Compressive Strength and Morphology of Rigid Polyurethane Foam for Road Applications

Abstract

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 (C4H10) or pentane (C5H12). 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 kg/m3, and the ambient mixing temperature and p/d ratio of 0.8 are suggested for P content of 34 kg/m3.