Microscopic and microanalytical investigation of concrete for road pavement slabs and highway pylons

Cement has good compressive properties but poor tensile strength, which is critical of its composites. To solve this challenge, in the last decades, different types of reinforcing fibers, such as glass, carbon, polyvinyl alcohol, steel, asbestos, aramid, or cellulosic fibers have been used. The main benefits of adding reinforcing fibers in cement are the improvement of tensile strength, flexural strength and toughness, due to this, in the late 1960s in some European motorways, have been used concretes for road pavement slabs and for pylon with asbestos and fibrous minerals in the mixture. Anyway, the cumulative traffic loading and the exposure to weathering, especially the impact of chloride diffusion for use of de-icing salt, can induce severe degradation phenomena affecting both the concrete and the asbestos mineral fibers. Highway and street pavements are massive civil infrastructures. Highway and street pavements are massive civil infrastructures and in Italy, in the last decade, the structural suitability of hundreds of thousands of kilometers of motorways is under verification due to degradation phenomena.

A combination of different analytical methods was used to characterize concrete samples affected by self-passivating due to calcite fouling and biofilm, presumably mainly caused by transporting water rich in salts. Samples have been studied by optical microscopic observation and by Scanning Electron Microscopy-Energy Dispersive (SEM-EDS) analysis. It has been hypothesized that seasonal variations of water temperature and high chemical interaction water-concrete should be responsible for the hydrolysis and Ca leaching that cause the degradation of the cement paste and the exposure of asbestos mineral fibers to weathering.

Potential risks during maintenance interventions should be taken into consideration, in this light, mineralogical and petrographic characterization of concrete for road pavement slabs and for pylon is a useful tool for investigating the presence of potentially dangerous minerals that required caution during degradation product removal with methodologies that pulverize the samples. To prevent effective post-degradation transformation into elements harmful to health and the environment, careful monitoring is recommended.