Polyalkylated gallic esters and acids, high performant warm mix asphalt and adhesion promoters for bitumen

The main use of bitumen is the construction of road pavements due to its role as binder in asphalt concrete. For this specific scope, it is important for bitumen to have low viscosity so that the working temperature is the lowest possible. This would allow it to be easily processed while reducing the toxic fumes emanated during coating. Furthermore, the final product must be resistant to aging phenomenon and harsh weather conditions while also having a good affinity with the stones underneath in order to avoid its peeling off the road with time. To achieve all these stipulated objectives, the addition of chemical additives to asphalt concrete is being studied. In the present study, bitumen has been modified by incorporating (1% w/w) alkylated gallic esters and acids of alkyl chains of different length (8, 14 and 18 carbon atoms) in low amounts with the aim of improving the rheological properties of bitumen as well as increasing the interaction forces between bitumen and stone aggregates usually employed as underneath layer for road pavement. For this purpose, gallic ester/acid additives were tested as rheological modifiers, adhesion activators and Warm Mix Asphalt (WMA) agents through Differential Scanning Calorimetry, Thermogravimetric measurements, Dynamic Shear Rheology and Boiling tests. The results show that alkylated gallic acids are bad WMA candidates increasing the viscosity of bitumen while corresponding gallic methyl esters are excellent for WMA showing that the shorter the chain, the better the performance. Thus, C8 alkylated methyl gallate decreases the overall viscosity of bitumen of about 70 Pa s at 70°C, which is nearly 4 times better than what commonly employed commercial waxes provide. Furthermore, gallic ester and acid derivatives are excellent adhesion activators showing increased efficiency as the alkyl chain length increases reaching a 95% coverage on Trentino porphyry stones obtained from the boiling test carried out on the C18 alkylated methyl gallate sample.