Ermüdungs- und Heilungseigenschaften von Asphalt

This thesis, consisting of 7 peer-reviewed international journal publications is devoted to the investigation of fatigue and recovery properties of asphalt materials. Concerning the cracking mechanisms, the effects of both cracking in asphalt mixture and cracking at layers’ interface were considered. Since several test types are available for determination of asphalt mixture fatigue resistance, there is no consensus between researchers about the appropriate fatigue test. Considering the stress controlled test mode, it was found that uniaxial tension-compression test is the most reliable for evaluation of the asphalt mixture fatigue resistance. Furthermore, a new fatigue procedure was introduced, able to overcome the shortcomings if only a single test temperature is considered for the fatigue evaluation process (cp. EN 12697-24). This procedure allows a plausible evaluation of the asphalt mixture fatigue performance considering wide temperature range, with a marginally increased laboratory effort. Recovery potential of asphalt mixtures was addressed based on the concept of dissipated energy. The influence of several internal and external factors (bitumen polymer modification, ageing condition, binder content, degree of compaction and rest period duration) on recovery properties of asphalt mixtures was investigated. In order to overcome large scattering of the experimental results and consequently an erroneous evaluation of asphalt mixture recovery potential, a new recovery index was introduced. Moreover, the recovery potential of a specific asphalt mixture was investigated in detail, taking into consideration biasing effects such as nonlinearity and self-heating, observed during cyclic loading. Considering various asphalt mixtures and tack coats, the influence of test temperature and compressive normal stress on layers’ interface fatigue behaviour was determined. Based on this preliminary work, optimal test parameters were proposed, allowing a successful fatigue evaluation of the layers’ interfaces. Additionally, the comparison between results from the proposed cyclic shear fatigue procedure and results from monotonic shear test was performed. It was found that the resulting shear strength from monotonic shear test can be used only as a rough indicator for long term interface bonding performance, because not all research and field experience could be reflected in the test results.Diese Dissertation, bestehend aus 7 internationalen Peer-Review Publikationen, widmet sich der Untersuchung der Ermüdungs- und Heilungseigenschaften von Asphalt. Hinsichtlich der Rissmechanismen wurden die Effekte der Rissbildung, sowohl im Asphalt, selbst als auch an der Grenzfläche zwischen den Asphaltschichten untersucht. Mit Hilfe der Auswertung, der während eines Ermüdungsversuchs dissipierten Energie, erfolgte der Vergleich der gängigen spannungsgeregelten Ermüdungstestmethoden. Es wurde festgestellt, dass sich der einaxiale Zug-Druck-Wechselversuch sehr gut für die Beurteilung des Ermüdungswiderstandes von Asphalt eignet. Weiterhin wurde das Problem der normgemäßen Analyse des Ermüdungsverhaltens (vgl. EN 12697-24) bei einer einzigen Prüftemperatur beleuchtet. Ein neues Ermüdungskonzept wurde entwickelt, das eine plausible Bewertung des Ermüdungswiderstandes von Asphalt über den gesamten Gebrauchstemperaturbereich mit einem geringfügig erhöhten Laboraufwand ermöglicht. Die Bestimmung der Heilungseigenschaften von Asphalt erfolgte auf der Grundlage des Konzepts der dissipierten Energie. Die Einflussgrößen unterschiedlicher Prüfvariablen (Bindemittelgehalt, Verdichtungsgrad, Lastpausendauer, Alterungszustand, Bindemittelsorte) auf die Heilungseigenschaften wurden analysiert. Weiterhin wurde ein neuer Index zur vergleichenden Bewertung des Heilungsvermögens entwickelt, der eine Reduzierung der materialbedingten Streuung im Prüfergebnis ermöglicht. Schließlich erfolgte eine detaillierte Untersuchung des Heilungspotentials, wobei die bei der zyklischen Belastung beobachteten Nebeneffekte Nichtlinearität und Selbsterwärmung von der eigentlichen Materialheilung isoliert wurden. Unter Berücksichtigung verschiedener materialspezifischen Parametern wurde der Einfluss der Prüftemperatur und Normalspannung auf den Ermüdungswiderstand der Grenzfläche zwischen den Asphaltschichten bestimmt. Es wurden die optimalen Prüfparameter vorgeschlagen, mit denen eine bestmögliche Ermüdungsbewertung des Schichtenverbundes erfolgen kann. Anschließend konnte mit Hilfe des Vergleichs der Ergebnisse aus zyklischen und monotonen Scherversuchen festgestellt werden, dass die Scherkraft aus dem monotonen Scherversuch nur als grober Indikator für die Bestimmung der Lebensdauer des Schichtenverbundes herangezogen werden kann

The Impact of Recycled Concrete Aggregate on the Stiffness, Fatigue, and Low-Temperature Performance of Asphalt Mixtures for Road Construction

The need for road (re)construction materials is constantly growing. At the same time, there is a limited quantity of new, high-quality materials available and a buildup of secondary/recycled construction materials. One possible solution may be the use of recycled concrete aggregate (RCA) in asphalt mixtures instead of natural aggregate (NA), which also promotes economic and environmental sustainability. The potential use of fine and coarse RCA in road asphalt mixtures is analyzed in this work. Nine asphalt mixtures were tested for base course layers, where RCA was used as a NA substitute. The impact of the quantity of RCA (up to 45% by mass) on the resulting physical and mechanical properties of asphalt mixtures was investigated, and consequently compared with the properties of a reference control mixture produced with NA only. Results reveal that the addition of RCA requires higher bitumen in comparison to the control mixture (up to 1%). Consequently, mixtures with RCA had 15 20% lower stiffness and up to 26% higher critical fatigue strain value (epsilon(6)). Although RCA mixtures contained more bitumen, their low-temperature resistance was slightly inferior compared with the control mixture (failure temperatures were up to 4.3 degrees C higher). In conclusion, asphalt mixtures with up to 45% RCA can be used without substantially reducing performance

Assessment of age and intersexual size differences in Bufo bufo

Numerous studies have underlined the complex nature of relationship between age, size, and reproductive traits in anurans. One of the most intriguing problems for evolutionary biologists is intersexual difference in body size (SSD). For testing various hypotheses about SSD, we need reliable estimates of its extent (the important issue being the choice of trait for analysis) as well as the accurate determination of individual age. The measures of SSD may be subject to error if estimated from populations with unknown age distribution; amphibians continue to grow throughout their life and SSD is linked to sex differences in traits such as age at maturity and lifespan. In the present paper, we analyze problems involved in accurate determination of age structure and factors that may lead to under- or overestimation of individual age, as well as the problem of appropriate choice of traits, in the light of our experience and results of investigating populations of common toad (Bufo bufo) in the vicinity of Belgrade.Brojne studije istakle su složenu prirodu odnosa između starosti, veličine tela i reproduktivnih osobina kod bezrepih vodozemaca. Za evolucione biologe jedan od najintrigantnijih problema je interseksualna razlika u veličini tela (SSD). Za testiranje hipoteza koje se tiču SSD, neophodne su tačne procene njene veličine (izuzetno je važno pitanje izbora osobina koje se koriste u toj analizi), kao i precizno određivanje starosti. Procena SSD može biti pogrešna ako nije poznata uzrasna struktura date populacije; vodozemci nastavljaju da rastu tokom života, a SSD je povezana sa interseksualnim razlikama u osobinama kao što su vreme polnog sazrevanja i dužina života. U ovom radu analiziramo probleme vezane za tačnu procenu uzrasne strukture i činioce koji mogu da dovedu do precenjenih ili potcenjenih vrednosti, kao i probleme adekvatnog izbora osobina za analizu, s obzirom na naša iskustva i rezultate proučavanja populacija Bufo bufo iz okoline Beograda.Projekat ministarstva br. 172

The Impact of Recycled Concrete Aggregate on the Stiffness, Fatigue, and Low-Temperature Performance of Asphalt Mixtures for Road Construction

The need for road (re)construction materials is constantly growing. At the same time, there is a limited quantity of new, high-quality materials available and a buildup of secondary/recycled construction materials. One possible solution may be the use of recycled concrete aggregate (RCA) in asphalt mixtures instead of natural aggregate (NA), which also promotes economic and environmental sustainability. The potential use of fine and coarse RCA in road asphalt mixtures is analyzed in this work. Nine asphalt mixtures were tested for base course layers, where RCA was used as a NA substitute. The impact of the quantity of RCA (up to 45% by mass) on the resulting physical and mechanical properties of asphalt mixtures was investigated, and consequently compared with the properties of a reference control mixture produced with NA only. Results reveal that the addition of RCA requires higher bitumen in comparison to the control mixture (up to 1%). Consequently, mixtures with RCA had 15-20% lower stiffness and up to 26% higher critical fatigue strain value (E6). Although RCA mixtures contained more bitumen, their low-temperature resistance was slightly inferior compared with the control mixture (failure temperatures were up to 4.3 C higher). In conclusion, asphalt mixtures with up to 45% RCA can be used without substantially reducing performance

Assessment of age and intersexual size differences in Bufo bufo

Numerous studies have underlined the complex nature of relationship between age, size, and reproductive traits in anurans. One of the most intriguing problems for evolutionary biologists is intersexual difference in body size (SSD). For testing various hypotheses about SSD, we need reliable estimates of its extent (the important issue being the choice of trait for analysis) as well as the accurate determination of individual age. The measures of SSD may be subject to error if estimated from populations with unknown age distribution; amphibians continue to grow throughout their life and SSD is linked to sex differences in traits such as age at maturity and lifespan. In the present paper, we analyze problems involved in accurate determination of age structure and factors that may lead to under- or overestimation of individual age, as well as the problem of appropriate choice of traits, in the light of our experience and results of investigating populations of common toad (Bufo bufo) in the vicinity of Belgrade.Brojne studije istakle su složenu prirodu odnosa između starosti, veličine tela i reproduktivnih osobina kod bezrepih vodozemaca. Za evolucione biologe jedan od najintrigantnijih problema je interseksualna razlika u veličini tela (SSD). Za testiranje hipoteza koje se tiču SSD, neophodne su tačne procene njene veličine (izuzetno je važno pitanje izbora osobina koje se koriste u toj analizi), kao i precizno određivanje starosti. Procena SSD može biti pogrešna ako nije poznata uzrasna struktura date populacije; vodozemci nastavljaju da rastu tokom života, a SSD je povezana sa interseksualnim razlikama u osobinama kao što su vreme polnog sazrevanja i dužina života. U ovom radu analiziramo probleme vezane za tačnu procenu uzrasne strukture i činioce koji mogu da dovedu do precenjenih ili potcenjenih vrednosti, kao i probleme adekvatnog izbora osobina za analizu, s obzirom na naša iskustva i rezultate proučavanja populacija Bufo bufo iz okoline Beograda.Projekat ministarstva br. 172

Elementi Waldorf pedagogije u praksi redovitog dječjeg vrtića

U ovom radu pobliže je opisan život i djelovanje tvorca Waldorf pedagogije, Rudolfa Steinera. Iznesena su waldorfska pedagoška načela, uređenje prostora, godišnji i dnevni ritam, te okruženje i materijali. Nadalje, uspoređujući Waldorf i Montessori pedagogiju, uvidjeli smo sličnosti i razlike u dvama pristupima. Prikazani su elementi Waldorf pedagogije u redovnom dječjem vrtiću „Bosiljak“, mjesečni planovi, okruženje, te opis dnevnih aktivnosti u odgojno obrazovnoj skupini.This paper describes in detail the life and activities of the creator of the Waldorf pedagogy, Rudolf Steiner. There were a Waldorf pedagogical principles, spatial planning, annual and daily rhythm and environment and materials. Furthermore, comparing the Waldorf and Montessori pedagogy, we saw the similarities and differences in the two approaches. Shown elements of Waldorf pedagogy in regular kindergarten „Bosiljak“, a monthly plans, environment, and a description of daily activities in the educational educational group

Elementi Waldorf pedagogije u praksi redovitog dječjeg vrtića

U ovom radu pobliže je opisan život i djelovanje tvorca Waldorf pedagogije, Rudolfa Steinera. Iznesena su waldorfska pedagoška načela, uređenje prostora, godišnji i dnevni ritam, te okruženje i materijali. Nadalje, uspoređujući Waldorf i Montessori pedagogiju, uvidjeli smo sličnosti i razlike u dvama pristupima. Prikazani su elementi Waldorf pedagogije u redovnom dječjem vrtiću „Bosiljak“, mjesečni planovi, okruženje, te opis dnevnih aktivnosti u odgojno obrazovnoj skupini.This paper describes in detail the life and activities of the creator of the Waldorf pedagogy, Rudolf Steiner. There were a Waldorf pedagogical principles, spatial planning, annual and daily rhythm and environment and materials. Furthermore, comparing the Waldorf and Montessori pedagogy, we saw the similarities and differences in the two approaches. Shown elements of Waldorf pedagogy in regular kindergarten „Bosiljak“, a monthly plans, environment, and a description of daily activities in the educational educational group

Reproductive traits in common toad Bufo bufo from the vicinity of Belgrade

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Experimental investigation of asphalt mixture containing Linz-Donawitz steel slag

Standard asphalt mixtures for road infrastructures consist of natural aggregate and bitumen. A number of research efforts have successfully investigated the possibility of replacing the conventional aggregate skeleton with industrial by-products such as slag originating from steel production process. However, little is known on the effect of steel slag on the mixtures performance properties such as resistance to low-temperature cracking and to permanent deformation, stiffness and fatigue. This paper presents a comprehensive investigation on the fundamental performance properties of different types of asphalt mixtures prepared with 100% LD slag aggregate and a conventional asphalt mixture containing natural Gabbro aggregate. Sophisticated testing methods were used to evaluate the key performance parameters for the set of asphalt mixtures investigated. In this study, low temperature cracking was addressed through thermal stress restrained specimen tests. Penetration tests and cyclic compression tests were used to evaluate the response of asphalt binder and asphalt mixture to permanent deformation due repeated loading, respectively. The cyclic indirect tensile test was selected for investigating both stiffness properties and fatigue resistance. For this purpose the complex stiffness modulus was measured to quantify material stiffness under different temperature and loading conditions providing information on the visco-elasto-plastic material behavior. Fatigue tests were used to determine the progressive and localized material damage caused by cyclic loading. The experimental results indicate that asphalt mixtures prepared with LD slag are suitable for asphalt pavement construction and that in most cases they perform better than conventional asphalt mixtures prepared with Gabbro aggregate