纳米颗粒对粉煤灰水泥基材料干缩变形的影响及机理

为探讨纳米颗粒对掺粉煤灰的水泥基材料干缩变形的影响,选取了纳米SiO2和纳米SiC两种纳米颗粒,分别制备了纳米改性粉煤灰水泥砂浆和混凝土试件,通过试验研究了纳米颗粒掺量对不同龄期粉煤灰水泥砂浆和混凝土干缩性能的影响,并分析了其作用机理.结果表明,掺纳米颗粒的水泥砂浆干缩率明显增大,掺量为2％的纳米SiO2水泥砂浆和纳米SiC水泥砂浆的28 d干缩率较普通水泥砂浆分别增大了90％和120％;掺量为2％的纳米SiO2混凝土和纳米SiC混凝土28 d干缩率较基准混凝土增大了124.8％和85.8％;纳米颗粒对粉煤灰水泥砂浆和粉煤灰混凝土干缩性能的影响很明显,而混掺与单掺纳米颗粒对混凝土的干缩率影响不大.分析认为,纳米颗粒比表面积大,吸附水分增多,造成内部自由水被大量消耗,同时由于纳米颗粒填充了混凝土内部结构中的微小孔隙,使得外部水分难以进入内部而被蒸发,造成内外变形不一致,最终增大了混凝土的干缩率.

Effect and Mechanism of Nano-particles on Drying Shrinkage of Cement-based Materials Containing Fly Ash

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.