CONICET | Buscador de Institutos y Recursos Humanos

The shelf-life stability of some redispersible polymer powders (RDP) used in the dry-mix mortar industry can be affected when subjected to rough climate conditions such as elevated temperature and exposure to moisture. This instability can be owed to the ageing of the anhydrous cement, the ageing of the polymer and the reaction of the cement with the RDP during the storage.In this project, two RDP latex of known chemistry were blended with anhydrous cement, simulating the conditions during storage of a dry mix mortar, and stored in a climate chamber at 40 ± 5 °C and 90 ± 8 % relative humidity. The goal was to evaluate the moisture-induced prehydration of the cement. Furthermore it was sought to find out whether the latex formed a film under those conditions. The storage periods were one, three, seven and fourteen days. The aged materials were studied by means of scanning electron microscopy, X-Ray microanalysis and isothermal calorimetry. The final properties of the dry mix mortar after storage were measured after 28 days of curing. The study revealed that the RDP did form a film when aged with cement, which however prevented the undesired prehydration of the cement. This way, the mechanical properties of the aged mortars were reduced much less than in the absence of RDP.