In 1979, during the construction of the motorway A3 Regensburg – Passau, southeast Germany, an embankment had to be built. The soil for this embankment was treated with quicklime to accelerate the chemical reaction and shorten the time for earthworks. The treatment results in water reduction, pozzolanic hardening and carbonation of the lime. Previous studies never addressed the scale of these reactions. Here, the degree of carbonation and pozzolanic reaction were determined for the first time to provide evidence for the long-term stability of lime-improved earthworks on a structure with high and long-term stability. In 1990 and 2013, samples from this embankment were taken and examined. The samples were tested using methods for compressive strength and chemical analysis. After 34 years, the results show compressive strengths up to 6 MPa, with 37% of the quicklime being used in carbonation and 47% in pozzolanic reactions. Sixteen per cent free CaO is still available.