화재진단을 위한 혼화재 혼입 시멘트 페이스트의 고온수열시 화학성분 변화에 관한 실험적 연구

Abstract

The extensive use of concrete as a structural material has led to the need to fully understand the effects of fire on concrete. Generally concrete is thought to have good fire resistance. With the further development and use of high strength concrete (HSC), however, some doubt about its fire resistance emerged. Results of these studies are used as basic data of fire-resistance standards at each structural member of reinforced concrete. Therefore the purpose of this study is to provide the basic data to determine heating temperature and damage degree of concrete mixed mineral admixture and evaluate the quantitative chemical composition of mineral admixture such as concrete mixed GGBFS and FA at each temperature as exposed to high temperature. The results of XRD and TGDTA analysis carried out on cement pastes have been combined in order to define the changes in the chemical properties of concrete subjected to elevated temperatures. In order to evaluate the chemical characteristics of concrete mixed mineral admixture at high temperature, experiments in which mixing ratios of GGBFS are 20%, 40% and 60% and mixing ratios of FA are 10%, 20% and 30% were carried out. Also specimens subjected to range of temperature 20, 100, 300, 600, 800, and 1000℃ were studied and lasted 3 hours with heated. TG-DTA and XRD were conducted to evaluate the amount of calcium hydroxide (Ca(OH)2) quantitatively and analyze the chemical composition in accordance with the type of admixture and heating temperature. The results are as follows: 1) The results of TGA analysis on cement paste mixed with GGBFS and FA showed that a major weight loss was observed at 450-500℃ that corresponded to the dehydration of calcium hydroxide. 2) By analyzing XRD results of cement paste at different heating temepratures, the components of the cement paste [Ca(OH)2, CaCO3, Ca2Al(AlSiO7), Ca2SiO4] have been identified at all the elevated temperature values studied. As temperature increases to 600℃, the amounts of Ca(OH)2 peak point was gradually reduced and exhausted at 1000℃. 3) The results of TGA analysis of cement paste mixed with FA is almost similar as the XRD results of cement paste with GGBFS but between 600℃ and 800℃ the weight ratio of Ca(OH)2 was slightly increased. 4) Through XRD analysis of cement paste mixed with FA, the peak of Ca(OH)2, CaCO3, Ca2SiO4 and CaO presented and as mixing ratio of FA increases, the peak of CaO increased and the peak of CaCO3 decreases. 5) The results of the weight ratio of Ca(OH)2 of cement paste mixed with mineral admixture according to heating temperatures from 20℃ to 300℃ showed that the ratio of the weight ratio of Ca(OH)2 is similar and from 30 0℃ to 600℃ rapidly decreased. 6) From these experimental results, the relative weight content of the calcium hydroxide was found to formulate a trend that can be need to estimate the weight ratio of Ca(OH)2 as in the following equations : y = -0.0094 x + 0.7672 (Cement paste mixed with GGBFS) y = -0.0232x + 0.7478 (Cement paste mixed with FA) .7) Through this results the analysis of chemical proportions of cement paste mixed with GGBFS and FA is valid and important in order to predict heating temperature of building exposed to high temperature.