Nano $SiO_2$ Katkılı Çimento Harçlarının Mekanik Özelliklerine Yüksek Sıcaklığın Etkisi

Nano malzemelerin çimentolu kompozitlerde kullanımına yönelik çalışmalar her geçen gün artmaktadır. Özellikle nano $SiO_2$ üstünpuzolanik özelliği ve boşluk doldurma yeteneği sebebiyle en fazla kullanılan malzemelerden biridir. Yalnızca harç ya da betonundayanım özelliklerini değil dayanıklılık özelliklerini de nasıl etkilediğinin irdelenmesine yönelik araştırmalar sürmektedir. Yükseksıcaklık yapıların doğrudan ya da dolaylı olarak maruz kaldığı etkilerden biridir. Yapı malzemelerinin yüksek sıcaklık altındakidavranışlarının bilinmesi dayanıklılık açısından önemli bir husustur. Bu çalışmanın amacı nano $SiO_2$’in çimento harçlarının yükseksıcaklık direncine etkilerini belirlemektir. Bu amaca yönelik olarak %0, 1, 2 ve 3 oranlarında nano $SiO_2$ çimento ile ikame edilerek dörtfarklı harç karışımı hazırlanmıştır. 7, 28 ve 90. günlerde harç karışımları üzerinde eğilme ve basınç dayanımı deneylerigerçekleştirilmiştir. Nano $SiO_2$’in harçların yüksek sıcaklık direncine etkilerini belirlemek amacıyla, 50x50x50 $mm^3$ boyutlarındaüretilen örnekler 90 günlük kürün ardından 3 saat süresince 300 ve 600 ⁰C sıcaklıklara maruz bırakılarak fırın içinde kendiliğindensoğutulmuştur. Referans sıcaklık olarak 20 ⁰C kullanılmıştır. Yüksek sıcaklık uygulaması sonrasında sertleşmiş harç örneklerinin ağırlıkkaybı, ultrases geçiş hızı kaybı ve basınç dayanımları incelenmiştir. Ayrıca, 600 ⁰C sıcaklık sonrası mikro yapı incelemesi amacıylaörneklerin SEM görüntüleri alınmıştır. Sonuç olarak, 7. günde %2 nano $SiO_2$ ikamesinin eğilme dayanımını %20.0, basınç dayanımınıise referans karışıma göre %24.25 arttırdığı, özellikle erken yaştaki dayanıma olumlu etkisi olduğu belirlenmiştir. Sıcaklık arttıkçaağırlık kaybının arttığı ve ultrases geçiş hızının azaldığı, yüksek sıcaklık direnci için optimum nano $SiO_2$ oranının %2 olduğu, ancakçalışmanın maksimum sıcaklığı olan 600 ⁰C’de nano malzeme ikameli ve ikamesiz tüm karışımların kalan basınç dayanımı sonuçlarınınbirbirine çok yakın olduğu ve SEM görüntülerinde tüm örneklerde çatlaklar meydana geldiği tespit edilmiştir.

Effect of High Temperature on Mechanical Properties of Cement Mortar with Nano $SiO_2$

Studies for the use of nano materials in cementitious composites are increasing day by day. Especially nano $SiO_2$ is one of the most used materials due to its superior pozzolanic feature and space filling ability. Researchs continue to examine how nano $SiO_2$ affects not only the strength properties of mortar or concrete, but also its durability properties. High temperature is one of the effects that structures are exposed to directly or indirectly. Knowing the behavior of building materials under high temperature is an important issue in terms of durability. The aim of this study is to determine the effects of nano $SiO_2$ on the high temperature resistance of cement mortars. For this purpose, four different mortar mixes were prepared by 0, 1, 2 and 3% nano $SiO_2$ substituting cement. On the 7th, 28th and 90th days, flexural and compressive strength tests were carried out on the mortar mixtures. In order to determine the effects of nano $SiO_2$ on the high temperature resistance of mortars, the samples produced in the dimensions of 50x50x50 $mm^3$ were exposed to 300 and 600 ° C for 3 hours after 90 days of curing. The samples were then self-cooled in the oven. 20 ⁰C was used as reference temperature. After high temperature application, weight loss, loss of ultrasonic pulce velocity and compressive strenght of hardened mortar samples were examined. In addition, SEM images of the samples were taken for microstructure analysis after 600 ⁰C temperature. As a result, it was determined that on the 7th day, 2% nano SiO2 substitution increased the flexural strength by 20.0% and compressive strength by 24.25% compared to the reference mixture and had a positive effect especially on early age strength. It was determined that as the temperature increases, the weight loss increases and the ultrasonic pulce velocity decreases, the optimum nano $SiO_2$ ratio for high temperature resistance is 2%, but the residual compressive strenght results of all mixtures with and without nano material substitution at 600 ⁰C are very close to each other. In SEM images, cracks occurred in all samples.

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