To improve the workability in gypsum plasters, additives are sometimes used, including citric acid, which provides acceptable setting times for low w/g ratios, maximizing the mechanical properties of the material. The influence of citric acid on the fire response of gypsum coatings is not well known, and so our aim was to analyze the effects that citric acid produces on the behavior of gypsum plasters exposed to fire. Temperature measurements were made with sensors and thermal imaging cameras while other instrumental techniques, including SEM, XRD and TG, were used to characterize the microstructure and composition of gypsum materials subjected to the action of fire. The fire had a greater effect on gypsum plasters containing citric acid as revealed by the cracking patterns and heat propagation profiles observed. Likewise, micro-cracks were observed in gypsum specimens, containing and non-containing citric acid, exposed to fire. In all cases, the alterations were consistent with the temperature profiles and chemical composition of the faces whether exposed to fire or not.

The addition of inorganic expanded aggregates, such as perlite or vermiculite is well known in gypsum plasters. However, the reuse of organic wastes in coatings like plasters and renders has been poorly studied. This paper shows the effect of tire rubber wastes on the mechanical properties and fire performance of gypsum plasters. The rubber waste was added to the mixture in mass percentages of 14.50% (C1) and 46.60% (C2). Flexural and compressive strength of plasters made with rubber wastes was visibly reduced as well as their surface hardness (Shore C). In addition, fire tests produced major damages through the entire 2 cm thickness of samples containing rubber wastes, as it was corroborated by X ray diffraction (XRD) and Thermogravimetric (TG) analysis. The heat transfer due to fire exposure modified considerably the chemical composition of plasters, since, on the non-exposed face to fire, the amount of gypsum (CaSO4·2H2O) equivalent to mass loss obtained by TG due to water released by these plasters made with rubber wastes, was 5.4-7.2 lower than that of conventional plasters. The results suggest that certain wastes may reduce the efficiency of gypsum plasters in protecting underneath construction and structural elements against fire.

El uso del yeso en el patrimonio arquitectónico ha sido muy variado, siendo muy importante su uso como material de revestimiento de otros elementos constructivos, ya que presenta importantes ventajas como transpirabilidad, adherencia, sensación de calidez y aislamiento térmico. Además, el yeso se considera un material excelente cuando se expone a fuego debido a que contiene agua en su composición química que hace que una cantidad importante de la energía térmica sea absorbida por el yeso reduciendo la transmisión de calor a los elementos que reviste y materiales cercanos. Es un material incombustible y no libera sustancias tóxicas por efecto del fuego. La cantidad de agua de amasado influye en las propiedades del yeso. A mayor relación a/y mayor trabajabilidad, menor densidad y menores resistencias. La influencia de la relación a/y en el efecto del fuego en revestimientos de yeso tradicionales no se conoce bien. El objetivo de este trabajo consiste en analizar el efecto que produce el fuego en revestimientos de yeso con diferente relación a/y, para lo cual se elaboraron probetas con relaciones 0.4 a/y y 0.7 a/y y se usaron medidas de temperatura con cámara termográfica y otras técnicas instrumentales (SEM, DRX y TG) para caracterizar la microestructura y composición de los yesos sometidos a la acción del fuego. En general, los estudios realizados no mostraron diferencias sustanciales entre las composiciones estudiadas si bien es cierto que el fuego produjo un considerable deterioro del conglomerante.

No abstract

No abstract