Micro-observations of different types of nano-Al2O3 on the hydration of cement paste with sludge ash replacement

Abstract

In recent years, sewer systems and wastewater treatment plants have become important in developing countries. Consequently, the amount of sewage sludge produced by these countries has been gradually increasing, and determining how to properly recycle this sludge is becoming an important topic for researchers. In this study, to expand the recyclability of sewage sludge ash (SSA) in engineering applications, two types of nano-aluminium oxides (Al 2O 3), MC2A and MC2R, were added to SSA/cement paste and mortar specimens. The MC2R type (γ phase) had a smaller particle size and larger specific surface area than the MC2A type (α phase). The results indicate that the addition of nano-Al 2O 3 to SSA/cement paste can effectively improve the hydration products of the paste. Moreover, the amount of hydration products increased as the amount of nano-Al 2O 3 added to the SSA/cement paste increased. The test results indicate that MC2A nano-Al 2O 3 can more uniformly distribute in the paste body and improve the hydration of cement than MC2R nano-Al 2O 3. Thus, more calcium-silicate-hydrate (C-S-H) gel and calcium aluminate hydrate (C-A-H) salts were produced, and the strength of the specimens was improved. This study suggests that MC2A nano-Al 2O 3 is preferable to MC2R nano-Al 2O 3 for SSA/cement specimen applications.