---
title: "Maintenance vs rehabilitation; flexible failure causes"
subject: "Transportation Engineering II"
chapter: 4
key: "semester_7/transportation_engineering_ii:maintenance-vs-rehabilitation-flexible-failure-causes"
source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/maintenance-vs-rehabilitation-flexible-failure-causes
site: BCT Engineering
---

# Maintenance vs rehabilitation; flexible failure causes

Transportation Engineering II · Chapter 4: Highway Maintenance, Repair, and Rehabilitation

- Asked in: 2080 Baisakh, 8 marks
- Video: [Failures in Flexible Pavement - Transportation Engineering - I](https://www.youtube.com/watch?v=xAFZohikrUo) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/maintenance-vs-rehabilitation-flexible-failure-causes
- Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-4

## Question

Differentiate highway maintenance from highway rehabilitation. Discuss about the major causes of flexible pavement failure.

## Short answer

Maintenance preserves existing condition (patching, crack sealing); rehabilitation restores structural strength and extends life (structural overlay, recycling). Major causes of flexible failure: traffic overloading, poor drainage (water weakens subgrade/base), weak subgrade, design defects, poor materials/workmanship, climate, aging, lack of timely maintenance, and utility cuts.

## Answer

#### Highway maintenance vs highway rehabilitation

| Basis | Maintenance | Rehabilitation |
|---|---|---|
| Purpose | Keep the road in service and preserve its condition | Restore or raise structural strength and extend life |
| Scale | Small, regular works | Major works over a longer length |
| Examples | Pothole patching, crack sealing, drain cleaning, resealing | Structural overlay, recycling, reconstruction of failed lengths, widening |
| Frequency | Annual, recurrent or every few years | Once, after 8-15 years or when the condition is poor |
| Cost | Low, funded from the maintenance budget | High, funded from the development/capital budget |
| Decision basis | Condition survey, inspection | Structural evaluation (deflection, roughness, traffic) |

#### Major causes of flexible pavement failure
1. **Traffic factors** - overloading, more load repetitions than designed for, high tyre pressure, channelised traffic.
2. **Poor drainage** - the main cause. Water in the subgrade and base reduces strength and causes pumping, ravelling, potholes and edge failure; typical sources are blocked side drains and culverts and a high water table.
3. **Weak subgrade** - low CBR, expansive or soft soil, poor compaction, inadequate sub-base.
4. **Design defects** - thin pavement, wrongly 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, laying at low temperature.
6. **Climate and environment** - temperature extremes (bleeding, cracking), rainfall and floods, freeze-thaw in the 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 they are not repaired.
9. **Utility cuts and other external causes** - trenches, oil spillage.

These causes show up as cracking, rutting, potholes, ravelling, bleeding, shoving and edge failure.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Maintenance differs from rehabilitation in that maintenance is:
   A. High cost from the capital budget
   B. Low cost, small regular works from the maintenance budget
   C. Done once at 8-15 years
   D. Based on structural deflection evaluation
   Answer: B. Maintenance is small, regular and low cost; rehabilitation is major, high cost and capital funded. (Key point: Funding difference)

2. Rehabilitation decisions are based mainly on:
   A. Condition inspection only
   B. Structural evaluation (deflection, roughness, traffic)
   C. Colour of surface
   D. Number of signs
   Answer: B. Rehabilitation needs structural evaluation, while maintenance relies on condition survey and inspection. (Key point: Decision basis)

3. Why is poor drainage called the main cause of flexible pavement failure?
   A. Water in subgrade and base reduces strength and causes pumping, ravelling, potholes and edge failure
   B. It increases CBR
   C. It hardens bitumen
   D. It reduces traffic
   Answer: A. Water weakens the subgrade and base and triggers several types of failure. (Key point: Poor drainage)

4. Which indicates a weak subgrade cause?
   A. High CBR
   B. Low CBR, soft or expansive soil, poor compaction
   C. Thick wearing course
   D. Wide shoulders
   Answer: B. Low CBR, expansive or soft soil and poor compaction give inadequate support. (Key point: Weak subgrade)

## Related in Transportation Engineering II

- [Highway maintenance and causes of pavement failure](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Amaintenance-flexible-failures) — Transportation Engineering II, chapter 4, asked 2×
- [Pavement evaluation; flexible failure types and causes](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Apavement-evaluation-flexible-failure-causes) — Transportation Engineering II, chapter 4
- [Flexible pavement failures: causes and remedies](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-pavement-failure-cause-remedy) — Transportation Engineering II, chapter 4
- [Repair vs rehabilitation; rigid pavement failures](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Arepair-vs-rehabilitation-rigid-failure-types) — Transportation Engineering II, chapter 4
- [Maintenance, rehabilitation, reconstruction; rigid failures](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Amaintenance-rehab-reconstruction-rigid-failures) — Transportation Engineering II, chapter 4
- [Maintenance, rehabilitation, reconstruction; evaluation methods](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Amaintenance-rehab-reconstruction-pavement-evaluation) — Transportation Engineering II, chapter 4

## Related in other subjects

- [Equipment for highway and pavement construction](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Ahighway-pavement-equipment) — Construction Management, chapter 4, asked 3×