Highway Maintenance, Repair, and Rehabilitation

Maintenance of bituminous surface

Highway maintenance is the work done to keep a road, its pavement, shoulders, drainage, structures and furniture in a safe and serviceable condition and to preserve the investment, without changing the original design standard.

Maintenance of bituminous surface (IRC:82 and Nepal DoR maintenance manuals) is done by the defect:

Drainage (cleaning side drains and culverts) and shoulder maintenance are essential, because water is the main cause of failure.

Typical failures of rigid pavement

Typical types of failure of a cement concrete pavement:

 Faulting at a joint        Corner break
        ______              +-------------+
 ______|  step              |             |
     joint                  |             |
                            |   crack ->  /
                            +-----------/-+

Remedies include full-depth repair, slab replacement, dowel retrofit, grinding of faults, crack and joint resealing, undersealing (grout) to fill voids, and improving drainage.

Highway maintenance

Highway maintenance is the work done to keep a road, its pavement, shoulders, drainage, structures and furniture in a safe and serviceable condition and to preserve the investment, without changing the original design standard.

Classification (Nepal DoR practice and IRC:82):

1. Routine maintenance - small, regular, yearly works such as patching potholes, cleaning drains and culverts, clearing slips, cutting grass, repairing shoulders and signs.
2. Recurrent maintenance - works repeated at intervals within a year or two, such as resealing cracks and shoulder re-gravelling, drain repair.
3. Periodic maintenance - works at intervals of several years (3 to 8) like resealing, regravelling, surface dressing and thin overlay to restore the surface.
4. Urgent (emergency) maintenance - immediate works to reopen the road after landslides, floods or accidents.

General causes of pavement failure

1. Traffic factors - overloading, more repetitions than designed, high tyre pressure, channelised traffic.
2. Poor drainage - the main cause. Water in the subgrade and base reduces strength, causes pumping, ravelling, potholes and edge failure; blocked side drains and culverts, high water table.
3. Weak subgrade - low CBR, expansive or soft soil, poor compaction, inadequate sub-base.
4. Design defects - thin pavement, wrong assumed traffic or CBR, no allowance for climate, poor geometric and drainage design.
5. Poor materials and workmanship - inferior aggregate or binder, wrong mix proportions, segregation, low compaction, poor joints and bond between layers, low temperature during laying.
6. Climate and environment - temperature extremes (bleeding, cracking), rainfall and floods, freeze-thaw in hills, landslides.
7. Ageing - oxidation and hardening of bitumen with time.
8. Lack of timely maintenance - small cracks and potholes grow rapidly into major failures when not repaired.
9. Utility cuts and other external causes - trenches, spillage of oil.

Typical failures of flexible pavement

A flexible pavement fails when it can no longer give a safe, smooth ride or carry traffic. Common failures:

 Alligator cracking      Rutting (cross-section)
 +--+--+--+--+
 |x |x |x |x |   ----.         .----
 +--+--+--+--+        '-------'
 small interlocked    depressed wheel path
 cracks

Causes of failure of cement concrete pavement

Typical types of failure of a cement concrete pavement:

 Faulting at a joint        Corner break
        ______              +-------------+
 ______|  step              |             |
     joint                  |             |
                            |   crack ->  /
                            +-----------/-+

Remedies include full-depth repair, slab replacement, dowel retrofit, grinding of faults, crack and joint resealing, undersealing (grout) to fill voids, and improving drainage.

General causes

• Design: inadequate slab thickness, joint spacing too long, poor load transfer, insufficient sub-base.
• Construction: poor compaction, honeycombing, late joint cutting, wrong dowel alignment, inadequate curing, poor quality concrete.
• Traffic: overloading, repetitions beyond design.
• Drainage and subgrade: water entering through joints causes pumping; soft subgrade settles.
• Environment: temperature and moisture cycles (warping, blow-ups).

Method

IRC:81-1997 (Benkelman beam overlay design), standard test load 4085 kg on dual wheel, tyre pressure 5.6 kg/cm2.

Step 1 - Rebound deflection at each point

The dial readings are in 0.01 mm. Rebound deflection $=2\,(d_0-d_f)\times0.01$ mm (the factor 2 is the lever ratio of the beam). The intermediate readings are used only to check that the lag is small, so the final readings are used.

Step 2 - Statistics

Mean $\bar D=1.016$ mm; standard deviation $\sigma=0.258$ mm.

Step 3 - Corrections

• Temperature: test at 30 C, standard 35 C, so add 0.01 mm per degree: $\bar D_{35}=1.016+0.05=1.066$ mm.
• Seasonal/moisture factor 1.3: $\bar D'=1.066\times1.3=1.386$ mm; $\sigma'=0.258\times1.3=0.335$ mm.
• Characteristic deflection (national/state highway): $D_c=\bar D'+2\sigma'=1.386+2\times0.335=2.06$ mm.

Step 4 - Design traffic

Assume a two-lane road ($D=0.5$), VDF = 3.5 (IRC:37 indicative value for 150-1500 CVPD), design life of overlay $n=10$ years, $r=7.5\%$, present traffic $A=750$ CVPD:

$$N_s=365\times\frac{(1.075)^{10}-1}{0.075}\times750\times0.5\times3.5=6.78\times10^6\ \text{standard axles}$$

Step 5 - Overlay thickness

Allowable deflection for about 6.8 msa is taken as $D_a\approx1.1$ mm (IRC:81 chart). The overlay thickness of bituminous macadam (BM):

$$h=550\log_{10}\frac{D_c}{D_a}=550\log_{10}\frac{2.06}{1.1}=149\ \text{mm}$$

The IRC:81 chart is the exact method; the expression above is its usual closed-form approximation.

Answer: characteristic deflection $=2.06$ mm; provide about 150 mm BM overlay (equivalent to roughly 100 mm of bituminous concrete/DBM, since 1 mm BC is equivalent to 1.5 mm BM), e.g. about 70 mm DBM plus 30 mm BC. If the paper provides the chart, read the thickness from it for $D_c$ and msa.

Failures of flexible pavement: causes and remedies

A flexible pavement fails when it can no longer give a safe, smooth ride or carry traffic. Common failures:

 Alligator cracking      Rutting (cross-section)
 +--+--+--+--+
 |x |x |x |x |   ----.         .----
 +--+--+--+--+        '-------'
 small interlocked    depressed wheel path
 cracks

The Benkelman beam deflection method (IRC:81-1997) designs a bituminous overlay from the rebound deflection of the existing pavement under a standard load.

1. Select the section and test points: divide the road into homogeneous sections; test at 50-100 m intervals in the outer wheel path (about 0.9 m from the edge) in alternate lanes; at least 10 points per section.
2. Standard test vehicle: truck with rear axle load of 8170 kg (dual wheels, 4085 kg per wheel pair) and tyre pressure 5.6 kg/cm2.
3. Measurement: place the beam probe between the dual wheels at the test point and note the initial dial reading $d_0$; move the truck slowly forward 2.7 m (intermediate reading $d_i$) and then 9 m (final reading $d_f$).
4. Rebound deflection: $D=2\,(d_0-d_f)\times$ least count, where factor 2 is the beam lever ratio; correct for lag when $d_i-d_f$ is large.
5. Corrections: for pavement temperature (standard 35 C, correction of 0.01 mm per degree C below 35 C for surfacing more than 40 mm) and for seasonal variation in subgrade moisture (factor 1.0-1.3 for dry season tests).
6. Characteristic deflection: $D_c=\bar D+2\sigma$ for national and state highways ($\bar D+1.65\sigma$ for other roads), where $\bar D$ is mean and $\sigma$ standard deviation.
7. Design traffic in msa over the overlay life (usually 10 years): from present CVPD, growth rate and VDF.
8. Overlay thickness: read from the IRC:81 chart of characteristic deflection against design msa (thickness of bituminous macadam in mm) - or computed by $h=550\log_{10}(D_c/D_a)$ where $D_a$ is the allowable deflection for the design traffic.
9. Convert to the actual overlay mix (1 mm of BC = 1.5 mm of BM) and add a minimum 40-50 mm wearing course; add correction for cracked areas and levelling course.

Maintenance, rehabilitation and reconstruction

Typical failures of rigid pavement

Typical types of failure of a cement concrete pavement:

 Faulting at a joint        Corner break
        ______              +-------------+
 ______|  step              |             |
     joint                  |             |
                            |   crack ->  /
                            +-----------/-+

Remedies include full-depth repair, slab replacement, dowel retrofit, grinding of faults, crack and joint resealing, undersealing (grout) to fill voids, and improving drainage.

Highway maintenance vs highway rehabilitation

Major causes of flexible pavement failure

1. Traffic factors - overloading, more repetitions than designed, high tyre pressure, channelised traffic.
2. Poor drainage - the main cause. Water in the subgrade and base reduces strength, causes pumping, ravelling, potholes and edge failure; blocked side drains and culverts, high water table.
3. Weak subgrade - low CBR, expansive or soft soil, poor compaction, inadequate sub-base.
4. Design defects - thin pavement, wrong assumed traffic or CBR, no allowance for climate, poor geometric and drainage design.
5. Poor materials and workmanship - inferior aggregate or binder, wrong mix proportions, segregation, low compaction, poor joints and bond between layers, low temperature during laying.
6. Climate and environment - temperature extremes (bleeding, cracking), rainfall and floods, freeze-thaw in hills, landslides.
7. Ageing - oxidation and hardening of bitumen with time.
8. Lack of timely maintenance - small cracks and potholes grow rapidly into major failures when not repaired.
9. Utility cuts and other external causes - trenches, spillage of oil.

These appear as cracking, rutting, potholes, ravelling, bleeding, shoving and edge failure, as described in the table of flexible pavement failures.

Common failures of flexible pavement

A flexible pavement fails when it can no longer give a safe, smooth ride or carry traffic. Common failures:

Deflection approach for overlay design

The deflection approach estimates the overlay needed to bring the structural capacity of an existing pavement to that needed for future traffic, based on the elastic rebound deflection measured under a standard wheel load (IRC:81, Benkelman beam; or FWD).

The Benkelman beam deflection method (IRC:81-1997) designs a bituminous overlay from the rebound deflection of the existing pavement under a standard load.

1. Select the section and test points: divide the road into homogeneous sections; test at 50-100 m intervals in the outer wheel path (about 0.9 m from the edge) in alternate lanes; at least 10 points per section.
2. Standard test vehicle: truck with rear axle load of 8170 kg (dual wheels, 4085 kg per wheel pair) and tyre pressure 5.6 kg/cm2.
3. Measurement: place the beam probe between the dual wheels at the test point and note the initial dial reading $d_0$; move the truck slowly forward 2.7 m (intermediate reading $d_i$) and then 9 m (final reading $d_f$).
4. Rebound deflection: $D=2\,(d_0-d_f)\times$ least count, where factor 2 is the beam lever ratio; correct for lag when $d_i-d_f$ is large.
5. Corrections: for pavement temperature (standard 35 C, correction of 0.01 mm per degree C below 35 C for surfacing more than 40 mm) and for seasonal variation in subgrade moisture (factor 1.0-1.3 for dry season tests).
6. Characteristic deflection: $D_c=\bar D+2\sigma$ for national and state highways ($\bar D+1.65\sigma$ for other roads), where $\bar D$ is mean and $\sigma$ standard deviation.
7. Design traffic in msa over the overlay life (usually 10 years): from present CVPD, growth rate and VDF.
8. Overlay thickness: read from the IRC:81 chart of characteristic deflection against design msa (thickness of bituminous macadam in mm) - or computed by $h=550\log_{10}(D_c/D_a)$ where $D_a$ is the allowable deflection for the design traffic.
9. Convert to the actual overlay mix (1 mm of BC = 1.5 mm of BM) and add a minimum 40-50 mm wearing course; add correction for cracked areas and levelling course.

Pavement maintenance is all work that keeps the pavement in good condition during its life. Types, with examples:

1. Routine maintenance - small works done every year: patching potholes, crack sealing, cleaning side drains and culverts, vegetation clearing, shoulder repair.
2. Recurrent maintenance - works repeated within a year or so: regrading of gravel roads, resealing of cracks, maintenance of signs and markings.
3. Periodic maintenance - larger works at intervals of 3 to 8 years: resealing, surface dressing, slurry seal, thin overlay, regravelling of gravel roads (as per Nepal DoR classification).
4. Urgent (emergency) maintenance - immediate works to restore access after landslide, flood, or accident: removal of slips, temporary repair of washed-out section.
5. Preventive maintenance - works done before major damage, like fog seal or crack seal on good pavements.
6. Corrective maintenance - repairs after a defect has occurred, like pothole repair.

Beyond maintenance, rehabilitation (overlay) and reconstruction are major works.

Pavement evaluation

Pavement evaluation is the systematic collection and analysis of data on the present condition of a pavement (surface and structure) so that its need for maintenance, strengthening or reconstruction can be decided and priorities set.

Functional evaluation (ride quality and safety)

• Roughness - measured by bump integrator, MERLIN, Roadroid or profilometer (International Roughness Index, IRI in m/km); Nepal DoR uses roughness in its Road Maintenance Management System.
• Skid resistance - pendulum tester (British Pendulum Number), skid trailer.
• Surface distress - visual survey of cracks, potholes, rutting, ravelling, bleeding, patching (IRC:SP:16 and Nepal DoR condition survey).

Structural evaluation (load capacity)

• Deflection tests - Benkelman beam (IRC:81), Falling Weight Deflectometer (FWD), Lacroix deflectograph.
• Destructive tests - test pits and cores to find layer thickness, density and subgrade CBR; Dynamic Cone Penetrometer (DCP) for in-situ strength.
• Non-destructive tests - Ground Penetrating Radar (layer thickness), plate load test, and back-calculation of layer moduli.

Use: the results give a condition index, which is combined with traffic to select the treatment: routine maintenance, periodic maintenance, overlay (strengthening) or reconstruction.

Types of failure and causes in flexible pavement

A flexible pavement fails when it can no longer give a safe, smooth ride or carry traffic. Common failures:

Repair vs rehabilitation of highways

Types of failure of rigid pavement

Typical types of failure of a cement concrete pavement:

 Faulting at a joint        Corner break
        ______              +-------------+
 ______|  step              |             |
     joint                  |             |
                            |   crack ->  /
                            +-----------/-+

Remedies include full-depth repair, slab replacement, dowel retrofit, grinding of faults, crack and joint resealing, undersealing (grout) to fill voids, and improving drainage.

Maintenance, rehabilitation and reconstruction

Methods of pavement evaluation

Pavement evaluation is the systematic collection and analysis of data on the present condition of a pavement (surface and structure) so that its need for maintenance, strengthening or reconstruction can be decided and priorities set.

Functional evaluation (ride quality and safety)

• Roughness - measured by bump integrator, MERLIN, Roadroid or profilometer (International Roughness Index, IRI in m/km); Nepal DoR uses roughness in its Road Maintenance Management System.
• Skid resistance - pendulum tester (British Pendulum Number), skid trailer.
• Surface distress - visual survey of cracks, potholes, rutting, ravelling, bleeding, patching (IRC:SP:16 and Nepal DoR condition survey).

Structural evaluation (load capacity)

• Deflection tests - Benkelman beam (IRC:81), Falling Weight Deflectometer (FWD), Lacroix deflectograph.
• Destructive tests - test pits and cores to find layer thickness, density and subgrade CBR; Dynamic Cone Penetrometer (DCP) for in-situ strength.
• Non-destructive tests - Ground Penetrating Radar (layer thickness), plate load test, and back-calculation of layer moduli.

Use: the results give a condition index, which is combined with traffic to select the treatment: routine maintenance, periodic maintenance, overlay (strengthening) or reconstruction.

Road maintenance

Highway maintenance is the work done to keep a road, its pavement, shoulders, drainage, structures and furniture in a safe and serviceable condition and to preserve the investment, without changing the original design standard.

Classification (Nepal DoR practice and IRC:82):

1. Routine maintenance - small, regular, yearly works such as patching potholes, cleaning drains and culverts, clearing slips, cutting grass, repairing shoulders and signs.
2. Recurrent maintenance - works repeated at intervals within a year or two, such as resealing cracks and shoulder re-gravelling, drain repair.
3. Periodic maintenance - works at intervals of several years (3 to 8) like resealing, regravelling, surface dressing and thin overlay to restore the surface.
4. Urgent (emergency) maintenance - immediate works to reopen the road after landslides, floods or accidents.

Measures for gully control

Gully erosion is the cutting of deep channels in road slopes, embankments, shoulders and the land by concentrated runoff. It is serious on hill roads in Nepal where steep slopes and heavy monsoon rain produce quick surface flow.

Measures for gully control

1. Diversion - catch-water drains above cut slopes, side drains and cross drains/culverts at close spacing to stop flow collecting; discharge on stable ground or into natural streams.
2. Lined drains and chutes - stone masonry, concrete or gabion lining for steep drains; stepped channels or drop structures to reduce velocity.
3. Check dams - small stone masonry, gabion or log dams across the gully at intervals to trap sediment and reduce slope and velocity.
4. Outlet protection - aprons and energy dissipators at culvert outlets and drain ends.
5. Bioengineering - grass (vetiver, bamboo, broom grass), shrubs and trees planted on slopes; brush layering and fascines (live check dams).
6. Slope treatment - reshape the gully, fill and compact, terrace slopes, mulching and geotextile or jute mats to hold topsoil until vegetation grows.
7. Retaining and breast walls at the toe of unstable slopes.
8. Maintenance - keep drains clean and repair erosion early.

Pavement evaluation is the systematic collection and analysis of data on the present condition of a pavement (surface and structure) so that its need for maintenance, strengthening or reconstruction can be decided and priorities set.

Functional evaluation (ride quality and safety)

• Roughness - measured by bump integrator, MERLIN, Roadroid or profilometer (International Roughness Index, IRI in m/km); Nepal DoR uses roughness in its Road Maintenance Management System.
• Skid resistance - pendulum tester (British Pendulum Number), skid trailer.
• Surface distress - visual survey of cracks, potholes, rutting, ravelling, bleeding, patching (IRC:SP:16 and Nepal DoR condition survey).

Structural evaluation (load capacity)

• Deflection tests - Benkelman beam (IRC:81), Falling Weight Deflectometer (FWD), Lacroix deflectograph.
• Destructive tests - test pits and cores to find layer thickness, density and subgrade CBR; Dynamic Cone Penetrometer (DCP) for in-situ strength.
• Non-destructive tests - Ground Penetrating Radar (layer thickness), plate load test, and back-calculation of layer moduli.

Use: the results give a condition index, which is combined with traffic to select the treatment: routine maintenance, periodic maintenance, overlay (strengthening) or reconstruction.

Importance of road maintenance

Importance of road maintenance:

1. Protects the investment - roads are costly assets; timely maintenance prevents rapid deterioration. A small amount spent early saves a large amount of reconstruction cost later.
2. Lower vehicle operating cost - smooth roads reduce fuel, tyre, repair and travel time costs.
3. Safety - good surface, drainage, markings and signs reduce accidents.
4. Continuous access - keeps the road open all year (especially in the monsoon in Nepal) for people, goods and emergency services; supports economic and social development.
5. Longer life - the pavement serves for its design life.
6. Environmental and comfort benefits - less dust and noise, better drainage reduces erosion and floods.

Maintenance of bituminous pavement

Maintenance of bituminous surface (IRC:82 and Nepal DoR maintenance manuals) is done by the defect:

Drainage (cleaning side drains and culverts) and shoulder maintenance are essential, because water is the main cause of failure.

Methods of structural evaluation of pavement

1. Deflection measurement - Benkelman beam (IRC:81), Falling Weight Deflectometer (FWD), deflectograph; the deflection under a standard load shows the strength.
2. Destructive tests - test pits and cores to find layer thickness and material properties, and CBR of subgrade.
3. Non-destructive tests - Dynamic Cone Penetrometer (DCP), plate load test, Ground Penetrating Radar, back-calculation of layer moduli from FWD data.
4. Pavement condition survey - cracking, rutting and patching (a condition index) to support the structural findings.

Overlay thickness from deflection (IRC:81)

Mean deflection $\bar D=1.5$ mm, standard deviation $\sigma=0.2$ mm, allowable deflection $D_a=1.0$ mm (all assumed to be corrected readings).

Characteristic deflection (national/state highway):

$$D_c=\bar D+2\sigma=1.5+2\times0.2=1.90\ \text{mm}$$

Since $D_c>D_a$ the pavement needs strengthening. Overlay thickness of bituminous macadam:

$$h=550\log_{10}\frac{D_c}{D_a}=550\log_{10}\frac{1.90}{1.0}=153\ \text{mm}$$

Answer: about 155 mm of bituminous macadam overlay (about 103 mm of bituminous concrete equivalent, since 1 mm BC = 1.5 mm BM). If the chart of IRC:81 is available, the thickness for $D_c=1.9$ mm is read from it for the design msa.

Maintenance of a bituminous road is done in these stages:

1. Routine maintenance - patching potholes (cut a square, clean, tack coat, fill with premix, compact), sealing cracks with bitumen emulsion, cleaning drains and culverts, repairing shoulders and edges.
2. Periodic maintenance - at intervals of 3 to 8 years: surface dressing, slurry seal, fog seal, premix carpet or thin bituminous overlay to renew the wearing surface.
3. Special treatment of defects - bleeding is treated by spreading hot coarse sand or chips; ravelling by seal coat; depression or rutting by levelling course; severe failure by removing and reconstructing the layers.
4. Drainage maintenance - keep side drains, cross drains and shoulders in good condition, because water is the main cause of damage (IRC:82 and Nepal DoR maintenance guidelines).