Pavement distress

This chapter discusses current research on the use of sulfur in recycled asphaltic concrete pavements. In addition, it describes the results of laboratory tests and theoretical predictions using the latest linear viscoelastic layered pavement analysis methods (15,16) to compare the performance of various sulfur-asphalt concrete pavements with conventional asphalt concrete pavements in a variety of climates. The relationship between pavement distress and performance used in the computer program was established at the AASHTO road test (17). Finally, the results of domestic field tests of sulfur-asphalt pavements are presented along with a discussion of future trends for the utilization of sulfur in the construction of highway pavement materials. 

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. 

The overall structural adequacy of pavements is given in probabilistic terms of the present serviceability index developed from the AASHTO road test (17). This index, which is a measure of the momentary ability of a pavement to serve traffic, is based on such factors as rut depth, slope variance, cracking, and patching of the pavement. The relationship between serviceability index and these pavement distress modes is given by the AASHTO road test equation (16) ... 

The OCED study (OECD 1988) concluded that an appropriate value for coefficient y to be considered for all types of pavement distress is 4. Hence, the equivalency factor, a, can... 

In the climate/environment analysis, detailed climatic data (hourly temperature, precipitation, wind, relative humidity, etc.) are required for predicting temperature and moisture content in each of the pavement layers and then pavement distress. Climatic data are available from weather stations but MEPDG has an extensive number of weather stations embedded in its software for ease of use. 

The visual condition survey of pavements consists of (a) recording of pavement distresses, (b) pavement rating and (c) detailed presentation of pavement condition. 

The visual recording of pavement distresses is usually conducted by crews of at least two trained people. The collection of pavement distress information may be carried out by viewing the pavement surface from a slow-moving vehicle or by walking on the pavement... 

Chong G.J., W.A. Phang, and G.A. Wrong. 1977. Manual for Condition Rating of Rigid Pavements Distress Manifestations. Ontario Ministry of Transportation and Communications. Ontario Downsview. 

McGhee K.H. 2004. Automated Pavement Distress Collection Techniques. NCHRP Synthesis 334. Washington, DC Transportation Research Board. 

Study (HDM Study), from which prediction models were established for almost all pavement distresses. The prediction models developed were reported by Paterson (1987) and incorporated in the highway design and maintenance standards model, HDM-III model (Watanatada et al. 1987). These models improved upon the introduction of the HDM-4 models (Morosiuk et al. 2004). These distress models could assist pavement management. 

Conservation of materials and energy resources Elimination of disposal problem of reclaimed asphalt Minimisation of transport cost of materials Correction of all pavement distresses and cross slope Pavement elevation may be maintained Ultimate energy savings... 

FDR is an in-place rehabilitation process that can be used for reconstruction, lane widening, minor profile improvements and increased structural capacity by addressing the full range of pavement distresses (Stroup-Gardiner 2011). 

The entire construction was accomplished without incident the conventional equipment and techniques worked as well as with Sulphlex binders as with asphalt. After 2.5 years service, at a traffic volume of 1000 ADT (10 percent trucks), distress is evident in a number of sections. In general, the distress has been primarily attributed to poor subgrade drainage placement of certain sections with mix at extremely low temperature (below 65C (150F)) ravelling of dry mixtures and lateral shifting of lifts due to the absence of adequate tack between them. None of the distress is uniquely related to the use of Sulphlex binders in lieu of asphalt cement in the pavement. 

Mechanical Characterization of Sulfur-Asphalt. The serviceable life of a pavement comes to an end when the distress it suffers from traffic and climatic stresses reduces significantly either the structural capacity or riding quality of the pavement below an acceptable minimum. Consequently, the material properties of most interest to pavement designers are those which permit the prediction of the various forms of distress—resilient modulus, fatigue, creep, time-temperature shift, rutting parameters, and thermal coefficient of expansion. These material properties are determined from resilient modulus tests, flexure fatigue tests, creep tests, permanent deformation tests, and thermal expansion tests. 

Finn, F., C. Saraf, R. Kulkami, K. Nair, W. Smith, and A. Abdullah, The Use of Distress Pridietion Subsystems for the Design of pavementStruetmes In Proe., 4th International Conferenee on the Struetural Design of Asphalt Pavements, AnnArbor, Mich. fJoU,1911. 

The great variety of CVs, axle configurations and loads causes different distress to the pavement structure. This alone creates a huge problem to the pavement designer. Many years ago, converting every axle configuration and load to an axial load was considered, causing an equivalent structural distress. 

The outcome of the road test was the establishment of complex equations (AASHTO 1986) from which load equivalency factor could be determined for any load of single, tandem or tridem axle. The structural distress caused by the traffic (all kinds of distresses cracking, rutting, etc.) was expressed in terms of pavement serviceability performance and is called terminal serviceability (pj. The variation of flexible pavement structures was expressed in terms of pavement structural number (SN), while the variation of rigid pavement structures was expressed in terms of thickness of slab, D (AASHTO 1993 HRB 1962). 

The load equivalency factors were derived from terminal serviceability factor (pj values equal to 2.0, 2.5 or 3.0 and pavement structural number (SN) values equal to 2, 3, 4, 5 or 6. The lower p value represents a pavement with serious structural distress where maintenance is unavoidable. The upper value of 3.0 represents a pavement with structural distresses needing maintenance, if high level of service is to be provided. The SN values represent different pavement structures. A sample of the equivalency factors derived from flexible pavements, for pt = 2.5 and SN = 5, for the three types of axles (single, tandem and triaxial), is given in Table 12.3. All equivalency factors for flexible pavements can be found in tabular form in the AASHTO pavement design guide (AASHTO 1993). 

The design criteria or distress modes adopted by most analytical and semi-analytical methodologies for flexible pavement design are as follows (a) fatigue of treated layers, that is, the asphalt layer or the hydraulically bound layer not to crack under the influence of traffic and (b) deformation of the subgrade, that is, the subgrade to be able to sustain the traffic without excessive deformation. 

All pavement design methodologies assume that rigid pavement failure due to load related distresses occurs at the end of the design period. 

The above factors, in combination with the reliability of the design, the compliance of materials used and the quality of the construction achieved, are the only reasons for the emergence of pavement surface distresses, fatigue failure and, finally, pavement disintegration. 

Freventive maintenance is defined as the number of activities aiming to prevent the premature emergence of distresses and consequently premature pavement destruction. 

One way to determine the rehabilitation time is by monitoring the provided level of service related to some surface distresses, mainly transversal/longitudinal evenness and cracking. Another way is by structural evaluation survey of the pavement. 

All types of surface distresses occurring in flexible pavements can be classified into four categories cracking, distortion, disintegration and loss of skid resistance. 

Pavement surface distortions are generally distresses related to pavement unevenness in the longitudinal or transverse direction. Surface evenness affects traffic safety and comfort. Distortions may be accompanied by cracking, which then affects the structural performance of the pavement. 

Corrugations and shoving are ripples formed in the longitudinal direction of the asphalt pavement surface (Figure 15.12c) owing to plastic displacement of the asphalt. When the plastic displacement is local, the distress is called just shoving. 

Loss of surface skid resistance is a skid hazard associated with smooth and slippery surface, which directly affects traffic safety. Unlike all other surface distresses, a smooth and slippery surface does not affect the structural deterioration of the pavement. 

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. 

Cracking is the most common distresses of rigid pavements. It is caused, to a great extent, not only by the concrete s volumetric behaviour under temperature variations but also by the repetitive loading caused by traffic and some other external factors. 

Timely maintenance sealing of the joints and of the cracks is of vital importance to prevent development of further distresses, which eventually accelerates the complete deterioration of the pavement. 

Surface deformation is another very common type of distress of jointed rigid pavements. Surface deformation is the difference in elevation across a joint or a crack resulting from vertical movements. 

Asphalt overlay is rarely laid directly on rigid pavement without any pre-treatment or maintenance of the existing surface. Even if the surface is almost free of distresses, reflective cracking at the joints are expected to appear after a certain period. 

Treatments are generally suggested depending on the nature of distresses and condition of the concrete pavement. With respect to overlays, the instructions and recommendations are summarised as follows ... 

The functional evaluation of the existing pavement is based on condition surveys for certain distress types and severities, depending on the overlay selected. 

Functional evaluation considers the surface characteristics of a pavement and is user related. Surface characteristics include longitudinal evenness (smoothness), skid resistance, rutting, cracking or any other surface distress that affects riding quality and safety. Functional evaluation is used to decide whether the pavement needs to be maintained, rehabilitated or reconstructed essentially, the necessity for intervention and its type is decided. 

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