Effect of Fly Ash on the Mechanical Properties and Microstructure of Cement-Stabilized Materials with 100% Recycled Mixed Aggregates

The use of recycled mixed aggregates (RMA) in cement-stabilized materials (CSM) is an effective way to dispose of and reuse demolition waste. However, this approach faces various challenges; for example, the drying shrinkage of CSM with 100% RMA is very high, which is unfavorable for use in road engineering. In order to use a simple method to reduce the drying shrinkage of the CSM with 100% RMA and give it reliable strength, the effect of fly ash on the mechanical properties, drying shrinkage, and abrasion resistance of CSM with 100% RMA was investigated in this study, and the mechanism was examined by X-ray Diffraction (XRD), Mercury Intrusion Porosimetry (MIP), and Scanning Electron Microscopy (SEM). The results revealed that the addition of fly ash would decrease the drying shrinkage of CSM with 100% RMA. Moreover, when the amount of fly ash was less than 20%, the later strength increased remarkably despite the slight decrease in the early unconfined compressive strength, indirect tensile strength, compressive and splitting elastic modulus, and abrasion resistance of CSM with 100% RMA. The microstructure analysis results indicated that fly ash increased the decline range of diffraction intensity of C2S and C3S at a later age and also helped to optimize the pore structure. Research results of this article can be used to optimize the mechanical properties of CSM with 100% RMA and guide its application in road base.