Bitümlü karışımların gerilme-şekil değiştirme davranışı

Bitümlü karışımların tasarımı için halen yaygın olarak kullanılmakta olan ampirik yöntemler, sıkıştırılmış karışımların gerçek malzeme özelliklerini tam olarak yansıtamamakta ve yalnızca kabul-red ölçütü olarak kullanılabilmektedir. Asfalt kaplama performanslarının tahminine yönelik tasarım yöntemlerinde kullanılan temel malzeme özelliklerinin belirlenmesine gereksinim duyulmaktadır. Üç Eksenli Kayma Mukavemeti (ÜKM) deneyi, özellikle zemin mekaniğinde kohezyonlu ve granüler malzemelerin davranışlarını belirlemekte halen yaygın olarak kullanılmaktadır. Marshall yönteminin yetersiz kaldığı günümüzde ÜKM deneyinin bitümlü karışımların deformasyon davranışının belirlenmesinde daha gerçekçi sonuçlar vereceği düşünülmüştür. Bu çalışmada, agrega gradasyonun ve bağlayıcı yüzdesinin bitümlü karışımların deformasyon davranışı üzerindeki etkileri ÜKM deneyi ile incelenmiştir. Kalıcı deformasyonların yüksek sıcaklıklarda oluştuğu dikkate alınarak deneyler 40, 50, ve 60 oC’lerde gerçekleştirilmiştir. Bu amaçla, 2006 yılında yayınlanan Karayolları Teknik Şartnamesinde yer alan üç farklı karışım tipi (Aşınma Tip-1, TMA Tip-1 ve TMA Tip-2) seçilmiştir. Tek tip bitümlü bağlayıcının (İzmit B 50-70) kullanıldığı çalışmada belirtilen karışım tipleri için Marshall ve statik sıkıştırma yöntemleri ile hazırlanan numuneler üzerinde Marshall tasarımları yapılmıştır. ÜKM deney numunelerinin hazırlanmasında çift taraflı statik sıkıştırma yöntemi kullanılmıştır. ÜKM deneyinden elde edilen gerilme-şekil değiştirme eğrileri, incelenen parametrelerin deformasyon direnci üzerindeki bilinen etkilerini çok iyi derecede açıklamaktadır. Marshall deneyi sonuçları Taş Mastik Asfalt (TMA) karışımların gerçek deformasyon direncini yansıtmazken, ÜKM deney sonuçları agrega gradasyonun deformasyon direncine olumlu etkisini açıkça ortaya koymaktadır. Bu sonuçlar, ÜKM deneyinin karışım tasarımında ve kalıcı deformasyon tahmininde kullanılabileceğini göstermektedir.  Anahtar Kelimeler: Bitümlü karışımlar, deformasyon direnci, üç eksenli kayma mukavemeti deneyi, gerilme-şekil değiştirme ilişkisi, agrega gradasyonu, bitüm yüzdesi.All over the world, established and new hot-mix asphalt design methods may be classified as recipe, empirical, volumetric, performed-related and per-formed based. Simulation and fundamental test methods are generally carried out in recently developed performance-related and performance-based mix design methods since they give the best relations between the results obtained in-situ and laboratory. In addition to this, simulation and fundamental test methods measure the material response under various stress conditions. In the analytical design, the fundamental properties of materials of pavement layers are required to determine stress-strain curve of the structure. Well known empirical design methods such as Marshall do not reflect the material properties. On the other hand, Superior Performing Asphalt Pavements (Superpave) which is the cutting edge method in mix design requires complicated and expensive equipment. For this reason, economical and less complicated methods are investigated. The triaxial shear strength test is not new in concept and theoretical development. The triaxial shear strength test has been shown to be suitable for evaluating the strength of asphalt concrete mixtures. The triaxial test is widely used in soil mechanics in order to determine the shearing resistance and stress deformation behavior of cohesive and granular materials under various conditions of axial loadings and confining pressures and drainage conditions of test specimens. Asphalt concrete mixtures which are composed of aggregates, bitumen and air are some extend analogous to soils which are composed of soil solids, water and air. Thus it is logical to apply the theory for the triaxial testing developed in soil mechanic to asphalt concrete mixtures. However, the use of the triaxial test for testing asphaltic paving materials is slow in acceptance by pavement engineers mainly due to the complexity of the test and also the lack of a standard procedure. This is evident by the scarcity of published information on the use of the triaxial test for strength testing of asphalt concrete mixtures since the pioneering work of the Triaxial Institute in the early 1950’s. Research in this direction was discontinued due to the complexity of the laboratory triaxial tests, which are time consuming and the difficulties in relating the test results to field behavior of asphalt mixtures. In this study the deformation resistances of hot-mix asphalt mixtures were investigated by the means of triaxial shear strength test. Effects of grading, bitumen content and the temperature on the deformation resistance were investigated. For this purpose, three different asphalt mixtures (Wearing Course Type-1, SMA Type-1 and SMA Type-) were selected. The Marshall mix design (ASTM D 1559) were carried out on three different mixtures. Triaxial shear strength test was conducted on the specimens prepared by double-plunger static compression method. In total, 132 and 145 were tested for the Marshall Design, triaxial shear strength test, respectively. A preliminary study investigated the compaction energy for Wearing Course Type-1 and Stone Mastic Asphalt (SMA) by using the double-plunger compaction equipment as detailed in ASTM D 1074. Later, optimum bitumen contents of mixtures prepared utilizing both static and Marshall Compactor were determined by Marshall Design method. In experimental study, the effect of mixture gradation and the bitumen content on the deformation resistance were examined by the triaxial shear strength tests. For this purpose, İzmir B 50-70 bitumen were used in three different contents. The triaxial shear strength tests were conducted at temperatures of 40, 50 and 60 oC. According to the results, compared to deviator stress values between Wearing Course Type-1 and SMA mixtures for specimens tested at 40 oC, the discrepancy were relating high than the specimens tested at 50 oC and 60 oC. In addition, the deformation resistance of Wearing Course Type-1 was reduced more than that of SMA mixtures at 50 and 60 oC. It should also be noted that the stress-strain curves related to Wearing Course Type-1 were located under those related SMA mixtures. The results revealed that the effects of gradation on deformation resistance were positive at higher temperatures such as 50 and 60oC. The results revealed that gap grading is superior to continuous grading in terms of deformation resistant. The results revealed that gap grading is superior to continuous grading in terms of deformation resistant. More realistic results were obtained from the stress-strain curves showing the effects of above parameters on the deformation resistance. Keywords: Bituminous mixtures, deformation resistance, triaxial shear strength test, stress-strain, gradation of aggregate, bitumen content.&nbsp

Evolutionary conservation of the lipopolysaccharide binding site of β₂-glycoprotein I

β₂-Glycoprotein I (β₂GPI) is a highly abundant plasma protein and the major antigen for autoantibodies in the antiphospholipid syndrome. Recently, we have described a novel function of β₂GPI as scavenger of lipopolysaccharide (LPS). With this in mind we investigated the conservation of β₂GPI in vertebrates and set out to identify the binding site of LPS within β₂GPI. The genome sequences of 42 species were surveyed. Surface plasmon resonance (SPR) was performed with peptides to characterise the binding site of β₂GPI for LPS. β₂GPI could be identified in most tested vertebrates with a high overall amino acid homology of 80% or more in mammals. SPR revealed that a synthesised peptide (LAFWKTDA) from domain V of β₂GPI was able to compete for binding of β₂GPI to LPS. The AFWKTDA sequence was completely conserved in all mammals. The peptide containing the LPS binding site attenuated the inhibition by β₂GPI in a cellular model of LPS-induced tissue factor expression. Other important sites, such as the binding site for anionic phospholipids and the antiphospholipid antibody binding epitope, were also preserved. β₂GPI is highly conserved across the animal kingdom, which suggests that the function of β₂GPI may be more important than anticipate