This study investigates the ameliorative effects on some properties of cement-based materials which can be obtained by incorporating rubber particles as part of the fine aggregates. The aim is to find out optimal cement composite/mortar mixtures, containing recycled-tyre rubber particles, suitable for specific engineering applications. Different percentages of rubber particles, from 0% to 75%, were used and, for each percentage, the suitable amount of sand was investigated in order to achieve the best fresh/hardened performances. In particular the following characteristics were examined: density, compressive strength, modulus of elasticity, shrinkage, weight loss, flexural behaviour, thermal conductivity, rapid freezing and thawing durability, and chloride permeability. The experimental results were compared with the ones of cement composite specimens without rubber aggregates. Test results show that the proposed rubberized mortar mixes are particularly suitable for some industrial and architectural applications, such as under-rail bearings, road constructions, paving slabs, false facades, and stone backing. 1. Introduction The growing amount of waste rubber produced from tires has been a major concern in the last decades because tires represent a huge no-biodegradable refusal with danger of fires and proliferation of rats and insects in the stocked refuse mass. The need to explore recycling strategies is so imperious. A variety of waste materials have been suggested as additives to cement-based materials, due to the need to ease the intake of resources for the production of concrete and to improve some performances of concrete with economic and technological advantages. During the last two decades, several international researches have been focused on the properties and performances of rubberized cement matrix composites [1–9]. The rubber obtained from the recycling of waste tyres, in fact, is a promising material with some interesting applications in the construction industry for its lightness, elasticity, absorption capacity of energy, and acoustic and thermal insulation. Rubber derives from postconsumption tires subjected to mechanical trituration or to cryogenic processes; the textile components are sometimes removed and the steel fibers unstrained. The rubber surface is usually subjected to chemical pretreatments to obtain an improvement of some final properties of concrete. It is very important to specify the rubber source because it influences the characteristics of concrete/mortar for the constituent materials, proportion of the components,
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