Pavement strengthening

During pavement maintenance or rehabilitation, it is also recommended that the case of simultaneous pavement strengthening be examined. However, pavement strengthening may be decided at any time regardless of the need for maintenance or rehabilitation of the pavement. In any case, the thickness of the strengthening overlay is determined after examining the structural condition of the existing pavement. 

Various procedures have been developed for determining the required thickness of the strengthening asphalt layer (overlay or inlay). All can be classified into either deflection procedure or effective thickness procedure. 

The deflection procedures for asphalt overlay design are based on pavement deflection data collected by dynamic, static or vibratory non-destructive testing (NDT) devices. Examples of such devices are as follows Benkelman beam, deflectograph, falling weight deflectometer (FWD), Dynaflect or Road Rater for details of the testing devices, see Section 16.4. 

Two of the most known deflection procedures requiring the use of the Benkelman beam or the deflectograph will be described below. 

The design procedures employing the use of FWDs or other devices require extensive analytical calculations and fall outside the scope of this book. 

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Highways Agency (2008a) recommends strengthening by overlay or partial reconstruction to be designed to extend the pavement life for a further 20 years. This procedure is known as pavement strengthening/upgrading. 

For similar pavement characteristics the use of this new S/A binder allows conventional aggregates to be replaced by low quality aggregates which are available on the spot. Moreover, with graded aggregates, the thicknesses of layers can be reduced as a result of the better characteristics of pavement. This is particularly interesting for the strengthening works. 

The terminology used for keeping the pavement at a tolerable level of service differs significantly from country to country. In most of the countries, the following terms are used routine maintenance, preventive maintenance, corrective maintenance, major maintenance or pavement rehabilitation, strengthening and rejuvenation. 

Major maintenance or pavement rehabilitation strengthening may be defined as the number of activities aiming to fully restore the qualitative state of the pavement. The works consist of constructing an asphalt layer of a certain thickness (asphalt overlay) consisting of new or recycled materials, with or without levelling course or milling of the old pavement surface. This asphalt layer may be catered to extending a pavement s service life. 

Generally, when the rigid pavement shows extensive deep spalling together with surface deformation or other cracking, strengthening the asphalt or concrete overlay is the only effective treatment. 

Surface dressing provides a simple and cost-effective pavement maintenance alternative solution contributing to road safety and protection of pavement. Today, considering proper design, careful application and use of appropriate material surface dressing can be used in any types of roads. It should be underlined, however, that surface dressing cannot restore the pavement s surface evenness nor can it contribute to the pavement s structural strengthening. 

The asphalt overlay laid on worn rigid pavements involves (entails) the concept of correcting functionally related surface defects rather than exclusively strengthening the pavement to carry future traffic load. In all cases, asphalt overlay on rigid pavements is very much affected by reflective cracking. 

Information regarding maintenance and strengthening of rigid pavements, in general, can be found in DMRB HD 32 (Highways Agency 1994). 

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