Compressive Strength and Morphology of Rigid Polyurethane Foam for Road Applications

Rigid polyurethane foam (RPUF) is a lightweight material similar to expanded polystyrene foam but which has undergone a safer manufacturing process, for instance without flammable gases such as butane (${\mathrm{C}}_4{\mathrm{H}}_{10}$) or pentane (${\mathrm{C}}_5{\mathrm{H}}_{12}$). RPUF is manufactured from the combination of polyol (P) and diisocyanate (D) and can be used as lightweight and load-bearing materials for pavement applications. This research studied the influence of P content, polyol to diisocyanate ratio (p/d ratio), and mixing temperature of P and D on the compressive strength and microstructure of RPUF. For a particular P content, the increase in mixing temperature and the reduced p/d ratio resulted in a large amount of small-sized cells with high cell-contact pressure. The sufficient cell-contact pressure increased the compressive strength of RPUF and toughness, and extremely large cell-contact pressure caused the cell damage and the reduction in strength and toughness. At low P content, both an elevated mixing temperature to 40°C and reduced p/d ratio improved compressive strength of RPUF. However, at a high P content, the elevated mixing temperature resulted in cell damage, and the ambient mixing temperature of 25°C is recommended. To meet the upper limit of 0.12-MPa compressive strength at 1% strain for geofoam according to current standards the 40°C mixing temperature and p/d ratio of 1.0 are suggested for P content of 23 and $28\mathrm{kg}/{\mathrm{m}}^3$, and the ambient mixing temperature and p/d ratio of 0.8 are suggested for P content of $34\mathrm{kg}/{\mathrm{m}}^3$.