Gary Chai

A study of the effects of pavement ageing on binder deterioration

This paper discusses the ageing of asphalt binder of long-term pavement performance (LTPP) sites in Southeast Queensland. The effects of pavement age on binder deterioration were examined by performing ‘Shell’ sliding plate micro-viscometer laboratory tests in accordance with Australian and New Zealand Standard AS/NZS 2341.5: 1997. The tests were carried out on bituminous core samples obtained from the LTPP sites to determine the apparent viscosity of the asphalt binder. A binder deterioration model (BDM) was developed by establishing a relationship between the apparent viscosities of the binder with pavement age. The apparent viscosity data generated using the BDM were compared with that computed using the bitumen hardening model developed by Oliver (2003). The two models show a consistent trend in the binder deterioration, and the results were analysed statistically using regression analysis, Root Mean Square Error and t-test methods. The t-test shows that the data generated by the BDM have no significant deviation from the prediction by Olivers model.

CHARACTERISTICS OF EMBEDDED PEAT IN COASTAL ENVIRONMENTS

This study examines the engineering characteristics and properties of peat soils in coastal environments in Ireland, Italy, Malaysia, Netherlands, Turkey and USA. The engineering properties to be examined are consolidation characteristics, Atterberg limits, density, organic content, shear strength, and moisture content. Moisture content and organic content are good indication of the occurrence of peat soils because these parameters are inherently high in this soil type. In addition, peat soil is highly compressible and is known to be problematic for geotechnical construction. The peat layer has an adverse effect on the long-term settlement of road embankments. A case study of peat soil deposits in Surfers Paradise in Australia will be presented in the paper. Peat soil in the study area is embedded at depth ranging between R.L. -10 to R.L. - 19.6 m below the ground surface and it has a thickness ranging from 0.1 to 7.0 m in some locations. It possesses low shear strength of between 30-40 kPa and the moisture content can be up to 247 %. Four empirical equations have been established for the peat soils and they are compared with those published in the literatures.

Laboratory Assessment of Kaolinite and Bentonite under Chemical electrokinetic Treatment

Electrokinetic treatment uses low intensity direct electric current or a low electric potential difference, to improve the engineering properties of subsurface soils while having minimum disturbance to the surface. This study aims to investigate the effects of chemical-electrokinetic treatment on properties of two types of clay soils at different intervals under the coupled Chemical, Hydraulic and Electrical (CHE) gradient. “Chemical-electrokinetic treatment” refers to improvement of soil with electrokinetic together with addition of chemical enhancement solution. The enhancement solutions used in this study are hydrated lime and saline solution. The combined effects of these processes together with various electrochemical and geochemical reactions would change the chemical composition of the soil porous medium, hence modifies the properties of the soil. The experiments were conducted in the laboratory using stainless steel electrodes under total applied voltage of 30 V for period of 15 days. Two types of fine-grained soils, kaolinite and bentonite, were used as they possess different mineralogy and geotechnical properties. The cumulative electro-osmotic flow and electric current flow through the soil samples were measured for period of 15 treatment days. Subsequently the specimens were tested for moisture content, pH and Atterberg Limit variations and the results have been reported. Test results revealed that there is a potential of developing this technique to improve engineering properties of finegrained soils, in particular to stabilise and improve soft soils for infrastructure management and constructions.

Modeling the Postflood Short-Term Behavior of Flexible Pavements

The January 2011 flood in Queensland caused severe damage to road infrastructures, which presented new challenges for the efficient management of the roads. To date, no deterioration model can accurately predict the impact of floods on pavements. To understand the impact of the January 2011 flood on the structural performance of flood-affected pavements, falling weight deflectometer (FWD) deflection data on flood-affected roads managed by the Brisbane City Council (BCC) and Roads and Maritime Services, New South Wales (RMS, NSW), Australia, were collected and examined. This paper proposes a deterministic model that expresses structural strength of pavements as a function of time. The model predicts the short-term behavior of a flexible pavement immediately after flooding. A comparison of before- and after-flood data, and flooded and nonflooded sections of the same road, indicates a consistent trend of decrease in strength due to its sustained submergence under flood water. The literature review indicates that structural strength deterioration was also observed for the pavements in New Orleans and Louisiana following Hurricanes Katrina and Rita in 2005. However, a trend of strength gain and even, in some cases, strength loss was also observed in the BCC data, which were collected 2 and 4 years postflood. The flood-affected pavements lost their structural strength faster than the predicted deterioration rate for which the road was designed. Importantly, the proposed model would facilitate the pavement engineers to quantify the postflood rapid deterioration of the structural strength. The model is sufficiently robust and can be adapted to other regions by calibrating for the local condition.

In Situ Assessment of Pavement Subgrade Using Falling Weight Deflectometer

The stiffness modulus and density of pavement subgrade contribute significantly to the long-term performance of a pavement structure. Subgrade functions primarily as a support for road pavement structures. Poor performance of the pavement structure is often a result of a lack of quality control during the construction of the subgrade layer. This paper presents a case study in which a falling weight deflectometer (FWD) test was used to evaluate whether the subgrade layer had achieved the required design stiffness modulus and density during construction. The characteristics of the FWD deflection basins were analyzed and the stiffness modulus was back-calculated using the CIRCLY5 pavement analysis program. The problems associated with FWD testing directly on subgrade are discussed, and an appropriate test load is proposed. Deflection-based models are developed by relating the FWD center deflection with the in situ stiffness modulus and density of the subgrade layer. A dynamic cone penetrometer test was carried out to determine the in situ stiffness modulus, and the results are compared with the back-calculated stiffness from CIRCLY5.

GIS-based examination of peats and soils in Surfers Paradise, Australia

Abstract The subsoil conditions of Surfers Paradise in Southeast Queensland of Australia have been examined in terms of soil stiffness by using geographic information system (GIS). Peat is a highly organic and compressible material. Surfers Paradise (as a study area) has problematic peat layer due to its high water content, high compressibility, and low shear strength. This layer has various thicknesses at different locations ranging between R.L. . 10 to R.L. -19.6 m. Buildings in Surfers Paradise are using piled foundations to avoid the high compressibility and low shear strength peat layer. Spatial Analyst extension in the GIS ArcMap10 has been utilised to develop zonation maps for different depths in the study area. Each depth has been interpolated as a surface to create Standard Penetration Test SPT-N value GIS-based zonation maps for each depth. In addition, 8 interpolation techniques have been examined to evaluate which technique gives better representation for the Standard Penetration Test (SPT) data. Inverse Distance weighing (IDW) method in Spatial Analyst extension gives better representation for the utilised data with certain parameters. Two different cross sections have been performed in the core of the study area to determine the extent and the depth of the peat layer underneath already erected buildings. Physical and engineering properties of the Surfers Paradise peat have been obtained and showed that this peat falls within the category of tropical peat.

A Study of the Semi-Perpetual Pavement Performance in Queensland

This paper presents the characteristics of a long-term pavement performance site constructed with semi-perpetual materials. The design life of a perpetual pavement is normally specified as greater than 40 years. The design requires asphalt overlays at the tenth, 20th, and 30th year for extending the life of the pavement structure. A case study of a semi-perpetual pavement with an application of the stage construction technique will be presented. The study shows that the falling weight deflectometer (FWD) central deflection of the semi-perpetual pavement was reported to be between 230 to 240 microns and the deflection curvature is less than 100 microns. The horizontal tensile strain of the semi-perpetual structure varies from 102 to 187 micro-strains and the vertical compressive strain was analyzed to be between 65 to 98 micro-strains. For the structural overlay at the 30th year of service life would improve the tensile and compressive strains of the structure to the levels which would satisfy the fatigue endurance limit and limiting subgrade strains of that of a perpetual pavement. The non-linearity behaviour of the subgrade material of the semi-perpetual pavement was analyzed by computing the surface modulus using Boussinesq’s equation and material constant of subgrade material model. The results obtained from both methods showed that the subgrade material of the semi-perpetual pavement exhibits linear elastic behaviour.

Establishment of calibration factors for pavement roughness deterioration model in southeast Queensland

Abstract This paper presents the outcomes of the research in establishing the calibration factors for pavement roughness deterioration model for six local council regions in southeast Queensland (SEQ). To achieve the objective, a large number of long-term pavement performance (LTPP) test sites were set up throughout the six SEQ regions. The methodology for the selection of the SEQ-LTPP test sites and the rationale behind the design of the LTPP site selection matrix are discussed. Pavement condition data were collected from the LTPP test sites over a period of five years. Modelling of the pavement deterioration at the test sites were carried out using the SMEC pavement management system (SMEC PMS) with HDM-III deterioration models. The aim was to determine the most appropriate HDM-III roughness deterioration factors for the six regions covered in the study. Three statistical techniques, namely, linear rate of roughness deterioration, regression analysis and statistical t test approach, were used in analysing the roughness data obtained from the LTPP sites and the predicted roughness data generated by the SMEC PMS. The statistical analysis established the accuracy of the prediction generated by a pavement deterioration dataset and confirmed whether the prediction yields significant or no significant deviation from the observed roughness data. Consequently, a set of pavement deterioration factors has been recommended for use in the SMEC PMS for SEQ regions.

An Easy to Implement Sustainability Index for Flexible Pavements

This paper proposes a simple low cost SIR (sustainability index for roads) that can be easily implemented by any local government that has a flexible pavement road network. The SIR includes the three pillars of sustainability, economic, social and environmental. The economic pillar is development from a new perspective of pavement deterioration from the Snowy Mountains Engineering Corporation’s Pavement Management System. The new perspective is easily seen when the deterioration is plotted in three dimensions. This new exponential curve provides an equation for the return on investment in a road network, in terms of a future pavement condition index versus the annual rehabilitation budget. The environmental pillar will be developed by determining which road rehabilitation treatments cause the most environmental damage and recreating the new curve with these treatments being incrementally removed. The resulting curves will provide the annual cost of minimizing environmental damage and the loss of pavement condition index for minimizing environmental damage. The social pillar is, consultation with the community on what pavement condition index they are willing to fund, that is, balancing annual cost, environmental damage and desired pavement condition. This more efficient reporting conforms with the USA Government Accounting Standards Board requirements but not necessarily with the International Financial Reporting Standards. This new SIR reduces the current financial reporting requirement for local governments in Queensland, Australia and can greatly improve comparability of financial reporting, where local governments calibrate the pavement deterioration factors in their Pavement Management Systems and use the newly developed regional rulebase.

A Study of the Structural Performance of Flexible Pavements Using a Traffic Speed Deflectometer

The falling weight deflectometer (FWD) is a non-destructive testing device that has been used by many road agencies worldwide since 1980 for structural evaluation of flexible pavements. In early 2000, the world first Doppler laser-based traffic speed deflectometer (TSD) was developed by Greenwood Engineering, and now eight TSD vehicles are in use worldwide. The two main advantages of the TSD technology are: (a) the ability to carry out continuous bearing capacity measurements instead of discrete points, (b) that testing can be carried out at traffic speeds without the need for lane closures with a stationary device such as FWD. The objective of this paper was to study the structural performance of flexible pavements using TSD deflection data. The study successfully established a correlation between maximum deflections TSD-D0 and FWD-D0 that are derived from the two devices. This study also drew some interesting conclusions in that deflection data collected by TSD could be transformed to FWD equivalent structural numbers with simple models as derived in the study. The outcome of this study was an established methodology for reporting structural performance at network level utilizing TSD