The design and optimisation of cold asphalt emulsion mixtures

Road structures are important to the survival of nations. As the cost for the rehabilitation and maintenance of highways soars, civil engineers and administrators face the ever present difficulty of meeting current resurfacing and rehabilitation needs. The deterioration of road structures under growing traffic weight and volume is occurring faster than agencies envisaged coupled with increasingly scarce and expensive new materials required. It is now apparent that for planning, design and construction for road structures, the most efficient and cost effective processes, materials and practices available must be appropriately considered. The use of recycled materials as a sustainable alternative is gaining significant worldwide attention. The overall purpose of this research was to conduct an in-depth investigation and analysis into the design and optimisation of Cold Asphalt Emulsion Mixtures (CAEMs) incorporating high contents of Reclaimed Asphalt Pavements (RAP). To achieve the objectives of the research, four proportions of RAP aggregate materials in addition to Virgin Aggregates (VA) were used as categorised below: - Category 1: 0% RAP (no RAP, 100% VA) - Category 2: 50% RAP (50% RAP, 50% VA) - Category 3: 85% RAP (85% RAP, 15% VA) - Category 4: 95% RAP (95% RAP, 5% VA) The effect of mixing and compaction temperatures at 5°C, 20°C and 32°C and how cement at 0%, 1% and 3% OPC influenced the CAEMs was also investigated. This study presents a practical mix design procedure to act as a guideline for CAEMs incorporating high RAP contents by identifying critical parameters for the various categories of CAEMs which stemmed from the fact that currently there is no universally accepted mix design. The proposed mix design guideline is presented in this thesis. The effect of accelerated curing was investigated to study the effects of temperature, curing duration, conditioning and the influence of cement on the CAEMs. The research showed that an increase in curing temperature results in an increase in the stiffness and strength of the CAEMs. The thesis presents results on the mechanical and performance properties which provided vital information on expected performance of CAEMs incorporating high contents of RAP for use as a road base material. The research was able to highlight the purported effects of residual binder in RAP which could contribute positively to the mechanical and performance properties of the CAEMs. This points to the fact that treating RAP as “black rock” is not the right approach. The RAP needs to be evaluated for its inherent properties and suitability for purpose. The stiffness and strength were investigated using the Indirect Tensile Stiffness Modulus (ITSM) and Indirect Tensile Strength (ITS) tests which proved useful in ranking them. The addition of 1% OPC improved the stiffness of Categories 1-3 mixtures by 32% with Category 4 having the highest increase at 89%. The inclusion of 3% OPC, more than doubled the stiffness values. The Indirect Tensile Fatigue Test (ITFT) was used to investigate the fatigue characteristics. Results showed that if the CAEMs with cement at 1% and 3% experienced strains in the region of 200µε, they tend to fail suddenly soon after crack initiation due to reduced flexibility of the CAEMs. This was more pronounced for the CAEMs at 3% OPC. Resistance to permanent deformation was investigated using the Vacuum Repeated Load Axial Test (VRLAT) which showed that the mixing and compaction temperature influenced the permanent deformation characteristics of the CAEMs. Increasing OPC content to 1% for Categories 2 and 3 resulted in a decrease in permanent strains of 47% and at 3% OPC, the decrease in permanent strains was 54%. Wheel Tracking Test (WTT) was conducted to ascertain the susceptibility of the CAEMs to deform under loading, investigate crack propagation and number of cycles to failure. The test showed that the performance of the specimens was affected by the test temperature. Increased test temperatures resulted in an increased rate of rutting and eventual failure of the specimens. The test further highlighted the positive benefits of adding cement to the mixtures which resulted in reduced strains and an increased number of cycles to failure for the CAEMs. Structural design and modelling was conducted using KENLAYER which was able to account for the non-linearity of the CAEMs. This was crucial in having a total overview of these mixture types. Although, the structural design was based on practical hypothetical layer thicknesses, the results provided useful insight into the structural capabilities of the CAEMs. The RAP CAEMs generally had lower horizontal tensile strain values in comparison to the VA CAEMs. The design charts showed that an increase in the thickness of the base course and surfacing layer resulted in an increase in the overall fatigue life of the pavement structure. Overall, evaluating the complete findings of this research, CAEMs produced with high RAP contents especially at 50% and 85% RAP had considerably enhanced mechanical and performance properties and are suitable for inclusion as a base material for reconstruction and rehabilitation

The design and optimisation of cold asphalt emulsion mixtures

Road structures are important to the survival of nations. As the cost for the rehabilitation and maintenance of highways soars, civil engineers and administrators face the ever present difficulty of meeting current resurfacing and rehabilitation needs. The deterioration of road structures under growing traffic weight and volume is occurring faster than agencies envisaged coupled with increasingly scarce and expensive new materials required. It is now apparent that for planning, design and construction for road structures, the most efficient and cost effective processes, materials and practices available must be appropriately considered. The use of recycled materials as a sustainable alternative is gaining significant worldwide attention. The overall purpose of this research was to conduct an in-depth investigation and analysis into the design and optimisation of Cold Asphalt Emulsion Mixtures (CAEMs) incorporating high contents of Reclaimed Asphalt Pavements (RAP). To achieve the objectives of the research, four proportions of RAP aggregate materials in addition to Virgin Aggregates (VA) were used as categorised below: - Category 1: 0% RAP (no RAP, 100% VA) - Category 2: 50% RAP (50% RAP, 50% VA) - Category 3: 85% RAP (85% RAP, 15% VA) - Category 4: 95% RAP (95% RAP, 5% VA) The effect of mixing and compaction temperatures at 5°C, 20°C and 32°C and how cement at 0%, 1% and 3% OPC influenced the CAEMs was also investigated. This study presents a practical mix design procedure to act as a guideline for CAEMs incorporating high RAP contents by identifying critical parameters for the various categories of CAEMs which stemmed from the fact that currently there is no universally accepted mix design. The proposed mix design guideline is presented in this thesis. The effect of accelerated curing was investigated to study the effects of temperature, curing duration, conditioning and the influence of cement on the CAEMs. The research showed that an increase in curing temperature results in an increase in the stiffness and strength of the CAEMs. The thesis presents results on the mechanical and performance properties which provided vital information on expected performance of CAEMs incorporating high contents of RAP for use as a road base material. The research was able to highlight the purported effects of residual binder in RAP which could contribute positively to the mechanical and performance properties of the CAEMs. This points to the fact that treating RAP as “black rock” is not the right approach. The RAP needs to be evaluated for its inherent properties and suitability for purpose. The stiffness and strength were investigated using the Indirect Tensile Stiffness Modulus (ITSM) and Indirect Tensile Strength (ITS) tests which proved useful in ranking them. The addition of 1% OPC improved the stiffness of Categories 1-3 mixtures by 32% with Category 4 having the highest increase at 89%. The inclusion of 3% OPC, more than doubled the stiffness values. The Indirect Tensile Fatigue Test (ITFT) was used to investigate the fatigue characteristics. Results showed that if the CAEMs with cement at 1% and 3% experienced strains in the region of 200µε, they tend to fail suddenly soon after crack initiation due to reduced flexibility of the CAEMs. This was more pronounced for the CAEMs at 3% OPC. Resistance to permanent deformation was investigated using the Vacuum Repeated Load Axial Test (VRLAT) which showed that the mixing and compaction temperature influenced the permanent deformation characteristics of the CAEMs. Increasing OPC content to 1% for Categories 2 and 3 resulted in a decrease in permanent strains of 47% and at 3% OPC, the decrease in permanent strains was 54%. Wheel Tracking Test (WTT) was conducted to ascertain the susceptibility of the CAEMs to deform under loading, investigate crack propagation and number of cycles to failure. The test showed that the performance of the specimens was affected by the test temperature. Increased test temperatures resulted in an increased rate of rutting and eventual failure of the specimens. The test further highlighted the positive benefits of adding cement to the mixtures which resulted in reduced strains and an increased number of cycles to failure for the CAEMs. Structural design and modelling was conducted using KENLAYER which was able to account for the non-linearity of the CAEMs. This was crucial in having a total overview of these mixture types. Although, the structural design was based on practical hypothetical layer thicknesses, the results provided useful insight into the structural capabilities of the CAEMs. The RAP CAEMs generally had lower horizontal tensile strain values in comparison to the VA CAEMs. The design charts showed that an increase in the thickness of the base course and surfacing layer resulted in an increase in the overall fatigue life of the pavement structure. Overall, evaluating the complete findings of this research, CAEMs produced with high RAP contents especially at 50% and 85% RAP had considerably enhanced mechanical and performance properties and are suitable for inclusion as a base material for reconstruction and rehabilitation

Bitumen stabilized ballast: a potential solution for railway track-bed

Railway ballast degradation under dynamic loads progressively leads to loss of mechanical performance and geometry of the track, so that maintenance interventions are frequently needed. In order to systematically avoid this issue, recently solutions have been proposed to reinforce track-bed by using polyurethane and/or resins as well as asphalt layers among others. Nonetheless, their main limitations are related to the high initial cost and low productivity. To cope with these limitations, in this study, bitumen stabilized ballast (BSB) is proposed as a new solution for ballast stabilization. This method aims at improving durability and reducing settlement by modifying both stiffness and the ability of energy dissipation of the layer. The paper introduces the potential of this technology as material to be used in railway track-beds by presenting the results of a laboratory-based investigation using the Precision Unbound Material Analyser (PUMA). Different variables such as ballast grading, bitumen emulsion dosage, compaction method and stress levels are considered. Results showed a significant decrease in permanent deformation and deformation rate associated with modified stiffness and energy dissipation properties of BSB, which suggest the potential for improving long-term performance and sustainability of ballasted track

Optimisation of bitumen emulsion properties for ballast stabilisation

Ballasted track, while providing economical and practical advantages, is associated with high costs and material consumption due to frequent maintenance. More sustainable alternatives to conventional ballasted trackbeds should therefore aim at extending its durability, particularly considering ongoing increases in traffic speed and loads. In this regard, the authors have investigated a solution consisting of bitumen stabilised ballast (BSB), designed to be used for new trackbeds as well as in reinforcing existing ones. This study presents the idea behind the technology and then focuses on a specific part of its development: the optimisation of bitumen emulsion properties and dosage in relation to ballast field conditions. Results showed that overall bitumen stabilisation improved ballast resistance to permanent deformation by enhancing stiffness and damping properties. Scenarios with higher dosage of bitumen emulsion, higher viscosity, quicker setting behaviour, and harder base bitumen seem to represent the most desirable conditions to achieve enhanced in-field performance

Mechanical, durability and microstructure properties of cold asphalt emulsion mixtures with different types of filler

The primary aim of this study is to investigate the enhancement of Cold Asphalt Emulsion Mixtures (CAEMs) using binary and ternary blended fillers (BBF and TBF), including an in-depth assessment of the microstructure. Ordinary Portland cement (OPC), fly ash (FA) and ground granulated blast furnace slag (GGBS) were used for the BBF while silica fume (SF) was added to the BBF to obtain TBF. The mechanical and durability results indicated that the TBF was more suitable than the BBF for the production of CAEMs. The microstructural assessment indicated that the effect of BBF on the internal microstructure of CAEMs was slightly negative and more noticeable in CAEMs containing FA. It is proposed that the addition of SF to BBF mixtures can eliminate the delay in formation of hydration products caused by the bitumen emulsion. Overall, the research suggests that the use of BBF-CAEMs might be appropriate for pavements in cold climate whereas TBF-CAEMs would be effective in road pavements exposed to severe conditions both in hot and cold climates

New developments with cold asphalt concrete binder course mixtures containing binary blended cementitious filler (BBCF)

A weakness in early strength and the need for longer curing times in the case of cold bituminous emulsion mixtures (CBEMs) compared to hot mix asphalt have been cited as barriers to the wider utilization of these mixtures. A binary blended filler material produced from high calcium fly ash (HCFA) and a fluid catalytic cracking catalyst (FC3R) was found to be very effective in providing microstructural integrity with a novel fast-curing cold asphalt concrete for the binder course (CACB) mixture. Balanced oxide compositions within the novel filler were identified as responsible for an enhanced hydration reaction, resulting in a very high early strength and a significant improvement in permanent deformation and fatigue resistance. Improved water sensitivity for progressive hydration with the new binary filler was also established while SEM analysis confirmed the formation of hydration products after various curing ages. © 2016 Elsevier Lt