Effects of microwave, thermomechanical and chemical treatments of sewage sludge ash on its early-age behavior as supplementary cementitious material

Xinyu Cong, Shuang Lu, Yunhe Gao, Yan Yao, Mohamed Elchalakani, Xianming Shi

Research output: Contribution to journalArticle


To better inform the recycling of sewage sludge ash (SSA) in cement-based construction materials, this laboratory study investigated a variety of modification methods aimed at improving the value of SSA. For pre-treatment, three different methods of physical modification including low-temperature drying, grinding, high-temperature calcination were selectively performed. Microwave treatment was also explored as an alternative to the calcination procedure. Subsequently, chemical modification of the SSA was performed by blending with quicklime (QL) for likely chemical activation. The effectiveness of these treatments was assessed in terms of leachability of heavy metals out of the treated SSA and the reduction in total organic carbon (TOC). High-temperature calcination of SSA enhanced the immobilization of heavy metals (e.g., Mn, Zn, and Ba). In contrast, the QL treatment helped immobilize some heavy metals (e.g., Mn and Zn) but re-liberated other metals (e.g., Ba). Compared with calcination at 500 °C for 2h, 15-min microwave heating of pre-treated SSA exhibited better performance in immobilizing the heavy metals and nearly as good performance in reducing the TOC in the SSA Finally, based on the compressive strength data of the cement pastes, microwave treatment is an effective alternative to thermal calcination, in terms of mitigating the side effects of admixed SSA on the cement hydration.

Original languageEnglish
Article number120647
Number of pages12
JournalJournal of Cleaner Production
Publication statusPublished - 10 Jun 2020


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