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thin bituminous seal 9 Maintenance and rehabilitation Analytical approach Structural approach Deflection approach Maintenance options Reflection cracking 10 References 11 Applicable standards Appendix A: Detailed surface condition survey Appendix B: Road roughness measurements Appendix C: Deflection beam measurements Appendix D: Deflection beam survey procedure Appendix E: Falling Weight Deflectometer (FWD) test procedure Appendix F: TRL Dynamic Cone Penetrometer (DCP) test procedure Appendix G: Test pit procedure Appendix H: Sand patch test Appendix I: The portable skid-resistance tester 21 21 21 21 30 30 30 30 31 31 31 33 33 34 34 35 36 41 43 44 45 50 53 54 56 61 65 66 iv .asphalt surfacing Longitudinal cracking Transverse cracking Block cracking Crocodile cracking Non-wheelpath cracking .Page 8 Identifying the causes of pavement deterioration Rutting without shoving Rutting with shoving Wheelpath cracking .thin bituminous seal Non-wheelpath cracking .asphalt surfacing Wheelpath cracking .
it is always advisable to verify the accuracy of data supplied from other sources before use. 1. the recommendations can be easily adapted. Carry out surface condition. Some authorities adopt a comprehensive approach with the support of formal road management systems and collect data on a regular basis for planning and programming purposes.5 During the preliminary design stage. the stages prior to the detailed condition survey (Figure 2. It also reviews alternative rehabilitation design procedures and comments on their limitations and advantages.1 This Road Note gives guidance on road pavement evaluation procedures suitable for bituminous-surfaced roads in tropical and sub-tropical climates and reviews alternative methods of maintenance and repair. the pavement evaluation study establishes the nature. During the detailed design stage. It is intended primarily for highway engineers who are responsible for maintaining roads in tropical and subtropical environments but the techniques and principles on which it is based are equally applicable in other environments. It gives guidance on the use of non-destructive and destructive pavement tests and describes how the results of these tests can be interpreted. is used to identify alternative maintenance or rehabilitation strategies which can be considered in the subsequent project appraisal. roughness and traffic surveys.1 and can be summarised as follows: • • • • • Collect and interpret existing design. high axle loads and inadequate funding for maintenance. because of the harsh climatic conditions and often a lack of good road pavement materials. This appraisal will consider the social impact. This Note gives guidance on pavement evaluation procedures which can be used during both the preliminary and detailed design stages of a project to maintain or upgrade an existing road. For example. 1. 1993a) and HDM III (Watanatada et al.1) may be carried out on a regular basis and therefore be completed already. both to identify the causes of the deterioration and to assess the strength of the existing road. the pavement evaluation is based on similar information but the frequency of measurement is increased. severity and extent of the road deterioration. This information. construction and maintenance data. severity and extent of the road deterioration. Carry out structural and materials testing. Establish the cause of the pavement deterioration. The economic viability is normally assessed using existing road transport investment models such as RTIM3 (TRRL.1 The process of selecting appropriate methods of maintenance or rehabilitation is shown in Figure 2. environmental impact and economic viability of each alternative. It can be summarised in the following stages: • • • • • Road project identification Feasibility and preliminary design Detailed design Implementation Evaluation released in 1999).2 Paved roads in tropical and sub-tropical climates often deteriorate in different ways to those in the more temperate regions of the world. The data collected as part of such a system are often sufficient for feasibility studies at project level but are rarely sufficient for detailed design. 2 Pavement evaluation and maintenance procedure 2. Project appraisal 1. to validate the findings of the feasibility study and to optimise the design of each segment of the project road. Nevertheless. 1.1 Introduction Scope of this note 1. The procedures described in this Road Note are based on the assumption that very little data are available.2 Each road authority will have a different approach to the management of the road network. 2. In addition.3 This Road Note describes methods of pavement evaluation designed to establish the nature. Select appropriate method of maintenance or rehabilitation. however. roads in many countries often suffer from accelerated failures caused by variable quality control during construction. in situations where this is not so. the cause of the deterioration and the strength of the existing road pavement.4 The process of road project appraisal is described in detail in Overseas Road Note 5 (TRRL. 1988). together with the material test results. 1987) and HDM-4 (to be 1 .
1 Road pavement evaluation and rehabilitation procedure 2 .Figure 2.
These techniques are described in Overseas Road Note 5. 3 . can be used to establish the type and approximate thickness of the pavement construction. Using the data. axle load data should be separated by direction of traffic as any differences in axle loads can be useful in identifying the causes of pavement deterioration.3 Interpretation of existing data 3. 1993b). If this information is not available then the total traffic loading to date can be estimated using traffic growth rates based on other information. If historical traffic data are available. for example. raw materials are being exported or imported. Often. 3. Techniques for carrying out such surveys are described in Road Note 40 (TRRL. the total commercial traffic loading that the road has carried since construction can be estimated. Each length of road is then treated as a separate evaluation exercise. If neither classified traffic counts nor axle load data are available then surveys should be carried out as part of the evaluation exercise in order to establish current values.3 It is important that. wherever possible. those lengths of road having the same nominal thickness and type of construction are identified. 1978). historical traffic counts are available but reliable axle load data will not have been collected.1 Design. Significant differences can occur on roads that lead to quarries or major ports where. if available.2 The traffic loading (in terms of equivalent 80 kN standard axles (esa)) that the road pavement has carried since its construction should be calculated (TRL. construction and maintenance data. 3.
the section or representative one kilometre length is permanently marked into `blocks' of equal length. There are.30). 4.5 The resources and the equipment required for the detailed condition survey and the operational details are described in Appendix A. a number of defects that tend to be common to all road pavements and these are described in Table 1. 4.2 Detailed condition surveys of the sections are then carried out. When the uniform sections are relatively short. Note that important aspects of road deterioration may be missed if the vehicle is not stopped and survey staff given the opportunity to inspect the road closely. traffic loading. 4.28-4.4 During the detailed surface condition survey the nature.1 After dividing the road into lengths of nominally similar construction. type of road deterioration. the length may be reduced to as short as 10 metres if the road is severely distressed. eg bleeding. fretting.27. It is important that rutting is measured at a discrete point as its severity may need to be 4 . This can be done by carrying out a windscreen survey. cracking deformation (excluding rutting) patching and potholes edge failures Rutting is recorded once at the beginning of each of the blocks. however. where resources are limited then a number of representative one kilometre lengths of road can be used to identify the cause of pavement distress (see para 4. These measurements are necessary for the economic appraisal and are useful in defining sections of road in similar condition. Table 1 Terms on the surface condition form 4. extent. and topography. 4.6 The recommended form for recording the surface condition data is shown in Figure 4. compared with other non-destructive tests carried out at the same location (see para 8.1. The best way to do such a survey is for the survey vehicle to stop at 500 metre or one kilometre intervals to enable the condition of the road pavement to be recorded accurately using a selection of the road pavement deterioration criteria described in paragraphs 4. it may be necessary to subdivide it again based upon the current condition of the road. described in Table 2.7-4. however. The roughness of the road should also be measured at this stage in the evaluation (see paras 4. the detailed condition survey is best carried out over the entire length of the section.3 Before the detailed surface condition is carried out. occur. For inter-urban roads the maximum block length should be either 50 or 100 metres.30). The length of road investigated by this method should represent no less than 10 per cent of each section. There are three blank areas on the surface condition form which should be used if the other defects. However. stripping etc. The road can then be subdivided into shorter uniform sections based upon the following: • • • • time since construction. severity and position of the following defects is recorded: • • • • • surfacing defects.5). It is designed to be as flexible as possible since the nature of paved road deterioration varies depending on factors such as the type of construction.4 Surface condition and roughness surveys 4. climate and traffic levels.
1 Detailed surface condition form .5 Figure 4.
2. It starts in the wheelpaths but. Table 3 Extent of the defect 4. as measured by the resistance to polishing of the aggregate.Table 2 Other defects beneath. with time.11 The ability of a bituminous surfacing to provide the required skid resistance is governed by its macrotexture and microtexture. The following definition is recommended: Fretting/Stripping: Shallow potholes having a diameter greater than 100mm. Although the mechanisms of failure differ. These areas then disintegrate under traffic and develop into shallow potholes.12 The microtexture of the surfacing. is the dominant factor in wet skidding resistance at lower speeds. Fretting and stripping 4. The macrotexture of the surfacing. In most cases there is a migration of the binder towards the surface of the road resulting in localised bleeding at the surface and unstable poorly coated aggregate Surface texture 4. As a guide. Loss of stone 4. The following definition is recommended: Loss of stone: Continuous film of bitumen visible due to the loss of aggregate. In surface dressings it can be caused by variability in the prepared surface or poor quality control during the spray and chip operation. the result of both of these types of deterioration will be a shallow pothole or a series of potholes.7 Bleeding is usually observed first in the wheelpaths and is the result of bitumen being forced to the road surface by the action of traffic. the categories shown in Table 4 (CSRA. exceeds the breaking strain of the bitumen. Stripping in asphalt surfacings is the result of the displacement of binder from the surface of the aggregate caused by the combined action of water and traffic. In asphalt surfacings this can be the result of variations in the mixing process. Surfacing defects Bleeding and fatting-up 4. The surface condition survey should include a qualitative assessment of texture in the wheelpaths so that it can be used to trigger quantitative testing if required. However. Smooth and shiny appearance but aggregate visible. it can often be identified by an accumulation of drippings at the edge of the road pavement. 1992) are suggested.8 Bleeding and fatting-up can often be discontinuous. contributes particularly to wet skidding resistance at high speeds by providing drainage routes for water between the tyre and the road surface. local over application of tack coat or secondary compaction by traffic.9 Fretting is the progressive loss of fine aggregate from the road surface and occurs when the small movements of individual particles. Hence the extent of the defect can be recorded as shown in Figure 4. The following definitions are recommended: Bleeding: Fatting-up: Continuous film of binder covering the aggregate. Fatting-up of the surface is a less extreme form of bleeding where the surface becomes very smooth but there is insufficient binder to form a continuous film on the surface. The introduction of denser asphalt mixes and the use of cement and hydrated lime as filler has largely reduced the occurrence of stripping in asphalt surfacings. The assessment of polishing is more difficult 6 . The extent of the defect is recorded according to Table 3. The loss of fine aggregate at the surface results in lack of mechanical interlock which can eventually lead to the loss of coarse aggregate and the formation of potholes. under the action of traffic.10 The loss of chippings from a surface dressing resulting from poor adhesion between the binder and the aggregate appears early in the life of the surfacing. Aggregate polishing 4. as measured by its texture depth. It tends to occur later in the life of the surfacing after the bitumen itself deteriorates with age and usually begins in areas of high traffic stress such as sharp bends. the problem may spread across the carriageway making it difficult to differentiate between this type of failure and bleeding.
Firstly. 1992) Table 4 Visual assessment of surface texture assessment will depend on the judgement of the technician.13 The assessment of cracking should fulfil two objectives. it should establish whether the severity of cracking will affect the 7 . and Table 5 (NIT'RR. When marginal quality aggregates have been used or if increased traffic flows have resulted in an increased state of polish. 1994a). Secondly.Figure 4. Table 5 Visual assessment of aggregate polishing than that of the surface texture. The qualitative Cracking 4. 1985) is suggested as a preliminary guide. it should identify whether the road pavement is suffering from load or non-load associated distress. skid resistance will be reduced. but will be unnecessary if surfacing aggregates having a satisfactory minimum Polished Stone Value were used during construction (Department of Transport.2 Extent of potholing and patching in a `block' (after CSRA.
If the intensity of crack in varies within any block. 0 .single crack 2 .more than one crack .not connected 3 . These are listed as follows and illustrated in Figure 4.performance of any subsequent new pavement layer by causing reflection cracking (Rolt et al.29. its appearance can provide a guide to its likely cause. Figure 4.longitudinal cracks T .3 Types of cracking 8 .interconnected 4 .severe crocodile cracking with blocks rocking under traffic. It is recommended that five types of crack are defined.crocodile cracking 5 .transverse cracks B . These objectives are best achieved by identifying five characteristics of the cracking: • • • • • type intensity position width extent L .parabolic cracks Intensity 4.14 Although there is often no single cause for any type of crack.15 The intensity of cracking is defined by six levels described below.no cracks 1 .3. 1996).more than one crack . it should be the intensity-that predominates that is recorded. The causes of cracking are discussed in more detail in paragraphs 8.crocodile cracks P .block cracks C . Type 4.9-8.
30. Figure 4. or can be spread over the entire carriageway (C/W).28-4.17 The measurement of crack width is difficult. The cracking can be confined to either or both of the vergeside (V) and offside (O) wheelpaths. On most roads this is usually the vergeside wheelpath because here the road pavement is generally weaker as a result of higher moisture contents and less lateral support. 1987).4.5. This is discussed in paragraphs 4.Position 4. those defects with short wavelengths. Width 4. cracks with substantial spalling are classified as width 4. Deformation 4.5).21 The width of the running surface and the traffic flow govern the number of observable wheelpaths on paved roads. the width of the cracks can be measured with a simple `Go/No Go' gauge shown in Figure 4.20 Rutting is load associated deformation and will appear as longitudinal depressions in the wheelpaths. but it is important because the width partly determines whether a crack can be sealed effectively. those defects with longer wavelengths that are best quantified by the use of more sophisticated road profiling instruments. a 3-metre carriageway will have two wheelpaths but at road widths greater than 6.5 metres there are generally four. Initially. The straight-edge is placed across the wheelpath. It is the result of an accumulation of non-recoverable vertical strains in the pavement layers and in the subgrade. pavement deformation divides into two groups.crack width < 1mm 2 . until technicians are familiar with the system.18 The extent of the cracking is defined as the length of block affected as shown in Table 3.4 Crack width gauge 9 . The extent of cracking should be recorded irrespective of intensity. the wedge can be held vertically and the depth recorded to the nearest l0mm. Four categories are recommended as shown below (Paterson. 1 . Secondly. where severity can be measured by the use of a simple 2 metre straightedge and calibrated wedge (Figure 4.16 The position of the cracking is recorded.19 In terms of its assessment. and so it is the width of crack that predominates that is recorded. and the maximum rut depth recorded as shown in Figure 4. Rutting 4.cracks with spalling Extent 4. The first three are for cracks which are not spalled. If the ruts are greater than 40mm deep. 4. with the central one being shared by traffic in both directions.crack width > 3mm 4 . at right angles to the direction of traffic. Firstly. At intermediate widths and low traffic flows there is the possibility of three wheelpaths. This type of rutting is not associated with any shoving in the upper layers of the pavement unless it becomes very severe. The width of the cracks usually vary within any block. For example.1mm < crack width < 3mm 3 . Rut depths should be recorded in the wheelpath showing most rutting.
22 Rutting can also be the result of shear failure in either the unbound or the bituminous pavement layers resulting in shoving at the edge of the road 10 pavement. Where the shear failure is occurring in the unbound roadbase or sub-base the displaced material will appear at the edge of the surfacing. because of a large volume of non-motorised traffic. This can be simply done by putting a circle around the value of rutting recorded on the surface condition form. 4. the displaced material will be evident in the surfacing itself. Where the failure is occurring in the bituminous material. In these circumstances the pattern of road deterioration will be different and some of the important clues relating to the position of the deterioration on the carriageway will be absent. This is illustrated in Figure 4. The severity of the shoving is difficult to measure without taking levels. together with the depth of rutting.Figure 4.5 Straight edge and calibrated wedge In some countries there are many roads where distinct wheelpaths do not exist. . should be recorded.6. for example. thereby clearly identifying the cause of the failure. This document does not specifically address this situation but many of the techniques for evaluation and assessment described will be appropriate to such conditions. However its occurrence.
25 Potholes are structural failures which include both the surfacing and roadbase layer. The extent of potholes and patching is recorded as shown in Figure 4. caused by settlement of the pavement layers. or wavelength. Further trafficking causes the surfacing to break up and a pothole develops. Although patches are not necessarily defects. they do indicate the previous condition of the road and are included in the assessment. be as much as 10 metres. There is generally no need to measure the severity of the corrugations as it will not affect the selection of the remedial treatment. 11 . The extent of the defect is recorded as shown in Table 3. Other types of deterioration Potholes acid patching 4. construction faults and differential movement at structures. These are easy to see after periods of rain as they take longer to dry than the rest of the road. Corrugations 4. In paved roads they are caused by instability in either the asphalt surfacing or in an unbound roadbase under a thin seal. particularly culverts. potholes are usually patched as a matter of priority. The depth should be measured using the 2 metre straight-edge and calibrated wedge.2. When the road is dry.5-1. should be recorded. in some circumstances.0 metre but can. Their spacing. Because of the obvious hazard to the road user. is usually in the range of 0.23 Localised depressions.Figure 4. They are usually caused by water penetrating a cracked surfacing and weakening the roadbase. they can also be identified by the oil stains that occur where vehicles cross the depression.6 Transverse core profile to investigate rutting Depressions 4.24 Corrugations consist typically of a series of ridges perpendicular to the centre line of the road and usually extend across the whole width of the carriageway.
automatic and expensive. or if the sections of the road under investigation are very long.5. roughness of the road is usually measured using a Response Type Road Roughness Measuring System (RTRRMS) which must be periodically calibrated to allow the values of roughness to be reported in terms of IRI. 1987). Most of the road defects described above contribute in some way to increasing the roughness of the road pavement. It is convenient to measure the defects with the scale on the side of the calibrated wedge. Both the roughness survey and calibration procedures are described in Appendix B. It is a mathematical quarter car simulation of the motion of a vehicle at a speed of 80 kph over the measured profile and can be calculated directly from road levels measured at frequent intervals. Deterioration caused by poor drainage 4. Paved roads do not remain waterproof throughout their lives and if water is not able to drain quickly. but it does not identify the nature of the failures or their causes. shown in Figure 4. Where pavement deterioration is the result of poor drainage design or maintenance this should be recorded on the surface condition form. E 1364-95) or a standard instrument. The length of the road affected is recorded according to Table 3. Hence. although in its early stages cracking may cause little or no change. such as the TRL Profile Beam (Morosiuk et al. if the water velocity in the side drain is too high it erodes the road embankment and shoulders. 1992) or the MERLIN (Machine for Evaluating Roughness using Lowcost INstrumentation) (Cundill. Edge failures (F) are recorded when they exceed 150mm in width at their maximum point or when the vertical step from the surfacing to the shoulder is greater than 50mm (S). However. roughness and windscreen survey data can be used to establish those lengths of road having failures of differing severity. 1986a).28 It is well established that vehicle operating costs increase as the roughness of the road pavement increases (Hide et al. This unsupported edge can then be broken away by traffic. narrowing the running surface of the road.Edge failures and shoulder erosion 4.29 The standard measure of road roughness is the International Roughness Index (IRI) which was developed during `The International Road Roughness Experiment' in Brazil (Sayers et al. the cracked surfacing deteriorates and the resulting potholes and subsequent patching cause a rapid increase in roughness. Conversely. Suitable methods of calibration include a rod and level survey (ASTM. without proper maintenance. Surface texture and variability in rut depth also have a significant effect on the roughness of a road pavement. if resources for the surface condition survey are limited. 4. Roughness measurements 4. However.27 Localised pavement failures are often caused by the poor design or maintenance of side and cut-off drains and cross drainage structures. When side drains and culverts silt up. it weakens the lower pavement layers and results in rapid road failure. 1996).30 The roughness of roads with similar pavement construction is a good measure of their relative pavement condition. 4.26 Edge failures are caused by poor shoulder maintenance that leaves the surface of the road pavement higher than the adjacent shoulder. Devices for measuring levels are usually either slow and labour intensive or fast. 1974) (Chesher and Harrison. More general failures occur when there is no drainage within the pavement layers themselves. the 12 . This allows representative lengths of road to be selected which can then be used to identify the cause or causes of deterioration. water ponds against the road embankment eventually weakening the lower pavement layers.
which can be treated at this stage without the need for further testing. decides where repairs are needed and what form of maintenance is required.1 After the surface condition survey has been completed. When the road pavement is either rutted or cracked. However. a programme of additional testing is usually required to establish the causes. Suggested treatments for these types of pavement distress are summarised in Tables 6 and 7. Table 6 Surfacing defects .roads with asphalt surfacings 13 . there are some surfacing defects. To do this effectively the engineer must first identify the causes of the deterioration.roads with thin bituminous seals Table 7 Surfacing defects . if localised.5 Localised surfacing defects 5. the engineer interprets the results. This is important as it is likely that treating the symptoms of pavement deterioration rather than their causes will prove unsatisfactory.
There may be some cases where the complete section of road will have reached a failed condition. 6. It is also important to establish if the failures are localised. In such cases the cause of the deterioration can only be established by comparing the thickness of the road pavement or the material properties of the pavement layers with relevant design standards and material specifications. with some areas deteriorating less rapidly than others.3 The cracking or rutting recorded during the windscreen or detailed condition survey may be displayed graphically in the form of performance charts. and it is in these areas that the initial form of deterioration can be most easily identified. suggesting that the rutting preceded the cracking.4 An example of the use of performance charts is illustrated in Figure 6. 6.1. However. perhaps because of poor drainage. 6. 14 . The initial form of deterioration was rutting which was associated with shoving whenever the failure became severe. An illustration of this is shown in Figure 6.6 Performance charts 6. However. bituminous surfaced roads will generally deteriorate either by rutting or by cracking. 6. Although there is some cracking which is coincident with high values of rutting. for example when the road pavement has been under designed or where there are serious material problems.5 Using performance charts similar to those described above. or whether they are affecting the road in a more general manner. there is no cracking in areas of less severe rutting. After further trafficking. The cracking and rutting can also be compared to other predominant forms of deterioration and this may help to promote a better understanding of the causes. In addition to the rutting. the initial cause of deterioration can be masked by subsequent deterioration. the charts show that there is no correlation between the bleeding and the rutting. A programme of additional tests (see Chapter 7) is then prepared to identify the causes of the differential performance between the sub-sections. having a range of pavement thicknesses and material properties. substantial lengths of the surfacing are suffering from bleeding.1 Apart from the surface defects described in Tables 6 and 7. indicating that the shoving is in a lower granular layer. even within nominally uniform sections. the section is divided into subsections having failures of differing severity. These enable the length of road affected by each form of deterioration to be quantified.2 When an evaluation takes place there will often be considerable lengths of road that have reached a terminal level of deterioration similar to that shown in Figure 6. It is important that the initial form of deterioration and its cause is identified. road pavements are inherently variable. because this determines the type of maintenance that is most appropriate. where the final appearance of the road deterioration is similar despite having different initial causes. This results in differential performance.1. not the bituminous surfacing.2 for a 20km section of paved road having a mechanically stabilised gravel roadbase with a thin bituminous surfacing.
most commonly 80 or 100 kN.7 Analysis of deflection bowl data is dependent on a suitable model to calculate the response of the pavement to the applied load. funds are not available to measure deflection bowl characteristics using one of the more sophisticated measuring devices. Therefore. Road materials display a variety of properties that do not comply with the assumptions of the model. in particular. This may be used to identify relatively weaker surfacing layers where fatigue cracking is more likely.4 Maximum deflection under a slowly moving wheel load is a good indicator of the overall strength of a pavement and has been shown to correlate well with long term performance of pavements under traffic. 7. If.6 Therefore there are advantages in using deflection equipment capable of measuring other deflection bowl parameters as well as maximum deflection and the Falling Weight Deflectometer (FWD) and the Deflectograph are the most widely used. Using such a model.7 Additional tests 7. For example. However. incorrect assessment of subgrade strength or traffic loading) the stresses in the lower layers of the pavement will 17 .1. can be used to estimate the relative properties of the upper layers of the pavement. for structurally adequate pavements where over-stressing is not a danger. it is possible to calculate the elastic modulus of each pavement layer from a knowledge of the shape of the deflection bowl. be too high and the pavement will deteriorate through the development of ruts. their loading regimes and output. or causes. However. Table 8 lists the more common deflection devices. Table 8 Deflection devices 7. the elastic modulus of unbound materials is not a constant but depends on the stresses to which Deflection tests 7. For example. then consideration should be given to using a curvature meter (NIRR.5 Apart from the maximum deflection.1 metres. Most analysis programs are based on the assumption that the pavement behaves. and such a correlation provides an indication of the reasons for failure. like a multi-layer structure made up of linearly elastic layers. in the first instance. shown in Figure 7. TRL recommends the use of a 63. if a road is underdesigned for the traffic it is carrying for any reason (eg. The radius of curvature (ROC) of the deflection bowl. This `back-analysis' procedure requires accurate deflection data extending from the central maximum deflection out to deflection values at radial offsets of as much as 2. This is a mechanical device that measures the maximum deflection of a road pavement under the dual rear wheels of a slowly moving loaded lorry. of failure. deflection values can be measured with these higher loads and then normalised to any standard load for comparison purposes. Under such circumstances the deflection will be correlated with rut depth. In these circumstances the tests should be carried out after the rainy season. especially the subgrade. when the road is at its weakest. once cracking is apparent the ROC will decrease considerably hence care is required in interpreting the ROC data.2 The strength of a road pavement is inversely related to its maximum vertical deflection under a known dynamic load.3 The least expensive of these instruments is the deflection beam. the linear elastic model is a very simple model of road pavements. 7.1 Deflection-based measurements and Dynamic Cone Penetrometer (DCP) tests are used to help identify the cause of differential performance between sub-sections and to provide information for the maintenance or rehabilitation of the section. is growing in popularity as it has the advantage of being able to apply impact loads which more accurately simulate the effect on pavements of heavy vehicles moving at normal traffic speeds than the slowly moving load applications associated with the Deflectograph or the deflection beam. there are other parameters and indicators from the deflection bowl that may be used to identify some of the structural differences between sub-sections and hence assist in identifying the cause.2 kN rear axle load. Over this range of loads the maximum deflection is usually linearly relatedto the applied load. however. Procedures for using FWD equipment for road surveys are given in Appendix E. as shown in Figure 7. The results from these non-destructive tests are usually confirmed by destructive sampling and material testing. The FWD. Similarly the deflection values at the extremes of the deflection bowl are indicators of the relative strength of the subgrade. The recommended test and survey procedures for the deflection beam are given in Appendices C and D. 1970) in association with a deflection beam to measure both the ROC under the rear wheels of the deflection lorry and the maximum deflection. changes seasonally.2. other authorities recommend different loads. In some cases the moisture content of the road pavement. 7. 7.
as this can only be done by further destructive sampling and subsequent laboratory testing.3) 8.1) 8. For roads with thin bituminous seals.7 Shoving parallel to the edge of the rut (see para 4. 8. interconnect to form crocodile cracks (see Figure 8. or where there is a significant difference in traffic loading between the two lanes. Unlike the rutting described in paragraph 8. Rutting without shoving (Figure 8.9 If cracking is caused primarily by traffic it must. rutting with shoving. If the pavement has an asphalt surfacing then a transverse core profile (Figure 4. as shown in Figure 8. a similar analysis can be completed by relating the severity of rutting to the strength of the road. then this relationship can be established. Where there is historical data on the progression of rutting and traffic. either insufficient load spreading or secondary compaction.thin bituminous seal. The causes of deterioration combined with the extent of the failures must be considered together when selecting the most appropriate method of maintenance or rehabilitation.10 Short irregular longitudinal cracks in the wheelpaths are often the first stage of traffic induced fatigue of the surfacing which. If the failure is not in the asphalt surfacing then the DCP can be used to identify which of the underlying pavement layers is the cause of the failure. If deflection equipment is unavailable. 8. This type of rutting is the result of two possible causes. the severity of the rutting will not usually be related to the overall strength of the pavement as indicated by either its deflection or modified structural number.9).3 A method of establishing the probable cause or causes of pavement deterioration is given in the flow charts shown in Figures 8. To help identify the cause of the deterioration. In particular. rutting and cracking have been subdivided into six categories based on the nature of the failure.1-8. A process of elimination is used to identify which layer has failed.asphalt surfacing. as illustrated in Figure 7. the charts do provide a framework that enables highway engineers to develop their own pavement evaluation skills.6 If the severity of rutting does not relate to the strength of the road pavement. In severe cases it is sometimes difficult to be sure whether the failures start in the wheelpath or whether they are a progression of another form of cracking. when a road has received a series of maintenance treatments or when the initial deterioration is masked by further progressive failures.11). wheelpath cracking . by definition.4 These ruts are usually wide as they are caused primarily by movement deep in the pavement structure. it will then be necessary to show a relationship between the severity of rutting and the deflection of the road pavement at the time of the evaluation.8 Identifying the causes of pavement deterioration 8.22) is indicative of a shear failure in one of the pavement layers and is caused by the pavement layer having inadequate shear strength to withstand the applied traffic stresses at that particular depth in the pavement. the most likely cause of the rutting is secondary compaction of one or more of the pavement layers by traffic during the early life of the road.2. its position and the type of road construction.asphalt surfacing (Figure 8. and there will be little or no evidence of shoving at the edge of the pavement. These are: • • • • • • rutting without shoving.8 The failures are usually confined to the upper pavement layers where the applied traffic stresses are at their highest.asphalt surfacing. and non-wheelpath cracking . they are not necessarily `traditional' fatigue cracks which start at the bottom of the asphalt surfacing and 21 . the problem of identifying the initial cause of failure becomes more complex.2) 8.9 (Dickinson.1. Although caused by the flexure of the surfacing. 8. 8. The charts identify general causes of deterioration but do not attempt to establish specific material problems. These charts will not cater for all the types and stages of pavement deterioration. It is characterised by an increase in rutting with traffic loading.6) can be used to establish in which bituminous layer. 1984). as measured by the DCP (see para 7. non-wheelpath cracking .5 Insufficient load spreading is the result of the pavement layers being too thin to protect the subgrade. However. Rutting with shoving (Figure 8. The initial type of cracking should be identified as described in paragraphs 6. bituminous surfaced roads will generally deteriorate either by rutting or by cracking.2 Besides the surface defects described in Tables 6 and 7. after further trafficking. This is done by comparing the strength of the layers in failed areas with those that are sound. originate in or near the wheelpaths.8. wheelpath cracking . 8.1-6.thin bituminous seal. 8. if any.1 The next stage in the evaluation procedure is to establish the cause or causes of the pavement deterioration by interpreting the data collected during the surface condition survey and the additional testing. a comparison of the ROC values from these different areas can also be used to identify substandard roadbase materials. More usually this information will not be available and Wheelpath cracking . In this case the rate of increase in rutting will decrease after the initial compaction phase. the failure is occurring.5.
1 Initial deterioration .Figure 8.Rutting without shoving 22 .
Figure 8.Rutting with shoving 23 .2 Initial deterioration .
26 Figure 8.Non-wheelpath cracking in asphalt surfacing .5 Initial deterioration .
Longitudinal cracking in asphalt surfacing 27 .6 Initial deterioration .Figure 8.
7 Initial deterioration .28 Figure 8.Transverse cracking in asphalt surfacing .
Inadequate quality control exercised during the manufacture and construction of dense surfacings can lead to poor particle size distribution. giving rise to large maximum deflections.Figure 8. 8. all of which will make the material more susceptible to cracking. 1986).13 Poor surfacing materials can also result in crocodile cracking. low bitumen contents.11 Where crocodile cracks are shown. because of shear failure in the roadbase (see paras 8.7). 1990). Excessive strains can be caused by a weak subgrade. the age of the surfacing and the traffic carried should provide the most important clues. However. or a weak roadbase leading to small radii of curvature. in other words no other form of failure has occurred beforehand.5 and 8.12 In some circumstances traditional fatigue cracking can occur simply because the road has reached the end of its design life.Block cracking in asphalt surfacing propagate upwards. to have started at the bottom of the asphalt layer.14 If the bond between the asphalt surfacing and the underlying layer is poor then the surfacing can effectively 'bounce' under traffic. This quickly results in crocodile cracking in the wheelpaths and is 29 . However. by coring. This is a relatively rare phenomenon and for this reason is sometimes difficult to identify because of the need to calibrate standard asphalt fatigue relationships for local conditions. Failures of this type can occur in areas where deflections are satisfactory and where little or no rutting is occurring 8. This causes the material to become brittle and results in cracking being initiated at the top of the surfacing rather than at the bottom. 8. in the latter case. In tropical climates the bitumen at the top of asphalt wearing courses oxidises rapidly (Smith et al. segregation and poor compaction. in both cases the cracking is frequently associated with rutting. then they are likely to be `traditional' fatigue cracks caused by excessive strains at the bottom of the surfacing. despite the strains being lower (Rolt et al.8 Initial deterioration . because of insufficient load spreading. In practice this type of crocodile cracking very rarely occurs without any rutting. in the former case. 8.
The cause of the poor bond can be ineffective priming of the roadbase. 8. particularly if the stabiliser is cement. Cores cut through cracks in the new overlay will establish whether they are being caused by existing cracks in a lower pavement layer. This type of cracking will most likely occur in areas subject to high diurnal temperature changes. or deficient tack coat prior to placing an overlay. resulting in the rapid formation of potholes. When cracks occur after 30 . However.24 and 8. As traffic has played little or no part in these road failures the cracks will not be confined to the wheelpaths and there will not be any substantial rutting.characterised by blocks of less than 200mm square. Often the cracking will progress to laminations. 8. However. Longitudinal cracking (Figure 8. 8.26 Transverse cracks confined to the surfacing and occurring at more regular and shorter spacings are probably caused by thermal or shrinkage stresses. 8. These cracks will be associated with a poor longitudinal road profile caused by the differential movement.23 Longitudinal cracks caused by subgrade movement will generally be quite long and can meander across the carriageway.26. and the settlement or collapse of embankments. This form of transverse cracking is often associated with longitudinal cracks and. Reflection cracking will generally occur early in the life of the overlay and is often associated with pumping of fine material from a lower granular layer. Transverse cracking (Figure 8.25 If the transverse cracks are irregularly or widely spaced they are likely to have been caused by some form of construction fault. age hardening of the bitumen can result in wheelpath cracking or fretting. These are described in more detail paragraphs 8. They can occur because of poor construction. if it is more extensive.16 Cracking in bituminous overlays. This can be a problem with stabilised roadbases if they are not primed effectively prior to surfacing. Cracks caused by the slippage of an embankment will often occur in semicircular patterns and both these and cracks caused by subgrade movement will often be associated with a vertical displacement across the crack. 8.asphalt surfacing (Figure 8. the probable cause is an inadequate tack coat or the use of soft aggregate in the surfacing which.5) 8.15 Parabolic shaped cracks in the surfacing which occur in areas of severe braking such as the approaches to junctions and sharp bends are caused by slippage and are also the result of a poor bond. block or crocodile cracking. they are likely to be either reflection cracks propagating from a lower stabilised layer or cracks caused by thermal or shrinkage stresses in the asphalt. 8. such as the edge of road markings. In this case any water going through the resultant cracking will aggravate the poor bond.14). 8. In their early stages neither of these types of crack is particularly serious.4) 8. Small areas of parabolic cracking are not indicative of serious failure. which are shallow potholes that are clearly the result of the surfacing `peeling' off.thin bituminous seal (Figure 8. Non-wheelpath cracking can take the form of longitudinal. transverse.20 The cause of non-traffic associated cracking in an asphalt surfacing is largely established by identifying its type (see para 4. in severe cases.19 Bituminous seals having a poor bond with the underlying roadbase will behave in a similar way to that of an asphalt surfacing. any subsequent cracking may be caused by the reflection of cracks from the previous surfacing.7) 8.21 Thermal stresses can cause cracks to appear along poor longitudinal construction joints and in areas of severe temperature gradients. 8. results in a poor bond and subsequent slippage. Errors in the design or construction of these seals are more likely to result in failures such as bleeding or loss of stone rather than cracking. however. Wheelpath cracking . the cracks will eventually spread into the wheelpaths where they will result in more serious deterioration. if left unsealed. particularly in the wheelpaths. block cracking. If cracking is being caused by excessive flexure under traffic then it will be associated with areas of high deflections. Slurry seals are particularly susceptible to reflection cracking. Differential vertical movement caused by consolidation or secondary compaction adjacent to road structures and culverts can cause transverse cracks in the surfacing. in breaking down. Non-wheelpath cracking . such as desert regions.18 Where the surfacing has been used to seal an existing cracked asphalt layer. as the seal gets older.22 Where longitudinal and transverse cracks occur in combination.17 The bitumen film in surface dressings is very thick compared to that in asphalt surfacings and it is more tolerant to flexure under traffic.24 Transverse cracks in the surfacing of a road pavement which includes either a chemically stabilised roadbase or sub-base are likely to be reflection cracks from the stabilised layer. can be caused by cracks in the underlying layer 'reflecting' through the overlay. and will be exacerbated by poor quality surfacing materials. swelling in plastic subgrade or embankment materials.6) 8.
These cracks almost always start at the top of the surfacing and propagate downwards.28 because their thicker bitumen film results in a higher strain tolerance. overheated bitumen and the use of absorptive aggregate. is usually the final stage of cracking due to thermal stresses. Where strains are large.27 Block cracking. Thermal stresses can also cause cracks to open up at transverse construction joints.thin bituminous seal 8. when confined to the bituminous surfacing. They are also less susceptible to thermal or shrinkage cracking. In these cases the precise cause of failure can only be determined by destructive sampling and laboratory testing. 31 . Block cracking can also occur through reflection of the shrinkage crack pattern in lower chemically stabilised layers. they will link up with longitudinal ones to form block cracking as shown in Figure 8. The more common production faults are poor particle size distribution. Block cracking (Figure 8. the surfacing failure will be similar to that described for asphalt surfacings. in particular.21-8. as in the case of reflection cracking from a stabilised roadbase or from subgrade movement.8) 8. segregation of the mix and poor bonding. are less likely to crack either at construction joints or alongside road markings.29 Roads having thin bituminous seals are less susceptible to the non-traffic associated failures described in paragraphs 8. Crocodile cracking 8. Non-wheelpath cracking .9. either between layers of bituminous material or the granular layer beneath. low binder contents.many years of good performance it is likely that progressive hardening of the binder has made the surfacing more `brittle' and therefore more susceptible to cracking. Construction faults include poor compaction. As transverse thermal cracks progress. Surface dressings.28 Crocodile cracking that is neither confined to the wheelpaths nor associated with rutting is indicative of a fault in the construction of the surfacing. however.
Figure 8. 1984) 32 .9 Crack development patterns in bituminous surfacings (after Dickinson.
the deterioration may result from some deep seated structural insufficiency or construction defect. of the deterioration without necessarily adding strength to the pavement. fatigue cracking or crushing of lightly cemented materials. The performance of the surface seal will generally depend on environmental effects ratherthan traffic loads.5 For roads having a thin bituminous seal the traffic carrying capacity is determined only by resistance to rutting. It is important. Very thin layers such as an existing seal are normally incorporated with the underlying roadbase or ignored. In such cases consideration must be given to full or partial reconstruction of the pavement to correct the situation. 1986) (Smith et al. The performance of road pavements has traditionally been dependent on the stress/strain values at two locations in the structure. These strains are then used to calculate the `life' of the structure using 9. to check the ability of the existing road pavement to carry the predicted traffic loading using at least two of the methods described below. This has mitigated against the use of lower quality materials and has theoretically restricted the range of likely 33 . • • • • fatigue cracking of the asphalt surfacing. Secondly. `Top-down' cracks often develop long before other types of cracks and thus the performance of asphalt surfaced roads rarely agrees with the analytical models.4 Theoretical models to predict the behaviour of granular and lightly cemented materials under the action of traffic are not well defined and therefore specifications for such layers have always been set in such a way that failures are unlikely. Analytical approach 9. shear failure of the granular materials.9 Maintenance and rehabilitation 9. although more sophisticated models can also be used. The horizontal tensile strain at the bottom of the asphalt layer controls one type of fatigue cracking and the vertical compressive strain at the top of the subgrade controls rutting. Other moduli values can be either calculated from the back-analysis of FWD deflection bowls or assigned values following DCP testing and/or the laboratory testing of samples taken from trial pits. for instance.2 It should not be assumed that when a road is in poor condition it inevitably needs strengthening. For example. elastic modulus and Poisson's ratio of each layer of the pavement. For example.1 The selection of an appropriate maintenance treatment or rehabilitation strategy is based on a number of considerations. 9. as input. Asphalt surfacings are usually assigned moduli based on mix constituents and binder properties at the design temperature although direct laboratory measurements of modulus can also be made on samples of material extracted from the road. the existing road structure is often thick enough to prevent long term rutting. nor will any form of thin surfacing provide a significant improvement to riding quality where this is poor. However. 9. or causes. 1990).6 The analytical approach requires a suitable mathematical model to describe the pavement. the thickness. The traffic carrying capacity of anasphalt surfaced road will be determined by both its resistance to fatigue cracking and wheelpath rutting. When traffic is low. In this case the maintenance treatment selected should address the cause. attention should be given to the nature. and wheelpath rutting resulting from subgrade failure. In order to do this. the cause of deterioration in the existing pavement must be correctly identified and its importance assessed. thin asphalt surfacings on their own will not provide a satisfactory repair where reflection cracking is likely. This model requires. Stresses or strains at the critical points in the pavement are then calculated under the application of a standard load designed to replicate a 40kN wheel load (80kN axle load). Where either of the methods are shown to accurately predict the present performance of the road under study then the method is equally applicable for the design of strengthening works in the event that the road is shown to be too weak to carry the future traffic. research has shown that the predominant form of surface distress of asphalt surfacings in tropical climates is not fatigue cracking starting at the bottom of the asphalt layer but `topdown' cracking which is initiated at the surface of the layer (Rolt et al. extent and severity of the deterioration to check what effect it will have on the treatments that are being considered. Nevertheless rehabilitation design should take account of all possible modes of future failure and therefore it is important to ensure that traditional fatigue failure of the surfacing and failure through inadequate protection of the subgrade do not occur within the design life required. the strategy must be economically viable taking into consideration both the costs of maintenance and the vehicle operating costs over a number of years. Almost all methods make use of the multilayer linear elastic model.3 The traffic carrying capacity of an asphalt pavement is governed by how effective the pavement layers are in preventing. analytical procedures properly calibrated to local conditions provide a suitable method. failure modes. Finally. Firstly. 9. The type and severity of this form of cracking is a complex function of material properties and both environmental and traffic stresses and its development has yet to be successfully described by means of a practical analytical model. therefore.
9.8 In this method the traffic carrying capacity of the road is estimated by comparing the existing pavement structure and its condition with established design charts. If 34 . However. however. it is clear that an overlay reduces the stresses in the lower layers of the pavement and therefore. 1983). the relationship between deflection and traffic carrying capacity) are not necessarily applicable to road pavements found in tropical and sub-tropical regions. then the engineer can be more confident in designing the thickness of any necessary strengthening overlay by this method. Where the comparison of the effective structural number. they can be used with more confidence to estimate the future traffic carrying capacity. and the in situ strength of the pavement layers and the subgrade determined by a combination of deflection and DCP data. If Road Note 31 is preferred then the lower 10 percentile of the in situ subgrade CBR should be used. After adjustment of the pavement model they can then also be used to determine overlay thickness. The severity of rutting is then plotted against the maximum deflection at each test point and a best fit line and confidence limits calculated as shown in Figure 9. 1992) (Rohde.7 Where the forms of these relationships are shown to predict the present performance of the road pavement.relationships (Powell et al. adjustments will need to be made to the deflection data and material properties to reflect the season during which the data were collected. The in situ strengths of the pavement layers obtained in this way. Deflection approach 9. The 90th percentile is recommended with a critical rut depth of l0mm for roads with asphalt surfacings and 15mm for those with thin bituminous seals. a and b = constants associated with material properties Subgrade deformation criteria Log Nd = a+ b Log z Where Nd = Deformation life in esa z = Vertical compressive strain at the top of the subgrade a and b = constants associated with material properties 9. should always be verified by laboratory tests to ensure they conform to normally accepted specifications. to prevent deformation in these layers and the subgrade. 1983). or other roads of similar construction in the region. one point can be plotted on the deflection trafficloading graph. a `calibrated criteria curve' can be obtained by drawing a new line through the point and parallel to the existing curve as illustrated. when the pavement can be expected to be in its weakest condition. 1994) (Roberts and Martin. appropriate deflection criteria can be developed (NITRR. 9. past traffic and design recommendations is shown to be consistent with the present condition of the road pavement. 1993). The thickness of the various pavement layers should first be established using the DCP and trial pits.9 The required strengthening measures are then established by comparing the effective structural number of the pavement with the required structural number of a pavement for the future traffic. With the development and refinement of these procedures it is likely that the rehabilitation of road pavements using the structural number approach will become increasingly popular. These tests should be carried out shortly after the wettest period of the year. are rutting because of a deficiency in the overall `strength' of the pavement (see para 7. 1993). at a representative value of in situ subgrade strength. 1996).10 There are presently a number of methods of determining the structural number of a road pavement directly from FWD deflection bowl characteristics (AASHTO.11 The representative maximum deflection is used by a number of road authorities to estimate the carrying capacity of a road (Kennedy and Lister.1. 1978) (Asphalt Institute. 9. is used. This point is unlikely to lie on an existing criteria curve. The deflection criteria curves recommended in these design procedures (i. Provided the past traffic loading is known. in particular the upper granular layers. assuming a similar form of relationship. where necessary. 1993) (Jameson. 1984)(Shell. obtained from an appropriate design method. 1985) between stress/strain and pavement life of the form: Asphalt fatigue criteria Log Nf = a + b Log r Where Nf = Fatigue life in esa r = Horizontal tensile strain at the bottom of the asphalt layer the AASHTO guide is used then a mean value of the resilient modulus of the subgrade.12 The deflection and condition surveys must be carried out after the wettest period of the year when the road pavement can be expected to be at its weakest.e. Structural approach 9. measured when the pavement is in its weakest condition. suitably corrected (AASHTO.4). The effective structural number of the pavement can then be obtained by using techniques described in the AASHTO Guide for Design of Pavement Structures (AASHTO. If this is not possible. The value of critical deflection corresponding to a defined level of critical rutting is then determined for any particular level of statistical reliability. Such an approach is particularly appropriate when investigations show that either the project road.
can be estimated by comparing the representative deflection of homogeneous sections (see Appendix D) with the calibrated deflection criteria curve as shown in Figure 9.3kN axle load.2mm and overlay thicknesses of 40 150mm. those areas where failure has already occurred should be repaired by some form of remedial treatment and.1.1 Diagrammatic calibration of deflection life criterion line (after NITRR. Pavement maintenance will generally result in two operations.Dd 0. the road should generally be resurfaced to prevent other lengths failing in a similar manner. Maintenance options 9. The relation between the thickness of a dense bituminous overlay and the reduction in deflection.14 The thickness of any necessary strengthening overlay can be determined based on reducing the representative deflection of the pavement to the design deflection obtained from the calibrated deflection curve.1. Firstly.0027Dr where Dd = Design deflection (mm) Dr = Representative deflection (mm) T = Overlay thickness (mm) (3) This relation is valid between representative deflection values of 0.818 Dr . 1983) 9. secondly.15 If it is established that the road does trot require strengthening. 9.036+0. in terms of rutting. has been shown to be: T = 0.13 The traffic carrying capacity of the road.Figure 9. Therefore the future traffic carrying capacity is the total traffic loading minus the traffic loading that the pavement has earned prior to evaluation. 35 . under a 62. Suggested methods of maintenance for the different types of pavement deterioration for roads having thin bituminous seals and asphalt surfacings are given in Tables 10 and 11 respectively.25 . the method of maintenance should be based upon the type of the existing surfacing and the cause of failure. The traffic carrying capacity represents the total traffic loading that the road will carry from construction.
16 Reflection cracking can have a considerable and often controlling influence on the life of thin bituminous overlays. 1991) suggest that the most successful techniques are: • • • asphalt-rubber interlayers. 1982)(Barksdale. However. Reviews of practice in North America (Sherman. The complete prevention of reflection cracking through thin overlays is not possible. it may be more cost effective to introduce a crack relief interlayer rather than to remove all the cracked material. when the existing cracked asphalt surface is relatively thin. interlayers of open-graded bituminous material. or heater-scarification and recompaction of the cracked layer. the most effective method of reducing reflection cracking in any subsequent overlay is to remove the areas showing cracking of intensity 3 or greater and to patch prior to construction. 1996). The rate of propagation of these cracks has been shown to be dependent on the strength of the road. the severity of the cracking before overlay and the future traffic (Rolt et al. Where the existing surfacing consists of several previous bituminous overlays. 36 .Reflection cracking 9.
Table 11 Existing road surface .Asphalt surfacing 39 .
Chesher A D and Harrison R (1987). Beaven P J and Tubey L W (1978). Transportation Research Board. Council for Scientific and Industrial Research. Department of Transport. Crowthorne. Rolt J and Jones T E (1975). Kleyn E G and Van Heerden (1983). Pretoria. Maryland. Council for Scientific and Industrial Research. Ishai I and Livneh N A (1995). Devon County Council. Jones C R and Osman M(1992). The polishing of roadstone in Peninsular Malaysia. Development of the Philippines Asphalt Overlay Procedure. The MERLIN road roughness machine: User guide. Singapore. Department of Transport (1994a). Hide H S. Technical Methods for Highways TMH No 9. Crowthorne. Department of Transport. Washington DC. Asphalt Institute (1983). Laboratory Report LR 673. Transvaal Roads Department. VicRoads. Laboratory Report LR 833. Nomenclature and methods for describing the condition of asphalt pavements. Transportation Research Board. Abaynayaka S W. Barkdale R D (1991). The Kenya road transport cost study: research on road deterioration. Volume 7: Sect 3: Part l: HD 28/94. Pretoria. Washington DC. of the Road Engineering Association of Asia and Australasia. Washington DC. Kennedy C K and Lister N W (1978). Design of pavement structures. Austroads. Washington DC. National Institute for Transport and Road Research (1985). Design Manual for Roads and Bridges. TRL Report TRL229. The John Hopkins University Press. The measurement of deflection and curvature of road surfaces. Pretoria. Morosiuk G. Report LS/83 Materials Branch. Hodges J W. Pavement design. Livneh M. A directory of pavement assessment equipment. Evaluation of a high-resolution profiling instrument for rise in road roughness calibration. UK. Draft Technical recommendations for Highways TRH 12. Manual Series No. Lexington. Synthesis of Highway Practice 171. (Asian Development Bank. CSIR Technical Guide K16. American Association of State Highway and Transportation Officials. Volume 7: Sect 3: Part 2: HD 29/94. 41 . County Surveyors Report No 5/10. Crowthorne. 17 (MS-17). Laboratory Report LR 936. Transport Research Laboratory. Supplementary Report SR 421. 7th Conf. Transportation Research Board. National Institute for Transport and Road Research (1983). Bertrand C. Sayer I and Wyatt R J (1974). Calibration and standardisation of road roughness measurements using the TRRL profile beam. Jones C R and Smith H R (1980). Bituminous roads in Australia. Sydney. 74th Annual Meeting. Technical Recommendations for Highways TRH No 6. The Kenya road transport cost study: research on vehicle operating costs. Committee of State Road Authorities (1992). Australian Road Research Board. Vehicle operating costs: evidence from developing countries. Crowthorne. Cundill M A (1996). Prediction of pavement performance and the design of overlays. Transport Research Laboratory. Pavement management systems: Standard visual assessment manual for flexible pavements. The effect of vertical confinement on the DCP strength values in pavement and subgrade evaluation. UK. National Institute for Road Research (1970). A guide to the structural design of road pavements. 1426 PHI. Fabrics in asphalt overlays and pavement maintenance. Council for Scientific and Industrial Research. Annual Transportation Convention. Harrison R and Hudson W R (1991). Structural assessment methods. Asphalt overlays for highway and street rehabilitation. Transport Research Laboratory. Highway Design and Maintenance Standards Series. Transport Research Laboratory. Report for ADB Technical Assistance Project TA No. Dickinson E J (1984). Crowthorne. Philippines). Using DCP soundings to optimise pavement rehabilitation. Crowthorne. Design Manual for Roads and Bridges. Pretoria. County Surveyors Society (1988). Skidding resistance. ARRB Transport Research Ltd. Manila. Victoria. Transportation Research Record 1291. Transport Research Laboratory. Laboratory Report LR 672. Bituminous pavement rehabilitation design. Walking Profilometer. Jameson G W (1992). ARRB (1996). SMEC and Queensland Transport. Austroads (1992). Transport Research Laboratory. Deflection temperature relationships for bituminous surfacings in Kenya.10 References AASHTO (1993). Pretoria. Department of Transport (1994b). Asphalt Institute. Committee for State Road Authorities.
Stationery Office. The John Hopkins University Press. Transport Research Laboratory. 46. Transport and Road Research Laboratory (1978). Strategic Highway Research Programme. Addendum to the Shell pavement design manual. Sayers M W. 42 .Paterson W D O (1987). Guidelines for conducting and calibrating road roughness measurements. The Rhodesian Engineer. Mayhew H C and Nunn M E (1984). Innovations in Road Building. World Bank. Washington DC. National Research Council. Technical Paper No. Victoria. Strategic Highway Research Programme. Overseas Road Note 8. Roberts J D and Martin T C (1996). Recommendations for monitoring pavement performance. Overseas Road Note 2. Transportation Research Board. The durability of bituminous overlays and wearing courses in tropical environments. Transport and Road Research Laboratory (1990). Australian Road Research Board. Measurement of pavement defections ill tropical and sub-tropical climates. Transportation Research Record 1448. Powell W D. A guide to surface dressing in tropical and subtropical climates. Crowthorne. ARRB Transport Research Ltd. Shell (1985). Sayers M W. Transport Research Laboratory. Falling weight defectometer relative calibration analysis. Crowthorne. SHRP-P-652. Queensland Transport (1992). A guide to the measurement of axle loads in developing countries using a portable weighbridge. Gillespie T D and Queroz C A V (1986a). Transport Research Laboratory. Maryland. Hameed M and Suffian Z (1996). Road Note 27. World Bank. Strategic Highway Research Programme (1993b). Washington DC. Transport and Road Research Laboratory (1993a). 45. London. Plymouth. Rapid determination of CBR with the portable dynamic cone penetrometer. Van Vuuren (1969). Crowthorne. Overseas Road Note 5. Laboratory Report LR 935. Crowthorne. Washington DC. SHRP'S layer moduli backcalculation procedure. Technical Paper No. Second Malaysian Road Conference 1996. Rolt J. Smith H R and Jones C R (1986).. A guide to road project appraisal. Road Research Laboratory (1969). Pavements and Asset Strategy Branch. Queensland Transport. Smith H R and Jones C R (1980). Potter J F. Strategic Highway Research Programme (1993a). Determining pavement structural number from FWD testing. Maryland. Gillespie T D and Paterson W D O (1986b). Australian Road Research 13(4) pp 285-294. Harral C G. Trondheim. Research Report ARR 293. Ltd. Crowthorne. The design and performance of bituminous overlays in tropical environments. Transport Research Laboratory. Smith R B and Pratt D N (1983). Dhareshwar A M. Afield study of in situ California bearing ratio and dynamic cone penetrometer testing for subgrade investigations. Rohde G T (1994). Watanatada T. Transport Research Laboratory.User's Manual. Washington DC. Smith H R. Overseas Centre. The structural design of bituminous roads. The Bearing Capacity of Roads and Airfields. Transport Research Laboratory. Transport and Road Research Laboratory (1982). Rolt J. Kuala Lumpur. 3rd Conf. National Research Council. Instructions for using the portable skid resistance tester. The John Hopkins University Press. The prediction and treatment of reflection cracking ill thin bituminous overlays. Maintenance techniques for district engineers. Pavement rehabilitation manual. A guide to tile structural design of bitumen-surfaced roads in tropical and sub-tropical climates. The international road roughness experiment: establishing correlation and a calibration standard for measurements. Queensland. Transport and Road Research Laboratory (1988). Bhandari A and Tsunokawa K (1987). Crowthorne. Rolt J and Wambura J (1990). Transport Research Laboratory. The highway design and maintenance standards model. Transportation Research Board. A users manual for a program to analyse dynamic cone penetrometer data. Overseas Road Note 3. Hasim M S. SHRP-P655. Synthesis of Highway Practice 92. Laboratory Report LR 1132. Highway Design and Maintenance Series. Road Note 40. Transport Research Laboratory. Sherman G (1982). Transport Research Laboratory. 2nd Conf. Washington DC. Transport and Road Research Laboratory (1993b). Highway Design and Standards Series. Crowthorne. Road deterioration and maintenance effects: models for planning and management. Minimising reflection cracking of pavement overlays. Paterson W D O. Crowthorne. Shell International Petroleum Co. The Bearing Capacity of Roads and Airfields. Washington DC. Baltimore. Crowthorne. Overseas Road Note 31. London. Transport and Road Research Laboratory (1985). The road transport investment model .
Enquiries should be addressed to BSI. 100 Barr Harbor Drive. products. Enquiries should be addressed to ASTM. Linford Wood. systems and services. PA 19428-2959. MK14 6LE.11 Applicable standards C 535-96 The British Standards Institution is the independent national body for the preparation of British Standards. BS 598 Sampling and examination of bituminous mixtures for roads and other paved areas Part 100:1987 Methods for sampling for analysis Methods of test for the determination of texture depth D 3319-90 Test method for resistance to degradation of large-sized coarse aggregates by abrasion and impact in the Los Angeles machine Test method for accelerated polishing of aggregates using the British wheel Test method for measuring surface frictional properties using the British pendulum tester Test method for measuring road roughness by static level method E 303-93 E 1364-95 Part 105:1990 BS 812 Sampling and testing of mineral aggregates. ultimate consumers and those having a general interest to meet on common ground and write standards for materials. West Conshohocken. C 131-96 Test method for resistance to degradation of small-sized coarse aggregates by abrasion and impact in the Los Angeles machine 43 . sands and fillers Part 2:1975 Methods for determination of physical properties Part 105:1990 Methods for determination of particle shape Methods for determination of aggregate crushing value Methods for determination of ten percent fines value Methods for determination of aggregate impact value Methods for determination of aggregate abrasion value Method for determination of soundness Part 110:1990 Part 111:1990 Part 112:1990 Part 113:1990 Part 121:1989 BS 1377 Soils for civil engineering purposes Part 2:1990 Classification tests Part 4:1990 Part 8:1990 Part 9:1990 Compaction-related tests Shear strength tests (effective stress) In-situ tests The American Society for Testing and Materials is a notfor-profit organisation which provides a forum for producers. Milton Keynes. users.
2 metre straight-edge and wedge (Figure 4. Many organisations will have on-site procedures which should be followed.Appendix A: Detailed surface condition survey The detailed surface condition survey is a walking survey carried out by a team of four technicians/ labourers and one support vehicle with driver. after the road has been permanently marked.5).1) and a clipboard. distance measurer. Increasing output by surveying both lanes of a two lane highway simultaneously is not recommended. 44 .4). Where there are no local safety procedures those described in Overseas Road Note 2 are recommended (TRRL. The results of the survey should be recorded on pre-printed forms as these provide a check list for the technician. and surface condition forms (Figure 4. crack width gauge (Figure 4. This team size should be able to complete 10 lane kilometres per day. The equipment needed by the team. 1985). telling him what items are to be examined during the inspection and so reducing the possibility that significant information is omitted. is: • • • • • traffic control signs or flags. A safe working environment should be maintained at all times.
Examples of Class 1 methods include the rod and level survey (ASTM. A 25mm hole needs to be cut in the floorpan and a bracket or hook fixed to the centre of the differential housing of the rear axle. The system is powered by the 12 volt battery of the vehicle. They can be used for relatively short sections where a high degree of accuracy is required but are not suitable for general roughness surveys. but which are not capable of the accuracy and/or measurement interval specified for a Class 1 precision profile. The systems are capable of surveys at speeds up to 80 km/h. E 1364-95). connection leads and an optional installation kit. This profile is then used to directly compute the IRI. Class 1 . 45 . While these systems can take the form of towed trailers. The BI system comprises of a bump integrator unit. The estimate of IRI has been found to be subject to errors of up to 40 per cent for new observers (Sayers et al. It is therefore essential that the roughness values obtained from a RTRRMS are converted to units of IRI by regularly calibrating it with a Class 1 or 2 device or the MERLIN.Subjective ratings Class 1 . 1986b) on the basis of how accurately they measure the profile of the road and hence International Roughness Index (IRI). for example as springs and shock absorbers wear. The roughness values recorded by RTRRMS depend on the dynamics of the vehicle and the speed at which it is driven.Precision profiles This class has the highest standard of accuracy. The TRL Bump Integrator (BI) Unit is a response-type road roughness measuring device that is mounted in a vehicle. It includes methods such as subjective evaluation involving rideability and visual assessment. such as the towed 5th wheel bump integrator. Class 3 . the Face Dipstick (Bertrand et al. the TRL Profile Beam.IRI from correlation Devices in this class measure roughness but need calibration to convert the data into units of MI. Uncalibrated RTRRMS also fall into this category. The instrument measures the roughness in terms of the cumulative uni-directional movement between the rear axle and the chassis of a vehicle in motion. the Machine for Evaluating Roughness using Low-cost INstrumentation (MERLIN) that can be used to both Roughness surveys using a RTRRMS. a RTRRMS is recommended. a counter unit with 2 displays. 1986b) and therefore this method should only be used when other methods are unavailable. Class 1 methods are those which sample the vertical profile of the road at distances no greater than 250mm to an accuracy of 0. so many hundreds of kilometres of road can be measured in a day. The MERLIN does not record the absolute profile but measures the mid-chord deviations over a predetermined base length for a section of road (see Figure B 1) and then relates a statistic from the frequency of those deviations to the IRI using a predetermined correlation. Examples of vehicle-mounted RTRRMS include the TRL bump integrator unit. the NAASRA meter and the Mays meter.51rim for smooth roads. The main advantages of these types of systems are their relative low cost and the high speed of data collection.Precision profiles Class 2 . 1991) and the ARRB Walking Profiler (ARRB. Class 2 . The unit is bolted to the rear floorpan of the vehicle directly above the centre of the rear axle.IRI by correlation Class 4 . When roughness measurements are required on more than a few short sections of road. 1996).Appendix B: Road roughness measurements The many methods for measuring road roughness in use throughout the world can be grouped into four generic classes (Sayers et al. Also in this class is a low cost alternative. Fitting the BI unit The BI unit is mounted in a rear-wheel drive vehicle as shown diagrammatically in Figure B3. The majority of road roughness data currently collected throughout the world are obtained with Response-Type Road Roughness Measuring Systems (RTRRMS). This is illustrated in Figure B2.Other profilometric methods Class 3 . they more frequently involve instruments mounted in a survey vehicle. The dynamic properties of each vehicle are unique and will also change with time. Class 4 . Class 1 methods are mainly used for the calibration and validation of other methods of roughness measurement.Other profilometric methods This class includes all other methods in which the road profile is measured as the basis for direct computation of the IRI. This class includes most high-speed profilometers. These instruments usually measure roughness in terms of the cumulative movement between the vehicle's axle and chassis when travelling along a road under standard conditions. estimate IRI and also calibrate other RTRRMS.Subjective rating This class has the lowest standard of accuracy.
a lower speed of 50 or 32 km/h can be used. This is necessary because the vehicle's response to a given profile varies with speed. Note: the pulley must NOT be ii iii iv 48 . pedestrians or restrictive road geometry. deceleration and gear changes. vi For general surveys. ix After the survey. it is recommended that readings are recorded at half kilometre intervals. Calibration must be carried out at this operating speed. It is usual to use the same operating speed for all of the surveys. The BI unit measures the unidirectional movement. The tyres should not have flat spots or be unduly worn. vii There are two counters in the recording unit. the results should be converted into vehicle response roughness values (VR). At all other times the cord should be disconnected to stop unnecessary wear to the BI unit. v When measurements are being taken the vehicle should normally be driven at constant speed. between the vehicle chassis and the axle as the vehicle is driven along the road. This allows the observer to throw the switch at the end of each measurement interval so that the reading can be manually recorded while the other counter is working. When attaching the cord to the rear axle. On completion of the survey. This can be achieved by driving the vehicle for at least 5km before measurements start. The use of the vehicle odometer or kilometre posts is not recommended for survey purposes. the cord should be pre-tensioned by turning the BI pulley 2. if this speed is unsafe for reasons of traffic. The wheels should be properly balanced and the steering geometry correctly aligned. avoiding acceleration. This cord must not touch the sides of the hole.5 turns anti-clockwise.Figure B3 Diagrammatical representation of the TRL Integrator Unit fitted to a vehicle Before each survey. This is displayed on a counter box. and no other load should be carried. To reduce reproducibility errors it is best to operate the RTRRMS at a standard speed of 80 km/h. the wile cord should be disconnected from the rear axle. The vehicle should be well maintained and in good working order. it should be clearly signed and fitted with flashing lights. turned clockwise or suddenly released after being tensioned as the internal spring mechanism could be damaged. usually fixed to the front passenger fascia. connected by a changeover switch. in centimetres. viii The type of road surfacing should also be recorded to aid future analysis of the data. These should be converted to vehicle response roughness values using the following equation. Software is also available which automatically records the roughness data. Many organisations will have on-site safety procedures which should be followed. The counts measured by the BI are in units of cumulative centimetres of uni-directional movement of the rear axle. The tension cord from the BI unit to the axle should only be connected during the survey. Ideally the vehicle should contain only the driver and observer. vehicle speed and distances in spreadsheet form. The load in the vehicle must be constant. However. Tension in the cord is maintained by a return spring inside the drum of the BI unit. This distance should be measured with a precision odometer. the flexible metal cord from the cylindrical drum of the BI unit is passed through the hole in the floor and hooked onto the bracket on the rear axle. The wire is then wound around the pulley 2 turns in the same direction as the arrow. The first counter can then be re-set to zero ready for the next changeover. The engine and suspension system should be fully warmed-up before measurements commence. As the vehicle may be moving slower than the majority of other traffic. Tyre pressures should be maintained precisely to the manufacturers specifications. Survey procedure i A safe working environment should be maintained at all times.
The roughness of each section should be measured by the RTRRMS at the same vehicle speed that is to be used for the general survey. The relationship obtained by this comparison can then be used to convert RTRRMS survey results into units of E[IRI]. The calibration equation for the RTRRMS is then derived by calculating the best fit line for the points. The value of VR (mm/km) should be the mean value of at least three test runs. The average of these IRI values (in m/km) is then plotted against the vehicle response for each of the test sections. The calibration sites should be on a similar type of road (ie paved or unpaved roads) to those being surveyed. The iii sections should have a minimum length of 200m and should be of uniform roughness over their length. E[IRI] = a + b VR + c VR2 Where E[IRI] VR a. In practice it may be difficult to find long homogeneous sections on very rough roads. using a calibration that is unique to the RTRRMS at that time. The calibration of the RTRRMS will need to be rechecked before any subsequent surveys or after any part of the suspension of the vehicle is replaced. with adequate run-up and slow-down lengths and should have no hazards such as junctions so that the vehicle can travel in a straight course at constant speed along the whole section. The calibration instrument should measure roughness in both wheelpaths. The results of a typical survey in terms of E[IRI] are shown in Figure B4. In this case it is better to include a shorter section than to omit high roughness sites from the calibration. The calibration exercise basically involves comparing the results from the RTRRMS and the calibration instrument over several short road sections. b and c = Estimated IRI (m/km) = Vehicle Response (mm/km) = constants The calibration equation can then be used to convert data from the RTRRMS into units of E[IRI]. The recommended practice for roughness calibration is described below. The sections should be straight and flat. This calibration should preferably be carried out before the survey and checked on ‘control' sites during the survey period to ensure that the RTRRMS remains within calibration. i A minimum of eight sections should be selected with varying roughness levels that span the range of roughness of the road network. This relationship generally has a quadratic form but has also been found to be logarithmic depending upon the characteristics of the vehicles suspension and the levels of roughness over which the RTRRMS is being calibrated. x ii Calibration of a RTRRMS The RTRRMS must be regularly calibrated against an instrument such as the TRL Profile Beam. E[IRI]. the MERLIN or a rod and level survey.VR = BI count x 10 section length (km) Where VR = Vehicle Response (mnVkm) BI = No of counts per section (cm) These vehicle response roughness values should then be converted to units of estimated IRI. Figure B4 Road roughness profile 49 .
vi The transient deflection is the average of the loading and recovery deflections. is a suitable standard temperature for roads in tropical climates. plastic flow of the surfacing between the loading wheels. As the wheels approach the tip of the beam. The recommended tyre size is 8. if deflections are to be measured in both wheelpaths. i Deflection readings can be affected by a number of factors which should be taken into account before the results can be interpreted. iii Insert the deflection beam between the twin rear wheels until its measuring tip rests on the marked point.25 x 20 and the tyres should be inflated to a pressure of 585 kN/m2. v The maximum and final reading of the dial gauge should be recorded while the lorry is driven slowly forward to a point at least 5m in front of the marked point. ii Mark the point. the road surface recovers and the dial gauge reading returns to approximately zero. As the surfacing is squeezed up between the twin wheels the transient 50 . Table C1 Repeatability of duplicate transient deflection tests Deflection test procedure The lorry should have a capacity of at least 5 tonnes and should be fitted with twin rear wheels having a spacing of 40mnn between the tyres. As the wheels move away from the tip of the beam. iv Adjust the footscrews on the frame of the beam to ensure that the frame is level and that the pivoted arm is free to move. Road temperature The stiffness of asphalt surfacings will change with temperature and therefore the magnitude of deflection can also change. in the vergeside wheelpath. When making a deflection measurement. The buzzer should remain on until the final reading is taken. The temperature of the bituminous surfacing is recorded when the deflection measurement is taken. Care must be taken to ensure that a wheel does not touch the beam. The lorry is loaded to give a rear axle load of 6350 kg (ie 3175 kg on each pair of twin rear wheels). The dial gauge is set to zero and the truck then drives slowly forward. approximately 3. The beam consists of a slender pivoted beam. If it does the test should be repeated. measured at a depth of 40mm in the surfacing.3m in front of each pair of rear wheels. At least two tests should be carried out at each chainage and the mean value is used to represent the transient test result. It is not possible to produce general correction curves to cover all roads found in tropical countries so it is necessary to establish the deflection/temperature relationship for each project. thus allowing the value of deflection to be corrected to a standard temperature. The frame is fitted with a dial gauge for registering the movement at one end of the pivoted beam. The relation between temperature and deflection for a particular pavement is obtained by studying the change in deflection on a number of test points as the temperature rises from early morning to midday (Jones and Smith. it is often found that little or no correction is required when the road surfacing is either old and age hardened or relatively thin. The test procedure used by the TRL is described in detail by Smith and Jones (1980) and is summarised below. Fortunately.7m long. These are the temperature of the road. originally devised by A C Benkelman. the tip of the beam is inserted between the dual rear-wheel assembly of the loaded truck. supported in a low frame which rests on the road. It is recommended that 35°C. Plastic flow Plastic flow of new bituminous surfacings can occur during deflection testing. Adjust the dial gauge to zero and turn the buzzer on. the other end of which rests on the surface of the road (Figure C1). the road surface deflects downwards and the movement is registered by the dial gauge.3m behind the marked point. It is helpful in positioning the lorry and aligning the beams if a pointer is fixed to the lorry 1. at which the deflection is to be measured and position the lorry so that the rear wheels are 1. Record the dial gauge reading which should be zero or some small positive or negative number.Appendix C: Deflection beam measurements The simplest method of measuring the deflection of a road pavement is to use a loaded lorry and the deflection beam. 1980). seasonal effects and the size of the deflection bowl. If the results of the two tests do not fall within the repeatability limits described in Table C 1 then a third test should be carried out. Insert a second beam between the offside wheels.
It is therefore normal practice to carry out surveys just after the rainy season. 1980) do not identify when plastic flow is occurring. it is usual to use values which are representative of the most adverse seasonal conditions. If feet movements larger than 0. the loading and recovery deflection will differ. Alternative test procedures such as the `rebound' deflection test (Smith and Jones. For overlay design purposes. If this cannot be done. the deflection will also change. 52 . This second beam can be used to measure any subsequent movement of the feet of the first beam as the lorry moves forward. The simplest way to check whether the differences in loading and recovery deflection are caused by the size of the bowl is to place the tip of another beam close to the front feet of the measurement beam at the beginning of the transient test. If this happens. Seasonal effects In areas where the moisture content of the subgrade changes seasonally.deflection obtained will be less than the true value. However. this requires a considerable data bank of deflection results and rainfall records before reliable corrections can be made. an attempt should be made to correct for the seasonal effect. Plastic flow can easily be identified by high negative final readings being recorded during the transient test.06mm are observed only the recovery part of the deflection cycle should be used for estimating the value of transient deflection. Size of deflection bowl The size of the deflection bowl can occasionally be so large that the front feet of the deflection beam lie within the bowl at the beginning of the deflection test.
i The coefficient of variation (CoV = standard deviation/mean) may be used to determine the level of homogeneity using the following guidelines. which is the 90th percentile value. Other authorities (NITRR. After all measurements have been made.Appendix D: Deflection beam survey procedure A safe working environment should be maintained at all times. The following strategy is adopted. can then be calculated as follows: Representative deflection = x m + 1. One of these techniques is the cumulative sum method.xm + S i-l where xi = Deflection at chainage xm = Mean deflection Si = Cumulative sum of the deviations from the mean deflection at chainage i Using the cumulative sums.2 0.3 usually indicate a highly skewed distribution produced. 1992) have recommended. There are a number of statistical techniques that can be used to divide deflection data into homogeneous sections.3 standard deviation 53 . that a homogeneous section is one where the deflection values have a CoV of 0. The minimum length of these sections should be compatible with the frequency of thickness adjustments which can sensibly be made by the paving machine. Changes in the slope of the line connecting the cumulative sums will indicate inhomogeneity. It is then convenient to plot the deflection profile of the road for each lane. Any areas showing exceptionally high deflections which may need reconstruction or special treatment can then be identified. pavement construction and maintenance history should all be considered.3 CoV > 0. Tests are carried out on a basic pattern of 50 or 100 metre spacings. The representative deflection. iii When a deflection value indicates the need for a significantly thicker overlay than is required for the adjacent section. by a number of relatively `stronger' points within a weaker section. The deflection profile is then used to divide the road into homogeneous sections. subgrade type. they should be corrected for any temperature effect (Appendix C).25 or less. Si = xi .3 good homogeneity moderate homogeneity poor homogeneity CoVs greater than 0. 1983) (AUSTROADS. where plots of the cumulative sums of deviations from the mean deflection against chainage can be used to discern the sections. The cumulative sum is calculated in the following way. whilst still maintaining satisfactory finished levels. The final stage of the procedure is to calculate the representative deflection for each homogeneous section of the road. for example. the extent to which the measured deflections on sections of road varies from the mean deflection of the whole road can be determined. Deflection beam measurements are made in both wheelpaths of the slow lane on dual carriageways and in both lanes of a two-lane road. Where there are no local safety procedures those described in Overseas Road Note 2 are recommended (TRRL. 1985).2 < CoV < 0. CoV < 0. in such a way as to minimise variation in deflections within each section. ii Additional tests should be undertaken on any areas showing atypical surface distress. the length of road involved should be determined by additional tests. as a guide. Many organisations will have on-site safety procedures which should be followed. When selecting the sections the topography. using the larger deflection of either wheelpath at each chainage. The proposed method will tend to separate out areas of very high deflections on areas that warrant special treatment or reconstruction and therefore the distribution of the remaining deflection measurements will approximate to a normal distribution.
This must be carefully monitored and temperature measurements at this critical time of the day may need to be taken every 15 or 20 minutes. as it is a mobile operation. in which case the load level should be reduced. The stiffness of the subgrade has a major influence on the shape of the deflection bowl and therefore there should be at least two sensors at such a distance from the load centre as to enable the stiffness of the subgrade to be assessed. In this check five test points. The deflection should be measured by at least five and preferably seven deflection sensors having a resolution of one micron. The relative consistency check uses a calibration tower. however. 54 . driver and traffic control personnel should always be extremely aware of both the movements of the testing equipment and other vehicles on the road. in which all the sensors are stacked vertically. The road sections selected should be representative of the pavement structures that are generally being tested. supplied by the manufacture. Many organisations will have on-site safety procedures which should be followed. normalised to a standard load and temperature. If measurements are being carried out over longer lengths of road then the operator. or as soon as possible after any sensor has been replaced. These are the consistency check and the relative consistency check. On roads with bituminous seals. In addition to static road signs. Examination of the variation in deflection. The calibration should be carried out by either the manufacturer or a recognised testing authority accredited by the manufacturer. be lightly trafficked and be efficiently drained such that any seasonal variation in deflection is minimised. The relative consistency check is used to ensure that all the deflection sensors on the FWD are in calibration with respect to each other. The procedure is fully described in the manufacturers literature or can be found in SHRP-P-652 (1993b). the recommended sensor positions are given in Table E1. The sensors are then all subject to the same pavement deflection. Test procedure A safe working environment should be maintained at all times. The location of the sensors depends on the stiffness of the pavement structure.Appendix E: Falling Weight Deflectometer (FWD) test procedure Calibration Evidence of a satisfactory absolute calibration of the deflection sensors and the load cell shall be provided by the operator of the FWD. the stiffness of the asphalt surfacing will need to be corrected to a standard temperature. in tropical climates the pavement temperature will rise quickly during mid-morning and can reach a temperature at which the asphalt surfacing is liable to plastic deformation during testing. The load should be applied through a 300mrn diameter plate and the load pulse rise time should lie between 5 and 15 milliseconds. Additional tests should be undertaken on any areas showing atypical surface distress. will provide an indication of any inconsistency in the equipment.10%. In the case where seven sensors are available. are tested at regular 6 week intervals. The absolute calibration should be carried out annually. It is therefore necessary to measure the temperature of the surfacing during testing. In addition to the annual absolute calibration other checks need to be carried out every 6 weeks. Also when the deflection bowl is to be used to estimate pavement layer moduli. the towing vehicle should always be fitted with flashing lights and direction signs and all personnel should wear high visibility safety jackets. On flexible pavements the load level should be set at a nominal load of 50kN +/. this level of load may possibly over-stress the pavement. Typically tests should be carried out at intervals of 20100 metres in the vergeside wheelpath in each direction. be in good condition. In temperate climates measurements taken hourly may be sufficient. If the sections have significant layers of bituminous material then the temperature of surfacing should be recorded during the tests. The consistency check is used to verify whether the central deflection sensor and the load cell are giving reproducible results over a period of time. Table El Recommended sensor positions Temperature measurements When the road has an asphalt surfacing the deflection may change as the temperature of the surfacing changes. and the supervising engineer should ensure that satisfactory procedures are followed. often found in the developing world. in three road sections. Where short lengths of road are being investigated they should be coned off. The safety aspects of a FWD survey are particularly difficult to manage.
The temperature of the pavement can be measured using either a short-bulb mercury thermometer or a digital thermometer.3m from the edge of the surfacing and. When the surfacing exceeds 150mm. The temperature holes should be at least 0. Glycerol or oil in the bottom of the hole will ensure a good thermal contact between the temperature probe or thermometer and the bound material. 55 . Where the asphalt surfacing is less than 150mm the temperature should be measured at a depth of 40mm. they should be pre-drilled to allow the heat to dissipate before temperatures are measured. it is recommended that temperatures should be recorded at two depths. The temperature of the surfacing should not be measured under any road markings. 40 and 100mm. where possible.
It is supplied with two spanners and a tommy bar to ensure that the screwed joints are kept tight at all times.Appendix F: TRL Dynamic Cone Penetrometer (DCP) test procedure The TRL DCP uses an 8 kg hammer dropping through a height of 575mm and a 60° cone having a maximum diameter of 20mm. weak spots may be missed and it 56 . To assist in this the following joints should be secured with a non-hardening thread locking compound prior to use: • • • Handle/hammer shaft Coupling/hammer shaft Standard shaft/cone will be more difficult to identify layer boundaries accurately. This is done by standing the DCP on a hard surface. Care should be taken when doing this. but if readings are taken too infrequently. It is more difficult to penetrate strongly stabilised layers. The lower pavement layers can then be tested in the normal way. Operating the DCP with any loose joints will significantly reduce the life of the instrument. It is recommended that a reading should be taken at increments of penetration of about l0mm. The TRL instrument has been designed for strong materials and therefore the operator should persevere with the test. before it is allowed to drop. 1985). 1995) has shown that there can be an overestimate of subgrade strength as a result of friction on the rod caused by either tilted penetration through. Little difficulty is normally experienced with the penetration of most types of granular or lightly stabilised materials. hence important information will be lost. After assembly. Many organisations will have on-site safety procedures which should be followed. When the extended version of the DCP is used the instrument is driven into the pavement to a depth of 400500mm before the extension shaft can be added. one to hold the instrument. It is therefore necessary to change the number of blows between readings. The instrument is held vertical and the weight raised to the handle. The DCP needs three operators. and when estimates of the actual subgrade strength are required (rather than relative values) it is recommended that a hole is drilled through the granular layer prior to testing the lower layers. For good quality granular bases readings every 5 or 10 blows are usually satisfactory but for weaker sub-base layers and subgrades readings every I or 2 blows may be appropriate. Penetration rates as low as 0. Under these circumstances a hole can be drilled through the layer using an electric or pneumatic drill. the first task is to record the zero reading of the instrument. Operation A safe working environment should be maintained at all times. The cone is a replaceable part and it is recommended by other authorities that it should be replaced when its diameter is reduced by 10 per cent. or collapse of. such as concrete. according to the strength of the layer being penetrated. any upper granular pavement layers. Care should be taken to ensure that the weight is touching the handle. If the DCP is used extensively for hard materials. There is no disadvantage in taking too many readings. If only occasional difficulties are experienced in penetrating granular materials. Where there are no local safety procedures those in Overseas Road Note 2 are recommended (TRRL. However it is usually easier to take a reading after a set number of blows. or by coring. The instrument is assembled as shown in Figure F1. Where there is a substantial thickness of granular material. After re-assembly a penetration reading is taken before the test is continued. one to raise and drop the weight and a technician to record the readings. the DCP leans away from the vertical no attempt should be made to correct it because contact between the shaft and the sides of the hole can give rise to erroneous results. but not lifting the instrument. it is worthwhile repeating any failed tests a short distance away from the original test point. After completing the test the DCP is removed by tapping the weight upwards against the handle. Research (Livneh. granular materials with large particles and very dense. To do this the metre rule is detached from its baseplate and the shaft is split to accept the extension shaft. other causes of wear can also occur hence the cone should be inspected before every test. However it is important that this joint is checked regularly during use to ensure that it does not become loose. high quality crushed stone. However.5mm/blow are acceptable but if there is no measurable penetration after 20 consecutive blows it can be assumed that the DCP will not penetrate the material. The operator must let it fall freely and not partially lower it with his hands. The instrument is usually split at the joint between the standard shaft and the coupling for carriage and storage and therefore it is not usual to use locking compound at this joint. wear on the cone itself will be accelerated. if it is done too vigorously the life of the instrument will be reduced. checking that it is vertical and then entering the zero reading in the appropriate place on the proforma (See Figure F2). If. The DCP can be driven through surface dressings but it is recommended that thick bituminous surfacings are cored prior to testing the lower layers. during the test.
The results can then either be plotted by hand. Relationships between DCP readings and CBR have been obtained by several research authorities (see Figure F4). or processed by computer (TRRL.Interpretation of results The results of the DCP test are usually recorded on a field data sheet similar to that shown in Figure F2. It is expected that for such materials the relationship between DCP and CBR will depend on material state and therefore. as shown in Figure F3. 1990). Agreement is generally good over most of the range but differences are apparent at low values of CBR in fine grained materials. 57 . if more precise values are needed it is advisable to calibrate the DCP for the material being evaluated.
as machine operations are usually more productive but more costly than manual methods. 1 or 2 spades (a fence post hole digger can also be useful). taking care not to disturb the surface of the roadbase. the following procedure should be adopted. the engineer should be clear as to the information required from each test pit. The choice will normally be determined by the availability of plant and the test pit programme. However. clean and even surface is required. Many organisations will have on-site safety procedures which should be followed. and sample log book. 1985). For the sand replacement method. deflection and DCP surveys. water and cold nix for resurfacing. equipment and materials Test pits can be excavated either by machine or manually. cement for stabilising gravel. iii iv 61 . 1 machine operator if applicable. Where there are no local safety procedures those described in Overseas Road Note 2 are recommended (TRRL. and for this reason the location of each test pit should be carefully selected to maximise the benefit of any data collected. road condition and weather. It is a time consuming and expensive operation. This will depend on the results of previous surveys. The average thickness of surfacing should be recorded. 1 chisel is often useful to assist with inspecting the wall of the test pit. test pit log forms and clipboard. Procedure A safe working environment should be maintained at all times. 1 tamper or plate compactor for backfilling test pit. but it can be increased later if found to be too small. with some means of labelling each. Record any relevant details such as surrounding drainage features. It is important for the accuracy of the test that the layer is homogeneous. the position of a pit will be apparent after completion due to the patched surface. Usually. Accurately locate position of test pit and record this on the Pavement Test Pit Log (see Figure G1).a minimum of one at each end of the site. 1 driver for vehicle. Not all these tests will be necessary and the engineer must decide on those which are required. Define the edge of the test pit and remove surfacing. The edge of the pit can be cut with a jack hammer or pick and the surfacing `peeled' off. equipment necessary to complete any required onsite testing. The condition of the road pavement and the primary purpose for the pit investigation should be recorded on the Test Pit Log (see Figure G1). Labour. If a nuclear density meter is used. if long term monitoring is required.8m by 0. The following personnel are required: • • • • • traffic controllers . sample bags and containers. the materials specifications in use and an understanding of the pavement behaviour.8m will be sufficient for manual excavation. Sampling and testing Before commencing the survey in the field. 1 broom to tidy area on completion. and the minimum working area required for a backhoe operation will be sufficient for machine excavations. 2 (if machine excavation) or 3 (if manual excavation) labourers.Appendix G: Test pit procedure Purpose The purpose of carrying out a test pit investigation is to confirm the engineers understanding of the information from surface condition. Some field testing might be necessary as well as subsequent laboratory testing of samples extracted from the pit. material to backfill and seal test pit : gravel. Table GI summarises the various tests that may be required and references the relevant standards with which the tests should comply. 1 pick. i ii Set up traffic control. and 1 supervising technician. Usually an area of about 0. Equipment and materials requirements are as follows: • • • • • • • • • • • • • 1 backhoe (for machine excavation). If density tests are to be performed. no prior knowledge is required of the layer thickness since this becomes obvious as the hole is excavated. a permanent location marker should be placed at the roadside. 1 tape measure and thin steel bar to span pit (to assist with depth measurements). 1 jack hammer with generator (to assist with manual excavation). Once it has been decided what testing is to be carried out and the location of the trial pits has been confirmed. The required size of pit will depend on the sample sizes necessary for the selected tests. a smooth.
a visual assessment made of the material and samples taken for laboratory testing. the layer can be removed over the extent of the trial pit. vi Continue to sample. 62 . A bituminous cold mix can be used to patch the backfilled pit. the total depth of pit should be recorded along with any other information such as appearance of water in any of the layers.the thickness of the layer can be estimated from the DCP results to determine the depth of testing. viii The pit should be backfilled in layers with suitable material which should be properly compacted. v On completion of any required density testing. All information should be recorded on the Pavement Test Pit Log. It is often good practice to stabilise the upper layer with cement accepting that full compaction will not be achieved. Care should be taken not to disturb the adjacent lower layer. ix The site should be cleared and left in a tidy and safe condition for traffic. vii All samples should be clearly labelled and proposed tests for the pit materials should be logged in a sample log book to avoid later confusion in the laboratory. The thickness of the layer and the depth at which samples are taken should be measured. Once it has been decided that there is no need to excavate further. test and excavate each pavement layer following the procedure above.
iv Measure the diameter of the sand patch to the nearest 1 nun at four diameters every 45° and calculate the mean diameter (D) to the nearest 1mm. strike off the sand level with the top of the cylinder. v Calculate the texture depth to the nearest 0.Appendix H: Sand patch test The sand patch test is described in detail in BS 598 Part 105 (1990). in a rotary motion so that the sand is spread into a circular patch. complying with the grading given in Table H 1. and spread the sand over the surface. 1000 Area of patch (mm2) 65 . The patch should be of the largest diameter which results in the surface depressions just being filled with sand to a level of the peaks. ii Fill the cylinder with sand and. The method is summarised below. Texture depth (mm) = 63660 / D2 Note: For surfacings having a texture depth of less than 1 mm the volume of sand will have to be reduced to 25ml or less. stuck to one face. if necessary. sweep clean with a brush. The texture depth is then calculated using the following equation: Texture depth (mm) = Volume of sand (ml) .01 nun from the following equation. Apparatus i ii Measuring cylinder of 50ml volume.5mm thick. Table Hl Grading of sand Procedure i Dry the surface to be measured and. iii Pour the sand into a heap on the surface to be tested. working the disc with its face kept flat. taking care not to compact it by unnecessary compaction. iii Washed and dried sand. A spreader disc comprising a flat wooden disc 65mm in diameter with a hard rubber disc 1. with rounded particle shape. The reverse face being provided with a handle.
Record the mean of five successive swings. To prevent undue wear of the slider when moving the pendulum arm through the arc of contact. If the range is greater than this. The apparatus is now ready for testing. by gently lowering the pendulum arm until the slider just touches the surface first one side and then the other side of the vertical. shown in Figure I1. It is recommended that in tropical climates the value should be corrected to a standard temperature of 35°C using the following relation (Beaven and Tubey. and hanging vertically. The pointer is then brought round to its stop in line with the pendulum arm. Place the pendulum arm in its locked position. This is done by first raising the swinging arm to the horizontal release position. Lower the head of the tester. was developed by the Road Research Laboratory and is described in detail in Road Note 27 (RRL. Repeat the process. spreading water over the contact area with a hand or brush between each swing. adjust to the correct length by raising or lowering the head slightly. provided they do not differ by more than three units. One slider edge can usually be used for at least 100 tests (500 swings). which carries the swinging arm. The pendulum arm is released by pressing button C. In this position it is automatically locked in the release catch. The testing procedure is summarised below. and note the pointer reading. iii Check the zero reading. The road temperature is measured by recording the temperature of the water after the test using a digital thermometer and surface probe. graduated scale. Release the pendulum arm by pressing button C and catch it oft the return swing. When the required height is obtained. the slider should be raised off the road surface by means of the lifting handle. At this standard temperature the corrected values will be 3-5 units lower than comparable surfaces in the UK. Movement of the head of the tester. until the slider just touches the road surface. Temperature correction The effect of temperature on rubber resilience makes it necessary to correct the measured value of skid resistance to a standard temperature. When the apparatus is set correctly the sliding length should be between 125 and 127nun as indicated by the measure provided. repeat swings until three successive readings are constant. 1969). and clamp in position with knob A. wet both the surface of the road and the slider. where results are corrected to 20°C. After unclamping the locking knob A at the rear of the column. 66 . v Sliders should be renewed when the sliding edge becomes burred or rounded. v Check the sliding length of the rubber slider over the surface under test. Record the indicated value. New sliders should be roughened before use by swinging several times over a dry piece of road. Operation of the tester i After ensuring that the road surface is free from loose grit. the head unit must be locked in position by using the clamping knob A.SRVt = Skid resistance value at 35°C = Measured skid resistance value = Temperature of test (°C) Setting the tester i Set the base level using the in-built spirit level and the three levelling screws on the base-frame. If necessary. The sliding length is the distance between the two extremities where the sliding edge of the rubber touches the test surface. Correct the zero setting as necessary by adjusting the friction rings. under the lifting-handle settingscrew to raise the slider. record this value. The pointer is carried with the pendulum arm on the forward swing only. iii Return the arm and pointer to the locked position. 1978). iv Raise the head of the tester so that it swings clear of the surface again and check the free swing for any zero error. the head may be raised or lowered by turning either of the knobs B/B1.Appendix I: The portable skid-resistance tester The portable skid-resistance tester. ii Raise the head so that the pendulum arm swings clear of the surface. place the spacer. SRV35 Where SRV35 SRVt t = (100 + t)/135. pointer and release mechanism is controlled by a rack and pinion on the rear of the vertical column. before the slider strikes the road surface. Remove the spacer. using knob B. Catch the pendulum on its return swing. on the right-hand side of the tester. which is attached to the base of the vertical column. ii Bring the pointer round to its stop. keeping the slider clear of the road surface by means of the lifting handle. iv With the pendulum arm free.
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