Production of Lightweight and Heat-Insulating Concrete Using Minced Tires

Abstract


Introduction
Using rubber particles as concrete aggregates can reduce the environmental impacts caused by the high volume of used tire buildup (Guo et al., 2017). More than one billion tires are discarded worldwide every year (Pilakoutas et al., 2004;World Business Council for Sustainable Development, 2008), of which only 4.46 million tons are in the USA (US Tire Manufacturers Association, 2017). The goal of sustainability in the modern construction industry can be achieved through the use of rubber tire parts used as a source for the formation of concrete (Thomas et al., 2016). Therefore, recycling tires into building materials is a sustainable alternative (Shu et al., 2014;Mohajerani et al., 2014;Al-Nuaimi et al., 2021).
The great development in transportation and the huge increase in the number of cars have dramatically generated various problems, the most important of which is environmental pollution. The burning of millions of tons of waste tires left very serious problems (Technical and economic study to expand tire production capacity in Iraq, 1989), for example, in 1990, more than 240 million used tires were thrown out in the United States, and in Iraq, it is estimated that two million tires are thrown into the environment in the year (Garrick, 2005). Countries such as the United States and Britain are adopting the method of burying used tires underground to get rid of them to avoid other pollution that may result from the combustion of these materials (Najim, 2007) to avoid the dangerous impact of the chemical gases that result from the combustion process such as sulfur dioxide and the distribution of carbon particles in the air. Many researchers have sought to use huge amounts of waste tire rubber and to reduce environmental pollution by mixing it with asphalt to produce mixtures used in paving roads because of their high flexibility to absorb shocks. On the other hand, some countries use these spent tires to manufacture shock protection layers for sidewalks (Garrick, 2005).
With the increase in environmental awareness, consideration turned to the use of industrial waste products, such as waste tires, as an additive to concrete. of coarse aggregate (gravel) using C/W = 55.0 for all concrete models and a concrete mixing ratio was used (3:5 and 1:1) and the results showed a decrease in the compressive strength and density in the concrete containing the crushed tires Where the percentage of loss in compressive strength at the age of 28 days.
An Arab scientific research study has concluded the possibility of benefiting from the spent tires in the implementation of rubber concrete by replacing four percent of car tires instead of sand as volumetric percentages to produce four mixtures of concrete containing rubber residues at percentages (100, 50, 30, 15%) in addition to a mixture of the main purpose was to study the behavior of rubber concrete and its resistance to heat conduction, in addition to studying the behavior of this concrete in sound insulation and showing can be used in hot weather. The results showed amazing efficiency in the use of rubber concrete for sound and thermal insulation (International Symposium on Urban Development in Desert Areas and Construction Problems, 2008;Al-Rawi, 1995).
The idea of using shredded spent tires in the manufacture of building materials is because of their appropriate properties such as high resistance to weather conditions such as temperature and humidity, light weight compared to other materials, and it's high insulation ability. The use of shredded spent tires in concrete and construction works has several economic benefits Al-Sakini (1998) and Al-khamisi (1999) using minced spent rubber tires as fine aggregate in the concrete industry. The advantages of this operation are: 1-Reducing environmental pollution and preventing the accumulation of used tires without the need to burn them.
2-Manufacture of lightweight insulating concrete. 3-The manufacture of light concrete blocks has an economic impact on the total cost of construction, as it reduces the weight of dead loads. On the basis, of time of completion, and savings in transportation and construction costs. 4-Providing high thermal insulation without the need to use cooling and heating devices. The research aims to show the effect of replacing the crushed spent rubber tires to replace the coarse aggregate (gravel) on the properties of concrete in terms of compressive strength, density, total absorption, thermal insulation, porosity examination, specific weight, and treatment of the model with alkaline solutions. It has suitable properties such as high resistance to weather conditions, low water absorption, and lightweight. In addition to ridding the environment of these wastes (Used tires) and avoiding the dangerous impact of toxic and polluting chemical gases on the environment.

Materials and Methods
With the increase in environmental awareness, consideration turned to the use of industrial waste products, such as waste tires, as an additive to concrete. of coarse aggregate (Gravel) using (C/W = 55.0) for all concrete models and a concrete mixing ratio was used (3:5 and 1:1) and the results showed a 254 decrease in the compressive strength and density in the concrete containing the crushed tires Where the percentage of loss in compressive strength at the age of 28 days.
An Arab scientific research study has concluded the possibility of benefiting from the spent tires in the implementation of rubber concrete by replacing four percentages of car tires instead of sand as volumetric percentages to produce four mixtures of concrete containing rubber residues at percentages (100, 50, 30 and 15%) (In addition to a mixture of the main purpose was to study the behavior of rubber concrete and its resistance to heat conduction, in addition to studying the behavior of this concrete in sound insulation and showing Can be used in hot weather. The results showed an amazing efficiency in the use of rubber concrete for sound and thermal insulation (International Symposium on Urban Development in Desert Areas and Construction Problems, 2008;Al-Rawi, 1995).
The practical aspect of this study is the use of a number of materials in the production of light concrete, namely: Kabaisa cement was used, and it conforms to the Iraqi specifications No. 5 for the year 1984, and it was stored well to preserve it from the influence of moisture.
• Fine Aggregate Karbala sand, which conforms to Iraqi specifications No:45 1984, was used (Table 1).  The spent tire rubber was used. The tires were shredded with a special chopper available on the market and then cut into small pieces measuring 7 x 7 x 10 mm ( Fig. 1) (Table 3).  Table 3. Chemical composition of chopped tires (Gutteridge, 1987) • Water Ordinary liquefaction water was used for all concrete mixtures and curing. The materials cement, sand, gravel, and crushed tires were mixed, then water was added to the mixer after that the mixing continued for about five minutes until the concrete became homogeneous, then the mixture were pressed into the metal molds. They were lubricated with oil. The concrete was placed in several layers and the vibrator was used for 15-30 seconds to get rid of air bubbles from mixture, then the surface was modified (surface modification for concrete). The samples were left in the laboratory for approximately 24 hours, after which they were weighed and immersed in water until the age of the test. Samples were tested according to ages of 7, 14, and 28 days.
In the Department of Mechanical Engineering, the University of Anbar, thermal conductivity measurements were taken using devices manufactured by the department (Fig. 2).

. Concrete Mixes
Concrete mix steps: The following materials (cement, sand, gravel, crushed tires) were mixed, then water was added to the mixer after that and the mixing continued for about 5 minutes until the concrete became homogeneous, then the molds were pressed after the metal molds. They were lubricated with oil, the concrete was placed in several layers and the vibrator was used for 15-30 seconds to get rid of air bubbles, then the surface was modified (surface modification for concrete) and the samples were left in the laboratory for approximately 24 hours, after which they were weighed and immersed in water until the age of the test. Samples were tested according to ages of 7, 14, and 28 days. The materials (cement, sand, gravel, crushed aggregate) were mixed, and then the molds were pressed after the metal molds.

Compressive Strength Test
Iron molds with dimensions of 100 x 100 x 100 mm were used. The molds were painted for each group of the sample before the casting process, for an average of three cubes for each model at ages 7, 14, and 28 days (Table 4).

Porosity
As for the current research, the porosity test was carried out according to the American Standard (ASTM c373), by taking the weights of dry 1W, saturated 2W, and 3W submerged concrete blocks (Table 5).

Specific Weight
This examination is of great importance in the concrete industry, where the specific weight is one of the characteristics that determines the weight of concrete and its suitability for lightweight construction uses. The specific weight of the concrete models was calculated according to the specification (ASTM c373) (Table 8). Table 8. Results of the specific weight of studied mixtures

The Reaction of Aggregates with Alkali
The reaction of aggregates and cement paste with alkalies is considered one of the most dangerous destructive reactions in concrete, and is the most common (Falak, 1989). The reaction forms a gelatinous substance called: Alkali-Silica Gel, which in turn continues to absorb water, gradually becoming a liquid, and thus able to flow through the drips in the concrete united with each other, generating a strong expansion pressure that leads to the demolition of concrete (Falak, 1989). For this purpose, NaOH and KOH were prepared in the laboratories of the Department of Chemistry -College of Science -University of Anbar.
Discs of the above-mentioned models were made and placed in a diluted solution of NaOH for 7 days, and the results showed that there was no interaction between rubber and the above-mentioned basic, which encourages the use of rubber gravel as an alternative to the usual gravel in concrete mixtures.

Thermal Conductivity Examination
Thermal conduction is defined as the ability of a body to transfer heat through the molecules of its body from one side to another, or heat transfer from a heat source in contact with the heat-conducting body (Garrick, 2005). Noting that the sample was homogeneous with a certain thickness. Table 9 shows that sample 2 is the lowest value for thermal conductivity. This is the most important characteristic of the product, which is chopped titers instead of gravel. As for light concrete produced from light aggregates, it contains in its structural structure air gaps of different sizes. They depend on the type of materials that make up the aggregate and the manufacturing method. This gives it the property of being as lightweight, as air at low temperatures. Concrete produced from this aggregate is characterized by having a lower thermal conductivity property than ordinary concrete. This shows the close relationship between the density of concrete and thermal conductivity, as the thermal conductivity generally increases with the increase in density. Table 9. Results of the thermal conductivity examination of the mixtures used

Discussion
• The decrease in the wet density of concrete is due to the ratio of the crushed spent rubber tire to the reference concrete, and this reduction increases with the increase in the percentage of the crushed tire relative to the gravel. Where the minced tire leads to making the rubber concrete lightweight. The minced tire was less than the specific weight of the coarse aggregate (gravel) and this led to a reduction in the weight of the dead loads and thus in the quality of the foundations. • The new product (2 minced tires + 1.5 sand + 1 cement) is the lowest value for thermal conductivity.
• The results showed a decrease in the compressive strength of concrete prepared from minced tire aggregate compared to the normal mixture for all ages, and that the reduction ratio increased with the increase in the proportion of minced tire aggregate because the chopped particles contained more voids. • Increasing the proportion of minced tire aggregates resulted in a decrease in the porosity value compared to the normal concrete. This conclusion is a catalyst for using this type of aggregate to reduce water run-off through concrete, especially in hydraulic structures. • The results showed the absence of any interaction between rubber and alkalies, which encourages the use of rubber gravel as an alternative to ordinary gravel in concrete mixtures.

Conclusions
The addition of minced rubber tire aggregats to the concrete mix has a positive effect on reducing the specific weight of concrete compared to regular concrete. Thus, the new product is lightweight concrete. In addition, it is characterized by low thermal conductivity. It is characterized by these two characteristics, which make it the best-used concrete in urban projects. Thermal conductivity (W/m.K) 1 2 Al-Nabai gravel + 1.5 sand + 1 cement 1.66 2 2 minced tires + 1.5 sand + 1 cement 0.33 3 1 minced tires + 1 Nabai gravel + 1.5 sand + 1 cement 0.97