نوع مقاله : پژوهشی اصیل (کامل)
کلیدواژهها
موضوعات
عنوان مقاله English
نویسنده English
One of the common ways to increase the life of concrete is the use of pozzolans, some pozzolans that have higher reactivity than ordinary cement lead to greater resistance and less permeability of concrete by reducing concrete pores. Structures made with ordinary Portland concrete generally do not have proper performance in harsh environmental conditions and destructive aggressive factors. Sulfate attack is the process of concrete destruction due to the expansion caused by sulfate reactions inside the concrete, and in the long term, it causes a decrease in cohesion, occurrence of cracks and collapse in the concrete structure, one of the effects of which is the reduction of concrete strength. The addition of metakaolin reduces the porosity in concrete, as a result, concretes containing metakaolin have lower permeability compared to normal concrete. In this research, calcined clay was used as pozzolan, first the soil was heated to a temperature of 700 degrees Celsius for 3 hours so that the calcination process takes place, then calcined clay along with a percentage of limestone powder and microsilica was replaced by cement. The purpose of this combination for cement materials is to achieve a mixture design that the concretes made by it have better resistance than normal concretes against aggressive and corrosive environmental conditions. In this study, ettringite crystals were formed on the samples processed in sodium sulfate solution, which were less in the pozzolanic samples than in the control sample. At early ages, the capillary absorption coefficient for samples containing calcined clay is higher than the control samples, but this difference is greatly reduced as the samples age and the pozzolanic reactions become more complete. The electrical resistance values of the samples also increased with the passage of time and the increase in pozzolan replacement percentage. Also, in all the experiments, the addition of microsilica fills the empty spaces in the concrete, because the microsilica particles, being smaller than the pozzolan particles of the clay used and the faster reactivity of microsilica produces more silicate gel in a shorter period of time than clay pozzolan and makes the concrete denser. In this research, 10 mixed designs were used in 2 ratios of water to cement materials: 0.35 and 0.4. In each proportion of clay in percentages of 10 and 20%, limestone powder in percentages of 30 and 20%, respectively, and microsilica along with the combination of soil and lime in 7% by weight as powder materials were replaced by cement. In order to check the properties of the prepared soil, XRD test was performed to ensure the amorphousness of the soil particles and the presence of pozzolanic compounds on it. Also, to check and analyze the durability of concrete, sulfate resistance, capillary absorption and electrical resistance tests were used on 10 cm cube samples at the age of 28 and 90 days. In this research, designs containing 20% calcined clay, 20% lime, and 7% microsilica have the best performance in pozzolanic designs and are introduced as optimal pozzolanic designs in the conducted experiments.
کلیدواژهها English
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