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The essential paving properties of soil, sand and stones
Published in Maxwell Lay, John Metcalf, Kieran Sharp, Paving Our Ways, 2020
Maxwell Lay, Metcalf John, Sharp Kieran
Eventually, as the magnitude of the stress or the number of stress cycles increases, the material will fail catastrophically by cracking if the stresses are tensile or squashing if the stresses are compressive. The associated strength of a material is a much more nebulous concept as most materials will fail gradually rather than catastrophically and so subjective definitions are needed that relate to a particular unacceptable circumstance. For example, when does a rut represent pavement failure? The rut is the product of permanent deformation of the pavement usually as a consequence of an increment of compaction caused by each passing traffic load. The damage occurs incrementally and slowly unless the rut creates new problems such as permitting water to enter the pavement. At the other end of the damage spectrum, the tensile stresses that cause cracking will also grow incrementally under traffic until they trigger some other undesirable effect. This type of damage is called fatigue failure. While some cracks are due to surface shrinkage, structural cracking usually begins at the base of a pavement layer or in the subgrade where the tensile stresses are highest. When such cracks grow over time and reach the surface, they are called reflection cracks.
Structural design of haul roads
Published in Thompson Roger J., Peroni Rodrigo, Visser Alex T., Mining Haul Roads, 2019
Thompson Roger J., Peroni Rodrigo, Visser Alex T.
The road bed should be prepared by shaping where necessary and compacting with a 20 t or similar heavy vibratory roller or 25 kJ three-sided impact roller. Water may be added where required to bring the in-situ to optimum moisture content (generally between 8% and 11% for granular materials, but more for fine-grained materials) to assist in achieving the required degree of compaction. Compaction should continue until negligible movement is seen under the roller or the minimum compacted layer thickness and CBR specified in the structural design is achieved. Figure 3.31 illustrates a DCP testing to determine the road bed CBR following compaction. Dry-back will often allow an increase in strength of this layer and as such the construction should be left to dry for 48–72 hours before layers are added above. Ruts and potholes that develop in the road-bed after completion should be repaired and damaged sections of the road-bed reshaped and re-compacted.
Distress and Performance
Published in Rajib B. Mallick, Tahar El-Korchi, Pavement Engineering, 2017
Rajib B. Mallick, Tahar El-Korchi
A rut is defined as a longitudinal depression in the wheelpath, with or without transverse displacement. It can be measured with a straight edge or a profiler at regular intervals. A rut is a physical distortion of the surface, and it also prevents the cross drainage of water during rains, leading to accumulation of water in the ruts and increasing the potential of hydroplaning-related accidents. Generally a rut depth of 0.5 in. is considered a rutting failure. Rutting is the result of repeated loading, which causes accumulation, and increase of permanent deformations. Rutting can be (1) low- to moderate-severity rutting—one-dimensional densification or vertical compression near the center of the wheelpath, caused by densification of mixes with excessive air voids in the in-place mix under traffic; (2) moderate- to high-severity rutting—a depression in the wheelpath along with humps on either side of the depression, caused by lateral flow due to plastic deformation, resulting from shear failure of the mix under traffic, and generally associated with very low air voids in the mix; and (3) rutting accompanied by cracks on the surface of the pavement, caused by rutting in underlying layers, such as the subgrade or subbase.
The use of deep neural networks for developing generic pavement rutting predictive models
Published in International Journal of Pavement Engineering, 2022
Angela J. Haddad, Ghassan R. Chehab, George A. Saad
Pavement researchers and practitioners alike consider rutting among the most critical distresses affecting the performance of asphalt concrete (AC) pavements (Gong et al 2018). Pavement rutting emanates from the accumulation of permanent deformations or depressions across the depth of the pavement layers along the wheel-path. Two deformations are particularly appreciable and common: asphalt rutting occurring in the asphalt layers close to the surface and subgrade rutting due to settlement of the subgrade. Pavement rutting is of major concern due to its negative effects on road safety, rideability, and serviceability (AASHTO 2015). The presence of rutting endangers the safety of road users due to the increased possibility of hydroplaning, where water or ice accumulate in the ruts leading to the loss of grip between the pavement and the vehicle tires, as well as steering problems (Mamlouk et al.2018). In addition to the safety concerns, rutting presents a major economic burden for road agencies because it often cannot be addressed by low-cost preventive maintenance activities (Zhang et al.2020). Due to the heavy burden incurred by DOT’s due to rutting failures in flexible pavements, significant effort and resources have been invested on the development, continuous improvement, and utilisation of rut depth prediction models.
Review of stone mastic asphalt as a high-performance ungrooved runway surfacing
Published in Road Materials and Pavement Design, 2020
Deformation resistance is the ability for the asphalt to resist distresses such as rutting, shearing/shoving and groove closure (as discussed earlier). Asphalt rutting appears as longitudinal depressions in the wheel paths with small upheavals to the sides. The primary mechanism that causes this phenomenon is shear deformation, a secondary mechanism is densification of the asphalt surface layer (Sousa, Solaimanian, & Weissman, 1994). The ruts can retain water, reducing the skid resistance of the pavement. Like rutting, horizontal shoving is also caused by excessive shear stress, however in the case of horizontal shoving the orientation of the critical stress is along the pavement surface rather than vertically through the pavement surface (White, 2018). Consequently, horizontal shoving is more likely to occur in areas of heavy braking and turning (Wang, Li, & Garg, 2017). The importance of protecting against asphalt deformation is high, as rideability and skid resistance are affected, necessitating early maintenance intervention in areas that experience this type of distress.
Research on heat reflective coating technology of asphalt pavement
Published in International Journal of Pavement Engineering, 2022
Yuanzhao Chen, Zhenxia Li, Siqing Ding, Xiaolan Yang, Tengteng Guo
Asphalt pavement has excellent flatness and driving comfort. Simultaneously, it is advantageous for short construction time, low noise, no dust, and simple maintenance. More than 80% of China’s highways in service are made of asphalt concrete pavement. However, asphalt is a kind of material with a high heat absorption rate, so the asphalt pavement will absorb more solar radiation energy at high temperatures, and transmit these energies down to store it in the road. In high-temperature weather, the asphalt pavement temperature will be much higher than the ambient temperature, and sometimes the pavement temperature will be greater than 60°C, exceeding the ambient temperature by more than 20°C. Asphalt is a viscoelastic body; asphalt pavement rutting, congestion and other deformations are caused by the decrease in viscosity and strength of asphalt at high temperature, the increase in fluidity, the strengthening of creep performance, and the pavement deformation under repeated major loads. There are data to show (Shen et al.2004) when the outdoor temperature is lower than 30°C, rutting will hardly occur, and even when the surface temperature is lower than 35°C (that is, road surface temperature is lower than 55°C); the rutting depth can be limited to less than millimetre level. However, as long as the ambient temperature is higher than 38°C, rutting will develop rapidly. If the temperature continues to be higher than 40°C, a significant damage will be caused to the asphalt pavement. The existence of the rut seriously affects the comfort and safety of the driving and causes certain damage to the driving vehicles, the main reason for this is the shear stress and shear flow in the layer.