Effect of Superpave Restricted Zone and Type of Filler on Hot Mix Asphalt Performance

Abstract

Load-induced pavement fatigue damage and rutting have become problematic on several road national pavements that are subjected to heavy static and dynamic traffic loads. The need for accurate and consistent laboratory tests of the volumetric properties of the hot mix asphalt (HMA) has become increasingly important in recent years. The objective of this study was to evaluate the effects of the Superpave defined restricted zone on HMA performance and determine the resulting improvements in pavement performance due to addition of hydrated lime and Portland cement to HMA mixes. To study these effects, a set of experiments included one gradation that violated (through) the restricted zone (TRZ), two gradations below the restricted zone (BRZ), and one gradation above the restricted zone (ARZ) with one type of binder. These were subjected to Marshall tests, analysis, and evaluation. From the analysis, it was found that mixes having gradations violating (TRZ) and passing above the restricted zone (ARZ) performed better than the mixes with gradations below the restricted zone (BRZ) with respect to laboratory tests. This conclusion was drawn from the results of experiments using 19.0 mm maximum aggregate size gradations and 75-blow design. The aggregates used were crushed aggregates (basalt) with different sizes, natural sand, and natural filler. One type of asphalt cement was used with 40-50 penetration grade and the design traffic level was taken to be greater than 106 EAL. Marshall test was used to evaluate HMA performance. The results also showed mixes having gradations below the restricted zone, which was commonly recognized to be rut-resistant, have lower stability than that having gradations above or through the restricted zone. VI In the second set of experiments, comparison was made between the effect of natural filler and that of hydrated lime on stability, flow, and stripping resistance. Two mixes were used, one below and the other above restricted zone. The results showed that the addition of lime increases the stripping resistance remarkably, on the other hand decreases stability, and increases flow. In the third set of experiments, comparison was conducted between the effect of natural filler and that of Portland cement on Marshall stability and flow with mix passing above the restricted zone, using data obtained from quality control tests performed during the paving of Al-Mak Nimir Bridge in 2008. Three mix designs were used in this comparison; the first one with three percent natural filler, the second with three percent cement, and the third with five percent cement. The results showed that the addition of cement increased the stiffness of asphalt mix, increasing stability and decreasing flow.