Surfacing, pavement structure

One of the primary factors in the deterioration of a pavement structure is the intrusion of surface water into the support structure of the pavement. When rehabilitating a pavement, the installation of a moisture barrier between the old, existing pavement surface and the new overlain surface acts to retard moisture intrusion, thus prolonging the life of the overlay. 

Pavement Structure Bases and Surfacing. Sand—asphalt—sulfur mixes may be used in the construction of all types of pavements or for overlaying existing road structures. As the mixes are cast in place without roller compaction, they are suitable for road widening or bridging weak spots in the subgrade. 

Generally, any proposal to incorporate a nonconventional material, and particularly a waste or by-product material, into a pavement structure requires, in addition to an engineering evaluation, an investigation of its physical (size distribution, specific gravity, specific surface area, hygroscopic moisture, plasticity index) and chemical properties (pH, composition, absorption capacity). These properties need be addressed prior to determining the acceptability of the material in order to determine the environmental, occupational health and safety, recyclabiUty, economic and implementation issues. Such an evaluation is complicated by the number of technical disciplines as well as institutional considerations that must be included in the process. 

This is a physical component of the system. The purpose of the drainage system is to redirect water from the pavement structure, ground water and surface water as well as infiltrating rainwater. Internationally, various designs of subdrainage systems exists (see, for example, [14]). 

Outward mass transport of contaminants at the system boundary. The emissions may spread in the surrounding environment with surface and ground water. Another type of emissions from the pavement structure is the contaminants that originate from the traffic, either deposited on the road surface, and carried to the shoulders of the road by surface runoff, or directly transported and deposited along the road through the exhaust fumes. 

Depending on the location and topography surface water may intrude directly into pavement structure horizontally. In cold regions the presence of snow along the road shoulders may prevent the thaw front to progress at the same speed as into the pavement structure. Under such conditions melt water and rain has been observed to infiltrate at the shoulders, flow into the structure and gradually saturate the pavement structure [12]. 

The incoming energy to the system is dependent on the location of the road. The net energy supplied to the surface is divided into change in heat storage in the pavement structure, sensible heat flux and latent heat flux. 

The local ground water conditions, together with the local rainfall pattern and surface water conditions, govern the amount of water supplied to the pavement structure. A rising groundwater table comes first in contact with the drainage system, which redirects the water and may prevent that the water table rises higher. 

The major pathways for gas into the pavement structure are through the shoulders and through the bounded layers. Due to its large surface exposed to atmosphere the gas exchange at the boimdary of the shoulders is likely to dominate [ 12]. In presence of water as a reactive medium both the gas and solid phases react together (oxidation, carbonation). The redox condition is controlled, to a large extent, by the pore gas composition and is therefore important to consider. 

In a recent study (Romero et al. 2011) on the premature surface cracking in flexible pavements in Utah, it was reported that the cracks were not attributed to pavement structural deficiency but to the low-temperature performance of the bituminous mixtures. Numerous other studies have found that the main form of deterioration in asphalt pavements within the freezing areas of the United States and Canada is thermal cracking (Marasteanu et al. 2007). 

The main structural function of a pavement is to sustain traffic loads and distribute them to the subgrade. The stresses transferred to the surface of the subgrade should be such as to cause minimal deformation of the subgrade soil layer. Additionally, part of the upper layers of the pavement structure should be almost impervious to water, so that the subgrade, as well as the unbound layers, is protected from the detrimental effect of surface water. Finally, the pavement surface should be skid resistant, resistant to the polishing action of tyres and even. 

Repetitive tensile strain applied during the pavement s service life will initiate the first crack at the underside surface of the bottom asphalt layer (or hydraulically bound layer), which will propagate to the surface causing surface cracking. Similarly, repetitive compressive strain at the surface of the subgrade will cause subgrade deformation, which will eventually spread to the surface of the pavement, resulting in surface or structural deformation. 

The maximum performance period is the maximum practical amount of time expected from a given pavement structure or stage construction. Theoretically, the maximum performance period should be equal to the analysis period, but in practice, this rarely happens (taking into consideration the effect of environmental factors, surface deterioration, etc.). 

The methodology has introduced the concept of the foundation and of the pavement structure being either flexible or rigid. The design criteria used to develop the design charts are as follows for the foundation design, the deflection of the foundation surface and the minimum thickness of the upper foundation layer (Chaddock and Roberts 2006), and for the pavement design, the strain of the asphalt layer and the stress of the hydraulically bound layer (Nunn 2004). 

The total thickness of the flexible pavement structure, comprising the surface course, binder course and base, is obtained from the right-hand portion of the nomograph shown in Eigure 13.19, and it depends on the type of base material. 

Rehabilitation is the extension of the pavement structure s life when maintenance techniques are no longer viable to maintain adequate serviceability. It requires structural evaluation, corrective action and at least a nominal hot mix asphalt (HMA) overlay. A nominal overlay has a thickness of three times the nominal maximum aggregate size. Since many agencies specify 12.5 mm nominal size aggregate for their surface mixtures, their minimum HMA overlay thickness (over a HMA pavement) should be at least 38 mm (Asphalt Institute MS-17 3rd Edition). 

The Asphalt Institute deflection method for asphalt overlay design (Asphalt Institute MS-17 3rd Edition) requires surface deflection measurements for the determination of pavement structural condition. The method can be used for asphalt overlay design for either flexible or rigid pavements. 

Table 15.21 Rehabilitation options/strategies to correct surface and structural deficiencies of all types of existing pavement...

Asphalt concrete is primarily used as a structural pavement surface constructed over a subgrade and a subbase. It is designed to support the traffic load and distribute the load over the roadbed. Asphalt concrete pavements can be constructed using hot mix or cold mix asphalt. Hot mix asphalt is a mixture of tine and coarse aggregate with asphalt cement binder that is mixed, placed, and compacted in a heated condition. Cold mix asphalt is a mixture of emulsified asphalt and aggregate, produced, placed, and compacted at ambient air temperature. Cold mix asphalt pavement usually requires an overlay of hot mix asphalt or surface treatment to resist traffic action. 

Filtration installations include wrapping the trench of a pavement-edge drain system to prevent contamination of the underdrain placement behind retaining walls and bridge abutments to prevent contamination of the sand blanket placed against the structure to allow dissipation of pore pressures in order to avoid failure of the structure as silt fences to allow surface runoff from a site while retaining the soil suspended in the runoff and on earth slopes beneath larger stone or other overlay materials to prevent erosion of the slope as water escapes from the interior of the slope. 

The temporal decrease in emitted mass flux can be explained by the phenomenon of pavement, which is linked to the strong inertia particles, which cannot take-off and which form a protection, called cover. It is supposed that these non-erodible particles remain at the bed surface, and consequently, overlay it completely from a certain depth, which is called erosion depth, /. erosion From this depth, the vortex structures bump only particles which they are not able to entrain. No more take-off is possible. 

Prediction of Performance. The VESYS IIM program was used to assess the structural integrity of the two assumed pavements with the various surface materials. This program computes pavement distress in terms of rutting, roughness, and crack damage. These distress indicators are then used in a distress performance relationship to predict the serviceability history of the selected pavement. 

There is another class of frictional interaction that we might call semi-deterministic. These actually behave like a hybrid between stick/slip oscillations and random peak/valley fiiction interactions. Most of these semi-deterministic interactions are caused by human-made objects, created through intentional engineering of the surface features of these objects. Essentially any surface that has a deterministic (especially periodic) structure has the potential to slide with a quasi-periodic motion. Some obvious examples of these come from our driving experience, like the ka-dunk, ka-dunk... sound produced by the seams between freeway concrete tiles, or the scored pavement patterns (or Botts dots) placed by the road edges to tell us we re straying from the allowed driving surface. 

K. Satoh and K. Komada Study on peeling behavior of bond interface of concrete members retrofitted by surface overlaying with polymer cement mortar (in Japanese). JSCE Journal of Materials, Concrete Structures and Pavements Vol.59, No.732 (2003), pp.77-87. 

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