Asfaltlarda bitümle birlikte granüler sülfür kullanımının stabiliteye etkisi

Özet

Kaliteli asfalt karışımlarının elde edilebilmesi için, kaliteli malzemenin yanı sıra, katkı maddeleriyle güçlendirilmiş modifiye bağlayıcının kullanılması da büyük önem taşımaktadır. Malzemenin ve bağlayıcının seçiminin doğru yapılması, asfalt kaplamaları direncinin güçlendirilmesinde en etkin yöntemlerden biridir. Son yıllarda bozulma probleminin araştırılması ve çözüme kavuşturulması amacıyla, çok değişik modifiye katkı maddeleri kullanılmıştır. Her biri farklı özellik taşıyan, söz konusu katkıların asfalt kaplamaları üzerindeki etkileri de farklılıklar göstermektedir. Geniş ve değişik bir ürün yelpazesine sahip olan modifiye katkı maddelerinin ortak dezavantajları ise bir yandan karışımın özelliklerini iyileştirirken, diğer yandan maliyetini yükseltmeleridir. Modifiye edici katkı maddeleri arasında yer alan sülfür, maliyet yükseltme kuralını bozan ender katkı maddelerinden biridir. Sülfür, diğer modifiye edici katkı maddelerinin aksine, karışımın özelliklerini iyileştirirken maliyetini düşürmektedir. Bu çalışmada, bitümle birlikte bağlayıcı olarak kullanılan Granüler Sülfür (GSF)’ün karışım üzerindeki etkileri araştırılmıştır. Silindirik Marshall numuneleri hazırlanmış ve bu numunelere stabilite-akma deneyleri uygulanmıştır. Karışımda kullanılan malzeme, ilgili şartname ve standartlara uygun olarak test edilmiş ve uygun olduğu tespit edilmiştir. Bitümlü Sıcak Karışım (BSK)’ın optimum bağlayıcı miktarını belirlemek için Marshall tasarım metodu kullanılmıştır. Laboratuarda, %10, %20, %30, %40 ve %50 GSF malzemesi B50/70 bitüm yerine bağlayıcı olarak karışıma ilave edilmiştir. Geleneksel karışımla GSF karışımına Marshall stabilitesi deneyleri yapılmış ve karışım numuneleri arasında bir karşılaştırma yapılarak “Sonuçlar” bölümünde değerlendirilmiştir.

Abstract

Permanent deformations, primarily in the form of ruts, are one of the basic asphalt pavement damages impairing its service properties. Application of ap-propriate asphalt mixtures and binder modification are effective methods for improving asphalt courses resistance. Many kinds of modifiers, in recent years, have been used for dealing and solving this problem. One of these modified materials is sulfur. The pre-sent cost of sulfur varies, dependent on transporta-tion costs. Readily the sulfur cost is approximately five-six times lover than the bitumen cost. It is antic-ipated that the future price of sulfur will be much lower because supply will exceed demand. The ex-cess sulfur will be obtained from desorbing natural gas, desulfurizing petroleum crude or coal, or re-covering elemental sulfur from stack emissions. Granular Sulphur (GSF) is added into the hot mix-ture of aggregates and bitumen during the mixing process. It is not pre-blended with bitumen. The ad-dition of GSF to the bitumen modifies the bitumen properties. Bitumen and GSF combine at a tempera-ture above the melting point of the GSF (120°C). Part of the GSF is chemically combined with the bi-tumen and acts as an extender. This part of GSF is dissolved in the bitumen modifying the bitumen properties - viscosity is lowered and its ductility is increased. Above a certain quantity of GSF in the bitumen, GSF remains predominantly as free sulfur and when the blend cools, it crystallizes. Depending on the amount of GSF added, the crystal-lization gives different levels of strengthening. Sulphur crystallization acts as a structuring agent in the asphalt mixture. The chemical combination between sulphur and hy-drocarbon during mixing requires close control of the temperature during the mixing process. The tem-perature must be maintained at 140°C ± 5°C. This operational temperature range is important to en-sure a safe-working operation. Above 145°C hydro-gen sulphide (H2S) and sulphur dioxide (SO2) will start to be emitted and these emissions will increase steeply with temperature increase. As the sulphur has a viscosity reducing effect on the bitumen it helps in achieving the ideal viscosity of the binder for coating at a lower temperature. In this study, the effects of Granular Sulfur Asphalt (GSF), which used as a binder in place of bitumi-nous binders, on the mix were investigated. Standard tests were applied to binder and aggregate to define their properties before producing of cylindrical samples. Marshall design was used to evaluate the optimum binder in the Hot Mix Asphalt (HMA). The Marshall Stability and flow test provides the perfor-mance prediction measure for the Marshall Mix de-sign method. Marshall samples were prepared in the laboratory by adding of 10%, 20%, 30% 40% and 50% GSF replacing with penetration grade B 50/70 to the mix. Details of the materials used, specimen grain size and procedures for the preparation of the GSF-containing asphalt mixture, is described below. The raw materials used for this study were obtained from different areas. The granular sulfur (GSF) was obtained from the Shell Canada Group. Bitumen with a penetration of 64.1, specific gravity of 1.022 g/cm3 at 25°C and softening point of 51.5°C was obtained from TÜPRAŞ İzmit Refinery. All kinds of aggregates (Coarse, fine and mineral filler) used throughout this study was obtained from a stone quarry in the Ömerli area of Istanbul. As the density of GSF is nearly twice that of bitu-men, the binder content in weight of GSF containing asphalt mixtures is generally increased for achiev-ing the same volume of binder in comparison with conventional hot mix asphalt (HMA). The gradation curve of the GSF-containing asphalt mixture is the same as for HMA. Marshall Stability test was carried out using Mar-shall Equipments. Comparisons were made between the conventional and GSF mixes test results. In comparison with HMA, the Marshall stability of GSF-containing asphalt mixtures is generally in-creased. The GSF 50 mix stability was much higher than the conventional mix. In addition GSF mixes are purported to be more resistant to water stripping and resistance to gasoline, diesel fuel and other sol-vents is improved. The laboratory test results of carried on the asphalt concrete samples and mix variables are presented in the “Conclusions” section.