پديد آورندگان :
طريقت امير دانشگاه تربيت دبير شهيد رجايي , مدرس ياقوت دانشگاه تربيت دبير شهيد رجايي , محمدي ميلاد دانشگاه تربيت دبير شهيد رجايي
كليدواژه :
حمله سولفاتي , شبيه‌سازي و ترموديناميك , سيمان پرتلند , خاكستر پوسته برنج
چكيده فارسي :
حمله سولفاتي مجموعه اي از واكنش هاي شيميايي و فيزيكي است كه بين خمير سيمان سخت شده و يون هاي سولفات رخ مي دهد. نفوذ يون هاي سولفات به داخل مواد سيماني منجر به تشكيل فازهايي همچون گچ و اترينگايت مي شود كه انبساط و خرابي بتن را به دنبال دارند. در اين تحقيق از شبيه سازي ترموديناميكي بر اساس روش به حداقل رساندن انرژي آزاد گيبس، براي درك بهتر حمله سولفات خارجي و رفتار خمير سيمان سخت شده در نمونه هاي ساخته شده از سيمان پرتلند معمولي و سيمان هاي آميخته با خاكستر پوسته برنج، استفاده شده است. با كمك اين روش علاوه بر بررسي غلظت محلول منفذي و نوع و حجم فازهاي تشكيل شده طي حمله سولفاتي، عوامل ديگري ازجمله تاثير خاكستر پوسته برنج، درصد بهينه جايگزيني آن و غلظت هاي مختلف محلول سولفات سديم موردمطالعه قرارگرفته اند. شبيه سازي خمير سيمان سخت شده در محلول سولفات سديم با غلظت هاي 4 و 44 گرم بر ليتر انجام شده و جايگزيني 10 و 15 درصد خاكستر پوسته برنج در نظر گرفته شده است. نتايج ارائه شده به وضوح نشان مي دهد كه غلظت محلول سولفاتي در نوع و حجم فازهاي تشكيل شده، به ويژه گچ و اترينگايت، تاثيرگذار است؛ در غلظت هاي پايين، 4 گرم بر ليتر، تشكيل گچ مشاهده نشده است. خاكستر پوسته برنج در 15 درصد جايگزيني، آب آهك را به طور كامل مصرف و بيشترين حجم ژل سيليكاتي را توليد مي كند و از اين درصد به بالا ديگر تاثير قابل توجهي در ژل سيليكاتي كه عمده مقاومت خمير سيمان را تامين ميكند، ندارد. به طور كلي نتايج شبيه سازي با مطالعات و نتايج آزمايشگاهي كه ريزساختار را بررسي نموده اند، تطابق خوبي دارد.
چكيده لاتين :
Sulfate attack is a series of physico-chemical reactions between hardened cement paste and sulfate ions. Sulfate ion penetration into the cement results in the formation of voluminous and deleterious phases such as gypsum and ettringite which are believed to cause deterioration and expansion of concrete; However, there is no direct relationship between Ettringite or solids formation during the sulfate attack and the amount of expansion. Concrete deterioration due to sulfate attack depends on multiple elements, however, in experimental studies, the implementation of the elements and obtaining the results in a short time are very difficult. Therefore, the significance of theoretical and software modelling along with in experimental studies, reducing the time and cost, increases so much as to achieve reliable results. Thermodynamic simulations, in this research, are employed according to the method of minimizing Gibbs free energy in order to better understand the external sulfate attack and the behaviour of mortar samples made of ordinary Portland cement and blended cements.GEM software helps in studying the microstructure of cement, volume and type of phases formed in sulfate solutions under different conditions. With this software, a virtual laboratory of materials could be created, which simulates natural processes such as hydration, sulfate attack, and factors that affect them with less time and cost. This modeling type could be utilized for cement systems in order to calculate sets of stable phases. A system achieves thermodynamic equilibrium when there is no more spontaneous tendency for change. GEM software which is able to calculate the stable phase as a function of reactants, temperature and pressure is employed. In this software chemical interactions involving solids, solid solutions, metls, gas/fluid mixture, aqueous electrolyte, (non-)electrostatic surface complexation, and ion exchange can be considered simultaneously in the chemical elemental stoichiometry (+ electrical charge) of the system, i.e. without any mass balance constraints for ligands or surface sites. GEMS simulates various mass-transfer processes and reaction paths, such as mixing; But this software cannot replace our knowledge of physical chemistry. Type and volume of phases formed during the sulfate attack and factors affecting that such as cement chemistry, rice husk ash and sulfate solution with different concentrations were studied With the help of this method. Simulation of mortar samples was performed in sodium sulfate with concentrations of 4 and 44 g per liter and 10 and 15 percent rice husk ash substitution. Mortar samples at 20 ° C and water-cement ratio of 0.5 is assumed. Rice husk ash substitution has an effective role in microstructures improvement, reduced impermeability, and volume of forming products. Sodium sulfate is more dangerous and destructive compared to other sulfates like calcium sulfate or potassium sulfate and forms phases with higher volumes. The results clearly indicate that rice husk ash, consumed portlandite completely and produced maximum volume of calcium silicate hydrate(C-S-H) by 15 percent replacement and also there is not a simple relationship between the increase of formed phases by the penetration of sulfate ions and the observed expansion. Generally, the results correspond to the studies and in experimental results which have examined micro structure.
