关键词: 纳米颗粒;粉煤灰;水泥基材料;干缩;机理

Abstract: In order to investigate the effect of nanoparticles on the drying shrinkage of cement-based materials containing fly ash,two kinds of nanoparticles(the nano SiO2 and nano SiC)were selected to prepare nano modified fly ash cement mortar and concrete specimens respectively,the effect of the nanoparticles content on drying shrinkage of fly ash cement mortar and concrete at different ages was studied by tests,and the action mechanism was analyzed theoretically.The results show that the drying shrinkage rate increases significantly on cement mortar mixed with nanoparticles,the 28 d drying shrinkage rate of sample with 2％nano SiO2 cement mortar and nano SiC cement mortar increases by 90％and 120％respectively compared to ordinary cement mortar;the 28 d drying shrinkage rate of the concrete with 2％nano SiO2 and nano SiC increases by 124.8％and 85.8％compared to reference concrete;the nano particles have obvious influence on drying shrinkage performance of cement mortar and fly ash concrete,and the double mixing and single mixing of nanoparticles have little effect on drying shrinkage rate of concrete.Therefore,it is concluded that nanoparticles have large specific surface area,which results in increasing of water adsorption and consuming of a large number of internal free water.Meanwhile,because tiny pores in the inner structure of concrete are filled by nano particles,making external water difficult to enter into the interior but be evaporated,resulting in emerging of internal and external inconsistent deformation,finally increasing the drying shrinkage rate of concrete.

Key words: nanoparticles;fly ash;cement-based material;drying shrinkage;mechanism