Cracking in asphalt materials

This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.Peer ReviewedPostprint (author's final draft

Impact of nanosized additives on the fatigue damage behaviour of asphalt mixtures

The study presented in this paper aimed at evaluating the impact of different nanosized additives, including an organophilic nanoclay and multiwall carbon nanotubes, on the fatigue properties of dense‐graded asphalt mixtures. Cyclic direct tension fatigue tests were carried out, and the corresponding results were interpreted by means of a simplified version of the visco‐elastic continuum damage model. The experimental investigation also included linear viscoelastic characterization of the considered materials. Results derived from tests carried out on the mixtures containing nanosized additives were compared with those obtained for a reference standard mixture. It was found that the use of the abovementioned additives can give a substantial contribution to the enhancement of the fatigue damage resistance of asphalt mixtures. Moreover, when comparing the two types of additives, it was observed that organophilic nanoclays can outperform multiwall carbon nanotubes

Segregation analysis in a family at risk for the Maroteaux–Lamy syndrome conclusively reveals c.1151G>A (p.S384N) as to be a polymorphism

Maroteaux–Lamy syndrome is an autosomal-recessive disorder due to the deficit of the lysosomal enzyme, arylsulfatase B (ARSB). Among the numerous genomic lesions reported till now, the sequence variant, c.1151G>A (p.S384N), has been associated with a severe phenotype in more than 10% of the patients. We now report the first in vivo demonstration of the polymorphic nature of p.S384N, revealed during the segregation analysis in a family at risk for Maroteaux–Lamy syndrome. The proband, compound heterozygous for c.[944G>A]+[245T>G] (p.[R315Q]+[L82R]), did not carry the p.S384N change, which was instead present in two healthy members of the family, in trans with the causative mutations, p.R315Q and p.L82R, respectively. The hypothesis that p.S384N was a polymorphism was further addressed by reverse dot-blot analysis of 400 control alleles, estimating an allele frequency of 4.5%. To predict the consequences of p.R315Q, p.L82R and p.S384N, we also modeled and compared the three amino-acid changes in the three-dimensional ARSB structure. The in silico analysis predicted a local protein misfolding in the presence of p.R315Q and p.L82R. On the contrary, no evident problem was predicted in the case of p.S384N, occurring on the protein surface, far from the active site. Overall, these findings strongly support the hypothesis that the non-synonymous change p.S384N is a polymorphism. Moreover, our results emphasize the need for caution in drawing conclusions from a novel variant allele before screening at least 50 healthy control subjects