Türkiye doğal puzzolanları ile üretilen çimentoların sülfata ve nitrata dayanıklılığı

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Tarih
1992
Yazarlar
Özkan, Salih Burak
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Özet
Bu araştırmada Türkiyemn 15 çimento fabrikasında KPÇ-325 üretiminde kullanılan puzzolanlann Sodyum Sülfat ve Ammonium Nitrata karşı dayanımlarının tespitine çalışılmıştır. Bunun için Normal Portland Çimentosu dozajının %30'u puzzolanla ikame edilmiş ve su/çimento oram 0.5 alınarak her puzzolandan harç numuneleri üretilmiştir. Üretilen harç numuneleri 28 gün suda ve 28 gün açık havada bekletildikten sonra, %3 ve %8 konsantrasyonlu Sodyum Sülfat ve Ammonium Nitrat eriyiklerinde 15 hafta saklanmışlardır. 15 hafta boyunca haftada bir kere olmak üzere numunelerin rezonans frekansları belirlenmiş ve bu frekanslar yardımıyla numunelerin elastisite modülleri hesaplanarak, hasarın gelişimi hakkında bir fikir edinilmesine çalışılmıştır. Numuneler 15 hafta Sodyum Sülfat ve Ammonium Nitrat eriyiklerinde saklandıktan sonra, eğilme ve basınç mukavemetleri belirlenmiştir. Yapılan çalışmalar sonunda, puzzolan ikamesinin normal saklama koşullarında bile ortalama %25 bir basınç mukavemeti azalmasına neden olduğu ve iddia edilenin aksine Sodyum Sülfat ve Ammonium Nitrata dayanıklılık yönünden bir gelişme sağlamadığı görülmüştür. Ancak piroklastik zeolite dönüşmüş altere olmuş tüf kökenli doğal puzzolanlann diğer türlere oranla daha dayanıklı oldukları fakat çok ince öğütülebilen doğal puzzolanlarda bu niteliğin kaybolduğu gözlenmiştir. Bazaltik andezitik tüflerin nitrata karşı dayamklı oldukları gözlenilebilen veriler arasındadır. Ayrıca, petrografik ve mineralojik özelliklere dayanarak sülfata ve nitrata dayanıklılık açısından doğal puzzolanları sıralamanın tam bir kesinlik taşımadığı, Ammonium Nitrat hasarının her zaman için Sodyum Sülfat hasarından daha etkili olduğu ve üretilen numunenin geçirimsiz ve az gözenekli olmasının agressif ortama dayanıklılık yönünden en önemli faktör olduğu saptanmıştır. Saptanan diğer bir konuda sülfat ve nitrata karşı dayanıklı oldukları gözlenen puzzolanlann Portland Çimentosuna ikame yolundan ziyade katkı olarak katılmasının daha yararlı olabileceğidir.
As it is known, in most of the cement factories in Turkey, Pozzolan Blended Cements are produced instead of Ordinary Portland Cement and these cements are commonly used in constructions. The pozzolans used in the cement production are mostly pozzolans which can be found in the vicinity of the factories. These pozzolans are blended with Portland Cement according to the limitations in the standards. By blending, the production cost of the cement can be decreased. For example replacement of 1% of Portland clinker by pozzolan diminishes the cost price in a range of 0.5%. Constructions which are in touch with water,-like bridge abutments, constructions below the underground water level and shore constructions-, especially have to withstand sulfate attack. On the other hand, the concrete construction parts in fertilizer factories where nitrate based fertilizers are produced and stored, are under the effect of nitrate attack, which causes damages. There is a common belief, that a concrete made of Pozzolan Blended Cements are more resistant to chemical attack than the Ordinary Portland Cement. Considering this belief, the sulfate and nitrate attack resistance of 15 different pozzolans, Used in 15 different cement factories for the Blended Cement production were tested in this study. In sulfate attack, calcium hydroxide and alumina-bearing phases of hydrated Portland Cement are more vulnerable. On hydration, Portland Cements with more than 5 percent potential C3A (3CaOv\lo03) will contain most of the alumina in the form of monosulfate hydrate, C3A CS-Hjo. If the C3A content of the cement is more than 8 percent, the hydration products wili also contain C3A*CH-H18. -v- In the presence of calcium hydroxide in Portland Cement pastes, when the cement paste comes in contact with sulfate ions, both the alumina-containing hydrates are converted to the high-sulfate form (ettringite, C3A"3CS*H32), which causes expansion in the concrete: ' C3ACS-H18 + 2CH + 2S + 12H-J»C3A-3CS-H32 (1) C3ACHH18 + 2CH + 3S + 11H^C3A3CSH32 (2) Depending on the cation type present in the sulfate solution (i.e., Na+ and Mg2+), both calcium hydroxide and the C-S-H of Portland Cement Paste may be converted to gypsum by sulfate attack: Na2S04 + Ca(OH)2 + 2H2O^CaS04-2H20 + 2NaOH (3) MgS04 + Ca(OH)2 + 2H20- CaS04-2H20 + Mg(OH)2..(4) 3MgS04 + 3Ca02Si02'3H20 + 8H20 - 3(CaS04-2H20) + 3Mg(OH)2 + 2Si02-H20 (5) Compared to sulfates, nitrates can be found in industrial constructions and industrial waste water. One of the most harmful nitrates is the Ammonium Nitrate. It is the most widely used nitrogen-based fertilizer and contains %75 NH4N03 and %25 CaC03 as filler. In the factories where this fertilizer is produced and in the depots where it is stored, concrete building elements suffer from corrosion. The corrosive effect of Ammonium Nitrate of Portland Cements is different from the well known classical sulfate attack. The nitrate ion forms highly soluble nitrate salts by reacting with the free lime. The Calcium Nitrate thus formed react with tricalcium aluminate hydrate to yield a double salt which forms with much less volume increase than ettringite. Ca(OH)2 + 2NH4N03 + 2H20- *Ca(N03)2 4H20 + 2NH3.,(6) 3CaOAl203-6H20 + Ca(N03)2-4H20- ?3CaO-Al2O3-Ca(NO3)2*10H2O....(7) *) C : CaO A : A1203 S : S04 H : H20 -VI- Based on these reactions» it has been argued that the resistance of concrete to the Ammonium Nitrate would improve if the free lime in the cement could be fixed by using additions of pozzolan and/or blast furnace slag. LABORATORY INVESTIGATIONS Materials used a. Pozzolans 15 different natural pozzolans were classified according to their petrographic and mineralogical characteristics. Following groups could be formed: I. Pyroclastic loose rocks-vesicular structure, II. Pyroclastic welded rocks-altered to clay minerals, III. Pyroclastic welded rocks-altered to zeolites, IV. Altered rocks originated from complex minerals. b. Cement Ordinary Portland Cement (Type I) were used. c. Sand In the production of mortars standard silica sand used in cement tests carried out according to RILEM recommendation was used. d. Aggressive Solutions Sodıum Sulfate and Ammonium Nitrate solutions with to different concentrations (3% and 8%) were prepared. Mortar Production All Pozzolans were dried in a oven (in 110°C temperature) and were grinded, so that they could pass through the 90 micron sieve. The pozzolans and Ordinary Portland Cement were blended and mortar specimens were prepared by using the proportions below: 3 15 gr Ordinary Portland Cement (%70) 135 gr Pozzolan (%30) 1350 gr Standard Silica Sand 225 ml Water (Water/Cement Ratio = 0.5) As it can be understand from the mix proportions above, 30% of the 450 gr Ordinary Portland Cement were replaced by the pozzolan. These mortars were cast in 4 x 4 x 16 cm prismatic moulds, the procedures of mixing, placing and curing were in accordance with RILEM recommendations. In addition, control specimens which consist of only Ordinary Portland Cement were prepared for comparison purposes.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1992
Anahtar kelimeler
Amonyum nitrat, Puzolan, Sodyum sülfat, Yapı malzemeleri, Çimento endüstrisi, Ammonium nitrate, Pozzolan, Sodium sulfate, Building materials, Cement industry
Alıntı