Study on the role of activators to the autogenous and drying shrinkage of lime-based low carbon cementitious materials

Abstract

In order to improve the recycling of industrial solid wastes in the build materials area, the long-term development of auotogenous and drying shrinkage of lime-based low carbon cementitious materials (LCMs) was investigated in this work. In addition, the influence of chemical admixture (Na2SO4 and NaOH) on the shrinkage behavior of LCMs was systemically studied and compared. Moreover, the hydration kinetics, evolution of the compositions of hydration products and microstructure of LCM were investigated and analyzed to reveal the mechanism of the shrinkage behavior of LCM. The results showed that LCMs have lower autogenous and drying shrinkage value compared to those of Portland cement (PC). The addition of Na2SO4 to the LCM mixture further mitigated the shrinkage value of the LCM, especially for autogenous shrinkage. Na2SO4 in the LCM led to an additional number of ettringite (AFt) crystals formed in the paste at the early age, and the autogenous shrinkage of LCM was effectively decreased due to the compensation effect of the AFt on the shrinkage. Moreover, a large number of AFt crystals as skeletons embedded in the C(A)SH gel contributed to restricting the shrinkage of the paste. However, NaOH in the LCM caused the alkali activated reaction of the slag particles in the LCM and resulted in a LCM microstructure with fewer AFt crystals and more fine pores. Thus, the NaOH increased the autogenous and drying shrinkage of the LCM to some extent.