Durability of expanded polystyrene mortars

The influence of the addition of various types and various concentrations of expanded polystyrene foam (both commercial and recycled) on the durability of Portland cement mortars is studied. In particular, the microstructure is studied utilizing the following methods: capillary absorption of water, mercury intrusion porosimetry, impedance spectroscopy and open porosity. In addition, the effects of heat cycles and freeze–thaw cycles on compressive strength are examined. Scanning electron microscopy is used as a complementary technique. An air-entraining agent, water retainer additive and superplasticizer additive are used to improve the workability of mortars. The results show that the presence of expanded polystyrene in mortar results in a decrease in the capillary absorption coefficient. The mercury intrusion porosimetry technique and the equivalent circuits previously used by researchers to interpret impedance spectra of ordinary cementitious materials were found to be inadequate for interpreting the microstructure of mortars with expanded polystyrene. This is due to the polymeric nature as well as the internal porous structure of expanded polystyrene. A slight increase of compressive strength is observed in mortars with expanded polystyrene subjected to heat cycles. The compressive strength of mortars subjected to freeze–thaw cycles likely improves because expanded polystyrene particles absorb part of the pressure of ice crystallization. It is concluded that the durability of mortars improve with the presence of expanded polystyrene, making them viable for more sustainable usage in masonry, stucco and plaster mortars.The authors wish to thank the Spanish Ministry of Science and Innovation and European Union (FEDER) for the BIA2007-61170 project funding, in the framework of which this work has been done, and the FPI scholarship (BES-2009-012166) award to Verónica Ferrándiz Mas which allows her to develop her doctoral thesis, which this present work is part