علی اکبر کفاش بازاری

Clinker phases have a significant effect on the technical characteristics of cement and its performance in concrete, but sufficient information is not available to determine the effect of each of these phases on the optimal performance of concrete. Therefore, in this practical essay, it was studied and a laboratory operation was designed. In the first stage, regular sampling of clinker from 2 kiln of Tehran cement factory was done in 3 months. Then 11 clinker samples (Portland type II) were selected which their phase values were different from each other. During the second stage, laboratory cementing was done in completely identical conditions using 11 clinker samples. A super plasticizer additive sample was also prepared. In the third stage, physical and chemical analysis was done on laboratory cement samples. During the fourth stage, 22 concrete mixes were prepared with 11 cement samples, and their slump were fixed (8cm in the first group and 12cm in the second group) so that 11 mixtures were labeled "without additives" and 11 mixtures were labeled "with additives". Slump loss tests within 1 hour, determination of density, determination of air content of fresh mixed concrete, compressive strength of 7, 28 and 90 days in hardened concrete were performed on concrete mixtures. Based on the results, the comparison of the effect of C3S amount of clinker on the compressive strength of standard mortar and concrete showed that the direct relationship between C3S amount and compressive strength (mortar and concrete) is not favorable; but it can be said that with each increase of C3S percentage of clinker, the 7 and 28 days strength of concrete increases by about 1.5 units (kg/cm2) and with the increase of C3S from about 57% onwards, a drop in concrete strength can be observed. These points out the negative effect of excessive increase of C3S phase. Based on the results of the tests which determine the percentage of air in fresh concrete mixes containing additives and its decrease after 30 minutes, it was determined that the optimal amount of C3A was about 5-6%.

The portion of phases and the quality of clinker crystal formation have a great impact on the performance of cement and concrete obtained from it; however, cement and concrete manufacturers often base their evaluation on chemical analysis or XRF and the values of phases with the help of Bogue formula. Therefore, in this extensive applied study, the relationship between the results of microscopic studies and the technical characteristics of cement and its performance in concrete has been traced. In the first stage, one hundred samples of Portland clinker type II were prepared from Tehran cement and microscopic studies and chemical analysis were performed on them. All clinker samples were grinded in industrial mill and physical and mechanical tests were performed on cement samples. Then laboratory concrete mixtures were made to evaluate the technical characteristics of cement and their performance in concrete. Based on the results of this extensive laboratory operation, innovatively, the microscopic results were summarized quantitatively (numerically). The relationship between the microscopic indicators and the properties of concrete mixtures was observed and its relationships were presented.

Common methods of controlling setting, hardness, process of strength concrete are tests for determining the setting time of mortar (ISIRI 392) and concrete (ISIRI 6046) and determining the compressive strength of concrete (ISIRI 3206). Since these physical and mechanical methods do not fully reflect the behavior of concrete and also it is time and money consuming, application of electrical resistance of concrete has been investigated. Therefore, in this study, an extensive laboratory operation was designed. In the first stage, 11 samples of cement were prepared, the phases of which varied, but due to laboratory cementation, their fineness and grading were almost the same. Physical and chemical analysis of cement samples were performed. In the next step, 22 concrete mixtures with 11 cement samples were prepared, so that 11 mixtures with the title of control (without additives) and 11 mixtures with constant dosage of commercial super plasticizer (based on poly carboxylate). Compressive strength tests has been performed at ages of 7, 28 and 90 days. Also, an electrical resistance test was performed, which was performed regularly from the time of cement contact with water until 31 days later. The results showed that at least three peaks of 8, 16 and 23 days in the electrical resistance curve are seen along the test time. In almost all samples, the electrical resistance is reduced to about 3 hours, which indicates the setting time of the concrete. Based on the results of this study, formula was presented

The studied organization is Tehran Cement Company which is one of the most important cement manufacturers. The research method is descriptive-survey and the statistical population is divided into two groups of industry experts and proficient. Through the Analytical Hierarchy Process (AHP), the relative importance of company strategies is determined based on the goals of the vision document. The incompatibility rate in different parts of the questionnaire is less than 0.1 and acceptable. In the second stage, a questionnaire is designed to assess the strategies, implementation and evaluation of Tehran Cement Company strategies using 5-point Likert scale and was distributed among 70 responsible experts in the studied company. This statistical population is selected by random sampling and based on Cochran formula. Cronbach's alpha coefficient of this questionnaire is 0.931 (acceptable) using SPSS software. The results of this applied study show that according to a survey conducted by Tehran Cement Company, targeting criterion have the lowest gap and evaluation of the highest gap. The strategic divide in the company is the most divisive for improving the level of organizational knowledge, optimizing technology portfolio, improving productivity and developing human capital.