Asphalt pavement reinforcement

For asphalt pavement reinforcement, stiff extruded geogrids are the best option and the best locations are [7] ... 

A large number of structural materials were evaluated for possible attack by run-off from a sulfur-asphalt pavement. Of the ten materials studied, copper and steel appeared to indicate a vulnerability. The former or its alloys should never be used in equipment or structures which could bring them in contact with sulfur due to the high probability of producing the sulfates of copper. Steel reinforcing rods would be susceptible to attack by H SO produced by moisture on contact. 

This paper present the result of laboratory tests carried out to study the relative performance of waste tire rubber in asphalt pavement. The result demonstrates that waste tire rubber reinforcement is the most advantageous pavement reinforcement technique for improvement of asphalt fatigue life. 

In many metropolitan areas, the RCM source is from existing Portland cement concrete curb, sidewalk and driveway sections that may or may not be lightly reinforced. The RCM is usually removed with a backhoe or pay loader and is loaded into dump trucks for removal from the site. The RCM excavation may include 10-30% sub-base soil material and asphalt pavement. Therefore, the RCM is not pure Portland cement concrete, but a mixture of concrete, soil, and small quantities of bituminous concrete [159-161]. 

The use of synthetic fiber for the reinforcement of road pavement not only enhances strength but also lengthens the useful life from normally 10-15 years to 20 25 years for concrete pavement, and from 3 5 years to 5-10 years for asphalt pavement. In addition, the eost of road maintenance is drastically lowered with fiber reinforcement. Mostly, polypropylene ST is used in the reinforcement of concrete pavement, while polyester ST in asphalt pavement. 

Figure 5.4 Locations for geogrid reinforcement and function in (a) asphalt pavement...

Compacted soils and aggregates generally have good compressive modulus but poor tensile modulus and hence can be readily separated when subjected to high tensile loads. Geotextiles with fibres of suitable tensile moduli can effectively be used as reinforcing tension elements when embedded in compacted soils and aggregates. Some major uses are over soft soil unpaved roads, mnways, railroads and landfills, to stabilize a temporary bunds slope, as closure systems over unstable landfills, ash ponds and to reinforce asphalt pavement layers. 

According to this experimental work, the waste rubber reinforcement can obviously improved characters of asphaltic samples. As stability, creep tests indicated that reinforcement by waste rubber reduced their permanent deformation significantly, it means that waste rubber provides a strong eomposite for designing mixes to avert both pavement rutting and low temperature cracking in order to prolong road life. 

Something similar also applies to the analytical design approach of flexible pavements. The main difference with other structures composed of reinforced concrete, or steel, lies in the fact that asphalts (bituminous mixtures) do not behave as elastic material but as viscoelastic material owing to the presence of bitumen. The rest of the structural materials of pavements, such as compacted aggregates, stabilised aggregates or soil with binders other than bitumen, as well as untreated soil, may be characterised as materials with elastic behaviour. 

Depending on the existence (or non-existence) of reinforcement, rigid pavements are divided into four types of pavements (a) unreinforced concrete pavements (URCPs), (b) jointed reinforced concrete pavements (JRCPs), (c) CRCPs and (d) CRCPs with asphalt surfacing layer, formerly known as composite rigid pavements. 

The CRCPs with asphalt surfacing layer may be further distinguished into CRCPs with thin asphalt overlay (minimum thickness of 30 mm) or CRCPs with an asphalt overlay of 100 mm. The latter is known as rigid pavement with continuously reinforced concrete base (CRCB) and asphalt overlay. 

Nowadays, there is a tendency to construct continuously reinforced rigid pavements with an asphalt overlay. In some countries, like the United Kingdom, when rigid pavement is to be constructed in motorways or heavily trafficked areas, it is advised to use exclusively continuously reinforced pavements with an asphalt overlay. 

Figure 14.1 Characteristic types of rigid pavements, (a) Unreinforced concrete pavement (URCP) (b) jointed reinforced concrete pavement (JRCP) (c.i) continuously reinforced concrete pavement (CRCP), without asphalt overlay (c.ii) CRCP, with thin asphalt overlay and (d) rigid pavement with continuously reinforced concrete base (CRCB) and asphalt overlay. (Adapted from Highways Agency, The Manual of Contract Documents for Highway Works [MCDHW], Volume 3 Highway Construction Details, Department for Transport. London Highways Agency, 2006c.)...

During the recent years in certain countries, the continuously reinforced pavements prevail, particularly those with an asphalt overlay. These pavements are more expensive than all the other abovementioned types but are more cost-effective, offer better serviceability level, are easily maintained and are ideal to the application of further asphalt overlays at stages during the future pavement life. 

The functions of steel reinforcement in rigid pavements are primarily to counteract the temperature- and moisture-induced stresses, to reduce the number of transverse joints (jointed reinforced slabs) or eliminate the transverse joints (continuously reinforced slabs), to minimise future maintenance cost and, to a certain extent, to reduce the thickness of the slab. The reduction or elimination of transverse joints has a direct impact on the improvement of the riding quality offered. Some countries like the United Kingdom recommend to use, almost exclusively, continuously reinforced slabs on new constructions, hence the absence of transverse joints, with an thin (30 mm) or thick (100 mm) asphalt layer on top. 

For continuously reinforced pavements (CRCP or CRCB), it has been assumed that no concrete slab maintenance or reinforcement will be required over the design period. As for the maintenance of thick or thin asphalt layers, it depends on the nature of the traffic. 

Before describing in detail the distresses and their causes, it should be mentioned that effective maintenance/treatment of the distresses in rigid pavements with cement mortar or concrete (unreinforced or reinforced) is too difficult and sometimes impossible. For this reason, bitumen and asphalt are the materials greatly used in maintenance of rigid pavements. 

Hot asphalt surfacing overlay restores micro- and macro-texture and is the most suitable treatment for restoration of skid resistance of continuously reinforced pavement surface. All types of hot asphalts used in restoration of skid resistance of flexible pavements can be used, namely asphalt concrete for very thin layers, SMA and porous asphalt. 

Respectively, the thickness of an asphalt overlay of jointed unreinforced/reinforced or continuously reinforced pavement, or of rigid pavements with existing asphalt overlay, cases (c) and (d) above, is determined by the following equation ... 

Asphalt overlay. It is placed onto a roadway on which a hot asphalt is poured (fabric-reinforced pavement). 

A. Horvath, C. Hendrickson, Comparison of Environmental Implications of Asphalt and Steel-Reinforced Concrete Pavements, Transportation Res. Record 2626,1998,105-113. 

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