HRE 313 Highway and Railroad Engineering PDF

HRE 313 Highway and Railroad Engineering This is a property of PRESIDENT RAMON MAGSAYSAY STATE UNIVERSITY NOT FOR SALE HRE 313 – Highway and Railroad Engineering First Edition, 2021 Copyright. Republic Act 8293 Section 176 provides that “No copyright shall...

HRE 313 Highway and Railroad Engineering This is a property of PRESIDENT RAMON MAGSAYSAY STATE UNIVERSITY NOT FOR SALE HRE 313 – Highway and Railroad Engineering First Edition, 2021 Copyright. Republic Act 8293 Section 176 provides that “No copyright shall subsist in any work of the Government of the Philippines. However, prior approval of the government agency or office wherein the work is created shall be necessary for exploitation of such work for profit. Such agency or office may, among other things, impose as a condition the payment of royalties. Borrowed materials included in this module are owned by their respective copyright holders. Every effort has been exerted to reach and seek permission to use these materials from their respective copyright owners. The University and authors do not claim ownership over them.  0323 Module Overview Introduction (A short discussion of the module as to what to expect by the learners, including topics included in this particular learning module as well as the scope and coverage.) Sample: Highway maintenance can broadly be defined as actions taken to retain all the highway elements in a safe and usable condition. The definition of this “condition” will depend on the purpose of the highway, the traffic volumes, and other technical, social and political considerations. It can have a flexible, rigid or unpaved surface. A highway is defined as an engineered interurban road. Highway maintenance normally excludes upgrading or strengthening of the highway elements, but may be done if these appear to be the most cost- effective actions in the long-term. Maintenance could be of emergency, remedial (also called routine or recurrent), and preventative (also referred to as periodic) types. Table of Contents Chapter/Lesson 1: Failures, Maintenance and Rehabilitation of Transportation Structures Highway and Railroad Engineering Chapter 1 Failures, Maintenance and Rehabilitation of Transportation Structures Chapter 1 Failures, Maintenance and Rehabilitation of Transportation Structures Introduction: It is seldom readily apparent which is the most economical rehabilitation method for a particular pavement. Each rehabilitation strategy has unique initial construction costs, performance expectations, and future maintenance needs. What is most economical for one pavement may not be for another. Local costs may differ from one location to another, and material performance expectations may be different from region to region. The only rational way to compare one rehabilitation strategy and another is to perform an economic analysis of the alternative strategies. 1. HIGHWAY MAINTENANCE Highway maintenance must be planned, managed, designed and executed. Planning and management are done by means of maintenance management systems and procedures. These systems and procedures are normally different from a pavement and bridge management systems since the latter do not focus on long-term and strategic repair and upgrading issues. Relevant pavement and bridges can be identified for protective and preventative actions as part of a highway maintenance program. On time maintenance is extremely important. Studies have proven that it is more cost-effective to implement preventative maintenance actions on the pavement on a regular basis than neglecting the same and later trying to rehabilitate the pavement. Typically, premature periodic maintenance is 20 times costlier than proper routine and recurrent maintenance, while it is 3 times costlier to strengthen the pavement rather than properly maintain it (Robinson, 1988). For the highway user it is equally important to avoid accidents due to unsafe conditions rather than to rectify the defect after an accident has occurred. Poor maintenance (in terms of quality and timing) can increase the vehicle operating costs by 15% and no maintenance by 50%. A further consequence of poor maintenance is the possible lack of accessibility. Poor maintenance of bridges, culverts, drainage structures and the pavement can lead to closure of roads for periods of time with the related detrimental social and economic consequences. DESCRIPTION AND DEFINITION OF HIGHWAY MAINTENANCE Highway maintenance has the following objectives:  the repair of the functional pavement defects  prolonging the functional and structural life of the pavement  maintaining road safety and signage  keeping the road reserve in an acceptable condition Road maintenance has been defined as:  Periodic or Preventive Maintenance – “Operations that are occasionally required on a section of road after a period of a number of years. They are normally large scale and require specialist equipment and skilled resources to implement, and usually necessitate the temporary deployment of those resources on the road section. These operations are costly and require specific identification and planning for implementation, and often require design.” Periodic or preventive maintenance is non-structural and is applied to extend the life of the pavement, to enhance the performance and to reduce user delays (Galehouse et al., 2003). Examples of preventative (or periodic) maintenance are regraveling of unpaved roads, resealing (with surface dressing, ultra-thin asphalt, etc.) of paved roads, and regraveling of shoulders  Routine Maintenance – “Operations required to be carried out once or more/year on a section of road. These operations are typically small-scale or simple, but widely dispersed, and require skilled or unskilled manpower. The need for some of these can be estimated and planned on a regular basis e.g., vegetation control.” Non-preventive maintenance can also be described as routine, recurrent and urgent (TRRL, 1981), where routine refers to the “fixed- cost” activities such as grass cutting, drainage maintenance and road sign maintenance; recurrent to activities required throughout the year such as pothole patching, crack sealing, and grading, and urgent to the repair of defects caused by disasters (e.g., floods) or accidents. Routine maintenance activities are not influenced by the traffic, while the recurrent maintenance  activities are. Both these sets of activities can also be defined as reactive maintenance, where activities are unscheduled and immediate response sometimes required.  Remedial maintenance – refers to actions associated with the rectification of defects on the carriageway or the road reserve.  Emergency maintenances – refers to activities associated with the urgent repair of defects caused by natural disasters or accidents 2. DESCRIPTION OF DEFECTS AND APPROPRIATE MAINTENANCE ACTIONS The purpose of highway maintenance is to rectify defects and preserve the pavement. It is necessary to define and record the defects, as well as to understand the mechanism of failure in order to select the most appropriate action. 2.1. FLEXIBLE PAVEMENTS DEFECTS Flexible pavements comprise all pavements with a bituminous surfacing even if the base or subbase layers have been stabilized. The defects and appropriate maintenance actions are summarized in the Table 1. i) Cracking  Surfacing cracks are associated with the aging and deterioration of the surface bituminous layer due to shrinking and hardening of the bituminous binder with a loss of volatiles. These cracks are in general not load-related. One type of surfacing cracks is cracking in an irregular pattern. These cracks are also referred to as map cracks, star cracks and amorphous cracks. Another type is block cracking with cracks in well-defined rectangular blocks. Surfacing cracks occur across the full-width of the pavement. The surface cracks are more prominent on thin surfacing such as slurries, sand seals, and the block cracking more pronounced on asphalt concrete surfacing. In the latter the cracks start from the top and progress to the bottom asphalt layer.  Fatigue cracks (commonly called alligator or crocodile cracks) are a series of interconnected cracks in a chicken-wire pattern. The cracks are caused by traffic loading, occur only in wheel-paths and are often associated with deformation. Early signs of fatigue cracks are fine parallel longitudinal cracks in the wheel-path.  Other types of cracks in flexible pavements are longitudinal, edge, transverse, reflection and stabilization cracks. These are well-defined fairly continuous cracks. Longitudinal and edge cracks are normally associated with the differential movement of the subgrade due to moisture variations (i.e. at embankments or on clays), and discontinuities in the pavement. Transverse cracks occurring in isolation are caused by movements under the surfacing such as at a culvert or bridge joint. When these cracks appear at regular intervals they are classified as reflection cracks where joints of an overlaid concrete pavement reflect through the asphaltic concrete surfacing. Cracking on longitudinal joints would also be present in such cases. Reflection cracks follow the dimensions of the concrete slabs beneath the asphalt concrete surfacing. A further type of cracking is stabilization cracks, which are rectangular blocks from 0.5 to 3 m in size and formed by the reflection of the cracked stabilized layer through the surfacing. Pumping, i.e., the movement of fine material from the stabilized layer through the cracks can occur as stabilization cracks. Closely spaced stabilization cracking (i.e., small blocks) is an indication that the stabilized layer has broken up into small pieces and is close to the end of its functional life. Stabilization cracks should not be confused with block cracks. Stabilization cracks develop from the bottom of the surfacing and block cracks from the top. Stabilization cracks tend to be more prominent in the wheel tracks, than between the wheel tracks, especially when the block sizes are small.  Maintenance/Repair: o Isolated and well-defined cracks, such as transverse, longitudinal and reflection cracks can be sealed with a penetration grade or polymer modified bitumen (PMB). Where cracks are active the application of a thin (150 to 300 mm) strip of geo-textile on the crack is appropriate. Extensive cracking cannot be sealed individually cost-effectively and the application of a membrane of bitumen, or PMB or geo-textile is more feasible (AUSTROADS, 1998a). o Low severity surface cracking can be addressed with the application of a rejuvenator to the surface. Extensive and severe surface cracking can be rectified by removal and replacement of the defective portion of the layer or by hot in-place recycling (HIPR) depending on the thickness which is affected. o Where fatigue cracking is extensive and associated with deformation, the appropriate action is to remove the defective material and replace it with new material. ii) Potholes Bowl-shaped holes of various sizes on the pavement surface. A pothole is normally only considered significant if the diameter of the hole is more than 150 mm and the depth more than 25 mm. Potholes are secondary forms of distress that develop from cracks. The ingress of moisture into the pavement layers reduces the structural capacity of the layers and thereby accelerates the progression of the pothole. The condition of patches must be recorded and repaired. Maintenance/Repair: Repair of the potholes entails patching which is the removal of the defective layers and the replacement with, normally, a bituminous mixture. Patch deterioration refers to the condition of the patch and requires the same remedial actions as potholes iii) Rutting The longitudinal surface depression in the wheel-path. Rutting is caused by compaction or shear deformation of the pavement layers through traffic loading. Wide-shaped rutting is normally an indication of deformation of the lower pavement layers or subgrade and narrower and more sharply defined rutting, of deformation in the upper layers (i.e., surfacing or base). Maintenance/Repair: Rutting can be repaired by the filling of the ruts with a slurry or thin asphalt or milling and replacement. A resurfacing  will rectify rutting, and if properly designed, reduce further rutting. If rutting is severe more than one application of the resurfacing layer may be required. iv) Shoving The longitudinal displacement of localized areas of the pavement caused by shear forces induced by traffic loading. Shoving is most evident where vehicles stop and start. The repair is similar to that of rutting. v) Other defects associated with the surfacing  Bleeding is the condition where a film of bituminous binder is present on the surface which creates a shiny, reflective surface which may be tacky in hot weather. Polished aggregate refers to the smoothness of the exposed aggregate. Bleeding and polished aggregate reduce the skid resistance of the pavement with resulting safety consequences.  Raveling (aggregate loss) describes the process where the aggregate particles are dislodged and weathering where the asphalt binder is removed. Raveling is caused by the abrasive action of traffic. This can be extensive on surface dressings when the binder content is too low, chippings contaminated or bituminous binder too cold to effectively adhere to the chippings during construction.  Binder condition refers to the freshness and the elasticity of the binder. The binder loses its elasticity with time, resulting in raveling and weathering. Maintenance/Repair: Repair of these defects comprises milling and replacement where the defects are isolated and resurfacing where the defects are extensive. Poor binder condition can be rectified with the application of a rejuvenator. vi) Other miscellaneous distresses  Edge breaks are the breaking away of the surfacing at the edges of the pavement and often caused by poor unpaved shoulder maintenance.  Lane-to-shoulder drop-off or separation describes the difference in elevation or width of joint between the pavement and the shoulder. Maintenance/Repair: Edge breaks are repaired by patching and the lane-to-shoulder drop-off by the reinstatement of the shoulder. The defects can be prevented by regular blading of the unpaved shoulder. vii) Roughness Deviations of the surface from a true plain. It is caused by one or a combination of the preceding defects, e.g., rutting, cracking, and potholes. The roughness can be improved slightly by patching, crack sealing and elimination of rutting, but only completely be rectified with a resurfacing of slurry (normally coarse slurry) or asphalt. viii) Skid resistance. Skid resistance is affected by the polishing stone value (PSV) of the chippings and the microtextured. The skid resistance can effectively be improved by  resurfacing, while sandblasting techniques have also been successful in some cases. ix) The macro-texture reflects the drainage capacity of the pavement under wet conditions and is an important safety issue. Resurfacing with the appropriate type will improve the skid resistance. RECORDING OF DEFECTS The magnitude of defects is normally recorded in terms of severity (or degree) and extent. The severity is commonly expressed as low, moderate, or high or on a scale of one to five with one indicating a very low severity and five a very high severity. The presence or extent of the defect is expressed as length, area or percentage, or in terms of occurrence i.e. as isolated, intermittent or extensive. Defects are recorded/preidentified section. The section length can range from 50 m to 1 km. The shorter sections are normally used for detailed level assessments and the longer sections for network level assessments. 2.2. RIGID PAVEMENT DEFECTS Three types of rigid (concrete) pavement are commonly in use i.e. jointed concrete pavement (JCP), jointed reinforced concrete pavements (JRCP), and continuously reinforced concrete pavements (CRCP). A fourth type, prestressed concrete pavements, have been used on airport pavements. Most of the defects apply to all three types of concrete pavements. i) Surface Defects Defects at the surface which do not protrude deeply into the concrete slab i.e. map cracking, scaling, polished aggregate and pop-outs. Map cracking is a series of random cracks that extend only into the upper surface of the slab. Scaling defines the process when thin layers of the surfacing get dislodged. Polished aggregate refers to the surface mortar and texturing worn away to expose coarse aggregate. Pop-outs are small pieces of pavement broken loose from the surface, normally ranging in diameter from 25 to 100 mm and depth from 13 to 50 mm. Maintenance/Repair: Not of major concern, but if action is needed milling, grooving, or resurfacing can be considered. ii) Durability cracking (D-cracking) Forms closely spaced crescent-shaped hairline cracking patterns and occurs adjacent to joints, cracks, or free edges initiated at the intersection of cracks and a free edge. Dark coloring of the cracking pattern and surrounding area are common. D-cracking is a progressive condition in that the first cracks that appear are at junctions of joints, cracks and pavement edges and progress outward to involve greater slab areas. The development of D-cracking is strongly dependent on the physical and chemical character of the ingredients of the concrete mixture, especially the coarse aggregate. Maintenance/Repair: D-cracking is considered to be a concrete material problem attributable to freeze – thaw cycles and a peculiar aggregate pore structure. Repair of D-cracking is by means of full-depth patching iii) Longitudinal cracking Describes cracks that are predominantly parallel to the pavement centerline. Most longitudinal cracking, and especially that which results when fracture does not take place at weakened plane longitudinal joints as planned (for instance due to late sawing or shallow cut-depths), does not become a performance problem nor is it usually a precursor of problem development elsewhere. Occasionally, and especially where progressive widening or spalling of the crack becomes evident, a longitudinal crack can signify the beginning of foundation settlement or base erosion that prompt treatment may control. If unattended, the open crack can provide easy entry for surface water to aggravate an already damaging condition. Longitudinal cracking, if not already present, may take place during the development of punch-outs in CRCPs. Maintenance/Repair: Timeous crack sealing is the most appropriate maintenance action, unless the slab support is affected in which case undersealing may have to be considered. iv) Cluster cracking A grouping of three or more closely spaced transverse cracks where spacings may be in the order of 150 to 600 mm. This can occur in CRCP & often develops into punch- outs. Cluster cracking is believed to be associated with such factors as localized areas of change in subgrade support, lack of concrete consolidation, inadequate pavement thickness, high base friction, poor drainage, & high temperatures at the time of construction. Concrete mixture variability might be added to the foregoing list. Because cluster cracking is so often seen early in the life of a pavement, traffic loads probably are not a basic cause. The appropriate repair is full depth patching. v) Diagonal cracking Cracking in a direction oblique to the pavement centerline and can be viewed as an indicator of the existence of a foundation problem (settlement, expansion or erosion) that may be controllable through early treatment. Maintenance/Repair: These cracks should be sealed to prevent water from entering and affecting the support. Undersealing to stabilize the slab and fill the voids should be considered if appropriate. Where more than one diagonal crack develops on a slab, a shattered slab situation will develop which requires the replacement of the slab. vi) Blow-ups Localized upward movements of the pavement surface at transverse joints or cracks, often accompanied by shattering of the concrete in that area. The rise can be sufficient magnitude to endanger the safe passage of traffic. The dominant feature of a shattering blow-up is an accumulation of debris from the shattering process. Blow-ups usually occur during periods of high temperature and precipitation. Blow-ups occur in concrete pavements when available expansion space is not sufficient to accommodate expansion. They almost never occur in new pavements. The longitudinal pressure buildup that produces them is initiated by the entry of incompressible into previously available expansion space in cracks & joints during periods of pavement contraction. Maintenance/Repair: Relief joints cut early in the blow-up process may avoid later major repair or at least allow some latitude in selecting the time for repair. When badly deteriorated full depth patching will be required to replace the damaged portions of the slab and construct proper expansion joints. vii) Corner breaks Recorded if a portion of the slab is separated by a crack which intersects the adjacent transverse and longitudinal joints, describing approximately a 458 angle with the direction of traffic. The length of the sides is from 0.3 m to one-half the width of the slab, on each side of the corner. These cracks are often caused by the loss of slab support due to erosion and pumping at the corners. Full depth patching is required to correct the integrity of the slab and load transfer. viii) Transverse cracking Cracking that is predominantly perpendicular to the pavement centerline and can also take the shape of a “Y.” This cracking is expected in a properly functioning CRCP and ideally 1 to 1.5 m apart. Tight transverse cracks showing little spalling in CRCP are, like transverse joints in a welldesigned and well-constructed jointed concrete pavement, deficiencies only to the extent that they are interruptions in what might be considered the ideal but so far unattainable concrete pavement — a single, unbroken ribbon of concrete. Transverse cracks in groups at close intervals, i.e. cluster cracking, can be the sign of a potential problem area (e.g., punchouts). Any abnormal increase in the amount of transverse cracking, especially when accompanied by an increase in spalling, also can be a sign of problem development. Y-cracking appears to develop mostly when nominally transverse cracks meander sufficiently to either branch or join. Like closely spaced transverse cracking, it can be a problem location if the underlying support weakens. Maintenance/Repair: Transverse cracking in jointed concrete pavements is often caused by late sawing of joints, constrained movements at the joints or the lack of slab support. Crack sealing is required as a maintenance option. Transverse cracking in CRC pavements is expected and only requires attention if it has developed into closely spaced cluster) cracking and punch-outs in which case full-depth patching is required. ix) A punch-out The area enclosed by two closely spaced (usually less than 0.6 m) transverse cracks, a short longitudinal crack, and the edge of the pavement or a longitudinal joint present only on CRCP. It also includes “Y”-cracks that exhibit spalling, break-up and faulting and occurs when two transverse cracks at a critical distance apart are connected by a longitudinal crack. Once a transverse crack has begun to open, repeated heavy loads continue the breakdown of aggregate interlock. The process may be aided by corrosion of the steel, which begins when the crack width becomes large enough to admit water and de-icing salts. A punch-out is a structural failure in which a small segment of pavement is loosened from the main body and displaced downward under traffic. The punch-out is usually bounded by two closely spaced transverse cracks, a longitudinal crack, and the pavement edge and sometimes by the branches of a Y-crack and the pavement edge. More rarely, a punch-out may occur in the interior of a pavement away from the edge, but these differ from edge punch-outs in severity and cause. Edge punch-outs are the major structural distress experienced in CRCPs. The repair of a punch-out entails deep patching of the portion of the slab which had failed. x) Water bleeding and pumping The seeping or ejection of water from beneath the pavement through cracks or joints. Most of the pumping in CRCPs is at the edges, while it can be at the joints or the edges in jointed pavements. In some cases, it is detectable by deposits of fine material left on the pavement surface, which were eroded (pumped) from the support layers and have stained the surface. Inadequate pavement thickness and erodible underlying material type are the main causes of pumping. Maintenance/Repair: Pumping can be rectified by undersealing (i.e., filling of the voids) and prevented by keeping water out of the pavement and proper load transfer. xi) Faulting of transverse joints and cracks is defined as the difference in elevation across a joint or crack. This is caused by the loss of slab support due to erosion or settlement. Faulting is the most important single defect influencing the riding quality of rigid pavements. Further faulting can be prevented by undersealing and repaired by grinding or slab jacking. xii) Patch deterioration describes the condition of a patch (asphalt or concrete) present on the rigid pavement. Deteriorated patches should be replaced. xiii) Steel rupture in CRCP is almost invariably associated with open cracks or open construction joints (.3 mm). Steel rupture in CRCP is breakage and full loss of continuity in the steel reinforcement. Loss of tightness at any crack or joint in CRCP is evidence that the steel reinforcement is not functioning properly and is either in a weakened condition or has already ruptured. Excessive spalling is likely to be present. Rust stains on the pavement surface suggest loss of cross-sectional area and the possibility of rupture. Faulting or slab settlement often indicates that rupture has taken place. Although the actual fracture that takes place may be a rather sudden occurrence, the weakening process may be gradual, taking place over a period of time. Maintenance/Repair: Asphalt sealing or application of cement grout at an early stage can postpone or avert failure. Failure usually requires repair by removing the damaged material and patching the area. xiv) Spalling of joints or cracks The cracking, breaking, chipping, breakdown, disintegration or fraying of slab edges within 0.6 m of the joint or crack. Slight spalling, in which the flaking is confined mostly to the mortar in the concrete matrix, is sometimes referred to as raveling. Spalling alone, without accompanying deterioration, rarely becomes so severe that some form of maintenance is required. Progressive spalling often is a good indicator of future distress. Progressive spalling that deepens more rapidly than it expands outward is primarily related to structural weakness. Spalling that widens more quickly than it deepens (often widening to over 50 mm while deepening less than 12 mm) usually is related more to weakness of the surface concrete. Maintenance/Repair: Severe spalling may produce holes that require partial depth patching for riding comfort xv) Joint seal damage is any condition which enables incompressible materials or a significant amount of water to infiltrate into the joint from the surface. Typical types of joint seal damage are:  Extrusion, hardening, adhesive failure (bonding), cohesive failure (splitting), or complete loss of sealant.  Intrusion of foreign material in the joint.  Weed growth in the joint. Damage of construction joints due to the ingress of incompressible can manifest as a series of closely spaced transverse cracks or a large number of interconnecting cracks occurring near the construction joint. xvi) Defects on shoulders can be:  Lane-to-shoulder drop-off which is the difference in elevation between the edge of slab and outside shoulder; and typically occurs when the outside shoulder settles.  Lane-to-shoulder separation which is widening of the joint between the edge of the slab and the shoulder.  Deterioration of the flexible shoulder 2.3. ROADSIDE DRAINAGE Roadside drainage refers to water standing on the road surface or road shoulder, as well as the facilities built to drain water away from the pavements. These facilities include side-drain or ditch (long narrow excavations designed or intended to collect and drain off surface water), miter or turn-out drains to (lead water away from the side drains), chutes (inclined pipes, drains or channels constructed in or on a slope) and subsoil drains (pipes or permeable material provided to collect and dispose of groundwater). Drainage structures are not included under roadside drainage. A defect occurs when the water is not effectively removed from the road surface or the pavement layers after rain. The reasons for this can be, inter alia, improper cross- falls, slacks, flat or high gravel shoulders, vegetation on the shoulder, lack of capacity of outlets, damaged or silted chutes or curbs, and blocked subsurface drains. The drainage problems can best be observed after heavy rain. The condition and effectiveness of roadside drainage features should be assessed visually on a regular basis to determine the extent and severity of the defect. The frequency of the inspections depends on the importance of the highway and can range from weekly to 6 monthly inspections. The extent is normally recorded as percentage of the highway section on which the defects are present. The severity is commonly reported as:  Low: Drainage effective and features on a satisfactory condition. No maintenance action required.  Moderate: Concern about effectiveness & condition. Maintenance required.  High: Drainage ineffective. Immediate maintenance required. 2.4. ROAD MARKINGS, RESERVE AND FURNITURE Road signs, markings reflectors, and guard-rails are features directly influencing the safety of the road, while the condition of the fences and the shoulders, and the length of grass and vegetation, can adversely affect road safety. The clearing of litter from the road reserve is important, not only from an aesthetic point of view, but also to prevent environmental contamination and clogging of drainage features. The maintenance of fencing is of particular importance in residential areas and in areas where livestock or game is present, mainly due to safety concerns. Fences are normally mended when damaged, but general replacement of old and deteriorated fences from time to time may be cost-effective. Removal of litter should take place on a regular basis. The frequency depends on the traffic volumes and location of the section of road (for instance, more litter is present close to towns or settlements). Frequencies vary from once a month to every 6 months. Damaged guard-rails are themselves a hazard and should be repaired promptly. The overall guard-rail system (i.e. the guard-rail and posts) should be inspected on a regular (often weekly) basis with special attention given to the condition of guard- rails in high risk or accident areas. Grass cutting is required for reasons of visibility (especially at curves and intersections), drainage and fire hazard. The frequency and width (e.g., from fence to fence or to a width of 4 m from the shoulder) vary, depending on the growth of the grass (influenced by the climate), the traffic volume and importance of the road. Performance criteria such as a limit on the height of the grass can be used to dictate the frequency. Traffic signs, road markings and reflectors are important from a road user safety point of view. Damaged signs should be replaced or repaired timely. Signs and road markings must be inspected on a regular (annual) basis and be replaced before they become ineffective. The life of a road sign could be 7 to 8 years and that of road markings 2 to 4 years. The life of the latter depends on the traffic volume, climate and type of surfacing. 2.5. GEOTECHNICAL FEATURES The maintenance of earth and rock slopes, cuttings and fills also falls under the domain of road maintenance. The failure of road embankments (fills), cuttings and lateral support can have severe consequences such as closure of the road, damage to property and injury or loss of life. Stable slopes can become unstable for a variety of reasons. Failure can take place within hours or over a long period of months or even years. Little can be done to prevent failure triggered by events such as abnormal downpours, floods, natural disasters or bust water pipes. Many failures can be prevented or the consequences reduced by monitoring typical indicators of instability. Regular inspections should be done to assess & monitor these features. These procedures rely on visual inspection of signs of cracking, offset fences, unexpected water flows, etc. More sophisticated measures, such as surface surveys, extensometric measurements across tension cracks, & installation of piezometers, can be considered. Routine maintenance of cuttings and embankments essentially entails controlling the flow of water and vegetation. 2.6. DRAINAGE STRUCTURES DEFECTS Drainage structures refer to structures constructed to allow water to flow from the one side of the road to the other, i.e., bridges and culverts. Defects occurring on bridge and drainage structures are associated with the waterway, the substructure (abutment and piers), superstructure, roadway (including expansion joints) and approaches. i) Waterway. The assessment of the waterway covers the free flow of water under the bridge, the stability of the waterway and the probable effect on the bridge. Specific defects are the build-up of debris, scouring, erosion damage of gabion stone pitching or paving blocks. Maintenance actions removal of debris, sand and vegetation; cutting of trees and brushes; erosion repair; and the repair of gabions, stone pitching and concrete slabs. ii) Substructure (abutment and piers). Elements to be assessed include abutment and pier foundations, concrete or masonry abutments, piers, concrete or masonry wing or retaining walls, and abutments bearings. Typical defects are excessive movement or scouring at abutments; foundations; cracking, spalling, honeycombing and staining of concrete abutments and walls; and damaged or contaminated bearings. Maintenance actions range from backfilling or underpinning, to repair of spalling, to cleaning, and to cleaning and replacement of bearings iii) Superstructure. The superstructure comprises soffits, deck slabs, concrete beams, steel girders and bracings, and steel trusses. All of these elements need to be assessed in terms of cracking, spalling, corrosion, or damage. Appropriate maintenance activities are repair of spalling, crack sealing, application of protective coating, repair of honeycombed concrete and strengthening or replacement of steel girder or truss elements iv) Roadway (on the bridge). The relevant elements include the asphalt or concrete surface, as well as guard-rails, parapets, drainage, kerbs and sidewalks. Defects on the road surface are the same as for pavements. While others are related to water ponding, cracking and spalling of concrete parapets, and corrosion and damage of guard-rails and metal parapets. Maintenance actions include those of pavements, as well as for concrete and metal elements. v) Roadway (on the bridge). The relevant elements include the asphalt or concrete surface, as well as guard-rails, parapets, drainage, kerbs and sidewalks. Defects on the road surface are the same as for pavements. While others are related to water ponding, cracking and spalling of concrete parapets, and corrosion and damage of guard-rails and metal parapets. Maintenance actions include those of pavements, as well as for concrete and metal elements. 3. MAINTENANCE CRITERIA Road authorities use different criteria to trigger highway maintenance actions (also called intervention levels) and to determine response times or urgency. The criteria depend on the traffic volumes, importance of the highway, available manpower and equipment, and budgets. Defects can be classified according to the required response: a) immediate response (i.e., w/in hours). These are normally the ones which cause major traffic disruptions and impede the safety of the highway. Examples are debris on the road, broken down vehicles, severely damaged or missing important road signs (e.g., stop signs), large potholes or punch-outs, rock or earth slides, wash-away and collapsed culverts. These maintenance actions would fall under emergency action. b) intermediate response (e.g., w/in a day or week). Defects such as all severely damaged or missing road signs, damaged guard-rails, ineffective fences, severe lane- shoulder drop-offs, sections of highway w/ very low skid-resistance in critical areas and missing bridge balustrades need to be repaired within a short time. These defects affect safety of the road and cannot be left unattended for a long period of time. The appropriate maintenance actions will fall under emergency or remedial maintenance. c) delayed response (i.e. w/in a period of months). Remedial maintenance actions such as grass cutting, cleaning of drainage structures, cleaning of roadside drains, sealing of severe cracks, cleaning or replacement of defective road signs, spot regraveling of unpaved roads, etc., can be executed according to a schedule based on availability of work and resources, as long as it is done at certain critical times d) preventive maintenance. Preventive maintenance actions are planned, programed and executed on an annual basis. 4. REMEDIAL MAINTENANCE ACTIVITIES a) Road sign repair and replacement. Road signs include all road signs, guide posts, and delineators. Road signs must be clearly visible at all times, including at night. Road signs can lose their effectiveness from deterioration due to environmental weathering or traffic accidents or vandalism. Missing or severely damaged road signs must be immediately replaced. Others should be replaced or repaired before they reach a critical level of effectiveness, e.g., cannot be seen at night-time under dimmed vehicle head lights. The life of a road sign is typically 7 to 8 years. Road signs are normally assessed annually by means of visual inspection or the measurement of the reflectivity. Repair and replacement can then be programed. Repair methods entail cleaning, repair of indentations, filling of holes, repainting and the replacement of adhesive coatings. Cleaning agents that can be used include kerosene or mineral spirits (for tar and bituminous products on the sign), a solution of sodium hypochlorite (for pollen and fungi), petrol, heptane or napthane (for certain types of graffiti). Repairs of road signs and delineators include maintenance of the posts which can either be timber, concrete or metal. b) Safety barrier repair and replacement. Safety barriers, guard-rails and New Jersey concrete barriers are placed in areas where extra safety precautions are required such as at high fills, at sharp curves and as direction dividers. Any ineffective or missing guard-rails must immediately be repaired, replaced or installed. This is normally the case after a traffic accident. Where accidents often occur, the road geometry should be checked and improved, if necessary. In general guard-rails should be inspected on a regular basis (monthly). The inspections for guard-rails include observation of the overall alignment, the condition of the reflectors, the poles and the spacer blocks, the overlapping, the height of the guard-rails and missing bolts. Guard-rails, which are effective but damaged, or deteriorated can be repaired and replaced as part of a maintenance program. c) Mending of fences. Fences are primarily provided to prevent animals and livestock from getting onto the road. Broken or missing fences should be repaired and replaced immediately. Fences can be damaged or lost as a result of ageing, accidents, theft or cutting to provide access to the road. The condition of fences is normally inspected on a monthly basis. d) Grass-cutting and pruning of vegetation. Grass-cutting and pruning of vegetation are required for reasons of visibility (at curves and intersections), drainage (shoulders and side-drains), plant invader control and fire hazard. The width of cutting grass can vary from 4 m from the shoulder to the full road reserve depending on the road function, layout and climatic conditions. The frequency of grass-cutting varies considerably due mainly to climatic conditions, but is normally done at regular intervals ranging from 1 month to 6 months. Alternatively, performance criteria are used which specifies a maximum height of grass in the road reserve. e) Removal of litter. Litter needs to be removed from the road reserve on a regular basis for aesthetic reasons and to prevent clogging up of the drainage system. The frequency of the removal of litter can range from 1 month in residential and rest areas, to 6 months in low volume traffic areas where drainage systems cannot easily be affected. f) Drainage. Drains are constructed to remove or keep water from the pavement surface and groundwater road formation. Subsurface drains are used to intercept water flowing towards the road formation while a variety of drain configurations are used to intercept or remove water from the road surface and shoulders. The latter are:  Side-drains or table-drains are channels parallel to the road with the function of collecting water that has fallen on carriageway, shoulder, or batters of a cutting.   Berms are shallow embankments or mounds usually placed transversely in the side- drain to deflect the flow of water.  Miter-drains (or turn-outs) provide a means for the water in the side-drain to be discharged away from the road. The spacing depends on the material and gradient. On erodible soils it can vary from 50 m spacings for gradients of ,1% to every 10 m for gradients of 0.10%.  Batter-drains (chutes) are drains constructed to channel water down either a fill or a cut batter  Catch water drains are positioned on the upslope side of a cut face parallel to the road to intercept sheet flow and to prevent erosion of the cut face. These drains become defective due to silting (or blockages) and erosion. The silting & blockages can be removed and the erosion be repaired. More often than not additional measures such as reshaping & realignment, reduction of ditch length & special erosion protection measures will require to reducing the amount of silting & erosion. Defects to the surface erosion system can easily be picked up by visual inspections. Regular inspections (often monthly) are recommended and remedial work should be done before rainy seasons. The effectiveness of subsurface drains is more difficult to assess and use has been made of standpipes, flow notches and piezometers to monitor the water-table levels and outflow. Most of the problems with the ineffective performance of subsurface drains can be related to the incorrect selection of materials, poor installation and inadequate outlets. Preventative and remedial maintenance may also warrant the installation of drainage during the repair of pavement defects such as potholes, and crocodile cracking. g) Patching (flexible pavement) Entails the removal and repair of edge breaks, potholes, showing severely cracked and deformed areas and surface failures. The patching can either be confined to the surface or involve replacement of a number of pavement layers. With all patching it is important to remove the failed area entirely and preferably cut 50 to 100 mm into the sound material as well. The side and bottom of the patch should be squared-off and all loose material removed. Shallow patches, up to 100 m can be done with cold and hot asphalts, while deeper patches can be filled with a high-quality gravel, crushed stone, cement or emulsion-stabilized material, or large aggregate asphalt before the bituminous surfacing is placed. h) Crack sealing (flexible pavements) Crack sealing comprises the cleaning of cracks, the application of a weed killer and primer (if necessary), and the application of a bituminous product as sealant. A bitumen emulsion is normally used to fill cracks less than 3 mm wide. Application is preferably by means of a lance fitted with a small nozzle, but the product can also be sprayed and spread with a broom or squeegee, in which case if must be covered with grit or clean sand. A primer should be used for cracks of more than 3 mm and applied to cover the sides of the top 20 mm of the crack. A bitumen emulsion modified with a polymer or hot poured PMB is the most effective for cracks more than 5 mm in width. Very large cracks can also be effectively filled with rubber crumb slurry or covered with a geo-textile strip of 100 to 150 mm. In such case a tack coat is sprayed and the geo-textile strip placed centrally over the crack and rolled. The geo- textile strip must be covered with clean sand or grit if not over-layed by a surface dressing or asphalt. Large and well-defined cracks can effectively be sealed. When cracks are fine and closely spaced it is often more cost-effective to apply a surface dressing or thin asphalt overlay directly i) Partial depth patching (rigid pavement) Used to correct severe spalling at joints comers, and cracks, or damage to the surface of the slab which does not extend more than 50 to 100 mm into the slab. The latter can be caused by mechanical damage, spillage of certain hazardous materials or burning of material on the slab during accidents. The patching entails removal of the spilled (or damaged) section to below the damage, cleaning the excavated area, the application of a bond breaker and the placement of fresh concrete. A normal or a quick setting concrete can be used depending on the time the patch can be kept closed to traffic. For normal concrete this time is about 3 days. j) Full depth patching (rigid pavement) Entails the replacement of sections of slabs to their full depth. This includes the replacement of reinforcement, dowels, tie bars and joint seals. Full depth patching is used to correct blow- ups, corner breaks, durability D-cracking, punch-outs, joint load transfer associated deterioration and spalling which extends to more than half the depth of the slab. Different patch layouts are used depending on the position of the defective area i.e., partial-lane (where the distress is confined to only a portion of the lane), full-lane (where the distress occurs across more than one half of a lane), and mid-slab (where the distress is more than 0.8 m from a joint or edge). In the first two cases joints and pavement edge define the outside edges of the patch in jointed pavements. Special care must be taken to reinstate dowel bars and joints. At CRC pavements the patch may extend to the outside pavement edge and longitudinal joint. k) Joint and crack sealing (rigid pavement) One of the major maintenance activities for rigid pavements — jointed pavement in particular. All joints and cracks, i.e., transverse as well as longitudinal, should be sealed to prevent water from infiltrating into the pavement effectively. A number of sealants can be used, e.g., preformed compression seals, hot-powered sealants and cold-applied sealants. Hot poured sealants are injected into the prepared sealant reservoir through nozzles shaped to penetrate into the joint and fill the reservoir from the bottom. The sealant should be applied when the ambient & pavement temperature is at least 10 8C and filled to 4 to 8 mm from the top of the pavement surface. Cold-applied sealants comprise two components combined in a special mixing head before applied. All existing sealants should be removed from the joints and cracks; the openings widened (or routed), if necessary, to obtain the required opening/closing conditions and reservoir, and openings be blown clear before the sealant is applied. l) Blading (or grading) An important maintenance activity for unsealed highways and intended to keep the road well drained and the riding quality in a satisfactory condition. The blading process consists bringing in material from the sides and cutting down corrugations and filling low spots. The effectiveness of grading is increased if a roller is utilized and the material is moist. m) Spot regraveling or patching of the wearing courses of unpaved roads is done where the material performs satisfactory but small potholes are present in isolated cases. A material with at least the same properties as that of a well-performing wearing course should be used. n) Mill and replacement. When the surfacing is in a poor condition the top 40 to 50mm can be removed & replaced w/ asphalt cement having same thickness as the removed portion. This is an effective technique where the surfacing has aged and is cracked, but no structural strengthening is required. This method is particularly cost-effective where only portions of the road, e.g., only the slow lane, needs attention or where clearance requirement limits the addition of layers of the road. An alternative to mill and replaces is HIPR also called remixing. The process entails heating, scarifying, rejuvenation & remixing of up to 50mm in depth of aged asphalt (FHWA, 2001). HIPR is an alternative to the milling and placement of a distressed asphalt layer. The major advantages are the potential savings in transport and processing costs, and the reutilization of existing materials. HIPR does not address any structural deficiencies since only the top 50 mm, at most, is treated and possible changes to the composition of the existing mix are limited. The structural equivalency should be the same as that of conventional asphalt. Pavements exhibiting base failures, irregular packing and poor drainage, are not suitable drainage candidates for HIPR. o) Slab jacking The process of pumping cement grout under pressure beneath the slab to slowly raise the slab until it reaches a smooth profile. Slabs can be lifted up to 9 mm. This procedure can be used to correct depressions and faulting but will not eliminate the causes of these defects. The areas to be treated can fairly easily be identified as opposed to the void to be undersealed. A general guideline for the position of the holes for slab jacking is that the hole should be placed in about some location as hydraulic jacks would be placed if it were possible to get them under the slabs. Holes (60 mm in diameter) should not be spaced less than 500 mm from a transverse joint or slab edge, and 1 to 2 m centre-to-centre. The slab is lifted by pumping a cement grout mixture (similar to that used for undersealing) into the holes at a pressure of about 1.5 MPa. p) Retexturing (grinding, grooving and cold milling). Diamond grinding, grooving and cold milling are three forms of retexturing and surface restoration. These maintenance activities address poor skid resistance, surface water (transverse) drainage, faulting, rutting from studded tires, map cracking, sealing and pop outs.  Diamond grinding. Patterns cut into the hardened concrete with closely spaced diamond blades. The spacing of the blades will depend on the hardness of the aggregate and normally varies between 2 and 3mm. The major purpose of grinding is to remove material, to provide a smooth surface and to improve skid resistance. Grinding is mainly used to remove faulting and ruts, improve riding quality and skid resistance. Grinding can be performed only at faulted joints but must be feathered back. A general guideline is 10mm for every 1mm of faulting removed. Grinding will  correct the levels, but not prevent further faulting. Grinding has been found not to be cost-effective if the faulting is more than 6mm. In such cases milling is more effective. This must be done by more extensive maintenance such as undersealing and slab replacement.  Grooving. Patterns cut into the hardened concrete with a center-to-center blade spacing of 20mm or greater. The major purpose of grooving is to reduce hydroplaning accidents i.e. to increase the texture depth and improve the drainage.  Cold milling. Use of carbide teeth cutting bits to chip off the surface of the pavement primarily to remove material and provide a textured pattern. This is an effective may of removing surface defects such as map cracking and scaling, and to produce of roughened clean surface for bonding a concrete overlay. q) Recementation of cracks Used to restore the structural integrity of cracked slabs. Recementation is accomplished by injecting a liquid epoxy under pressure into the cracks. The pavement condition will be changed since the cracks are removed, but pumping and faulting rates may not be greatly changed. The ingress of water into the cracks should be greatly reduced. The performance of recemented cracks has been very poor to good. r) Bridge and culvert repairs. Preventative maintenance of bridges and culverts primarily comprises cleaning and clearing of the water pathways, controlling of scour & erosion & repair of minor structural damage.  The waterways should be cleared of windblown debris, water-borne soils, gravel and vegetation. The area in the vicinity of the structure should also be kept clear of undergrowth and rubbish. Regular usual inspection programs should be used to identify defects. It is important to get the waterways cleared before rainy seasons and after flooding. In some cases, silting is caused by design deficiencies such as incorrect waterway openings, and incorrect culvert invert levels and longitudinal slopes. Some of these can be alleviated by the construction of protective structures upstream, but will in most cases require major reconstruction work.  Control of scour and erosion. This type of damage consists of the loss of materials from both ends of the culvert, or the erosion of slopes and bedding at bridges. The erosion can affect the stability of the structure. The damage can be prepared by backfilling of the eroded areas and the installation of gabion protection, rock beds, and concrete protection structures.  Damage can comprise degradation of parapets, guard-rails, kerbs, sidewalks or roadway surface. If any of these defects are significant enough to endanger the structure or the safety of the traffic immediate action must be taken. Normal maintenance actions include tightening of guard-rails, replacement of joint filler, replacement of concrete nose and seals, crack sealing & repainting.  Minor damage to the sub- and superstructure. These include concrete deterioration, cracking, and scouring or displacement of foundations. Repair of these defects are often of a very specialized nature requiring expertise, special materials & equipment. 5. PREVENTIVE MAINTENANCE ACTIVITIES Preventive maintenance actions have as objectives the restoration of the condition of the highway and reducing the rate of deterioration. The actions are identified and scheduled through some form of management system. a) Rejuvenation. An application of a diluted emulsion or commercial product with the aim of replenishing the bituminous binder. The rejuvenation makes the binder more elastic and pliable, and retards the aging (hardening) process. Small (hairline) cracks are normally also sealed in the process. Single and double surface dressings greatly benefit from the application of a rejuvenator every 3 to 4 years. The life of slurries can also be increased, but care must be taken that the rejuvenator penetrates sufficiently. A typical diluted emulsion application is 0.8 l/m2 of an emulsion with 30% bitumen (i.e., a net bitumen application of 0.24 l/m2 ). b) Resurfacing can be one of the following: i) Single surface dressing (single seal) where a single form of binder (the tack coat) is followed by a single layer of chippings. The size of the chippings (or aggregate) can range from 6 to 20 mm. The larger the size of aggregate the larger the application of bituminous binder that can be accommodated. The chipping must have a certain hardness, polishing value, and flakiness. ii) Double surface dressing (double seal) has two layers of chippings and two applications of binder, the second (the penetration coat) placed between the layers of chippings. The size of the second layer of chippings is normally half or less the size of the first layer of chippings, and can be sand used to lock in the first layer of chippings. A slurry can also be used to lockin the first layer of chippings (this is also called a Cape seal). The use of sand or crusher dust to lock the larger chippings is very effective at intersections where the turning movement of vehicles can easily dislodge single chippings. Double surface dressings produce lower texture depths than single surface dressings. Typical double surface dressings comprise 20 and 10 or 6mm chippings or 14 and 6mm chippings. iii) Inverted double surface dressing comprises the application of a single dressing of small chippings followed by an application of larger chippings. This surface dressing is used on a nonuniform surface to produce a uniform surfacing before the larger chippings are applied. iv) Slurry seal, which is a mixture of crusher sand, bitumen emulsion, water and often cement or lime combined to form a fluid mixture. The mixture can be spread by machine or by hand. A slurry seal can be applied as a fine slurry (1 to 3 mm in thickness), a medium slurry (4 to 6 mm in thickness), or a coarse slurry (7 to 10 mm in thickness). Quick-set polymer bitumen can be used instead of the emulsion to increase the setting time. Thin slurry is often applied on a non-uniform surface before a single surface dressing, while thick slurry, especially when modified bitumen is used, is effective in filling ruts. v) Otta seal is similar to a single chip seal except that graded chippings (instead of single size) are placed on a relatively thick film of comparatively soft binder which on rolling & trafficking, makes its way upwards through the aggregate (Botswana, 1999). vi) Surface enrichment is the application of a bituminous product such as a diluted emulsion or rejuvenator to add volatiles to an aged bituminous binder. This is a very cost-effective maintenance treatment of brittle surfacing. vii) Thin (,50 mm) asphalt concrete wearing courses are used extensively and successfully as preventative maintenance action. viii) Ultra-thin (,25 mm) asphalt concrete wearing courses have also successfully been used as preventative maintenance action. Some of the major advantages of an ultra-thin surfacing are that it can be opened to traffic soon after construction, is normally very rut resistant and can easily be tied-in to the surrounding surfacing. ix) Porous asphalt is an open graded (.20% voids) mixture, which is very effective in draining rainwater from the surface of the pavement, has a good skid resistance and reduces road noise. It has been used successfully as overlay on CRCP and on roads where water drainage and road noise are issues. c) Undersealing. The loss of support from underneath concrete slabs is a major factor in the deterioration of the pavement. The support must be reestablished to reduce the rate of further deterioration and before an overlay can be applied. Undersealing is defined as the insertion of a cement grout mixture or bitumen under pressure beneath the slab through holes in the slab. Only the voids are filled and the support reinstated. Undersealing is a very specialized operation and care must be taken not to lift the slabs and create additional voids. d) Load transfer improvement. Perfect load transfer can reduce stresses and deflections to half that of a pavement with no load transfer. All faulty joints and cracks with load transfer of less than 50 to 60%, when measured in the early morning, should be provided with load transfer devices (NCHRP, 1983). A number of different load transfer devices are available, e.g., Vee, Double Vee, Figure Eight, Georgia split pipe device, and dowels. e) Pressure relief joints relieve the stresses in the slab due to restriction of the slab movement. A relief joint usually consists of replacing a piece of the slab with a strip of asphalt material. Neither the pavement serviceability (such as the Pavement Serviceability Index, PSI) nor the rate of pumping, faulting or cracking will be changed significantly. f) Provision edge support. Slab deflections can be reduced by providing edge support. Edge support can be in the form of a tied PCC-shoulder or the installation of an edge beam. Tied PCC-shoulders with 100% load transfer reduce the deflection and stresses of the slab corners by 50%. A 600 mm-wide edge beam can also reduce slab deflections by at least 50%. Retrofit (edge, longitudinal or trench) drains have been used to reduce pumping and faulting. Retrofit drains increase the drainage of water from the pavement and can improve the shoulder stability. Drains extended the life of the pavement from 20–25 yrs to 30–35 yrs. The rate of faulting after the installation of the drains was found to be about an 1/8 of the rate before installation. g) Regraveling. Material from the wearing course on a gravel road gets removed by the traffic, rain and wind actions and needs to be replenished. Action, i.e., regraveling, is normally taken when the wearing course is 25 mm thick. h) Road markings have to be reapplied on a regular basis. The frequency depends on the environment (faster deterioration in region with high percentage of sunshine days); traffic (faster under high traffic volumes), type of surfacing (faster deterioration on coarser surfaces), and the type of paint used. i) Repair of shoulders. Material on unpaved shoulders, like wearing courses, needs to be graded and replenished with time. The types of appropriate maintenance action are smoothing and reshaping by means of a grinder or by hand; the addition of new material to replace material lost from the action of traffic, water erosion and grading operations; and watering and rolling. 6. DUST SUPPRESANTS A number of products have been developed to eliminate or reduce the loss of fine material, and thereby reduce the development of dust (AUSTROADS, 1991; Foley et al., 1998). The suppressants can be classified into one of four types (also see Table 20.21), i.e.: a) Chlorides or salts (calcium, magnesium or sodium chloride). These products are most effective for materials with fines (i.e., material ,0.075 mm) between 10 and 20%, moderate or low PI and a moderate or higher CBR. The material leaches into the pavement, but can only leach out. The surface can become slippery during wet weather but the products can lose effectiveness during long dry periods. b) Organic, non-bituminous (calcium, lignosulphonate) products are most effective for materials with high percentage of fines (i.e., 10 to 30%) in a densely graded material. The construction process is critical. The product remains effective during long dry periods with low humidity. c) Petroleum-based products (bitumen emulsion, waste oils), typically performs the best with materials containing low percentages of fines (,10%). Maintenance is more cumbersome than with the previous two types where surface defects can be corrected by blading. With petroleum-based products some type of patching is normally required to rectify defects. d) Electro-chemical stabilizers (sulphonated petroleum, ionic products, and enzymes). These stabilizers can be effective in all climatic conditions and work best with a material with PIs in excess of 8 and more than 15% fines. A curing period is required. None of these dust suppressants produces maintenance-free surfaces and allowance must be made for reapplications, regular bladings and patching. Other measures that have been used successfully to control dust are:  Good construction and maintenance practices such as the provision of a crowned cross-section, well-graded materials, and adequate drainage.  Mechanical stabilization where natural materials are used to enhance the properties of the material to meet the requirements of a high-quality wearing surface. (i.e., proper grading and plasticity content.) General guidelines are:  for roads carrying less than 50 vehicles/day (vpd) the use of dust suppressant will probably not be justifiable. Mechanical stabilization will be an option.  for roads carrying between 50 and 250 vpd dust suppressants could be viable.  for roads carrying more than 250 vpd sealing of the road will probably be more cost-effective than regular spending on maintenance even with a dust suppressant. References/Additional Resources/Readings (list down all references/additional resources/readings used; you may also provide links)  This includes all third-party materials or sources in developing the material. It shall follow the American Psychological Association (APA) Manual of Style 6th or 7th Edition. Hwa, T. F. (2006). The Handbook of Highway Engineering. Taylor & Francis Group. Mannering Fred, Washburn Scott, Kilaresky Walter. (2004). Principles of Highway Engineering & Traffic Analysis. John Wiley & Sons, Inc. Assignment Direction: Watch the given video link and then answer the question(s) below. Submit your file in PDF format. Use Font Style: Times New Roman, Font Size: 12: 1. Enumerate the types of cracks and defect in asphalt pavement, refer to: https://www.youtube.com/watch?v=qIUKypWI2FE 2. Enumerate and explain each pavement failures, refer to: https://www.youtube.com/watch?v=OlcSiq25XdE Learner’s Feedback Form Name of Student: ___________________________________________________ Program : ___________________________________________________ Year Level : ____________________ Section: _________ Faculty : ___________________________________________________ Schedule : ___________________________________________________ Learning Module : Number: _________ Title : ______________________ How do you feel about the topic or concept presented? □ I completely get it. □ I’m struggling. □ I’ve almost got it. □ I’m lost. In what particular portion of this learning packet, you feel that you are struggling or lost? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Did you raise your concern to you instructor? □ Yes □ No If Yes, what did he/she do to help you? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ If No, state your reason? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ To further improve this learning packet, what part do you think should be enhanced? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ How do you want it to be enhanced? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ NOTE: This is an essential part of course module. This must be submitted to the subject teacher (within the 1st week of the class).