Effect of Shale Powder on the Performance of Lightweight Ultra-High-Performance Concrete

In this study, lightweight ultra-high-performance concrete (L-UHPC) was prepared by using SP to replace part of the cement. The main study investigated the effect of the amount of SP on the spread diameter, apparent density and mechanical properties of L-UHPC. The mechanism of the effect of SP on the hydration product of L-UHPC was studied and the pore structure of L-UHPC was also analyzed. The results show that the incorporation of SP can effectively improve the spread diameter and reduce the apparent density of L-UHPC to a certain extent. With the increase in SP content, the compressive strength of L-UHPC at 7 days of age did not change significantly. However, the compressive strengths at 3 and 28 days of age changed significantly. When the amount of SP was less than 12%, there was no significant decrease flexural and compressive strength at 28 days of age. However, the flexural and compressive strength of L-UHPC gradually decreased when the amount of SP was greater than 12%. The microstructure shows that SP can reduce the content of portlandite. This is mainly due to the fact that the addition of SP improved the stacking compactness of L-UHPC and promoted secondary hydration reactions. The content of portlandite and the hydration degree of cement were reduced. At the same time, the exothermic hydration of L-UHPC with SP was less, the hydration process was slow, and the exothermic rate of initial hydration was low. An appropriate amount of SP can effectively improve the pore structure of L-UHPC and significantly reduce the pore volume of harmful pores (50~200 nm). SP can make the L-UHPC structure more compact and has a positive effect on the development of L-UHPC strength.