The compressive strength and microstructure of blended cement was investigated in this study. The hydration products of cements were identified by means of scanning electron microscopy (SEM) and polarising microscopy (thin section). Results indicated that the blended cement required pozzolanic activity in addition to its cementing property with the addition of 30% material. Aggregations of belite grains were observed which were surrounded by alite. Blended cement exhibited high early-term strength. However, its 3d-age strength is lower than ordinary Portland cement. On the other hand, all blended cement mortars fulfil the compressive strength requirements of TS 24. Hence, it can be said that blended cement can achieve adequate early compressive strength. A reduction in the amount of CSH gel and the porosity of the matrix in mortars were found to be responsible for the poor compressive strength of the cement paste in early the age. (C) 2007 Elsevier Ltd. All rights reserved.