Mechanical characterization and influence of water on WMA by adding synthetic zeolite

The Warm Mix Asphalt (WMA) can be produced through different techniques, including the use of asphalt emulsion, waxes and paraffins, two binder components (soft and hard) and synthetic zeolite. Synthetic zeolite is principally composed of a siliceous structure with large and interconnected spaces, which can accommodate molecules of water. Synthetic zeolite can hold water in its structure at low temperatures and drive it out after heating. From a technical point of view, at mixing temperature, synthetic zeolite gradually releases a small amount of water and, as a consequence of water vapor emission, generates a foaming effect in the bitumen. This process allows to increase the workability of the asphalt mixture or lower mixing and laying temperatures. However, the released water could affect the adhesion between aggregates and bitumen or the cohesion of the mastic. The present experimental project was conducted in order to investigate mechanical performance and the influence of water on WMA by adding synthetic zeolite. Two bituminous mixtures were studied, an HMA as referred material and a WMA by adding synthetic zeolite. Static test (Marshall test) and dynamic test (Indirect Tensile Stiffness Modulus) were carried out in order to evaluate the mechanical properties of WMA in comparison to HMA. Since the presence of residual moisture in the aggregate blend during the mixing phase of WMA might affect the adhesion between aggregate and bitumen, the experimental program was extended with Indirect Tensile Test in wet and dry conditions. Moreover, the water sensitivity was also investigated in terms of stripping of the asphalt film from the aggregate surface by means of the Ancona Stripping Test.