Content area
Abstract
Bitumen content of 5.9% for gradation type 1 with 3% filler content, 6% for the same gradation and 5% filler and about 6.2% for the same gradation with 7% filler were found to be the optimum bitumen contents. Similar studies were undertaken to determine the optimum bitumen contents of the specimens from the type 2 gradation group. The results indicate that the optimal bitumen content rises in comparison to that of the gradation type 1. The filler stiffens the binder, which is reflected in the observation that E increases in most cases with increasing the filler content. Additional specimens were tested to obtain more precise results. On the basis of these results, it was recognized that the peak value of [Young]'s modulus occurred at a bitumen content close to the optimum bitumen content of the mixtures. For all bitumen contents, the specimens with greater F.P% exhibit a greater Young's modulus (E). There is a balance between achieving higher density and higher E. If a mix has high shear resistance due to a high fraction of fractured particles, it is more difficult to compact, which could reduce density while keeping E higher. The presented effective range of filler content could be discussed on the basis of the Rheological impact of filler content for HMA mixtures. Some deviations from the presented amount were observed in the case of different F.P% for each group of gradations. This could be because interlocking particles of the gradation with 90% F.P are held weakly together in comparison to those of 100% F.P gradation, and therefore, different voids are provided. Similar studies were undertaken on the type 2 gradation, and those results are also presented in Fig. 2.
Many factors affect the mechanical properties of HMA mixtures, such as the percent of fractured particles (F.P %), bitumen content, temperature, gradation and filler content [1, 2]. Based on the literature, it would be useful to study the relation between Stiffness Modulus (SM) and UPV test parameters. For this purpose, the first step is to investigate the effect of different mix parameters and the accuracy of results presented by UPV. The purpose of Non-Destructive Test (NDT) methods is to obtain information on a given structure without causing any destruction or damage to the investigated area. Various NDT methods have been developed and applied in engineering with varying degrees of success [3-5]. Current wavebased NDT methods, such as UPV, impact echo, and spectral analysis of surface waves (SASW), have been used for the evaluation of material properties. In this study, the variation of UPV test results of HMA mixtures with regard to changing the gradation, filler and bitumen contents of mixtures were investigated. Assessment of the UPV test results were done by means of a comparison of the indirectly derived Young's modulus of the HMA specimens from the UPV test and their stiffness modulus from ITSM test.