The 4th Asian Concrete Federation Symposium on Emerging Technologies for Structural Longevity (ACF2023- ETSL)

To achieve carbon peaking and carbon neutrality goals and the diversified utilization of resources, it is necessary to speed up the process of combining the improvement of the ecological environment governance system with the industrial upgrading of all walks of life, which is a top priority for the cement industry with huge carbon emission pressure and insufficient raw material reserves. Considering the current situation that river and lake sludge reserves are huge and cannot be treated in an environmentally friendly way, its utilization in building materials to replace cement provides a new idea for solving the above problems. Therefore, a green and low-carbon cement with sintered sludge is innovatively proposed in this report. The process of "grinded-calcined at 750℃-grinded" is the primary treatment for application and activation of the dried sludge. Subsequently, the cement with different sintered sludge contents is systematically studied from the aspects of macroscopic properties and microstructural characteristics. With the enlargement of sintered sludge content, the water absorption, shrinkage resistance and durability are enhanced, and the mechanical properties show a trend of first increase and then decrease, with the maximum value at 10% sintered sludge. Due to high specific surface area, the incorporation of 10% sintered sludge plays the role of micro-filling in early hydration stage, leading to the densification of the microstructure and the addition of potential nucleation sites. In later hydration stage, numerous amorphous silica in the sintered sludge undergoes secondary hydration based on pozzolanic activity and generates massive C-S-H and C-A-H, which is marked the formation of a stronger cement matrix. The improvement in long-term mechanical properties and durability is the combined result of the pozzolanic activity and internal curing properties of the sintered sludge. In the future, considering the shortage of fresh water and river sand caused by concrete mixing and the abundance of seawater and sea sand, research will focus on the combination of seawater, sea sand and cement with sintered sludge.