Komsun Siripun

The Effects of Moisture Characteristics of Crushed Rock Base (CRB)

This paper reports the deformation behaviour of crushed rock with unsaturated condition under repeated cyclic loading triaxial (RLT) tests performed at different stress levels, in order to investigate the effect of moisture content to crushed rock performances and permanent deformation behaviour. Road surface rutting is the core basis of damage in flexible pavements which the mainly significant is crushed rock still unclearly thoughtful regarding deformation behaviour under real situation. RLT test is used to describe the various deformation responses of unbound granular materials (UGMs) by macro-mechanical observations. The main study focused on the influence of the moisture content. Moreover permanent deformation behaviour of crushed rock will be investigated and limit ranges of crushed rock should be considered in pavement analysis and design.

The use of fibre reinforced crushed rocks for the improvement of tensile strength

This study aims to report the possible use of fibre to improve the tensile strength of crushed rock base in a pavement in order to reduce the cracking of cemented material. As well is known, stabilized materials always present brittle responses under applied loads and suddenly collapse after peak loading. From this point, it means that cemented material only advances compressive behaviour and will never enhance long term performances such as fatigue and durability. Cemented crushed rock with fibre was selected to represent the tensile strength of pavement base material. Sophisticated tests were conducted to observe mechanical responses under applied loads such as indirect tensile and unconfined compressive strength, and the resilient modulus. The test results showed that fibre reinforcement improved the tensile strength and ductility of stabilized materials.

Permanent Deformation Behaviour and Model of Crushed Rock Base

Abstract This study aims to report on the permanent deformation behaviour of a crushed rock base (CRB) subjected to repeated cyclic loads from repeated load triaxial tests with different stress levels in order to gain more understanding of such materials for Western Australian roads based on mechanistic-empirical pavement design and analysis. As is well known, road surface rutting is generally considered one of the main types of damage in flexible pavements. One factor contributing to the rutting of an asphalt road surface is the excessive deformation of a base course layer. CRB is the commonly used base course material in the Western Australia metropolitan area. In recent times, CRB has not been fully characterised based on fundamental pavement analysis, therefore the behaviour of a plastic deformation response of CRB under service loads is not well understood. In this study, CRB was mechanically investigated and the shakedown concept was utilised to explain its behaviour under cyclic loading conditions, and the limited use of CRB subjected to various degrees of stress conditions was defined. While the plastic shakedown limit of an unbound granular material is known from macro-mechanical observations of its response following the shakedown concept, the limitations of the accumulated plastic deformation in an unbound granular layer causing deterioration in pavements is predictable. The investigation was designed such that compacted CRB samples, at a compaction condition of 100% maximum dry density and 100% optimum moisture content, were subjected to applied load conditions at various stress levels (the ratio of a vertical principal stress, σ1 and a horizontal principal stress, σ3). The limitations on the use of CRB as a base course material will be introduced, as well as its appropriate working stress ranges.

Cracking and flexural behaviors on cement treated crushed rock for thin flexible pavement

Fatigue cracking is considered to be one of the most important types of distress affecting the performance of flexible pavements on major highways. This report analyses the results of a laboratory study of the static and fatigue response of a typical Western Australia Cement Treated Base (CTB) to evaluate its mechanical parameters i.e. flexural strength, flexural stiffness and tensile strains. Five different series of cement content were evaluated in the mix of 1%, 2%, 3%, 4% and 5%. Two major types of testing were conducted for the purpose of this study, i.e. Flexural Fatigue Tests (dynamic loading) and Flexural Beam Tests (static loading). The flexural fatigue tests were carried out with strain control mode. From the tests, the flexural stiffness for each specimen was calculated. The flexural stiffness was obtained from maximum tensile strains on the bottom of the specimens. The outcomes of the paper are as summarized as follow: First, 1% to 3% CTB was found out to be classified as modified material while 4% and 5% TB are categorized as stabilized materials. Second, fatigue cracking phenomenon can be seen in stabilized materials (4% and 5% CTB) while other types of distress may affect the behavior of modified materials (1 to 3% CTB). Third, 4% cemented material is observed to be the most suitable material to perform under fatigue loading conditions. Fourth, a series of recommendations are presented for further research i.e. the Flexural Fatigue Test be conducted at a suitable (lower) strain value instead of the 400 μe magnitude used in this research.

Characterization of Hydrated Cement Treated Crushed Rock Base (HCTCRB) As a Road Base Material in Western Australia

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is widely used as a base course material for Western Australian roads. HCTCRB has been designed and used based on an empirical approach and practical experience, respectively, but those are not capable of explaining behavior of HCTCRB. Presently, a mechanistic approach is considered more reliable in pavement design and analysis. Mechanistic methods also provide effective tools in better understanding of pavement performance. The study provides laboratory testing and the corresponding analysis so as to assess the mechanical characteristics of HCTCRB. Conventional triaxial tests and repeated load triaxial tests (RLT tests) were performed. Factors, which would affect the performance of HCTCRB such as hydration periods and the amount of added water, were also investigated.

Visualization of road segment for road analysis and design

Current road design and analysis approaches lack an appropriate model to fill the gap between past empirical and mechanistic empirical methods. The current approaches also lack current developments in pavement materials, traffic loading and importantly the rate at which traffic loading develops in the design period. This causes road disruptions well before the design life reach. Early road damage can lead to other road issues including serious accidents. In this paper, we aim to visualise road segment to allow for all the important analysis and design factors affecting actual pavement performance. As a result, all sectors of the road system are analysed and designed to simulate the road system.

Characterisation, Analysis and Design of Hydrated Cement Treated Crushed Rock Base as a Road Base Material in Western Australia

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is widely used as a base course in Western Australian pavements. HCTCRB has been designed and used as a basis for empirical approaches and in empirical practices. These methods are not all-encompassing enough to adequately explain the behaviour of HCTCRB in the field. Recent developments in mechanistic approaches have proven more reliable in the design and analysis of pavement, making it possible to more effectively document the characteristics of HCTCRB. The aim of this study was to carry out laboratory testing to assess the mechanical characteristics of HCTCRB. Conventional triaxial tests and repeated load triaxial tests (RLT tests) were performed. Factors affecting the performance of HCTCRB, namely hydration periods and the amount of added water were also investigated. It was found that the shear strength parameters of HCTCRB were 177 kPa for cohesion (c) and 42° for the internal friction angle (). The hydration period, and the water added in this investigation affected the performance of HCTCRB. However, the related trends associated with such factors could not be assessed. All HCTCRB samples showed stress-dependency behaviour. Based on the stress stages of this experiment, the resilient modulus values of HCTCRB ranged from 300 MPa to 1100 MPa. CIRCLY, a computer program based on the multi-layer elastic theory was used in the mechanistic approach to pavement design and analysis, to determine the performance of a typical pavement model using HCTCRB as a base course layer. The mechanistic pavement design parameters for HCTCRB as a base course material were then introduced. The analysis suggests that the suitable depth for HCTCRB as a base layer for WA roads is at least 185 mm for the design equivalent standard axle (ESA) of 10 million.

The design model of unbound granular materials for flexible pavement

This study aims to introduce an alternative design model of unbound granular base course materials by utilising laboratory test results such as resilient modulus, permanent deformation and bearing capacity of base course materials. Current pavement designs mostly overlook all problematical behaviours of unbound granular base layers and consider only as a layer transferring traffic loads to underneath layers regardless on the unbound granular base course deteriorations. Based on the existing design protocols in Australia, there are only the design criteria of the horizontal tensile strains at the bottom of the asphalt layer and the vertical deformations occurring at the top of the subgrade. The actual performances of granular base course materials under traffic loads have been rarely accounted into the pavement design protocol. Currently, road activities are growing in terms of magnitude and frequency far beyond the past and causing the early road damages leading to major road maintenances. The study presents hypothetically the more rational approach of the stress and strain distribution in a flexible pavement using the finite element method with sophisticated laboratory results. In this study, the effects of a traffic load and material attributes which they were generated when vehicle travels, hence stress and strain contributing between tires and characteristics of unbound granular pavement materials were investigated. Moreover, the alternative design model for unbound granular layers was defined in order to draw up the guideline and recommendation on the current pavement analysis and design.

Ultimate Design of Unbound Granular Base Courses for Flexible Pavements

This study aims to introduce alternative design procedures for a flexible pavement base course by utilizing ultimate strength criteria with the sophisticated laboratory results of base course materials. Based on the design protocol, only the design criteria of the horizontal tension and the vertical compression occurring at the bottom of the asphalt layer and at the top of the subgrade, respectively are employed. The real behavior of a base course under traffic loads has been rarely accounted for in the pavement design protocol. Nowadays, traffic is growing in terms of magnitude and frequency far beyond the past causing premature deterioration in base course layers leading to major damage in pavements. The study presents theoretically a more suitable approach of stress and strain distributions in a flexible pavement using the finite element method. The effects of uniform design pressure and material attributes generated when a vehicle travels, namely the stress and strain contributions between tires and pavement layers, were investigated. Moreover, new design criteria for an unbound granular layer were defined as the ultimate strength design and the bearing capacity factor resulting from the application of the shallow foundation bearing capacity concept within the California Bearing Ratio (CBR) results.