*Article* **Experimental Evaluation of Cement Mortars with End-of-Life Tyres Exposed to Different Surface Treatments**

**Eduardo García 1, Bárbara Villa 2, Mauricio Pradena 1,3,\*, Bruno Urbano 2, Víctor H. Campos-Requena 2, Carlos Medina <sup>4</sup> and Paulo Flores <sup>4</sup>**


**Abstract:** An end-of-Life Tyre (ELT) is a type of waste that can generate negative social and environmental impacts due to its disposal. Considering that rubber can improve concrete properties and the massive use of concrete as construction material, the addition of ELT rubber in concrete mixes is attractive. However, concrete mechanical properties are negatively affected due to the rubbercementitious matrix interaction. Although rubber treatments have been developed to minimise the negative effects, the geo-dependency of the mix makes necessary to find cost-effective and practical solutions that will allow a real use of the ELT waste. Therefore, the objective of the present study is to characterise the properties of cement mortars with the addition of ELT rubber under three surface treatments: hydration, oxidation-sulphonation, and hydrogen peroxide. The results show that hydration is the most favourable treatment from a technical, practical, and economical point of view. In fact, with this treatment, it is possible to add up to 5% ELT rubber, with respect to the aggregate weight, and still exceed the design strength without adding more cement or additives as other investigations. The use of Portland Pozzolana Cement, with local fly ash waste, contributes as well to the promissory results obtained.

**Keywords:** cement mortar; End-of-Life Tyre; waste; surface treatment; compressive strength; flexural strength; workability; fly ash
