Calcium Leaching of Cement Asphalt Paste and Its Effects on Dynamic Mechanical Properties

Abstract

Calcium leaching is an important durability issue of cement asphalt (CA) mortar used in high-speed rails. Calcium leaching affects CA mortar’s mechanical properties, which are critical for its structural performance. In this paper, the calcium leaching of CA paste and its effects on the dynamic mechanical properties of CA paste are studied. CA pastes were immersed in 6 mol/L ammonium nitrate solution for different ages. The concentrations of the calcium and silicon ions in the leaching solution were monitored by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Changes in porosity, bulk density, and contents of calcium hydroxide and calcium silicate hydrate (C-S-H) in leached specimens with time were measured. The dynamic mechanical properties of CA paste were measured by dynamic mechanical thermal analysis (DMTA). Results showed that the calcium leaching of CA paste by 6 mol/L ammonium nitrate solution was mostly completed within 7 days. Thermal gravity analysis (TGA) results showed that the calcium leaching, which caused significant mass loss and porosity gain, was mainly contributed by the decomposition of calcium hydroxide (CH) and partly by C-S-H gel. The addition of asphalt only changed the volume fraction of cement hydrates in the CA paste, but did not improve the leaching resistance of cement hydrates. The calcium leaching negatively affected the storage modulus, but positively affected the loss factor of CA pastes.