A 50-year-old pavement from the city of La Plata (Province of Buenos Aires, Argentina), which had recently been replaced due to significant deterioration (cracks, sinking, etc.), was examined. The aim of the present work was to conduct a petrographic analysis of the concrete, in order to identity the causes leading to pavement failure. Petrographic studies were performed on two slabs and thin sections (ASTM C 856). The coarse and fine aggregate characteristics, the mortar and the paste–aggregate interface were examined, and the reaction products were analysed by XRD and SEM–EDS. The coarse aggregate is an orthoquartzite composed of angular quartz, with some particles exhibiting undulatory extinction, rare argillaceous matrix and microcrystalline siliceous, micaceous and/or ferruginous cement. The fine aggregate is natural siliceous sand. Commonly unfilled microcracks in the mortar and in some interfaces, as well as carbonated zones, were observed. Ettringite in entrained air voids was identified by XRD and SEM–EDS. No evidence of deleterious reaction development (e.g. ARS) was found. Concrete failure was attributed to high heavy traffic as it is an access area to La Plata port and the city.