Mechanical properties and hydration mechanism of low carbon concrete with recycled aggregate

Collaborative and effective disposal of construction and industrial solid waste is of great significance for protecting the ecological environment. In this paper, low carbon concrete with recycle aggregate (LCCRA) mainly made of phosphogypsum, fly ash, slag and recycled aggregate was studied. The uniaxial compression test was carried out to determine the stress-strain relationship of LCCRA and a constitutive model for LCCRA under uniaxial compressive loading was established. Scanning Electron Microscopy (SEM) was used to explore the hydration process of LCCRA. The results demonstrated that the uniaxial compressive strength of LCCRA achieved 30.8 MPa with a 100 % replacement rate of recycled coarse aggregate and a water-binder ratio of 0.54. The constitutive model of LCCRA under uniaxial compression fits well with the experimentally measured stress-strain curve. SO42- in low carbon cementitious materials reacts with [SiO4](4-), [AlO4](5-) to generate C-S-H gel, C-A-S-H gel and AFt crystals, which enhance the density of LCCRA interfacial transition zone (ITZ) and thus improve its basic mechanical properties.