Stiffness and deformation properties of asphalt open graded friction course containing cement coated natural aggregates
The primary objective of this research study was to observe the changes in the physical properties of cement coated secondary aggregates, namely surface roughness and angle of internal friction and how these properties are related to the performance of Open Graded Friction Course asphalt mixtures, OGFC made from these materials under laboratory Uniaxial, deformation and rutting testing simulating the traffic loading and temperature of the materials in service. The secondary aggregates, namely Croxden natural gravel aggregates, which is rejected by road engineers for use in road surfacing was upgraded with a specifically designed cement coating. Asphalt mixtures mechanical properties in terms of stiffness modulus, deformations and rutting were determined and analyzed using state-of-the-art laboratory test equipment and supported by technical literature from different information and resources. Three aggregate types were considered in this study; Arcow rock crushed aggregates( as a control aggregate), Croxden aggregate (as a secondary or low quality aggregates) and cement coated Croxden aggregate (as an upgraded material). One aggregate gradation was designed for all mixture types and the adopted aggregate gradation had a nominal maximum aggregate size (NMAS) of 14mm. Two binder types were selected, 100/150 pen binder and 40/60 pen binder to represent the soft and hard binders respectively that are commonly used by road engineers. This research also documents a survey of literature review that led to the design of a novel machine that is eagerly needed by the pavement industry to boost the knowledge and understanding of real tyre-road interaction. Computer software, SOLIDWORKS, was used to create a 3-dimentional model of the machine that was jointly named by the Highway Agency and Tarmac ltd., as Low Cost Asphalt Tasting Equipment (LoCATE). The machine was designed for use and for the first time to investigate the performance of the said mixtures under real traffic loading and environmental conditions and to correlate its results with those obtained using Repeated Load Indirect Tensile Test (RLIT) and Repeated Load Axial Test (RLAT), which were carried out at 10°C, 20°C, 30°C and 45°C. At an advanced stage of this research work and when the cost of fabricating LoCATE was found impossible to be met by LJMU, wheel tracking tests were done on the materials studied as a replacement of LoCATE and this part of the research program was achieved at Wolverhampton's bituminous testing laboratories in collaboration with Tarmac Ltd. In general, the results of this research investigation indicate that the introduction of cement coated aggregates to OGFC led to an outstanding improvement in the chemical properties of the coated natural aggregates and the stiffness and deformation properties/resistance of the road mixtures containing them. This was in comparison with that made from the uncoated aggregates in all the tests that have been carried out within this research study. Also, the effects of elevated temperature were investigated and it was found to have significant influence on the engineering properties, Indirect Tensile Stiffness Moduli (ITSM) and permanent deformation/rutting characteristic of the mixtures were also investigated. Outstanding new results were achieved, using LJMU cement coating paste for coating the waste natural aggregate and as thus this will hopefully eliminate the restriction imposed by road engineers on the use of natural gravel aggregates in road pavement surfacing layers. This is an outstanding knowledge extension in this field and marks a starting point for more research in this ever growing industry i. e. the use of waste and recycled aggregates in construction industry.
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