بررسي آزمايشگاهي مولفه‌هاي موثر بر خواص مكانيكي و پايايي بتن فوق توانمند با رويكرد اقتصادي

Laboratory Study of Factors Affecting the Mechanical Properties and Durability of High Performance Concrete with the Economic Approach

افزايش مقاومت فشاري به بيش از 50 مگاپاسكال، كيفيت و دوام بتن جزء اهداف مهم سند چشم انداز بتن 1404 است. همواره توليد بتن با مقاومت زياد نيازمند توجه خاص در طرح اختلاط اجزاء، استفاده از مواد مناسب، لزوم بهينه سازي مصرف سيمان و تركيب مصالح تشكيل دهنده ي آن بوده است. در اين مقاله، نمونه هاي مكعبي بتني طوري تهيه شده اند كه 5 متغير موثر شامل سه نوع متفاوت منحني هاي دانه بندي درشت دانه و ريزدانه، 3 نوع ابر روان كننده، ميكروسيليس با نسبت هاي 5، 7 و 12 درصد وزني سيمان در دو رده ي مقاومتي مختلف با عيار سيمان متفاوت، تاثير عيار سيمان بصورت 375، 400 و 425 كيلو گرم بر متر مكعب با نسبت آب به سيمان ثابت و تاثير افزودن فيلر بر مشخصات مكانيكي، دوام و اقتصاد طرح بطور كامل بررسي شده است. در اين آزمايش ها نسبت آب به سيمان براي مقايسه نتايج، ثابت در نظر گرفته شده است. نتايج نشان مي دهند كه متغيرهاي درنظر گرفته شده بر مقاومت فشاري بتن هاي پرمقاومت بسيار تاثير گذار بوده و استفاده از حالات بهينه ي طرح هاي فوق مي تواند سبب بهبود مشخصات مكانيكي بتن شوند به گونه اي كه با بهينه سازي اجزاء مورد استفاده مي توان با عيار سيماني 400 كيلوگرم در متر مكعب، به ساخت بتن هاي بسيار توانمند با رويكردي اقتصادي دست يافت.

The most important aims in Concrete-1404 are compressive strength more than 50 Mpa, quality and durability. These items seems to ignore before that in Iran. The high strength concrete production always needs to use suitable materials, attention to mix design, optimizing cement percentage and other component in concrete. For reaching to a trustable mix designs and aspects of high strength concrete, it needs to be evaluated by a complete investigation which can provide all three aspects of strength, workability and durability of a 1404-concrete. In this paper, cubic concrete samples are made in a way which is affected by 5 variables. These 5 Effective ranges are included: 1) Three different types of coarse and fine aggregate gradation curves which are made of finnest through roughest grading of aggregates according to ASTM C33. 2) Three types of high water reducers used in exact same mix design to compare the effects of these 3 different kind of superplasticizers on high strength concrete. These three type are grade F with polycarboxilate-ether based, grade F with sodium naphthalene solphonate based and grade G as a super high water reducer admixture. 3) Effects micro silica with 5, 7 and 12 percentage of total cement amount are added to compare the results on high strength concrete. 360 and 410 kg cement per m3 are used in source concrete mixtures as the regular using amount in practical projects in Iran. 4) The effect of cement content, with fixed w/c and 5% micro silica, which are between 375 through 425 kg/m3. an‎d 5) the effects of adding filler which are thoroughly investigated on mechanical properties, durability and economy plan. There are 20 mix design in 6 groups are prepared with total cementitious materials from 360 to 425 kg/m3. To compare the results, in these experiments the water cement ratio has been fixed to 0.25. The tests used in experiments were compressive strength test by 3000 KN hydraulic compressor and 24 hours water absorption test. The mechanical and durability properties are recognized by these tests. For evaluating fresh concrete properties, slump test was done. Economical aspect is studied and compared by comparing price of materials and content that are used in each mixture. The results show that the variables were impressively affected the compressive strength in high strength concrete. Using optimum conditions of the studied mixture design can improve the mechanical properties of concrete. By optimizing components in mixture design, high strength concrete can be made even with cement content of 400 kg per cubic meter. The 360 and 410 kg cement with adding 5% micro silica showed the best improving in compressive strength. Enhancing cement more than 400 kg results to decrease compressive strength. High water reducers with polycarboxilate ether based show better results in mechanical and fresh concrete properties and also in economical aspect. Adding filler to mixture led to decrease compressive strength and increase durability, however it had no effects on economical properties of high strength concrete. It can be concluded that aggregate grading can still lead to changes in compressive strength, durability and workability of HSC.