The enhancement of the 1 day strength of cementinous systems by a combination of calcium chlonde (CaCl2) and diethanol-isopropanolamine (DEIPA) was studied, particularly in blended cement systems A combination of quantitative X-ray diffraction with Rietvelcl refinement (QXRD). scanning electron microscopy (SEM)/backscattered electron image analysis. thermogravimetnc analysis (TGA), and isothermal calonmetry were used to investigate the mechanism of strength enhancement by the additives The additives were found to increase the early age mortar strength by enhancing the cement hydration, with the DEIPA enhancing primarily the aluminate hydration DEIPA also affected the morphology of portlandite which was formed as thin plates In parallel, the calcium-to-silica ratio of the C-S-H was found to increase with the use of DEIPA. possibly because of the inclusion of microcrystalline portlandite After 48 h DEIPA was found to directly enhance the rate of reaction of granulated blast-furnace slag and fly ash (C) 2010 Elsevier Ltd All rights reserved