# The Effect of Ageing on Chemical and Mechanical Properties of Asphalt Mortar
## 1 Introduction  
Ageing of bitumen is believed to be a major contributor to many pavement distresses, such as raveling, cracking, and fatigue [1; 2; 3; 4; 5; 6]. Ageing occurs during the process of storage, mixing, transportation, construction, and service. Studies have demonstrated that ductility and penetration of bitumen diminish as a result of ageing, while softening point and ignition temperature increase in the process [7; 8; 9]. Moreover, the viscosity increases and bitumen becomes stiffer.  
Asphalt mortar, commonly known as fine aggregate matrix, is a mixture of bitumen, filler, and sand. It is the binding medium that holds the aggregates of an asphalt mixture together, and it plays an important role as the link between bitumen properties and mixture performance. Past studies have shown that the testing of bituminous mortar is an efficient and repeatable approach to predict the performance of asphalt mixture [10; 11; 12]. The ageing of bitumen, through the asphalt mortar as an intermediate medium, causes the mixture to become excessively hard and brittle and consequently more susceptible to producing pavement distress [13]. For this reason, some studies have considered asphalt mortar ageing. For instance, [PERSON] et al. investigated the effect of laboratory long-term ageing on the rheological properties of asphalt mortar. The long-term ageing test is a combination ofultraviolet ageing, thermal ageing, and humidity [14]. [PERSON] et al. studied the effects of ageing on the mechanical characteristics of bituminous binders in porous asphalt (PA) concrete. The results showed that ageing increased the tensile strength of the bituminous binders but decreased the strain at break [15]. In addition, the fatigue results showed that the adhesive zone between stone and mortar tended to be the weakest link because there was a bitumen-rich interlayer [16]. [PERSON] et al. evaluated the moisture and ageing damage of asphalt mortar using the repeated direct tensional test method. The results showed that fatigue crack growth of asphalt mortar increased substantially after ageing [17]. [PERSON] et al. quantified the ageing effect on the rheological characteristics of two types of asphalt mortar and applied the results to evaluate the raveling resistance of PA wearing courses in finite element simulations. It was found that ageing had more influence on the complex shear modulus of the base mortar compared to the SBS (Styrene-Butadiene-Styrene) mortar, but its effects on fatigue resistance were the opposite [18]. These studies proved that mortar ageing had a negative influence on pavement performance, such as fatigue and raveling. However, the studies were limited in considering the rheological changes of asphalt mortar subject to various conditions.  
The main objective of this study was to investigate the effect of filler and sand on ageing and determine the evolution of mortar properties due to ageing. To achieve this, two different ageing conditions were applied on mortar by an oven. The ageing method differed with respect to the order of ageing and mixing of the constituents. The chemical composition of asphalt mortar was evaluated by means of Fourier transform infrared (FTIR) spectrometer. Cylindrical mortar samples were then prepared and tested using dynamic shear rheometer (DSR) tests. In addition, the original bitumen was tested after the same ageing conditions as that of asphalt mortar.