Kendiliğinden yerleşen betonlarda uçucu kül ve kalker tozu kullanımının durabilite özelliklerine etkisi

Abstract

Geçtiğimiz 50 yıla kadar betonarme yapılarda betonun gerekli mekanik dayanımı sağlaması performansı için yeterli görülmüştür. Ancak ilerleye zamanda mekanik dayanımın yanında betonun zamana ve çevre şartlarına olan dayanıklılığı (durabilite) konusu da dikkate alınmaya başlanmıştır. Bu sebeple betonarme tasarımlarda yeni katkılar kullanılmaya başlanmıştır.Dayanıklılık problemlerinden bir tanesi de betonun iyi yerleştirilememesidir. Kalıba iyi yerleşmeyen beton boşluklara sebep olmakta, bu da betonun durabilitesini etkilemektedir. Bu yerleştirme sorununu azaltmak ve su altında beton dökümü gerçekleşirken betonun bütünlüğünü kaybetmemesi için kendiliğinden yerleşen beton teknolojisi geliştirilmiştir. Kendiliğinden yerleşen beton içerdiği ince malzemeler sebebiyle akışkan ve viskozitesi yüksek bir kıvama sahiptir. Kalıba kendi ağırlığı dışında herhangi bir işlem uygulanmadan rahatça ve boşluksuz bir şekilde yerleşir. Karışımda kullanılan farklı mineral ve kimyasal katkılar ise KYB'lerin özelliklerini değiştirmektedir.Bu çalışmada KYB betonlarının üretiminde kullanılan uçucu kül ve kalker tozunun betonun durabilite özelliklerine etkisi incelenmiştir. Ayrıca bu özellikler geleneksel beton ile de kıyaslanmıştır. Bu amaçla maksimum agrega boyutu 22 mm olan bir geleneksel beton, maksimum agrega boyutu 16 mm olan ve mineral katkı içermeyen bir KYB ve içerisinde 36, 72 ve 108 dm3/m3 hacimde kalker tozu ve uçucu kül içeren KYB'ler üretilmiştir. Bu grupların hepsinde çimento dozajı 350 kg/m3 olup su/çimento oranı ise 0,51 olarak sabit tutulmuştur.Beton gruplarının taze halde çökme-yayılma ve taze birim ağırlıkları ölçülmüştür. Tüm gruplarda işlenebilirlik ve birim ağırlıklar istenilen düzeylerde elde edilmiştir.xviiiSertleşmiş betonlarda ise durabilite özelliklerini belirlemek için standartlardan ve literatürdeki yöntemlerden faydalanarak bir dizi deney yapılmıştır. Bu deneyler; kılcal su emme deneyi (ASTM C 1585-3), basınç altında su geçirimliliği (TS EN 12390-8), vakumlu su emme deneyi, donma-çözünme deneyi, karbonatlaşma deneyi (TS EN 14630), magnezyum sülfat deneyi (TS EN 1367-2), hızlı klorür iyonu geçirimliliği (ASTM C 1202-18) ve elektriksel özdirenç ölçüm (4 elektrotlu Wenner ) deneyidir.Deneylerden elde edilen veriler genel olarak bakıldığında mineral katkı kullanımının betonun durabilite özelliklerinde iyileştirme yaptığı görülmüştür. Özellikle uçucu kül kullanımı betonun geçirimlilik ve su emme deneylerinde geleneksel beton ve mineral katkı içermeyen GB'ye göre daha iyi sonuçlar verdiği görülmüştür.Özellikle uçucu kül kullanımı kalker tozuna göre betonun geçirimlilik özelliklerini daha iyi iyileştirmiştir. Geleneksel betonda agregaya göre daha geçirimli olan ve boşluk bulunduran çimento matrisi uçucu külün puzolanik ve filler özelliklerinden dolayı daha geçirimsiz hale gelmiştir.

It has been commonly accepted for last 50 years that mechanical strength of concrete is enough for structures. Not only importance of mechanical strength but also importance of strength against environmental and over time effect (durability) has been discovered. Because of this reason, new chemical and mineral admixtures has been started to use.One of the durability problems is compaction of concrete properly. Insufficient compaction of concrete to molds causes pores in concrete and pores reduce strength and durability of concrete. To avoid this compaction problem and produce concrete under water, self-compaction concrete (SCC) technology has been developed. SCC has high viscosity and high fluid consistency. SCC can be compacted to molds with very low porosity without any vibration or compaction operation.To provide superior properties of SCC than traditional concrete, some chemical and mineral admixtures are needed. Super plasticizers are the most important chemical admixtures. Flying ash, different types of slags, silica fume, metakaolin, limestone powder are common mineral admixtures. Different chemical and mineral admixtures affect the properties of SCC.In this experimental research, effects of usage flying ash and limestone powder in SCC were investigated and compared with conventional concrete and SCC without any mineral admixtures. With this purpose several concrete groups were produced. To compare with SCC's, a conventional concrete (CC) that has 22 mm maximum aggregate size and a SCC that has 16 mm max aggregate size and without any mineral admixtures. Furthermore, with addition 36, 72 and 108 dm3/m3 fly ash and limestone powder to 350 dm3/m3 cement;6 different group of SCCs were produced. Water/cement ratio of all these group is 0,51 and cement dosage is 350 dm3/m3.After production, in fresh condition, unit weight and slump-flown values of concrete were measured. All groups provide expected units weight values and workability conditions. After that, hardened concrete specimens were cured 90 days inside water at laboratory condition.To determine durability properties of concrete groups several experiments were applied with help of standards and methods that used in literature. Alignment of experiments are capillary water absorption test (ASTM C 1585-3), permeability under pressure test (TS EN 12390-8), compressive strength test (TS EN 12390-3), water absorption with vacuum test, freezing-thaw test, carbonation test (TS EN 14630), magnesium sulphate test (TS EN 1367-2), rapid chloride permeability test (ASTM C 1202-18) and resistivity test.Experimental studies have showed fallowing statements:1. Compressive strength test results have indicated that mineral admixture increases strength of concrete for same W/C ratio with compare CC and SCC that has any mineral admixtures. If we compare effects of fly ash and limestone powder, fly ash has better effect to compressive strength for same water/fine material ratio.2. Mineral admixtures fill pores in concrete and block transportation of deleterious materials inside concrete. Capillary water absorption test, permeability under pressure test and water absorption with vacuum test have shown that increasing mineral admixture ratio decreases the permeability of concrete. For same water/fine material ratio, it has been determined that flay ash and limestone powder have similar effect of permeability properties.3. Usage of fly ash has increased freeze/thaw resistance of concrete according to loss of weight and loss of compressive strength compare with references groups. Unlikely, limestone powder has negative effect on freeze/thaw properties of concrete. References groups has better freeze/thaw resistance unlike concrete groups which insists limestone powder.4. Increasing limestone powder ratio has decreased carbonation coefficient of concrete with compare with references groups. But fly ash has negative effect on carbonation resistance. Usage of fly ash has increased carbonation coefficient. Fly ash has reacted with CaOH which occurred after hydration of cement. So, CO2 molecules can penetrate inside of concrete without crossing with CaOH. Even if fly ash fills pores in concrete, CO2 molecules can react with deeper CaOH from surface.5. After numerous cycles of MgSO3 solution, no considerable differences have been determined between concrete ultrasound velocity with compared from beginning of cycles. But it has been seen that mineral admixtures increased the ultrasound velocity of concrete than references groups.6. Limestone powder has no considerable improvement on concrete with a bit reduction in terms of chloride resistance. But, increasing fly ash ratio also increased chloride resistance of concrete with compare references groups CC and SCC that has no mineral admixtures.7. With similarly rapid chloride permeability test, fly ash has improved resistivity of concrete about 5 times than reference CC and SCC. Limestone powder has similar results with reference SCC. But, compare with reference CC, resistivity values have decreased almost ½ with lime stone powder.In generally, it has been found usage of mineral admixtures has positive effects on durability properties of SCC. Especially, usage of fly ash in SCC showed very high performance about durability compare with CC and SCC that has any mineral admixtures.In comparison with limestone powder, fly ash showed reasonably better performance to develop durability of concrete. It can be explained with filler and pozzolanic properties of fly ash. In contrast to limestone powder, fly ash has pozzolanic property. This property provides to bind free CaOH that presents in cement matrix. It can assert that fly ash decreases porosity and permeability of concrete. Concrete that has less pores, has superior resistance against hazardous chemicals and environmental effects.