Conference on Asphalt Pavements for Southern Africa (CAPSA15), 11th, 2015, Sun City, South Africa, Aug 1, 2015
Higher traffic volumes and traffic loads have led to an increase in premature pavement failures a... more Higher traffic volumes and traffic loads have led to an increase in premature pavement failures as empirical binder testing has increasingly failed to predict pavement performance. Moreover, empirical tests cannot effectively characterize polymer-modified binders which are being increasingly used in South Africa. This has resulted in a move to establish bituminous binder specifications based on fundamental engineering properties capable of accurately predicting the performance of asphalt mixes. Asphalt pavements are most susceptible to rutting at high in-service temperatures, where the in situ binder plays an important role in resisting deformation from repeated loading, along with the complementary resistance provided by the aggregate structure. The non-recoverable compliance, Jnr, as determined by the dynamic shear rheometer has been found to be an improved indicator of asphalt deformation. Jnr is measured using the multi-stress creep recovery (MSCR) method and considerable work has been done in the last three years in South Africa in preparation for adopting a modification of the Jnr as part of a performance graded specification. The paper reviews the advantages the MSCR method has over other methods confined to measurements within the linear viscoelastic (LVE) region of the binder. Constraints undermining the current MSCR test method are demonstrated. Two temperature zones for South Africa are presented and the Jnr-stress characterisations for typical binders were determined for these zones. A correlation plot of shear strain (permanent deformation indicator) for four asphalt mixes versus Jnr demonstrated the effectiveness of the non-recoverable compliance parameter. The paper concludes by statistically examining the precision and bias of the test method as currently practiced in South Africa and presents a recommendation for the parameters to be implemented for the South African version of the test method.
This paper presents data of a laboratoty investigation on the measurements of air permeability of... more This paper presents data of a laboratoty investigation on the measurements of air permeability of a range of dense bituminous composites using a simple air permeameter developed at the Civil Engineering Materials Unit (CEMU) at The University of Leeds. A wide range of gap graded Hot Rolled Asphalts and Asphaltic Concrete gradations compacted at several levels of compactive effort and using a range of bitumen contents were assessed for air permeability and Marshall Stability. The results show that the permeability of the composites tested at low bitumen contents are high and that these values decrease sharply with an increase in the bitumen content demonstrating that the test can be used with advantage to determine the minimum value of binder content for minimum permeability. The air permeameter is a non destructive test and can detect minor changes in the aggregate gradation, level of compaction or bitumen content. The results show a good correlation between permeability and compacted density and porosity for any one mixture type. The results also show that contrary to what is normally believed, the measured permeability values of selected dense continuously graded Asphaltic Concrete mixtures at their optimum bitumen contents of 5 to 5.5% were considerably lower than conventional gap graded Hot Rolled Asphalt wearing course mixtures at 7 to 7.5% bitumen contents. For the covering abstract see ITRD E107185.
From a performance point of view, bitumen is one of the most important constituents of asphalt mi... more From a performance point of view, bitumen is one of the most important constituents of asphalt mixtures. The quality and properties of bitumen depend largely on its chemical composition. Evidence obtained form laboratory oven ageing tests suggests that bitumens having the same grade, but originating form different crudes, can age quite differently. This evidence is further supported by data from laboratory compacted asphalt mixtures. The first part of this study reviews in some detail the effect of the chemical composition of penetration grade bitumens on ageing performance. Simple explanations of the ageing mechanisms are presented in the paper primarily based on chromatographic separation techniques. For the covering abstract see ITRD E145817
Semi-flexible pavements are manufactured by producing a very open porous asphalt skeleton and fil... more Semi-flexible pavements are manufactured by producing a very open porous asphalt skeleton and filling the voids with selected cementitious grouts. The resultant composites, referred to as "grouted macadams", combine the flexibility of the bituminous component with the strength and rigidity of the cementitious component. In this investigation, a range of cementitious grouts was formulated using a variety of binders including ordinary Portland cement, silica fume and fly ash. The grouts were designed to provide improved strength and performance characteristics with reduced water/binder ratios, whilst maintaining high workability. This was achieved with the aid of chemical admixtures that allowed the grouts to penetrate the porous asphalt skeleton under gravity action (i.e. without vibration). The properties of the grouted macadam composites were assessed using a range of engineering, deformation and performance tests. These included compressive strength, stiffness modulus, creep resistance, shrinkage, porosity and permeability up to the curing age of 28 days. The formulated cementitious grouts attained high strength characteristics (90-120 MPa at 28 days), with the pozzolanic materials (silica fume and fly ash) having improved permeability and shrinkage properties. When the grouts were impregnated into the porous asphalt skeleton, the resultant grouted macadam composites showed superior strength to conventional asphalts and much higher resilient properties than that of concrete pavement materials. In addition, the grouted macadams exhibited much lower porosity (<8%) indicating enhanced durability performance. For the covering abstract see ITRD E117840.
2021 Third International Sustainability and Resilience Conference: Climate Change, Nov 15, 2021
Plastic consumption has increased tremendously over the years due to their versatility which enab... more Plastic consumption has increased tremendously over the years due to their versatility which enables them to be used in various industries. However, the properties of plastics which are non-biodegradable have created serious environmental problems especially polluting the oceans, harming marine organisms, and putting them at risks of extinction. At the same time, conventionally used construction materials such as clay bricks and concrete blocks also lead to other environmental issue such as the over-utilization of natural resources and emission of greenhouse gases. In current study, waste polyethylene terephthalate was used as a sand replacement in the production of interlocking concrete blocks for masonry wall application. Concrete mixtures with various percentages of PET were produced and evaluated for compressive strength and split tensile strength. In addition, microstructural characterization was also performed using Scanning Electron Microscope (SEM). The recycling of waste PET in the production of concrete interlocking blocks will produce sustainability in the construction industry.
Journal of Materials in Civil Engineering, Mar 1, 2010
ABSTRACT A novel construction unit (Bitublock) composed entirely of recycled and waste aggregates... more ABSTRACT A novel construction unit (Bitublock) composed entirely of recycled and waste aggregates and bound with bituminous binders is currently being developed. At present, the manufacturing process requires the new units to be heat cured to convert the bitumen binder from a viscoelastic material into an elastic-brittle material (known as hardening or bitumen aging). The paper investigates the effect of aging and curing processes on the compressive strength of Bitublocks. In this investigation, samples were compacted at pressures of between 8 and 20 MPa and cured at temperatures of between 60 and 160 degrees C for up to 48 h. Compressive strengths approaching 45 MPa were achieved. The range of compressive strengths achieved indicated that the behavior of the bituminous binder during heat curing significantly influences the performance of the Bitublocks and suggested that bitumen hardening is highly influenced by the curing temperature. Oxidation as opposed to polymerization and loss of volatiles was confirmed to be the key role in the bitumen hardening process (only approximately 7% of the total long-term hardening was due to volatilization). The oxidation process can be directly linked to the compressive strength development of Bitublock.
Polyethylene Terephthalate (PET) is one of the most commonly available kinds of plastic present i... more Polyethylene Terephthalate (PET) is one of the most commonly available kinds of plastic present in the municipal solid waste and it is a non-biodegradable semi-crystalline thermoplastic polymer, studied as polyester material. This paper intends to assess impacts of using PET (regular and irradiated) as aggregate that would replace by volume of equal size (10.00-5.00mm) in asphalt blend on the engineering properties of dense graded asphaltic concrete. The volumetric and mechanical properties of the blends incorporating different percent of PET (0, 5, 10, 15 and 20) were determined. In all mixtures, 5.0% optimum bitumen content was utilized. The outcome revealed that aggregate substitution of 10% (equivalent to 2.4% by weight of total mix) with irradiated PET result in optimum Marshall Stability and flow value of 3.6mm. It also showed that mixes with irradiated PET at 100kGy radiation dose have Marshall Stability values higher than mixes with same contents of regular PET. The finding also shows that the addition of PET and utilization of gamma radiation has a critical constructive outcome on the properties of asphalt concrete mixes as the stability increases for mixes with irradiated PET when compared with mixes with regular PET (RPET).
The seme-flexible pavement surface is a hybrid type of pavement surface that combines the effect ... more The seme-flexible pavement surface is a hybrid type of pavement surface that combines the effect of both asphalt mix skeleton and cement grout. The current study investigates the influence of cement grouts containing irradiated waste polyethylene terephthalate (PET) on the performance of semi-flexible mixtures. The ordinary Portland cement was partially replaced by regular and irradiated PET as well as with fly ash (FA) in cement grouts. The air voids analysis, degree of grout saturation, Marshal stability, indirect tensile strength (ITS), and tensile strength ratio (TSR) of semi-flexible specimens were evaluated. The semi-flexible mixtures showed superior performance in terms of strength properties. The results indicate that with the irradiation process more waste PET (almost double) can be recycled as compared to regular waste PET in cement grouts for semi-flexible pavement surfaces. This approach will lead to a sustainable solution for recycling waste PET in highway materials for the construction of a hybrid type of pavement surface.
Grouted Macadams consist of a single sized porous asphalt layer laid with a traditional asphalt p... more Grouted Macadams consist of a single sized porous asphalt layer laid with a traditional asphalt paver typically to a thickness of up to 60 mm. The porous asphalt skeleton is designed to achieve a high void content (28-32%) whilst maintaining a thick bitumen coating on the aggregate particles. The hot asphalt is rolled using a steel wheeled compactor without vibration. As soon as the bituminous mixture has cooled, the voids in the porous asphalt mixture can be filled with the selected fluid grout (cementitious slurry). The Grouted Macadam sections can normally be opened to vehicular traffic 24 h after the voids have been filled with the cementitious grout. Grouted Macadams thus combine the best qualities of concrete and asphalt pavements, namely the flexibility and freedom from joints that characterize asphalt and the high static bearing capacity and wear resistance of concrete. The aim of this investigation was to establish techniques that would reduce the initial cost of Grouted Macadams whilst maintaining their excellent mechanical and performance properties. Two techniques were established; the first was to redesign the conventional hot mix, hot laid porous asphalt skeleton using bituminous emulsions, thus creating a cold mixed, cold laid porous asphalt skeleton suitable for filling with a cementitious grout. A range of tests including: compressive strength, drying shrinkage, indirect tensile stiffness and dynamic creep tests were carried out on these cold mixes and the results compared with a conventional limestone Grouted Macadam. The second technique progresses even further by investigating the potential for utilizing substandard dolomitic aggregates as an alternative to the conventional limestone aggregates in Grouted Macadams, as a cold mixed, cold laid porous asphalt. For the covering abstract see ITRD E117840.
Conference on Asphalt Pavements for Southern Africa (CAPSA15), 11th, 2015, Sun City, South Africa, Aug 1, 2015
Higher traffic volumes and traffic loads have led to an increase in premature pavement failures a... more Higher traffic volumes and traffic loads have led to an increase in premature pavement failures as empirical binder testing has increasingly failed to predict pavement performance. Moreover, empirical tests cannot effectively characterize polymer-modified binders which are being increasingly used in South Africa. This has resulted in a move to establish bituminous binder specifications based on fundamental engineering properties capable of accurately predicting the performance of asphalt mixes. Asphalt pavements are most susceptible to rutting at high in-service temperatures, where the in situ binder plays an important role in resisting deformation from repeated loading, along with the complementary resistance provided by the aggregate structure. The non-recoverable compliance, Jnr, as determined by the dynamic shear rheometer has been found to be an improved indicator of asphalt deformation. Jnr is measured using the multi-stress creep recovery (MSCR) method and considerable work has been done in the last three years in South Africa in preparation for adopting a modification of the Jnr as part of a performance graded specification. The paper reviews the advantages the MSCR method has over other methods confined to measurements within the linear viscoelastic (LVE) region of the binder. Constraints undermining the current MSCR test method are demonstrated. Two temperature zones for South Africa are presented and the Jnr-stress characterisations for typical binders were determined for these zones. A correlation plot of shear strain (permanent deformation indicator) for four asphalt mixes versus Jnr demonstrated the effectiveness of the non-recoverable compliance parameter. The paper concludes by statistically examining the precision and bias of the test method as currently practiced in South Africa and presents a recommendation for the parameters to be implemented for the South African version of the test method.
This paper presents data of a laboratoty investigation on the measurements of air permeability of... more This paper presents data of a laboratoty investigation on the measurements of air permeability of a range of dense bituminous composites using a simple air permeameter developed at the Civil Engineering Materials Unit (CEMU) at The University of Leeds. A wide range of gap graded Hot Rolled Asphalts and Asphaltic Concrete gradations compacted at several levels of compactive effort and using a range of bitumen contents were assessed for air permeability and Marshall Stability. The results show that the permeability of the composites tested at low bitumen contents are high and that these values decrease sharply with an increase in the bitumen content demonstrating that the test can be used with advantage to determine the minimum value of binder content for minimum permeability. The air permeameter is a non destructive test and can detect minor changes in the aggregate gradation, level of compaction or bitumen content. The results show a good correlation between permeability and compacted density and porosity for any one mixture type. The results also show that contrary to what is normally believed, the measured permeability values of selected dense continuously graded Asphaltic Concrete mixtures at their optimum bitumen contents of 5 to 5.5% were considerably lower than conventional gap graded Hot Rolled Asphalt wearing course mixtures at 7 to 7.5% bitumen contents. For the covering abstract see ITRD E107185.
From a performance point of view, bitumen is one of the most important constituents of asphalt mi... more From a performance point of view, bitumen is one of the most important constituents of asphalt mixtures. The quality and properties of bitumen depend largely on its chemical composition. Evidence obtained form laboratory oven ageing tests suggests that bitumens having the same grade, but originating form different crudes, can age quite differently. This evidence is further supported by data from laboratory compacted asphalt mixtures. The first part of this study reviews in some detail the effect of the chemical composition of penetration grade bitumens on ageing performance. Simple explanations of the ageing mechanisms are presented in the paper primarily based on chromatographic separation techniques. For the covering abstract see ITRD E145817
Semi-flexible pavements are manufactured by producing a very open porous asphalt skeleton and fil... more Semi-flexible pavements are manufactured by producing a very open porous asphalt skeleton and filling the voids with selected cementitious grouts. The resultant composites, referred to as "grouted macadams", combine the flexibility of the bituminous component with the strength and rigidity of the cementitious component. In this investigation, a range of cementitious grouts was formulated using a variety of binders including ordinary Portland cement, silica fume and fly ash. The grouts were designed to provide improved strength and performance characteristics with reduced water/binder ratios, whilst maintaining high workability. This was achieved with the aid of chemical admixtures that allowed the grouts to penetrate the porous asphalt skeleton under gravity action (i.e. without vibration). The properties of the grouted macadam composites were assessed using a range of engineering, deformation and performance tests. These included compressive strength, stiffness modulus, creep resistance, shrinkage, porosity and permeability up to the curing age of 28 days. The formulated cementitious grouts attained high strength characteristics (90-120 MPa at 28 days), with the pozzolanic materials (silica fume and fly ash) having improved permeability and shrinkage properties. When the grouts were impregnated into the porous asphalt skeleton, the resultant grouted macadam composites showed superior strength to conventional asphalts and much higher resilient properties than that of concrete pavement materials. In addition, the grouted macadams exhibited much lower porosity (<8%) indicating enhanced durability performance. For the covering abstract see ITRD E117840.
2021 Third International Sustainability and Resilience Conference: Climate Change, Nov 15, 2021
Plastic consumption has increased tremendously over the years due to their versatility which enab... more Plastic consumption has increased tremendously over the years due to their versatility which enables them to be used in various industries. However, the properties of plastics which are non-biodegradable have created serious environmental problems especially polluting the oceans, harming marine organisms, and putting them at risks of extinction. At the same time, conventionally used construction materials such as clay bricks and concrete blocks also lead to other environmental issue such as the over-utilization of natural resources and emission of greenhouse gases. In current study, waste polyethylene terephthalate was used as a sand replacement in the production of interlocking concrete blocks for masonry wall application. Concrete mixtures with various percentages of PET were produced and evaluated for compressive strength and split tensile strength. In addition, microstructural characterization was also performed using Scanning Electron Microscope (SEM). The recycling of waste PET in the production of concrete interlocking blocks will produce sustainability in the construction industry.
Journal of Materials in Civil Engineering, Mar 1, 2010
ABSTRACT A novel construction unit (Bitublock) composed entirely of recycled and waste aggregates... more ABSTRACT A novel construction unit (Bitublock) composed entirely of recycled and waste aggregates and bound with bituminous binders is currently being developed. At present, the manufacturing process requires the new units to be heat cured to convert the bitumen binder from a viscoelastic material into an elastic-brittle material (known as hardening or bitumen aging). The paper investigates the effect of aging and curing processes on the compressive strength of Bitublocks. In this investigation, samples were compacted at pressures of between 8 and 20 MPa and cured at temperatures of between 60 and 160 degrees C for up to 48 h. Compressive strengths approaching 45 MPa were achieved. The range of compressive strengths achieved indicated that the behavior of the bituminous binder during heat curing significantly influences the performance of the Bitublocks and suggested that bitumen hardening is highly influenced by the curing temperature. Oxidation as opposed to polymerization and loss of volatiles was confirmed to be the key role in the bitumen hardening process (only approximately 7% of the total long-term hardening was due to volatilization). The oxidation process can be directly linked to the compressive strength development of Bitublock.
Polyethylene Terephthalate (PET) is one of the most commonly available kinds of plastic present i... more Polyethylene Terephthalate (PET) is one of the most commonly available kinds of plastic present in the municipal solid waste and it is a non-biodegradable semi-crystalline thermoplastic polymer, studied as polyester material. This paper intends to assess impacts of using PET (regular and irradiated) as aggregate that would replace by volume of equal size (10.00-5.00mm) in asphalt blend on the engineering properties of dense graded asphaltic concrete. The volumetric and mechanical properties of the blends incorporating different percent of PET (0, 5, 10, 15 and 20) were determined. In all mixtures, 5.0% optimum bitumen content was utilized. The outcome revealed that aggregate substitution of 10% (equivalent to 2.4% by weight of total mix) with irradiated PET result in optimum Marshall Stability and flow value of 3.6mm. It also showed that mixes with irradiated PET at 100kGy radiation dose have Marshall Stability values higher than mixes with same contents of regular PET. The finding also shows that the addition of PET and utilization of gamma radiation has a critical constructive outcome on the properties of asphalt concrete mixes as the stability increases for mixes with irradiated PET when compared with mixes with regular PET (RPET).
The seme-flexible pavement surface is a hybrid type of pavement surface that combines the effect ... more The seme-flexible pavement surface is a hybrid type of pavement surface that combines the effect of both asphalt mix skeleton and cement grout. The current study investigates the influence of cement grouts containing irradiated waste polyethylene terephthalate (PET) on the performance of semi-flexible mixtures. The ordinary Portland cement was partially replaced by regular and irradiated PET as well as with fly ash (FA) in cement grouts. The air voids analysis, degree of grout saturation, Marshal stability, indirect tensile strength (ITS), and tensile strength ratio (TSR) of semi-flexible specimens were evaluated. The semi-flexible mixtures showed superior performance in terms of strength properties. The results indicate that with the irradiation process more waste PET (almost double) can be recycled as compared to regular waste PET in cement grouts for semi-flexible pavement surfaces. This approach will lead to a sustainable solution for recycling waste PET in highway materials for the construction of a hybrid type of pavement surface.
Grouted Macadams consist of a single sized porous asphalt layer laid with a traditional asphalt p... more Grouted Macadams consist of a single sized porous asphalt layer laid with a traditional asphalt paver typically to a thickness of up to 60 mm. The porous asphalt skeleton is designed to achieve a high void content (28-32%) whilst maintaining a thick bitumen coating on the aggregate particles. The hot asphalt is rolled using a steel wheeled compactor without vibration. As soon as the bituminous mixture has cooled, the voids in the porous asphalt mixture can be filled with the selected fluid grout (cementitious slurry). The Grouted Macadam sections can normally be opened to vehicular traffic 24 h after the voids have been filled with the cementitious grout. Grouted Macadams thus combine the best qualities of concrete and asphalt pavements, namely the flexibility and freedom from joints that characterize asphalt and the high static bearing capacity and wear resistance of concrete. The aim of this investigation was to establish techniques that would reduce the initial cost of Grouted Macadams whilst maintaining their excellent mechanical and performance properties. Two techniques were established; the first was to redesign the conventional hot mix, hot laid porous asphalt skeleton using bituminous emulsions, thus creating a cold mixed, cold laid porous asphalt skeleton suitable for filling with a cementitious grout. A range of tests including: compressive strength, drying shrinkage, indirect tensile stiffness and dynamic creep tests were carried out on these cold mixes and the results compared with a conventional limestone Grouted Macadam. The second technique progresses even further by investigating the potential for utilizing substandard dolomitic aggregates as an alternative to the conventional limestone aggregates in Grouted Macadams, as a cold mixed, cold laid porous asphalt. For the covering abstract see ITRD E117840.
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