Luís Picado-Santos

Production of Hot-Mix Asphalt with PMB: Compactability and Mechanical Behaviour Characterization

The traditional approach used to select production (mixing and compaction) temperatures for hot-mix asphalts (HMA) with polymer modified bitumens (PMB) often lead to extremely high temperatures, which increase energy consumption and may cause bitumen-polymer bond degradation. Moreover, field experience indicates that lower temperatures can be used without compromising aggregate coating with bitumen and on-site compaction. This paper presents a lab study aiming to assess the influence of production temperatures in the on-site paving operations and the in-service performance of asphalt pavements. An AC 14 Surf PMB 45/80-65 (EN 13108-1) was produced and compacted at three different mixing-compaction temperatures groups, based on the suppliers’ recommendation and the temperatures determined with the traditional (Superpave) and the high-shear rate viscosity (HSRV-E) methods. The results showed an important effect of the production temperatures in the asphalt behaviour. Minimum compaction resistance value was obtained with the Superpave temperatures while HSRV-E produced the highest resistance. The water sensitivity test values and the rutting resistance values were very similar for the three temperatures groups. Independently of the test frequency, the stiffness modulus was always higher for the HMA produced at the suppliers’ recommended temperatures. The resistance to fatigue is very similar for the Superpave and HSRV-E temperatures, and higher than with the suppliers’ recommended temperatures. Fatigue resistance was not affected by the use of a higher mixing temperature, recommended by the Superpave method. The best performance was not obtained with any single temperatures group tested and the results show that both mixing and compaction temperatures are very important for the HMA behaviour.

Assessment of warm-mix asphalt concrete containing sub-products as part of aggregate blend

ABSTRACT The study compares warm-mix asphalt concrete (WMA) and a traditional hot mix asphalt concrete (HMA), evaluating permanent deformation, fatigue, stiffness modulus, and water sensitivity. The cost (construction only) differences are also addressed. Three WMA blends were prepared. One WMA was manufactured with the stand alone organic wax and incorporated 60% of recycled concrete aggregate (RCA). The other two used organic wax embedded in cellulosic fibres, one of them incorporated 35% of reclaimed asphalt pavement (RAP), and the other had no added sub-product. Trial sections were constructed with plant-produced mixtures, laid and compacted with conventional equipment. When considered a global indicator representing mixtures mechanical behaviour involving deformation, rutting, fatigue and moisture resistance, the results showed that performance of WMA blended with RAP and RCA was similar to HMA, and the conventional WMA was 25% better. The construction process proved to be feasible for any WMA. The direct construction costs as compared to conventional HMA were 6% higher for the conventional WMA and 5–8% lower when WMA used sub-products. The use of these sub-products is aimed to find innovative approaches to be undertaken throughout the product lifecycle, from manufacture through reuse, with the goal of reducing waste going to landfill.

Tecnico accelerated ageing (TEAGE) – a new laboratory approach for bituminous mixture ageing simulation

ABSTRACT The available methods for accelerated ageing simulation in laboratory of compacted bituminous mixtures are often not representative of the ageing mechanisms experienced in the field. The objective of this study was to develop an alternative ageing method, Tecnico accelerated ageing (TEAGE). The method is intended to simulate the ageing of bituminous mixtures under specific environmental conditions by applying watering/drying cycles and ultra-violet (UV) radiation in equivalent levels to those observed in the field during a certain time. In this study a type of mixture was aged using TEAGE and LTOA (long-term oven ageing) methods and then tested for mechanical performance conducting stiffness, fatigue resistance and indirect tensile strength tests. Additionally, the chemical composition of the water used for the watering/drying cycles was analysed and recovered binders were tested for softening point and penetration. TEAGE-aged specimens showed clear evidence of an ageing gradient through the specimens’ depth, substantial reduction in fatigue life (15% reduction in Ԑ6) and a visible effect on the colouration of the UV exposed surface when compared with LTOA-aged specimens. The overall results and comparison with other studies indicate that TEAGE framework addressed in a more consistent way the ageing mechanisms that could be seen in the field.