فهرست مطالب سمیرا کاظمی راد

Considering the high consumption of concrete, especially in structures, and the increasing need for cement production, it seems necessary to pay attention to the harmful environmental effects of this material. In the construction industry, to solve this problem, alternative adhesives are used in concrete, and geopolymers are one of these alternatives. Making geopolymer concretes based on slag can be one of the ways to produce environmentally friendly materials that reduce the harmful effects of cement production. Also, using lightweight concrete has valuable advantages, such as reducing the structure's dead load, and combining geopolymer with lightweight concrete can be beneficial. In this research, two series of lightweight geopolymer concrete have been used. In the first series, by keeping geopolymer ratios constant (Al/Bi=0.65, SS/SH=1 and sodium hydroxide concentration 2 M), Geopolymer concretes with different percentages (50, 60, 70, 80, 90, and 100) of scoria were made instead of coarse aggregate. Then, the designs with structural conditions (compressive strength above 17 MPa and specific weight below 2000 Kg/m3) were selected by comparing the samples' specific weight and compressive strength. In the second series of making lightweight geopolymer concretes by adding steel fibers (0.5, 1, and 1.5%), polypropylene fibers (0.1%), and hybrid, the mechanical characteristics of the samples were evaluated. By examining the compressive strength test, as expected, the compressive strength of the light geopolymer samples increases with the increase in the percentage of steel fibers. Also, samples containing 0.1% of polypropylene fibers face decreased compressive strength. When combined with steel fibers with percentages (0.5, 1, and 1.5), this decrease in compressive strength will be increased. By checking the compressive strength and specific weight, the samples containing 70, 80, and 90% scoria has structural conditions.  By examining the tensile strength test, it can be concluded that adding steel and polypropylene fibers both increase the tensile strength can be seen. In the flexural strength test, flexural strength increases with an increase in the percentage of steel fibers.  It can also be seen that the effect of steel fibers is more significant than polypropylene fibers in increasing the bending strength. An ultrasonic pulse speed test determines the quality of manufactured concrete. According to the observed results, it can be concluded that with the increase in the percentage of fibers (steel and polypropylene), the speed of the ultrasonic pulse also increases. The samples of 70% scoria-containing steel fibers are of excellent quality; this indicates that this design has a better quality geopolymer paste than other samples. Also, the geopolymer concrete sample containing 90% scoria has the lowest value of ultrasonic pulse speed. This reduction can be attributed to many voids in the scoria aggregate. The modulus of elasticity test results showed that the samples containing steel fibers were far more than the other samples, and the most significant increase was seen in steel fibers with a percentage of 1.5. Finally, by examining the microstructure of fiber geopolymer lightweight concrete using scanning electron microscope (SEM) images, it can be seen that the geopolymer sample without fibers contains voids, which are filled to a large extent when steel and polypropylene fibers are added.

Today in the world, including in our country, the use of nuclear technology in various fields of power plants, industry, agriculture and medicine is expanding. One of the most important issues in nuclear technology is nuclear radiation protection to prevent harmful environmental, pathogenic and harmful effects on some of the precision measuring instruments. From the perspective of preservation, all the radiation and particles are not of the same importance, because their penetration and impact on different materials, such as living tissue, are not equal. In the discussion of conservation, neutron and gamma radiation is of particular importance because, due to its unloaded nature, they can pass relatively large thicknesses of the shield and contribute to raising the dose rate outside the shield. In addition to the many uses of radioactive waste, it should be noted that this radiation damages cells and living tissues and protection against it is essential and inevitable. In order to protect against radiation, absorbent materials should have a high density, high attenuation coefficient, and structural properties with high strength, easy to provide and cheap production. According to the above, the use of concrete is a suitable alternative for radiation protection. Due to its high specificity and low cost, barite is widely used in the oil and gas drilling industry, coloring industry, pharmaceutical plastics (due to the absorption of radioactive wastes), chemicals and so on. So it can be a good option for gamma radiation protection. In this research gamma-ray linear attenuation coefficient and neutron beam dispersion cross-section of two series of concrete samples containing barite powder as a substitute of sand with and without graphite powder under gamma rays with Cs-137 fountain and NaI (Tl) detector under neutron beam With the Am-Be 241 fountain and the BF3 detector. The compressive strength, tensile strength and ultrasonic pulse velocity were also determined. All concrete samples, with the exception of control samples, have been made with 400 kg / m3 cement and 0.4 water/cement ratio with 10% microsilicon replacement in two series. In the first series, barite powder was replaced with 10, 25, 50, 75 and 100% replacement of sand, and in the second, 10% of the graphite powder was added to samples containing various powdered barite powder. The result of this study showed that a sample containing 10% barite powder plus 10% graphite powder could be an optimal amount for a concrete protected against gamma and neutron rays.

With regard to the development of nuclear technology in the world and the use of this technology in the industry and medical centers, the attention of countries to this topic and investment in this area has increased. In this research, concrete is made in two series. In the first series, barite powder was replaced with 10, 25, 50, 75 and 100 percent sand replacement and in the second series, barite powder with the percentages mentioned and 10 percent graphite powder was prepared. In present study, the amount of cement 400 kg/m3 and water to cement ratio of 0.4 and additives have been added to the concrete containing 10% microsilica. The mechanical properties of these concrete were determined such as compressive strength and tensile strength. Their effect was also tested as a protection against gamma radiation using the CS-137 source, and then examined by comparing the MCNP simulation code by Monte Carlo method. The results indicated that a sample containing 10% barite powder plus 10% graphite powder could be an optimal amount of protection against gamma rays. Also, the comparison of experimental results with the MCNP code showed a fairly good agreement, and the trend of increasing and decreasing it was almost the same.