1:10, preferably in a range of about 5:1 to about 1:5.