**2. Waste and recycling materials in the research area of construction**

Discovered and patented in England in 1941, polyethylene terephthalate (PET) has been used in the packaging industry for a broad range of applications. Annual average consumption per person of 234 l of bottled water is reported. As it has become a widely used material, all disposed bottles are actually a serious environmental issue. Pollution caused by PET bottles includes not only the final disposal of them, but also the by-products obtained during PET fabrication process. Plastic bottles take centuries to decompose and if they are incinerated, toxic by-products, such as chlorine gas and dioxins, are released into the atmosphere. Solid handles of materials have experienced an important impact because of the nonbiodegradability nature of PET. The world consumption of PET is about 15 million tons, of which 3.5 million tons are used in the manufacture of packaging materials, including jars and bottles.

Two methods for recycling of polyethylene terephthalate (PET) bottles are mechanical process and chemical process. (1) Mechanical process includes three well-defined stages such as separation, washing, and grinding. The recycled PET is used for elaborated laminates, metal sheets, and food and nonfood packages. Moreover, recycled PET flakes can be directly employed to elaborate pellets in the creation of products by injection or extrusion. (2) Chemical process consists of separation of the basic components or monomers. The methanolysis, glycolysis, and hydrolysis are the elemental processes to achieve this transformation.

**Keywords:** waste, recycled materials, composite materials, mechanical properties,

In recent years, due to high demand of construction materials, some actions have been developed such as extraction of large amounts of raw materials, development of new materials, use of recycled and demolition waste; all of them generating higher costs and environmental problems. Special attention on the development of economic and ecological materials through the use of waste materials has generated a novel research area. Moreover, in order to reduce the ecological impact, many efforts have been made for reducing the consumption of nonrenewable resources in the production of construction materials, one of these is the production or addition of waste or recycled materials into the mixture in substitution of the common mineral aggregates, taking care of the final quality that includes parameters such as resistance, modulus of elasticity, and

Although some advantages are obtained when adding waste or recycled materials for improvement of the toughness of construction materials, they present some disadvantages such as lower values on the compressive strength, which should be attended. One alternative is the use of gamma radiation. Recent works have studied the effects of gamma radiation on compressive properties; in one of them, the results show more resistance to crack propagation; moreover, compressive strain and the elasticity modulus depend on the combination of the particle sizes and the radiation dose. This chapter attempts to use gamma irradiation as modifier of the physicochemical properties of waste and recycled materials, and use them as reinforcements of construction composites and as a consequence improve their mechanical properties. This chapter promotes the use of waste and recycled materials in the construction industry, as one alternative for reducing environmental pollution.

**2. Waste and recycling materials in the research area of construction**

used in the manufacture of packaging materials, including jars and bottles.

Discovered and patented in England in 1941, polyethylene terephthalate (PET) has been used in the packaging industry for a broad range of applications. Annual average consumption per person of 234 l of bottled water is reported. As it has become a widely used material, all disposed bottles are actually a serious environmental issue. Pollution caused by PET bottles includes not only the final disposal of them, but also the by-products obtained during PET fabrication process. Plastic bottles take centuries to decompose and if they are incinerated, toxic by-products, such as chlorine gas and dioxins, are released into the atmosphere. Solid handles of materials have experienced an important impact because of the nonbiodegradability nature of PET. The world consumption of PET is about 15 million tons, of which 3.5 million tons are

gamma radiation

162 Composites from Renewable and Sustainable Materials

**1. Introduction**

durability, among others.

PET can be recycled many times and can be used in a variety of products, such as fibers for clothes, fiberfill for bags, or industrial strapping. One interesting alternative to recycled PET materials consists of using them as a substitute of concrete aggregates; in this, silica sand is partially substituted by waste PET particles. The main goal is improvement of mechanical properties, including compressive strength, deformation, and modulus of elasticity. Demand of technological development in different construction areas makes possible the generation of alternative materials that can be applied with increasing functionality, low costs, and better physical, chemical, and mechanical properties than conventional materials. Fiber-reinforced concrete, in which new materials are applied in order to obtain more efficient crack-resistant concrete, is an important research field these days. PET has been widely used to produce fibers, particles, or flakes to obtain cement-based products with improved properties.

Different kinds of fibers have been used in the concrete, including steel, glass, carbon, nylon, polyester, propylene, among others; however, in order to reduce the environmental impact of industrial or postconsumer waste, recycled fibers have been used. They offer advantages in reducing waste and conserving resources.

Another waste with potential applications in different technological areas is that related with the automotive tires. The typical components of automotive tires are synthetic and natural elastomers, sulfur and its compounds, phenolic resins, oils, and steel wires among others; while zinc oxide, titanium dioxide, and carbon black are used as pigments. Moreover, manufactured tire includes: synthetic elastomers (27%), natural elastomers (14%), carbon black (28%), steel (15%), as well as fabric, infill materials, accelerators, and anti-ionizer (16%) [1, 2].

The most common method to dispose waste tires is to burn them for vapor, heat, or electricity. The usage of waste tires as alternative fuel in cement furnaces is generalized across the U.S. and Europe. However, these practices result in the generation of organic and inorganic compounds such as zinc oxide (ZnO) and zinc sulfide (ZnS), in hydrocarbon gas, aromatic volatile compounds, and liquids formed by heavy and light oils, all these by-products which are highly polluting.

Recycling of automotive tire includes reuse in plastic and rubber products as well as alternative fuel in cement furnace or as material in the carbon black production. Another approach for the application of waste tires includes hot bituminous mixes as pneumatic dust for the agglutinative modification in asphalt pavements. This application has been more or less effective, but not enough for reducing the reserves of waste tires, since these novel technologies are more expensive than conventional methods. Moreover, components of the recycled waste tires have been used in the construction industry, for example: (a) waste steel fibers as mechanical reinforcement of concrete [3] and (b) recovered rubber as replacement of natural aggregates (fine and coarse), in which the elasticity features are improved and a lower diminution on the compressive strength and brittleness values is found [4–6]. In general, use of them as a substitute of fine or coarse aggregate can improve mechanical properties of concrete such as strength and modulus of elasticity, instead of those achieved by sand or stone.

Addition of particles into concrete produces internal stresses, which promote sooner cracking and subsequent failure, which can be avoided with the control of the particle sizes. Early studies pointed out that those elastomeric particles can reduce propagation of cracks, show increment in tensile strength, and have capacity in energy absorption. One advantage of the rubber particles is concerning energy absorption through ultrasonic waves, in order to benefit the concrete elasticity. However, differences in the values of Young's modulus modulus between rubber particles and concrete matrix, besides concentration of rubber particles into concrete, could promote great deformations when applying loads and thus results in progressive diminution of the mechanical properties. Other properties of concern for concrete workability include diminution of slump and increment of air content when increasing the elastomeric concentration, which promotes a low unit weight.

Tetra Pak is an aseptic packaging material, elaborated of several laminated layers of three raw materials: paper (75%), low-density polyethylene (20%), and aluminum (5%). The barriers consist of six layers of these materials. After recycling Tetra Pak packages through hydropulping process, cellulosic fibers are recuperated, which have superior quality when compared to those found in the waste paper market. Moreover, they are used in the production of tissue and paper towels. Percentage of recovery of the Tetra Pak components in a separate way shows 63 wt% for paper, 30% for polyethylene, and 7% for aluminum.

Recycling of these materials is based on mechanical milling and chemical attack, from which it is possible to obtain size reduction and component separation. In the case of the cellulosic fibers, the surface energy is closely related to the hydrophilicity of the fiber. Another important parameter is concerning reduction of the moisture adsorption of cellulose fibers, which are involved in reduction of the number of cellulose hydroxyl groups and the hydrophilicity of the fiber's surface, as well as restraint of the swelling of the fiber. Moreover, degradation produces water-soluble or insoluble oxygenated compounds.

Cellulose is the most abundant, inexpensive, and readily available carbohydrate polymer in the world, traditionally extracted from plants or their wastes. Currently about 30 million tons of natural fibers are produced by year around the world. The current interest for using such fibers is based on the environmental preservation; there is great interest for replacing synthetic fibers for natural ones [7, 8]. However, due to environmental problems caused by products made using cellulose (boxes, bags, containers, office supplies, etc.), different ways to recycle thosematerials have been developed.

Some natural fibers are composed mainly of cellulose (54%), hemicellulose (20%), and lignin (15%). Natural fibers are a resource that is environmentally clean, renewable, and biodegradable; one of them that has captured attention in applied research is Luffa fiber, due to its physicochemical properties. They are obtained from a subtropical plant of the Cucurbitaceae family, which produces a fruit with a fibrous vascular system (luffa), with sizes between 1.5 cm and 1.5 m and an average diameter 8–10 cm [9]. Their morphological surfaces show roughness surfaces, containing width channels (4–12 μm), and particles with different lignin shapes (indicated by arrow), and thin layers of lignin and hemicellulose covering the cellulosic fibers (**Figure 1**).

**Figure 1.** Morphological surfaces of Luffa fibers.

reinforcement of concrete [3] and (b) recovered rubber as replacement of natural aggregates (fine and coarse), in which the elasticity features are improved and a lower diminution on the compressive strength and brittleness values is found [4–6]. In general, use of them as a substitute of fine or coarse aggregate can improve mechanical properties of concrete such as

Addition of particles into concrete produces internal stresses, which promote sooner cracking and subsequent failure, which can be avoided with the control of the particle sizes. Early studies pointed out that those elastomeric particles can reduce propagation of cracks, show increment in tensile strength, and have capacity in energy absorption. One advantage of the rubber particles is concerning energy absorption through ultrasonic waves, in order to benefit the concrete elasticity. However, differences in the values of Young's modulus modulus between rubber particles and concrete matrix, besides concentration of rubber particles into concrete, could promote great deformations when applying loads and thus results in progressive diminution of the mechanical properties. Other properties of concern for concrete workability include diminution of slump and increment of air content when increasing the

Tetra Pak is an aseptic packaging material, elaborated of several laminated layers of three raw materials: paper (75%), low-density polyethylene (20%), and aluminum (5%). The barriers consist of six layers of these materials. After recycling Tetra Pak packages through hydropulping process, cellulosic fibers are recuperated, which have superior quality when compared to those found in the waste paper market. Moreover, they are used in the production of tissue and paper towels. Percentage of recovery of the Tetra Pak components in a separate way shows

Recycling of these materials is based on mechanical milling and chemical attack, from which it is possible to obtain size reduction and component separation. In the case of the cellulosic fibers, the surface energy is closely related to the hydrophilicity of the fiber. Another important parameter is concerning reduction of the moisture adsorption of cellulose fibers, which are involved in reduction of the number of cellulose hydroxyl groups and the hydrophilicity of the fiber's surface, as well as restraint of the swelling of the fiber. Moreover, degradation

Cellulose is the most abundant, inexpensive, and readily available carbohydrate polymer in the world, traditionally extracted from plants or their wastes. Currently about 30 million tons of natural fibers are produced by year around the world. The current interest for using such fibers is based on the environmental preservation; there is great interest for replacing synthetic fibers for natural ones [7, 8]. However, due to environmental problems caused by products made using cellulose (boxes, bags, containers, office supplies, etc.), different ways to recycle

Some natural fibers are composed mainly of cellulose (54%), hemicellulose (20%), and lignin (15%). Natural fibers are a resource that is environmentally clean, renewable, and biodegradable; one of them that has captured attention in applied research is Luffa fiber, due to its physicochemical properties. They are obtained from a subtropical plant of the Cucurbitaceae

strength and modulus of elasticity, instead of those achieved by sand or stone.

elastomeric concentration, which promotes a low unit weight.

164 Composites from Renewable and Sustainable Materials

63 wt% for paper, 30% for polyethylene, and 7% for aluminum.

produces water-soluble or insoluble oxygenated compounds.

thosematerials have been developed.

One of the main characteristics of raw luffa fibers (without surface treatment) is its capacity to absorb moisture easily and its high potential as reinforced material in hybrid composites, mainly on the mechanical properties. In the case of Tetra Pak packaging, an optional recycling way for this is based as a substitute of mineral aggregates in the elaboration of composite materials, which improving its properties, including lower weight and density, higher mechanical strength and toughness [10].

Some investigations are concerning use of natural fibers, such as cellulose, for elaboration of composite materials. Different thermosetting polymers, namely polymeric resins, have been used for such purpose. The main idea is to use inexpensive and abundantly available fibers. Mechanical properties, including tensile strength, flexural strength, compressive strength, and wear resistance, increase their values when increasing the concentration of the cellulosic fibers. Moreover, the impact properties significantly increase. Such behavior is due to an excellent dispersion of the reinforcements. But for higher content of fibers, decrement on the values is observed; this is due to agglomeration of the fibers. Composite elaborated with cellulose fibers has light weight. Surface modification of the cellulose fibers facilitates elaboration of composites. Silane and alkali treatments are used for such proposal, having higher fiber-matrix adhesion strength. Moreover, reduction of water absorption is observed, as a consequence of the strong interface. Another treatment is referred to coupling agents; the presence of double bonds is necessary to obtain the formation of covalent bonds between fiber and matrix. Residue cellulose can act as a natural coupling agent and improve the interfacial bonding by reducing the hydrophilicity of the fiber. The water absorption increases with an increase in fiber content. Moreover, fibers can be further subdivided into microfibrils with high elastic modulus by hydrolysis, followed by mechanical disintegration. Such fibers are produced commercially by the pulp and paper industry.
