| چکیده انگلیسی مقاله |
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.
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