In the Netherlands Blast Furnace Slags (BFS) are used as a self-cementing road base material on a wide scale for many decades. An example is the motorway A32 which was built in the years 1986-1988. Some 10 years after construction the first transversal heaves occurred at the asphalt pavement surface. Since then the number of heaves has considerably increased and the heaves kept on growing in height. Finally the pavement was fully reconstructed in 2008 and 2009. In 2007 an extensive research was initiated into the performance of the BFS base material on the motorway A32. This research included: (1) Inventory of the number, length and height of the transversal heaves at the pavement surface. (2) Falling Weight Deflection measurements at some heaves, but also in between some heaves, from which the modulus value of the BFS road base was backcalculated. The modulus values show an extreme variation. (3) Materials research on bound BFS base material obtained by taking cores. The modulus of elasticity, compressive strength, tensile strength and coefficient of linear thermal expansion has been investigated. (4) Development of a mechanical model which describes the birth and growth of the heaves. The model enables to quantify the effects of the magnitude of the mechanical properties of the BFS road base and the season of construction of the base on the development of the pattern of transversal heaves. (5) Chemical and mineralogical analyses of the BFS road base material. This research is intended to indicate possible deleterious reactions and their effects on the long-term performance of BFS.