Influence of acetic acid and calcium hydroxide treatments of rubber waste on the properties of rubberized mortars

The main goal of this study consisted in improving the performance of cementitious materials containing a percentage of rubber particles as a substitution for aggregates. Rubber surface was modified: new chemical and simple treatments based on calcium hydroxide or acetic acid solutions were applied. The effect of the above treatments was compared with that produced by sulphuric acid or sodium hydroxide solutions or by the use of plain rubber particles, already studied and reported in the literature. Fourier transformed infrared spectroscopy-attenuated total reflectance (FTIR-ATR) was used in order to characterize the rubber surface and chemical modifications. The rubber particles were observed by optical microscopy (OM) with the aim of detecting the possible physical changes on their surface. Then, the modified rubber particles were included in the composition of mortar specimens and their properties in the fresh (consistency) and the hardened state (porosity, flexural and compressive strength, capillarity water absorption and ultrasonic pulse velocity, UPV) were examined. Regarding the properties of rubber particles, their surface hydrophilicity, absorption and roughness increased after acid or alkaline treatments. Considering mortars including chemically treated rubber particles, calcium hydroxide gave rise to mortars with lower porosity and acetic acid to mortars with lower density. Mechanical properties of mortars were improved in comparison with these properties in mortars containing plain rubber particles. Alkaline solutions prompted the highest values of compressive strength. A delay in the hardening time for rubberized mortars may be deduced from the mechanical properties evolution. The partial substitution of natural aggregates by chemically treated rubber particles, improves the properties, in terms of flexural and compressive strength, of rubberized mortars.