Effects of nano-TiO2 on strength, shrinkage and microstructure of alkali activated slag pastes

For alkali-activated slag (AAS), high drying shrinkage is an obstacle which impedes its application as a construction material. In this investigation, nano-TiO2 was added to AAS, and its mechanical properties and shrinkage were tested to examine its effect on hardened alkali-activated slag paste (AASP). To understand the impact of nano-TiO2 on AASP at micro scale, FTIR, MIP and SEM were carried out. Experimental results indicate that the addition of nano-TiO2 to AAS enhances the mechanical strength, and decreases the shrinkage of AASP. FTIR and SEM results demonstrated that the addition of nano-TiO2 into the AASP accelerates its hydration process, resulting in more hydration products and denser structure. MIP results showed that the addition of nano-TiO2 reduces the total porosity of AASP and changes the pore structure. The porosity of 1.25–25 nm mesopores, which is believed to be responsible for the high shrinkage of AASP, is remarkably reduced due to the addition of nano-TiO2.