Coarse bauxite residue for roadway construction materials

About 25 million tonnes of bauxite residue (BR) from alumina refining are generated in Australia each year. Managing this residue is costly, and the reuse of coarse BRs is becoming an increasingly attractive and sustainable solution to the problem. Using coarse BR in road construction has the potential for large volume reuse. This study investigated whether coarse BR is a viable road base material in Western Australia. A pozzolanic-stabilised mixture was created to improve the properties ofthe residue to satisfy the minimum requirements for road base. Laboratory tests for resilient modulus and permanent deformation were then carried out. Comparisons were made between the stabilised residue and conventional road base material used in Western Australia. The performance of the stabilised residue was superior to that of the conventional material, which can provide improved performance when used as road base material in Western Australia

Permanent Deformation Behavior of a Cement-Modified Base Course Material

AbstractOne of the major failure modes in flexible pavements having thin asphalt surface associates with rutting or permanent deformation in a base course layer. Thus the material characterisation in term of permanent deformation is important for the mechanistic-empirical pavement design. This study investigated the permanent deformation behaviour of a modified granular material used for the base course layer. According to the Austroads definition, modified granular materials are granular materials stabilised by adding a small amount of stabilising binder such as bitumen, cement or pozzolanic material. The performance of the original materials is thus improved with regard to aspects such as strength, plasticity, and moisture susceptibility. However, the improvement of tensile strength is not one of the purposes of stabilisation. Hydrated cement treated crushed rock base (HCTCRB), which is stabilised with cement, was used for this study. HCTCRB is made by blending standard crushed rock base (CRB) with 2% cement (by mass of dry CRB) at the optimum amount of water. Then the fresh mixture is cured for specified hydration periods. Consequently, the hydrated mixture is returned to the mixer to break the cementitious bonds generating during the hydration reaction. This procedure aims to produce a cement-modified material whilst maintaining unbound base course characteristics. This study evaluated the effect of hydration period and moisture content on the permanent deformation of the material. The hydration periods of the test specimens varied from 7 to 28 days. The moisture contents ranged from 60% to 100% of OMC, by wetting and drying the specimen. It was found that the moisture content of samples significantly influenced the performance of HCTCRB. However, a consistent performance trend over various hydration periods was not conclusive

Performance, Evaluation, and Enhancement of Hydrated Cement Treated Crushed Rock Base (HCTCRB) as a Road Base Material for Western Australian Roads

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 becomes more reliable in pavement design and analysis and behavior of pavements can be more understood. Consequently, characterization of HCTCRB following the mechanistic approach is necessary. This study aimed to analyze the results of laboratory testing 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 water added, were also investigated

Performance, evaluation, and enhancement of red sand for road bases, embankments, and seawall fills

Australia produces approximately 40% of the world’s bauxite and over 30% of the world’s alumina. Each year, about 25 million tonnes of bauxite residue is produced in Australia, requiring storage and maintenance. The construction and operation of such large impoundment areas is costly. During the extraction of alumina from bauxite ore using the Bayer process, a fine residue is produced called Red Mud. In West Australia, Darling Range bauxite deposits contain high levels of quartz which result in a coarse residue fraction also being produced. This fraction has been termed Red Sand with a typical particle size in excess of 90 microns. Typically, red mud and red sand are produced in almost equal quantity. Processing of red sand can neutralise the residual caustic and lower the salt content as required. Magnetic separation is also possible to produce a high silica fraction having low iron oxide content. The sustainable use of coarse bauxite residues for road construction is an attractive option with a high potential for large volume reuse.This study focuses on whether red sand is a viable option for use as a road base, embankment fills and as seawall fills in Western Australia. Red sand comes from bauxite ore, a product of intense tropical weathering. Hence, there are various physical properties resulting from the weathering process. Thus it is necessary to fully understand the characterisation of red sand with respect to its engineering properties in the initial part of this research. To satisfy minimum requirements of road bases, a soil stabilisation technique (a Pozzolanic- Stabilised Mixture, PSM) was used. The intent of this stabilisation technique was to use Western Australia’s by-products as stabilising materials. A Pozzolanic - Stabilised Mixture consisting of Class F fly ash (a by-product from a coal power station) and activators (the byproduct from the quicklime manufacturing in terms of lime kiln dust) were employed to develop pozzolanic activity. Once the appropriate mixture of red sand, fly ash, and activators was established (based on a maximum dry density and a value of unconfined compressive strength), a set of laboratory tests were performed which included a triaxial compressive strength test, a resilient modulus test, and a permanent deformation test.Comparisons were made between the stabilised red sand and the conventional road base material in Western Australia (crushed rock added with 2% General Purpose (GP) Portland Cement named Hydrated Cemented Treated Crushed Rock Base, HCTCRB). As for the use of red sand for embankments, the representative stabilised red sand (from red sand for road bases) was used to be an alternative fill embankment material. A testing program to evaluate the important properties of stabilised red sand for embankments including permeability, compressibility and strength was undertaken. The permeability, compressibility, and strength of the representative type of red sand were examined to assess the suitability of red sand as seawall fill. The application of red sand and stabilised red sand on three structures (road bases, embankments and seawalls) is also discussed

Characterization of cement-modified base course materials for Western Australia roads

The cement-modified soil (CMS) is described as a soil that has been treated with a relatively small amount of cement in order to improve its engineering properties so that it is suitable for construction. This soil stabilization technique is employed for the typical base course material in Western Australia named “Hydrated Cement Treated Crushed Rock Base (HCTCRB)”. In present, the mechanistic approach of pavement design and analysis become more important and widely used internationally but HCTCRB has been created from the empirical approach empirical approach point of view. In order to be able to use this material effectively relating to the new pavement design method, its shear strength, resilient modulus, and permanent deformation characteristics need to be more investigated and deeply understood. This study aimed to perform the results of the laboratory testing which was carried out to assess the mechanical characteristics of HCTCRB. Our findings show that HCTCRB can be characterized as a relevant cohesive granular material with significant shear strength parameters. Based on the laboratory results, the suitable models of the resilient modulus characteristics and the permanent deformation characteristics were determined and introduced

Evaluation of a stabilized sand residue for use as roadway materials

Australia produces approximately 40% of the world’s bauxite and over 30% of the world’s alumina. Each year, about 25 million tons of sand residues are produced in Australia. The management and containment of large impoundment areas are costly. The sustainable use of coarse sand residues for road construction is an attractive option with a high potential for large volume reuse. During the extraction of alumina from bauxite ore using the Bayer process, a fine residue is produced called red mud. In Western Australia, Darling Range bauxite deposits contain high levels of quartz, which results in a coarse residue fraction also being produced. This study focuses on whether a coarse sand residue is a viable option for use as a road base material in Western Australia. The soil stabilization technique, a pozzolanic- stabilized mixture, was used to improve the properties of a coarse sand residue to satisfy minimum requirements of road bases. The intent of this stabilization technique is to use potential by-products from industry in Western Australia as stabilizing materials. A pozzolanic - stabilized mixture consisting of Class F fly ash, a by-product from a coal power station, and activators, the by-product from the quicklime manufacturing in terms of lime kiln dust, were employed to develop pozzolanic activity.Once the appropriate mixture of a coarse sand residue, fly ash, and activators was established (based on a maximum dry density and a value of unconfined compressive strength), a set of laboratory tests were performed. These included an unconfined compressive strength test, a resilient modulus test, and a permanent deformation test. Comparisons were made between the stabilized residue and the conventional road base material in West Australia (crushed rock with the addition of 2% General Purpose (GP) Portland Cement.). The results of this study show that the performance of the stabilized residue is superior to that of the standard use material. Our findings indicate that stabilized residue can provide improved performance when used as road base material in Western Australia

Failure Criteria Evaluation and Shear Strength of Granular Base Course for Thin Flexible Pavement

This study aims to report theoretically the possible approach of confinement evaluation of unbound granular base course using the finite element method and the permanent deformation evaluation of crushed rock under repeated cyclic loading triaxial tests performed at different stress levels in order to implement current pavement material test algorithm. Road rutting is the main cause of damage in flexible pavements which the most explanation is crushed rock still not obviously understanding about plastic deformation under service load. The permanent deformation that accumulates under the repeated loading can normally describe and define the types of responses. Theoretical approach of the unbound granular materials (UGMs) permanent deformation used to describe the behaviour of tested materials subject to repeated loading triaxial (RLT) tests by macro-mechanical observations of the UGMs response. The plastic limit is able to use predict the accumulated plastic deformation in the UGMs layer of road pavement or whether deterioration will be unacceptable. Tested material will determine the limit of working stress level and the plastic deformation should be considered in this behaviour. As is well known, triaxial and California bearing ratio (CBR) test are used to simulate the real condition of pavement materials under traffic loads by using static confinement and actuator loads. However static confining conditions in pavement structure occur only when no vehicle travels.As the effects of traffic loads and material attributes are generated when vehicles travel, horizontal stress and confinement behaviours of pavement structure were determined. CBR sample of crushed rock base was modelled using finite element in order to study the confining pressure behaviour of such material subjected to applied stress. During the load application procedure, a single wheel with a standard pressure of 750 kPa was selected to compare with the analysed strength of crushed rock base (CRB) based on laboratory test results. The results showed that horizontal stress of base course layer consists of overburdened soil and passive force from applied stress. When vehicle travels pass observed point, horizontal pressures of base course layer increase from overburdened weight and complete with passive force effect depend on applied stress and its internal friction. Seemingly, the conventional triaxial test results with finite element back calculation are able to describe the confining behaviour of unbound granular base course. In this study, triaxial tests and the confinement evaluation using finite element approach on an unbound granular base course were introduced to explain and define its limited use in order to implement the current performance test of unbound granular base course material

Effects of Active Filler Selection on Foamed Bitumen Mixture in Western Australia

This study investigated the effects of different active filler types and contents on the mechanical properties of foamed bitumen treated materials under laboratory conditions. Four different active fillers were tested namely Portland cement, hydrated lime, quicklime and fly ash, at varying concentration of 0%, 1%, 3% and 5%. To evaluate the effects of the additional active fillers, samples were prepared under laboratory conditions and tested using indirect tensile strength, indirect tensile resilient modulus and unconfined compressive strength tests. Based upon our findings, all active filler types except fly ash contributed in improving the strength of foamed bitumen mixtures at different levels. Cement, regardless of adding contents, always provided the highest mechanical performance compared with the other two counterparts: hydrated lime and quicklime. Fly ash was deliberated to be precluded because fly ash on its own did not affect any mechanical strength of foamed bitumen mixesinsteadit acted as a mineral filler to modify aggregate gradation. The addition of active filler content should be limited within 3% in terms of strength gain and potential cracking prevent when mixing with 4% foamed bitumen content and locally sourced raw materials for base course

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

An evaluation of the suitability of SUPERPAVE and Marshall asphalt mix designs as they relate to Thailand’s climatic conditions

The most commonly-used asphalt mix design in Thailand still relies on the Marshall Mix design procedure which is empirical in its nature, in the sense that it is based on data produced by experiment and observation rather than reliable “in-field” data. As a result of this, the Marshall Mix design procedure has substantial drawbacks with respect to replicating the real or actual behaviour of asphalt during construction and in actual in-service conditions. The Strategic Highway Research Program (SHRP) has developed the Superior Performance Asphalt Pavements (SUPERPAVE) mix design procedure, which shifts to a large degree away from the empiricism of the Marshall Mix design to provide a more reliable and responsive solution to actual pavement conditions. This study aims to evaluate whether the SUPERPAVE mix design procedure can be reliably implemented under Thailand pavement conditions. A map of the Performance Grade (PG) asphalt binders was generated to cover the study area, namely the North part of Thailand, according to the SUPERPAVE asphalt classification with the highest and lowest temperature ranges that the asphalt might be subjected to. Using local materials, and considering loading and environmental conditions, a comparative study of the performance of two mixes, designed using SUPERPAVE and Marshall Mix design procedures, was carried out. The SUPERPAVE mixes proved superior to the Marshall Mixes. However, the asphalt binder commonly used in Thailand is not suitable for Thailand pavement conditions, based on the PG grade asphalt classification system