In this paper, the effect of DMA-MMA diblock copolymer on the properties of ordinary Portland cement and cement containing boron has been studied. Variation in setting time, compressive strength and volume expansion has been determined. Cement hydration was monitored by X-ray diffraction (XRD) and by Fourier transforms infrared spectroscopy, in combination with the thermoanalytical methods (TG/DTA). The microstructural observation of the hydrated cement paste was performed by scanning electron microscopy (SEM). The result showed that DMA-MMA prolongs the early setting time of the Portland cement and composite cement, and had no noticeable effect on the final setting time of the both cement types. DMA-MMA diblock copolymer reduced the water-to-cement ratios (w/c) from 0.5 to 0.42, which improved the compressive strength of the mortars at all curing ages. The experimental results also indicated that DMA-MMA did not only change the rate of cement paste hydration, but also the microstructure of calcium-silicate-hydrate (C-S-H). (c) 2007 Elsevier Ltd. All rights reserved.