تاثير افزايش دماي اوليه بر دوام بتن‌هاي حاوي ميكروسيليس– مقاومت بتن در برابر خوردگي

Influence of High Initial Temperature Casting on Microstructure and Chloride Penetration in Concrete Containing Silica Fume

در اين مقاله تاثير افزايش دماي اوليه بر نفوذ يون كلر و ريز ساختار بتن‌هاي حاوي ميكرو سيليس بررسي شده است. براي اين منظور دو طرح اختلاط بتن معمولي و بتن حاوي ميكروسيليس در سه دماي ساخت 20، 30 و 40 درجه سانتي‌گراد مطالعه شده‌اند. تمامي نمونه‌ها با نسبت آب به سيمان ثابت 45/0 و عيار (kg/m3)400 در اسلامپ ثابت ساخته شده و آزمايش مقاومت الكتريكي، پتانسيل الكتريكي و نفوذ يون كلر روي نمونه‌ها انجام شده است. نتايج آزمايش‌هاي خوردگي نشان مي‌دهد كه در دماي بالا مقاومت بتن در برابر خوردگي كاهش يافته و نفوذ يون كلر افزايش پيدا مي‌كند. در حالي‌كه با افزوده شدن ميكروسيليس به طرح، مقاومت الكتريكي افزايش و نفوذ يون كلر در نمونه‌ها كاهش پيدا مي‌كند. مشاهدات SEM نشان مي‌دهد كه ذرات ميكروسيليس هسته‌هايي براي هيدراسيون سيمان ايجاد كرده و در نتيجه ساختار همگن‌تر و منافذ كوچك‌تري را به‌وجود مي‌آوردند.

Abstract: The durability of concrete structures against corrosion due to high concentration of chloride ion is considered as a main concern in these kinds of structures in Persian Gulf area. However, increasing the initial temperature its effect on concrete microstructure can intensify this issue & severely increase the concrete corrosion rate. This article deals with the high initial temperature effect on chlorine ion penetration in concrete, particularly concretes consisted of silica fume. Evaluation of high initial temperature has been done by making samples in different temperature till initial setting & keeping in the same conditions in the environment temperature to simulate the environmental conditions of Persian Gulf. For this purpose, the changes of concrete micro structure due to initial temperature increase & its effect on concrete resistance properties against chloride ion penetration have been studied. In this paper, the influence of high initial temperature on chloride penetration and microstructure of concrete containing silica fume was investigated. Two different mixes at three different initial casting temperature (20-40°c) were studied: a control mix in which no cement replacement materials were added and a mix where cement was partially replaced 6% silica fume (by weight), at a constant water-to-binder ratio of 0.45 and a cement content of 400 kg/m3. High initial temperature casting was employed to simulate concrete temperature in Persian Gulf hot climate. The results show that chloride penetration at 40°c is directly related to increase in the porosity of the binder phase and the absorption of concrete. The Higher chloride penetration resistance was observed when cement is partially replaced with silica fume. From SEM result recognized silica fume particles make core sites to cement hydration, therefore make more consistency micro structure and decrease pore size distribution. It is concluded that increasing the initial temperature of the concrete in the time of casting & formation, leads to accelerating the hydration & therefore the heterogeneous distribution of products in the mixture. This phenomenon causes the bigger pores in the concrete structure by increasing the temperature and more space for chloride ion penetration. So, high casting and initial temperature leads to increasing chloride ion penetration & reduction of concrete resistance against corrosion. By adding silica fume to the mixture, size & the distribution of pores improve and the temperature increase effect on parameters of chloride penetration & corrosion decrease. Hence, the corrosion behavior (Chlorine ion penetration coefficient & electrical potential) of 40°c silica fume included specimen are improved than reference concrete.