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While there is an increasing interest in using photocatalytic cement-based materials, a lack of an appropriate standard procedure for testing the photocatalytic activity and efficiency of such materials makes comparisons among materials and data from different sources challenging. Current standard test methods are not appropriate for assessing photocatalytic nitrogen oxide conversion by cement itious materials because the standards do not consider surface properties of cementitious materials, nor are the test conditions appropriate for evaluation of cementitious materials. Therefore, the main objective is to propose a standard procedure for assessing the photocatalytic activity of cement mixtures with TiO2 additives and to define a parameter the photocatalytic efficiency factor (PEF) that could be used to compare the photocatalytic activity of different TiO2 cement mixtures, even for extended exposure conditions. The use of PEF is demonstrated, and values of PEF ranging from 8.40 to 51.55 mu mol.h(-1).m(-2) (0.78 to 4.79 mu mol.h(-1).fr(-2)) was observed for mixtures with TiO2 up to 15% replacement.