Abstract
This article gives the summary of the author’s PhD thesis supervised by Prof Dr Sc Ing Juris Rihards Naudžuns and defended on 10 November 2010 at the Riga Technical University. Introduction provides characteristics of the object of the research – asphalt concrete – from chemical, physical and mechanical aspects. The current situation on the roads and in Latvian transport industry has been described, and urgency of the problem, the necessity to eliminate deficiencies and the economic effect has been substantiated. The aim and tasks of the thesis have been formulated. Chapter 1 is devoted to survey of the literature which provides new and the already known (classical) modelling methods of stress and strain of road pavement layers, as well as description of advantages and deficiencies of these methods. Chapter 2 contains description of test methods used in the Promotion thesis. Properties of experimental specimens and their raw materials have been compared. Methods of designing asphalt mixtures are described. Chapter 3 provides analysis of external factors causing asphalt concrete permanent strain – temperature and transport load. In Chapter 4, test specimens have been experimentally tested with the help of the performance testing methods (wheel tracking test, uniaxial cyclic compression test and triaxial cyclic compression test). Plastic deformations have been determined and deformation rates have been calculated. In Chapter 5, the asphalt pavement quality provision system has been developed on the basis of the analysis of the obtained results and recommendations have been provided for minimising rutting. This thesis is written in Latvian and is available on http://ortus.rtu.lv/ web page and from the author upon request.
Highlights
State of the problemSignificant changes took place on the roads and in Latvian transport industry during the last nineteen years
This article gives the summary of the author’s PhD thesis supervised by Prof Dr Sc Ing Juris Rihards Naudžuns and defended on 10 November 2010 at the Riga Technical University
To enable prediction of permanent strain, the following assumptions have been used: −−rutting appears on roads or streets in accordance with the “number of loading cycles – strain” correlation, which is obtained by performing the permanent strain; −−laboratory research with the help of the wheel tracking test (WTT) method; −−rutting appears only in the asphalt concrete (AC) surface layer and is not related to strain properties of the bottom layers, i.e. ruts are not the structural or impress result; −−the surface layer has no temperature gradient, the temperature is constant in the entire material; −−the traffic load expressed in equivalent single-axle load (ESAL) units is 16.7 mln during twenty years (Table 2); −−rutting appears at the temperature of +40 °C and higher
Summary
Significant changes took place on the roads and in Latvian transport industry during the last nineteen years. ISSN 1822-427X print / ISSN 1822-4288 online http://www.bjrbe.vgtu.lt specifikācijas 2005 [Road Specifications 2005] requirements from 2004, started to be used for the asphalt pavement wear course These mixtures, being new for Latvian conditions, have been the object of investigation of the world’s leading researchers for more than 40 years. Aim and tasks of the research – to develop asphalt mixes by using conventional and unconventional raw materials and to determine their strain development dynamics by using for this purpose the developed methods of predicting the road pavement permanent strain on the basis of comprehensive evaluation of external factors. To develop and manufacture the AC and SMA mixtures by using conventional and unconventional aggregates, as well as modified and unmodified bitumen binders and to compare the results and to evaluate their conformity to requirements of the technical regulations; 5. Tasks of the Thesis: 1. to analyse the mechanism of asphalt pavement permanent strain formation, the existing prediction methods and main (internal and external) factors influencing the strain; 2. to determine properties of the steel manufacturing byproduct – Martin steel slag (MSS), as an aggregate, and to compare them with properties of conventional granite, diabase and dolomite aggregates; 3. to mutually compare properties of the unmodified bitumen binder B70/100 and the styrene-butadiene-styrene SBS polymermodified binder; 4. to develop and manufacture the AC and SMA mixtures by using conventional and unconventional aggregates, as well as modified and unmodified bitumen binders and to compare the results and to evaluate their conformity to requirements of the technical regulations; 5. to determine strain properties of the developed asphalt mixtures by means of the cyclic loading and wheel tracking tests and to evaluate the results obtained by different methods; 6. to statistically process the observation data – the traffic load and external air temperatures characteristic for Latvian circumstances - and to analyse the asphalt pavement high performance temperature dynamics; 7. to adapt the methods of the equivalent single-axle load (ESAL) estimation for the intensively loaded Latvian streets and roads and to develop the ESAL estimation equation (Eq) for the period with the max high performance temperatures; 8. by using strain properties of the asphalt mixtures obtained in the laboratory, the VESYS model, the load of heavy transport vehicles expressed in ESAL units, as well as, by considering the specific features of local climatic circumstances, to investigate permanent strain accumulation of the developed asphalt mixtures; 9. to develop a concept of the asphalt pavement quality provision system for the intensively loaded Latvian streets and roads to allow performing systematic evaluation
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