Modification effects of nanosilica on asphalt binders: A review

Nanosilica (NS) may be obtained as a by-product in several industrial processes and is associated with high availability and affordability among other nanoadditives. NS has been used for asphalt modification, and improvement in high-temperature performance and several other physical properties has been reported. However, due to the wide varieties and intrinsic variability of asphalt materials, concerns have been raised about the reproducibility of some conclusions, and therefore, a review was conducted. According to the results, NS additives with a purity of over 99% were usually used for modification and the specific surface area was over 100 m(2)/g, leading to the superior absorption of asphalt and thus improvement in rutting resistance of the mixtures. Due to a lack of guidance for the blending procedures, inconsistency exists among studies in the shear speed, blending duration, and temperature, leading to possible excessive blending and unnecessary energy and time consumption. Rises in NS concentration would cause higher softening point and rotational viscosity, and therefore elevated temperatures for mixing and paving, but penetration would be reduced. According to rheological evaluations, with the rise of NS concentration, the rutting parameter would increase, indicating an improvement in the high-temperature performance, but the low-temperature performance may deteriorate.