Microstructural examination and potential application of rendering mortars made of tire rubber and expanded polystyrene wastes

This paper studies the microstructure and potential application of rendering mortars containing tire rubber and expanded polystyrene wastes. The mortars were scanned at the Centre for X-ray Tomography (UGCT - Ghent University) and the μCT images were studied using 3D analysis software package Octopus. The samples' porosity increased due to the incorporation of the wastes and particularly, expanded polystyrene. Optical microscopy (thin sections) and SEM examination showed that tire rubber particles were not entirely bonded to cement, while expanded polystyrene showed better adhesion to the matrix. In addition, EDS Ca-mapping analysis confirmed expanded polystyrene was almost totally enclosed by a cementitious phase rich in calcium. The practical application of the mortars was tested taking into account the basic requirements applicable to rendering mortars (EN 998-1 standard). Despite the above microstructural limitations, it was found that using low doses of sodium oleate (0.25% w/w) the mortars accomplished the highest performance in terms of capillary water absorption and mechanical strength.