Lightweight Cement Conglomerates Based on End-of-Life Tire Rubber: Effect of the Grain Size, Dosage and Addition of Perlite on the Physical and Mechanical Properties

Abstract

Lightweight cement mortars containing end-of-life tire rubber (TR) as aggregate were prepared and characterized by rheological, thermal, mechanical, microstructural, and wetting tests. The mixtures were obtained after total replacement of the conventional sand aggregate with untreated TR with different grain sizes (0–2 mm and 2–4 mm) and distributions (25%, 32%, and 40% by weight). The mortars showed lower thermal conductivities (≈90%) with respect to the sand reference due to the differences in the conductivities of the two phases associated with the low density of the aggregates and, to a minor extent, to the lack of adhesion of tire to the cement paste (evidenced by microstructural detection). In this respect, a decrease of the thermal conductivities was observed with the increase of the TR weight percentage together with a decrease of fluidity of the fresh mixture and a decrease of the mechanical strengths. The addition of expanded perlite (P, 0–1 mm grain size) to the mixture allowed us to obtain mortars with an improvement of the mechanical strengths and negligible modification of the thermal properties. Moreover, in this case, a decrease of the thermal conductivities was observed with the increase of the P/TR dosage together with a decrease of fluidity and of the mechanical strengths. TR mortars showed discrete cracks after failure without separation of the two parts of the specimens, and similar results were observed in the case of the perlite/TR samples thanks to the rubber particles bridging the crack faces. The super-elastic properties of the specimens were also observed in the impact compression tests in which the best performances of the tire and P/TR composites were evidenced by a deep groove before complete failure. Moreover, these mortars showed very low water penetration through the surface and also through the bulk of the samples thanks to the hydrophobic nature of the end-of-life aggregate, which makes these environmentally sustainable materials suitable for indoor and outdoor elements.

Recycled Materials in Civil and Environmental Engineering

“…In the papers by Petrella and coworkers [ 8 , 9 ], industrial and agricultural by-products such as end-of-life tire rubber and wheat straw were used as aggregates for the production of unconventional cement mortars prepared by a cheap and environmentally safe process. The artifacts resulted in thermal insulating with respect to the sand-based references, while the presence of another aggregate as perlite was used to improve the mechanical strengths with no detrimental effects on the thermal conductivities due to the porous nature of the inorganic material [ 10 , 11 ].…”

Selected issues concerning the use of Shredded Rubber Waste (SRW) in binder-bound mixtures

“…-Geotechnics (lightweight embankment fill, ground improvement, slope stability improvement, retaining wall construction, drainage and cut-off layers, road culverts) [28,29,[38][39][40][41]; -Technologies for the production of mineral and asphalt mixtures [28,29,33,42,43]; -Production of lightweight concretes [30,34,35,[44][45][46][47][48][49][50][51][52][53][54][55][56].…”

Experimental Investigation on Environmentally Sustainable Cement Composites Based on Wheat Straw and Perlite

“…In terms of the circular economy, these conglomerates were in accordance with current policies for environmental sustainability. Worthwhile processes were being carried out since these artifacts were prepared by a cheap process in which pre-treatment of renewable aggregates and complex or expensive procedures were not required [37,[66][67][68][69][70].…”