Influence of additives on rheological behavior and structure evolution of cement asphalt mortar

Abstract

Cement Asphalt Mortar (CAM) is a composite organic-inorganic material, composed of cement, emulsified asphalt, river sand, and various admixtures. It is used in ballastless track systems of high-speed railways to damp vibrations. The rheology of the mortar in its fresh state is mainly characterized by the constituents and their proportions. This study investigates the effect of different constituents such as asphalt emulsion, calcium sulfoaluminate, aluminium powder, and defoamer on the rheological properties and structural development of CAM in its fresh state. Time sweep tests were conducted in a coaxial cylinder geometry in a dynamic shear rheometer to assess structure development. Shear rate sweep tests were conducted to obtain rheological properties. The results illustrate the critical impact of additives on the early strength, hydration rates, and rheological properties of CAM. Specifically, the storage modulus of CAM systems was found to be approximately 1/10th of CM systems, highlighting the influence of asphalt emulsion on structural formation. The addition of calcium sulfoaluminate accelerated structure development, while defoamer increased the dynamic modulus. In contrast, aluminium had minimal effect on strength gain. These findings demonstrate the significant role of additives in governing the viscoelastic behavior of fresh CAM.