A new type of magnesia modification alkali-activated cement was prepared, the strength, setting time, shrinkage ratio and cracking behavior, as well as the composition and structure of the hydration product were investigated. The results indicate that the setting time of this cement is similar to that of the ordinary commercial cements; its strength reaches the standard of 42.5 degree cement, its cracking resistance has been remarkably improved because of the micro-aggregate effect of fly ash and shrinkage compensating of magnesia.
The shrinkage of the cement paste with low water-cement ratio at different relative humidity was observed and analyzed with ESEM and deformation map technique.The crack morphology was observed with different magnification with SEM and FESEM,and the formation of the crack was observed with AFM between two C-S-H nano particles.The observation by multi technique at multi scale indicated that the shrinkage was increase with the decrease of the humidity due to the increase of the pressure of the capillary pressure,the morphology of the crack in smaller scale was similar to that in the bigger scale,the smaller crack distributed in the latticework of the bigger ones,and the crack propagated along the gap between two nano particles of C-S-H with weaker bonding.
