Integration of monitoring indicators for self-sensing alkali activated cementitious materials: From electrical signals - resistivity to autogenous shrinkage

The chemical shrinkage and autogenous shrinkage of alkali-activated materials (AAMs) are usually more significant than that of ordinary Portland cement (OPC). Therefore, both searching for efficient methods to reduce shrinkage and exploring the shrinkage mechanism of AAMs are of great significance in promoting the application of AAMs. In this paper, metakaolin is used to reduce the chemical shrinkage and autogenous shrinkage of AAMs, while an innovative resistivity measurement is used to concretize the electrical signal of AAMs and the relationship between autogenous shrinkage and resistivity was explored. The early resistivity and heat of hydration curves of AAMs can be divided into five stages with high similarity, demonstrating the feasibility of indirectly quantifying the autogenous shrinkage and chemical shrinkage by resistivity. The results of TG-IR, MIP, and heat of hydration prove that the early reaction rate of AAMs decreases with the increase of metakaolin content, which further leads to the decrease of early chemical shrinkage and autogenous shrinkage. The reduction of autogenous shrinkage reached the maximum (49%) when the metakaolin content was 50%. A mathematical model between autogenous shrinkage and resistivity was established, which means that the resistivity of self-sensing materials can be used as an index to evaluate the early autogenous shrinkage of AAMs.