Karbon elyaf ile betonun güçlendirilmesi

Abstract

Günümüzde yapılar birçok nedenden dolayı hasar görmektedir. Hasar gören yapılar ve düşük standartlara sahip yapıların güçlendirilmesi tüm dünyada hızla gelişmekte olan konulardan biri haline gelmiştir. Kullanım amacı değişmiş yapılar, deprem yönetmeliğine uyumlu olmayan eski yapılar ve hasar gören yapılar güçlendirme ihtiyacı taşımaktadır. Kullanılabilen güçlendirme tekniklerinden CFRP (Carbon-Fiber-Reinforced Polimer) uygulaması, geleneksel güçlendirme tekniklerine nazaran çok daha hızlı ve kolay uygulanması, malzemenin çok hafif olması nedeniyle yapıda ilave yük artışına neden olmaması ve çelikten yaklaşık 10 misli yüksek mukavemete sahip olma gibi özellikleri nedeniyle bu metodun inşaat alanındaki kullanımı hızla artmaktadır. Bu çalışma kapsamında güçlendirme malzemesi olan karbon elyafın beton numuneler üzerindeki dayanımlılık etkisi laboratuar ortamında mukayese edilerek incelenmiştir. Deney aşamasında standartlara uygun silindir kalıplardan temin edilen beton numuneler laboratuar ortamında hazırlanmıştır. Bu numunelerin bir kısmına epoksi yapıştırıcı yardımıyla tek kat ve çift kat olmak üzere karbon elyaf sarılarak güçlendirilmiştir. Hazırlanan tüm numunelerin laboratuar ortamında tekrarlı eksenel yükler altındaki davranışları incelenmiş ve sarılan elyafın yapıdaki mukavemet etkisi gözlemlenmiştir. Ayrıca numunelere monte edilen yatay ve dikey transducerlar aracılığıyla eksenel ve çapsal deformasyon değerleri incelenmiştir. Bu deneyler neticesinde sargı sayısının artması, dayanım artışı sağlaması ile birlikte sismik performansın en önemli parametrelerinden biri olan süneklilik artışını da sağladığı tespit edilmiştir. Ancak genel olarak karbon elyaf ile sargılanan numunelerden standart silindir beton numunelerin ortalama değerleri incelendiğinde karbon elyaf ile güçlenen numunelerde yaklaşık olarak % 25 oranında dayanım artışı tespit edilmiştir.

In the recent years, strengthening of Reinforced Concrete (RC) elements using Carbon Fiber Reinforced Polymers (CFRP) sheets tends to be more popular depends on development of civil engineer materials. Due to lightweight with high strength and corrosion properties, CFRP become an alternative strength material in strengthening reinforced concrete structures. Buildings can be damaged because of many reasons nowadays. Damaged buildings and strengthening buildings with low standards became one of the fast developing subjects all over the World. Buildings that purpose of use has been changed, old buildings not in compliance with earthquake regulation and damaged buildings need to be strengthened. Carbon fiber, used in one of the strengthening techniques Carbon Fiber Method, despite being thin and light as shirt fabric, increases the strength of component element acting as a steel plate when applied with epoxy cement. Additionally, as it is more faster and easier to apply according to traditional strengthening techniques and being very light that does not cause extra load increase and giving 14 times more strenght than steel, use of this method in construction is increasing fastly. Concrete known as a typical brittle material which is too weak in tension with respect to its compression strength is mostly used with reinforcements for bending of structures. It can be defined as inelastic, nonhomogeneous and nonlinear material. In this study it is aimed to investigate behavior of reinforced concrete sections strengthened by wrapping with Carbon Fiber Reinforced Polymers (CFRP), which has high tension strength, to eliminate weakness property of concrete in laboratory conditions. For this purpose, the 10 pieces of concrete samples of standard cylindrical specimens have 150 mm diameter and 300 mm height were prepared. Ready mixed concrete was used for preparing the concrete specimens with appropriate amount of cement, water, sand, gravel, stone powder, admixtures. After 28 day curing period, lets the concrete to gain its desired strength, can be accepted as water content in the mix not allowed to evaporate from the concrete the standard cylindrical samples obtained for wrapping process. Firstly, all surfaces of the dried standard specimens with the help of a brush have been cleared of dust and similar substances providing dust-free surface for the fiber application. Then required amounts of carbon fiber samples were prepared with suitable dimensions for jacketing the samples as a confinement. 4 of 10 samples prepared as unconfined, 3 of them wrapped with CFRP as single layered and the other 3 double-layered with the help of epoxy. Then the 28 days old specimens tested under monotonic uniaxial compression to determine the strength-strain relation. Also via horizontal and vertical transducers assembled to samples, axial and iametrical values have been examined. In order to define the descending portion of the concrete behavior curve several compressive loading proceeds repeated for each sample. Such cyclic loading, unloading under high deformations and reloading, process were evaluated to discuss the CFRP effects on concrete behavior. The results obtained in this experimental study shown that confining by wrapping with CFRP of concrete sections examined under repeated axial load in laboratory environment and strengthening effect of wrapped fiber has been observed. As a result of these study, increase of wrapping number has been determined to increase in strength also with increase in ductility which is one of the most important parameters of seismic performance. In the case of average values of cylinder concrete samples were examined, samples strenghtened by carbon fiber were observed to show 25% more strength. It should be noted that the CFRP has no significant effects on behavior of concrete with high strength.