Sludge‐based geopolymer materials: A review

Abstract Sludge refers to the solid waste produced after sewage treatment. Unreasonable disposal of sludge can cause environmental pollution. Nonetheless, the sludge contains large amounts of silica‐aluminate, which has pozzolanic activity by treatment, and the sludge can be used as a sustainable building material. The previous studies have recommended that it is reasonable to produce geopolymers, that is, a green low‐carbon cementitious material with excellent mechanical and durability properties, from sludge. This article provides an overview of recent advancements in the study of sludge‐based geopolymer. It delves into the mechanisms behind alkali‐activated geopolymer, examines the feasibility of preparing geopolymer from sludge, and discusses various preparation methods. Additionally, it elaborates on the impact of incorporating different auxiliary materials on sludge‐based geopolymer. The comprehensive performance of sludge‐based geopolymer, encompassing mechanical properties, durability, and setting time, is thoroughly summarized. An environmental assessment is conducted, evaluating heavy metal leaching and the lifecycle of sludge‐based geopolymer. Finally, we briefly discuss some problems in the current research and development trends in the future on sludge‐based geopolymer. The aim of this article is to provide comprehensive support and guidance for both the research and practical engineering applications of sludge‐based geopolymer.