In this chapter, we propose the use of gamma radiation as a method for modifying waste materials; for instance, polyethylene terephthalate plastic bottles, automotive tire rubber, and the cellulose in Tetra Pak containers, and their reuse to enhance the properties of concrete. Evolution of Ionizing Radiation Research. Concrete is the most widely used structural material in the world, due to its easy preparation and low cost.
Nevertheless, it has some disadvantages: a pores, which can become entrance points for water, water vapor, gases and chemical substances that might damage concrete; b the rapid deterioration in roughness of the concrete surface because of its high abrasion; c poor resistance to aggressive substances and salty water; and d low resistance to heating.
One alternative for remediating these problems is the incorporation of polymeric materials, which bind well with mineral aggregates that are the main components of concrete. Currently, because of the more stringent legislation regarding the environment and the market demand for environmentally friendly products, manufacturers are interested in developing approaches aimed at reducing the environmental impact of industrial processes through reductions in the amount of residues produced or by treating those that are inevitably generated.
The environmental damage caused during the extraction of raw materials, as well as the high cost of extraction methods, provides good motivation for the use of industrial and domestic residues as substitutes or complements of fresh materials in several areas of manufacturing. The depletion of reliable, secure raw material reserves and conservation of non-renewable sources are also incentives to develop ways to reuse waste materials.
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In recent years, various tools and strategies have been proposed to meet environmental challenges within the building industry, including a increasing the use of waste materials, especially those that are by-products of industrial processes; b using recycled materials instead of natural resources, which will make the industry more sustainable; and c improving durability as well as mechanical and other properties, thus reducing the volume of construction replacement materials for structures that are damaged or destroyed.
In principle, the molecular structure of composite materials can be modified using gamma radiation.
Cross-linking and polymer degradation by chain scission can occur with radiation; the chemical composition of the polymer is the key factor determining the extent to which these processes occur. Materials with superior properties can be obtained from recovered scrap polymer cross-linked by gamma radiation. The application of radiation technology in the recycling of polymers is a good option from both an economic and ecological point of view. The purpose of this chapter is to show how the combination of gamma radiation with waste and recycling materials can provide alternative tools for improving the physical and chemical properties of concrete.
Waste materials such as polyethylene terephthalate PET bottles, tire rubber, and cellulose in Tetra Pak containers are discussed in terms of their physicochemical modification by radiation and their use in enhancing the properties of concrete. Such information is focused on contributions to improving the care of the environment. In light of the growing awareness of environmental concerns, the use of waste materials in industrial processes is an attractive area of opportunity.
The recovery and recycling of solid waste has long been the subject of research. Its use in building, road construction and paving materials is beneficial in helping to reduce environmental pollution and as a solution to waste disposal issues [ 1 , 2 ]. Solid waste is classified by its chemical nature as organic and inorganic. Glass, ceramics and metals such as aluminum used in packaging materials are the main components of inorganic solid waste; others include zinc, copper and iron [ 3 ].
In the case of organic solid waste, one of the most representative components is polyethylene terephthalate PET. In the United States 50, million bottles are discarded in landfills each year. Since PET waste is not biodegradable, it can remain in the environment for hundreds of years.
PET waste can be used to produce an unsaturated polyester resin UPR in the presence of glycols and dibasic acid. This material can serve as a binder to produce polymer concrete PC with high compressive strength. Due to the increasing number of cars worldwide, the accumulation of huge volumes of discarded tires has become a major waste management problem. In , approximately million of scrap tires were generated in the U.
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Over , tons of waste tires are generated annually in Taiwan. The final disposal of used tires is a major environmental concern; landfills where tires are discarded represent a severe fire and health hazard. Burning tire scrap to provide energy for the production of vapor or electricity is one of the most common methods for eliminating tire waste [ 5 ]. The use of waste tires as alternative fuel in cement furnaces has been established across the U. Applications utilizing waste tires include the bituminous hot mixing of pneumatic dust for agglutinative modification in asphalt pavement [ 6 , 7 ].
Another alternative is its use as a substitute of fine or coarse aggregates in concrete. Its characteristics can improve the mechanical properties of concrete such as strength and modulus of elasticity over those achieved by sand or stone. Recycling of waste tires in the construction industry can aid in preventing environmental pollution and in the design of more economically efficient buildings.
In this respect, the use of waste tire rubber in ready-mixed concrete has become increasingly popular globally, generating significant research interest in the last two decades. A modest quantity of unprocessed scrap tires is used to provide shock protection for marine platforms against the impact of waves or ships. In some regions of the world, people still resort to burning tires, which produces unacceptable levels of pollution. As such, new and innovative techniques to promote recycling are important.
One of such strategies involves the transformation of scrap tires into alternative aggregates, generating increased economic value while reducing aggregate consumption [ 8 ]. Materials from tires are used in a variety of elastomers and plastic products, as well as for asphalt rubber AR pavement.
Oxychloride cement is a binder for rubberized concrete mixtures. In a recent study, asphalt rubber was prepared in two ways, one with a gap-graded design and the other using open gradation. The results showed satisfactory performance and the potential for household use. The wet process is the most suitable for normal asphalt mixtures with ground tire rubber GTR.
Through the use of different concentrations of AR and GTR, modified asphalt can represent a superior alternative to conventional mixtures for use of local materials and paving techniques [ 7 ]. In a study,, the mechanical properties of polymer concrete made from reinforced epoxy powder tire rubber were studied. Mixtures were optimized using direct neural modeling and reverse neuronal modeling at minimal cost; in this case, the most important cost variable is resin content.
Direct neural modeling gave the optimum composition for obtaining maximum values of compressive, flexural and tensile strength. Reverse neural modeling was used to analyze the maximum values of mechanical properties obtained with varying concentrations of the epoxy resin powder. The results show a high resistance to compression for composition of 0.
The maximum flexural strength of 0. The use of tire rubber as aggregate reduces the compressive strength of the concrete, which may limit its usefulness in some structural applications. Nevertheless, it has desirable characteristics including lower density, higher impact resistance and toughness, higher ductility, and better sound insulation properties.
These features may be advantageous for a variety of construction applications, such as access roads. A significant reduction in used tire waste could be accomplished by using scrap tires for concrete-coated tire rubber particles. The use of magnesium oxychloride makes it possible to produce high-strength concrete with better elastomer adhesion characteristics and with significantly improved performance.
Moreover, the adhesion between tire rubber particles and other constituent concrete materials may be improved by pretreatment of the aggregates of magnesium oxychloride tire rubber. Adhesion depends on several factors, including size and concentration of tire particles, type of cement, the use of chemical and mineral additives, and methods of pretreating tire rubber particles. In terms of size, it is possible to use tire powder in both mortars and concrete [ 10 ]. Additionally, higher amounts of textile fibers from used tires in plasters and plasterboards of pressed gypsum cause less resistance reduction compared to plaster without additives.
Composites incorporate various waste materials, including granulated cork, cellulose fibers from waste paper, and fibers from the recycling of used tires. Several studies have concentrated on developing new composite materials through the use of different processes for composite production, including simple molding or pressing.
The main components of natural fibers are cellulose, hemi-cellulose and lignin, with minor concentrations of pectin, waxes and water-soluble substances.
Linear cellulose molecules are linked laterally by hydrogen bonds to form linear bundles, giving rise to a crystalline structure. The degree of crystallinity is one of the most important structural parameters of cellulose. The rigidity of cellulose fibers increases, while flexibility decreases, with an increasing ratio of crystalline to amorphous regions. Moreover, the addition of cellulose fibers improves the bending behavior of the composites [ 11 ].
Some of the most important waste materials are those containing cellulose, for example, Tetra Pak containers. Discarded containers are recycled through a simple, well-established process called hydropulping.
In this process, the cellulosic fibers are separated from thin layers of polyethylene and aluminum. Most of the waste from the paper industry is known as paper sludge PS , which is burnt and becomes PS ash. It is used as a soil improvement material and raw material for cement. PS ash increases the strength of extremely stiff concrete with its high water absorption capacity. It can be added to concrete, and undergoes a pozzolan reaction with calcium hydroxide due to the hydration of cement, resulting in an obtained material with increased compressive strength relative to concrete without PS ash.
The material contains SEM images of PS ash show particles with a rough shape, but no spherical particles are present. The results show that compressive strength decreases as pulped fiber content increases, largely due to the fact that increasing fiber content induces more voids that reduce weight and weaken the composite. The fibers are thus used as cement replacement. This behavior is due to the porosity that occurs in the packing of fibers that is induced by bubbles of air formed during the mixing operation, and to the insulation properties of the fibers themselves. When more voids are in the mix, a lighter composite specimen is obtained and its thermal conductivity is diminished.
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Better thermal insulation of the cement matrix and low density provide for a lightweight construction material. This type of lightweight concrete is used for the construction of partition walls compressive strength 8. One important alternative for recycling PET materials is their use as concrete aggregate substitutes. Given the technological demands in the construction area, studies are exploring the possibility of generating alternative materials with increasing functionality, lower cost, and better physical, chemical and mechanical properties than those of conventional materials [ 14 , 15 ].
In the last two decades, virgin polymers used in road surfaces have shown advantages by virtue of certain improved characteristics of these materials. Researchers have used different polymers which, when properly mixed with asphalt, have resulted in improved road surface yield and lifespan. However, waste polymers can be dangerous and remain in the environment; and thus it is important that they would be recycled or reused effectively. Road surface yield can be improved through modification of the asphalt with various substances, most of which are virgin materials that are scarce and costly.
An alternative is the use of waste materials, such as plastic bottles, which can help reduce waste material and potentially improve its yield [ 16 ].