Waste tire rubber particles modified by gamma radiation and their use as modifiers of concrete

Gonzalo Martínez-Barrera, Juan José del Coz-Díaz, Felipe Pedro Álvarez-Rabanal, Fernando López Gayarre, Miguel Martínez-López, Julián Cruz-Olivares
2020 Case Studies in Construction Materials  
A B S T R A C T Nowadays the excessive amount of waste tire rubber generates serious environmental problems. One of the alternative ways for its recycling is as filler in cement concrete. Nevertheless, as it is known recycled materials added to cement concrete decrease certain mechanical properties due to the poor adhesion between fillers and cement matrix. For resolve this problem, ionizing radiation has been used. For these reasons, in this work, cement concrete specimens were produced with
more » ... ere produced with cement, water, rock crushed and sand; this last was partially substituted by particles of waste tire rubber. Then the compression properties of the specimens were evaluated following the experimental parameters: a) gamma irradiation dose (200, 250 and 300 kGy), b) particle size of tire rubber (0.85 and 2.8 mm), and c) particulate concentration of tire rubber (1, 3 and 5 wt. %). In addition, the mechanical compression results were related with the changes on the physicochemical properties of the irradiated tire particles, which were analyzed by Fourier Transform Infrared (FT-IR), Raman and UV-vis spectroscopies, as well as by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA) an Differential Scanning Calorimetry (DSC). The results show improvements on the: a) elasticity modulus, up to 161 %, for cement concrete with non-irradiated particles of tire rubber, and up to 108 % when adding irradiated ones, b) deformation, up to 21 %, when adding non-irradiated tire particles; and c) compressive strength up to 8 % when adding non-irradiated tire particles. Such improvements on the mechanical features were related with the physicochemical changes provoke by gamma rays on the waste tire particles. Such changes were evaluated by the mentioned analytic techniques. Every year millions of waste automotive tires are produced, 75 % of them are thrown into landfills and illegal dumps, and the remainder go to cement manufacturers as alternative fuel; which is a current practice in many countries [1] . Environmental and social problems are generated by such final disposition as well as for the slow degradation of the tire rubbers. During the burning of tires in open places, there are not control on the emissions of aromatic hydrocarbons, nitrogen dioxide, sulfur dioxide, carbon monoxide and suspended particles. In consequence, the air quality and the human health are deteriorated. Moreover, concentration of waste tires in urban zones generate leachates, and together with the contaminants (aluminum, zinc, manganese, iron, cadmium, lead and organic compounds) contaminate soil, surface water and groundwater. In addition, due to its hydrophobic characteristic, the waste tires thrown into illegal dumps hold water and becoming breeding grounds for disease-carrying mosquitoes [2] . Applications of waste tires in asphalt pavements have been effective, but not enough for reducing their quantity in landfills and illegal dumps. Nevertheless, an alternative is to use them as partial substitute of fine or coarse aggregates in cement concrete. According to the published works, rubberized concrete shows improved properties, for example: a) high resistance to freeze-thaw, acid attack and chloride ion penetration. In addition, silica fume enables to achieve high strength and high resistance to sulfate, acid and chloride environments [1], b) durability properties, water absorption and permeability increase with increasing crumb rubber concentrations, for cement concrete specimens with crumb rubber (up to 5.5 wt. %), as a substitute of fine aggregates. Nevertheless, the workability, compressive and flexural strength decreases with increasing crumb rubber concentrations. Moreover, the abrasion resistance also decreases due to low adhesion between crumb rubber and cement paste [3], c) the abrasion resistance increases with increasing tire rubber concentration, for concrete with replacing up to 20 % of fine aggregates by tire rubber particles (0.6-4.0 mm). High abrasion resistance can ensure applications where abrasive forces between surfaces and moving objects are present, for example, in pavements, floors and concrete highways [4] . In other studies, d) the freeze-thaw resistance of concrete increases, up to 89 %, when crumb rubber concentration increase (5-20 %), which replacing sand. Nevertheless, some properties decrease, as the compressive strength values (up to 68 %), the ultrasonic pulse velocity and the capillary-wall thickness and the pores space [5], e) improvements on the abrasion resistance and water absorption, not so for compressive strength, flexural tensile strength, pull-off strength and depth of water penetration, for high strength cement concrete with scrap tire rubber, replacing the natural fine aggregates (up to 20 %). In particular, the crumb rubber may be used up to 12.5 wt. % for obtaining strength above 60 MPa, or to use 2.5-7.5 % crumb rubber for diminution on the depth of chloride penetration, have little loss of the weight and compressive strength after acid attack [6, 7] . In the case of self-compacting rubberized concrete (SCRC): f) highest compressive and tensile strength values were obtained for concrete with different concentrations of crumb rubber (10-40 %) and different size (2, 5 and 10 mm) [8]; g) the deformation and energy absorption increase, not so for workability and mechanical properties, for concrete with crumb rubber (10-40 %), heating from 100 C to 600 C. The fine aggregates were replaced with 2-5 mm crumb rubber particles, and coarse aggregates by 5-10 mm crumb rubber [9] . Combination of waste rubber and polymers have been used as fillers into cement concrete, for example: a) waste crumb rubber (15 wt. %) and polyethylene terephthalate (PET) (5, 10 or 15 wt. %) with 9 mm size, for producing sustainable and ecologically safe concrete submitted to acidic environment. The results show highest resistance when adding PET or PET and crumb rubber particles, after 60-day sulfuric acid exposure [10], b) crumb rubber (CR) and steel fibers coated with rubber (FCR), were added (20-100 %), as substitutes of mineral aggregates. The results show diminution on the mechanical properties and thermal conductivity for high concentrations of CR and FCR. Moreover, concrete with FCR had higher mechanical values than that with CR [11] . There are a lot of information concerning to add tire rubber for improvement of the mechanical properties of cement concrete. Nevertheless, information concerning to add irradiated materials into concrete is very limited. Respect to the effects of gamma irradiation on the physicochemical properties of tire rubber, a lot of studies have been reported, but not so for its use as filler into concrete. Mainly, those studies related to natural rubber (NR) and styrene butadiene rubber (SBR). The latter is a mix of the styrene and butadiene monomers, which is polymerized either by solution or emulsion processes. The SBR have good abrasion resistance and aging stability when protected by additives. In a study, natural rubber and styrene butadiene rubber were irradiated from 50 kGy to 250 kGy. The results show improvement on the tensile strength and tensile modulus as well as high thermal stability. Nevertheless, the elongation at break decrease when gamma radiation dose increase. Such results are due to cross-linking and scission of the polymer chains caused by the irradiation process. In fact, higher values on the cross-linking density generate better thermal stability, as it is known, ionizing radiation cause thermal decomposition of vulcanizates and increase the density [12, 13] . In other study, the tensile strength, hardness and gel content increase according to gamma radiation dose increase (up to 100 kGy), in mixtures of styrene-butadiene rubber (SBR) and waste tire rubber [14] . In the case of crumb rubber, it was irradiated at 300 kGy, shown ductility at low temperature, stability at high temperature and high anti-aging performance [15] . As it is known, there a lot of information concerning to heavy density concrete and its use as shielding against gamma rays, for example, it is known that the shielding efficiency and mechanical properties of the concrete depended on the concentrations and the type of coarse aggregates (magnetite, barite, goethite, serpentine) and fine aggregates (silica fume, fly ash, ground granulate blast-furnace slag) [16] . Nevertheless, little information about ionizing radiation applied to polymer
doi:10.1016/j.cscm.2019.e00321 fatcat:xlpi34wafjbldojoow5b2gu3da