The ternary blended cement with finer slag and silica fume (SF) could improve the packing density (PD) through the filling effect. The excess water (water more than needed for filling into voids between the cement particles) can be released to improve the fresh properties and densify the microstructure which is beneficial for improving the hardened properties. To verify the hypothesis and reveal how and why (cement + slag + SF) the ternary blends could bring such advantages, the binder pastes incorporating slag and SF with various water-to-binder ratios were produced to determine the PD experimentally. To evaluate the optimum water demand (OWD) for maximum wet density, the influence of the dispersion state of the binder on PD was investigated using the wet packing density approach. The effect of PD of various binary and ternary binder systems on water film thickness (WFT), fluidity, setting time, and compressive strength development of cement paste was also investigated. The results show that the ternary blends could improve the PD and decrease the water film thickness (WFT). The enhanced PD and altered WFT are able to increase fluidity and compressive strength. The ternary blends could improve the compressive strengths by increasing PD and exerting nucleation and pozzolanic effects.

Although the importance of the interfacial transition zone (ITZ) to sulfate attack is obvious, the relation between the ITZ and the rate of degradation is still unclear. The impact of ITZ volume content on the degradation of concrete, including length, mass, and elastic dynamic modulus ($E_d$ ) variation, fully immersed in magnesium sulfate solution were investigated in this work. The microstructure was analyzed by backscattered electron imaging (BSE) and energy dispersive X-ray spectroscopy (EDX) mapping analysis. The performance of concrete exposed to magnesium sulfate highly depended on the aggregate and the composition of raw materials. There was a trend toward more serious deterioration with increasing ITZ in the reference and limestone filler blended group after 12 months of exposure. The degradation of specimens made with slag was independent of the variation of ITZ content. Gypsum tended to precipitate in the ITZ under magnesium sulfate attack. The EDX analysis confirmed the decomposition of C-S-H, accompanied by the formation of degradation products M-S-H.