Temperatūriniai plyšiai asfalto dangose. Kaip galime jų išvengti?

Abstract

Vidutinių platumų klimato juostai priklausančioms valstybėms būdingas sezoniškumas: šalta žiema, šilta vasara ir tarpiniai sezonai - pavasaris ir ruduo. Lietuva yra viena iš tokių valstybių. Žiemos laikotarpiu asfalto dangų paviršiaus temperatūra čia nukrinta iki - 20 oC ir žemiau. Tačiau vasaros metu pakyla iki + 60 oC ir daugiau. Toks platus asfalto dangų paviršiaus temperatūros kitimas nustato poreikį, parenkant bitumą asfalto mišinio gamybai, įvertinti jo eksploatacines savybes. Pabrėžtina, kad mažas bitumo elastingumas žemose temperatūrose nulemia kritinių įtempių asfalto dangos paviršiuje susidarymą. Būtent dėl jų žiemos laikotarpiu asfalto dangose atsiveria temperatūriniai plyšiai - viena reikšmingiausių asfalto dangų pažaidų, nulemiančių spartesnę kelio degradaciją.

In order to prevent the formation and development low temperature cracks in asphalt pavements, it is necessary select a bitumen for the asphalt mixture production that is low temperature cracking. However, the existing test methods and limiting values fail in evaluation of bitumen performance at temperatures. It has resulted from the introduction new types bitumen; the determination of limiting values bawd on the limiting values of another method rather than on the actual asphalt pavement performance; insufficient repeatability and reproducibility the test method, etc. Therefore, dr. Judita Gražulytė from Road Research institute of Vilnius Gediminas technical university has spent four years in developing new test method and determining limiting values of bitumen characteristics based on the actual pavement performance to evaluate its resistance to low temperature cracking. As a result, on 17 December 2019 she successfully defended her thesis "Bitumen stress relaxation modulus as an asphalt pavements resistance to tow temperature cracking” (supervisor prof. dr. Audrius Vaitkus). Based on the results of the severity of low temperature cracking determined in the 26 analysed road sections and results of the stress relaxation modulus and its slope determined for the recovered bitumen of the asphalt samples (cores) taken from these sections limiting values have been determined.Test temperature was higher by 10 0C than the lowest surface temperature of the asphalt pavement recorded during the operation of those sections. The formation and development of low temperature cracks in asphalt pavements is limited when the stress relaxation modulus of the bitumen used for the asphalt mixture production of the upper asphalt pavement layer and its slope at 60 s is not higher than 52 MPa and not lower than 0.370, respectively. Temperature higher by 10°C than the lowest surface temperature of the asphalt pavement recorded in the location of the bitumen's application has to be applied in the test. The exceeding of at least one limiting value leads to foe formation of low temperature cracks. In addition to this, an algorithm was designed to select the bitumen for foe asphalt mixture production of the upper layer of asphalt pavement irrespective of the type of the foreseen construction (new construction, repair rehabilitation or reconstruction).