In this article we will discuss about how to maintain roads.
Maintenance of Highway:
A well-constructed highway that is designed for a particular category would need minimum maintenance. The nature and extent of maintenance needed would depend on the degree of deterioration of the pavement, the most common road characteristic used to assess this being the ‘roughness’.
It is generally observed that the deterioration of a road is reflected by its roughness over time under traffic. As roughness increases, the road user costs rise.
Various levels/degrees of maintenance operations are:
(i) Routine maintenance, which includes that of drainage facilities.
(ii) Periodic maintenance/Patch repair
(iii) Special repairs/relaying/overlay provision.
Standards for road roughness suggested for Indian conditions are given in Table 10.1.
MORTH has proposed to divide the maintenance programme for national and state highways into three levels – 1, 2 and 3.
Level 1 represents the highest level of comfort and safety.
Level 2 signifies the level to which the road deteriorated after two years of service before any maintenance is implemented.
Level 3 represents the minimum level needed to provide a reasonable level of safety.
The proposed levels based on certain serviceability indicators are shown in Table 10.2.
Maintenance of Earth Roads:
Since earth roads form a major percentage of rural roads, their effective maintenance is of great importance. Good maintenance can preserve the elements and geometries and prolong their life.
The primary maintenance operation consists of maintaining the cross-section. Earth roads are known to cause dust nuisance in dry weather/summer; they are damaged by rutting, mostly longitudinal, because of the abrasion caused by traffic. They are also damaged by heavy rains, which may cause transverse rutting.
In the case of low-traffic rural roads, the routine/periodical maintenance of adding earth and rolling to bring the cross-section to the designed shape may be done manually.
For other types of earth roads, a motor grader and a drag with iron plates or angle irons are used for shaping the cross-section.
Dust nuisance is controlled by sprinkling water or using a dust palliative.
Maintenance of Gravel/Moorum Roads:
The maintenance operations are practically similar to those for earth roads – filling lost material, grading, dragging and addition of gravel, along with adequate rolling.
Re-gravelling may be done by adding 25-75 mm loose thickness of gravel once in 2 to 5 years, depending upon traffic conditions and the periodic maintenance, in addition to environmental factors.
Maintenance of Water-bound Macadam Roads:
Un-surfaced water-bound macadam is very commonly used in India.
The following defects arise owing to the deterioration of a WBM surface:
(e) Edge damage.
Mixed traffic conditions have adverse effects, causing the road to be dusty in summer and slushy in monsoon.
Ruts are repaired by scarifying and removing loose stones, filling with metal – partly salvaged and partly fresh, adding screenings and gravel, and rolling with moisture. A 6 mm sand layer is sprinkled.
Pot-holes are formed because of poor quality stones and local failure of subgrade. Patch repairs are done to fill the pot-holes in a rectangular shape with metal in a manner similar to the repair of ruts.
Corrugations result in a wavy surface and cause discomfort. A variety of factors such as inadequate and defective rolling, vibrations set up by the pneumatic tyres of vehicles and shock absorbers and also those set up by braking action contribute to the formation of corrugations. The excessive blindage material, if any, collected on the surface, should be removed by dragging and/or brooming.
Ravelling can be prevented to some extent by blinding with a good binder material and watering.
(e) Edge Damage:
Since edge damage can be caused by loss of shoulder support, repair should be done promptly.
Periodic renewals of WBM surface is required, preferably once in 3-6 years.
Maintenance of Bituminous Roads:
In addition to standard causes such as traffic, weather and ingress of water for the deterioration of earth, gravel and WBM roads, loss of volatiles, oxidation of the binder material and inadequacy of the specification and construction standards also could be the reasons for distress and disintegration of bituminous pavements.
Depending upon the degree of deterioration of the highway facility, the nature of the maintenance operations for bituminous pavements could be:
(a) Patch repair
(b) Surface treatment
(a) Patch Repair:
This consists of patching up of pot-holes and localised failures, and may be up to about 25 per cent of the surface area annually. For patching, sand premix, open-grade premix, dense-graded premix, or penetration patching may be adopted.
(b) Surface Treatment:
The aim of surface treatment may be renewal of the surface course when patch repair becomes uneconomical; it may also be to improve skid resistance when the surface is worn out badly. Standard specifications for tack coat, prime coat and seal coat, along with surface dressing/premix carpet should be used.
This is taken up when the pavement has deteriorated badly. When the pavement is of inadequate thickness, an ‘overlay’ of adequate thickness should be designed and provided.
A brief description of the defects, symptoms, probable causes, and possible treatment is given in the Table 10.3, extracted from “IRC; 82-1982: ‘Code of Practice for maintenance of bituminous surfaces’, Indian Roads Congress, New Delhi, 1982”: Defects, Symptoms, Causes and Treatment of Defects in Bituminous Surfacings.
Maintenance of Concrete Pavements:
A cement concrete pavement needs very little maintenance if it is well-designed and properly constructed. In fact, this is considered to be the most important advantage which offsets the high initial cost. However, defects are likely to occur due to ingress of water, especially through ill-maintained joints and cracks, inadequate pavement thickness and poor workmanship.
Appearance of cracks, which may be shrinkage cracks or warping cracks due to temperature changes.
Cracks which appear in the corner and edge regions are called ‘structural cracks’ as they are due to the excessive stresses caused by wheel loads. They indicate inadequacy of the pavement thickness and should be viewed seriously and treated differently.
Hair cracks are not harmful, but medium and wide cracks allow water to seep through and cause progressive loss of subgrade support. Such cracks should be filled up with low-viscosity epoxy grout, after cleaning the cracks of dust. Compressed air is used for effective cleaning. The material is topped up with sand or fine aggregate chips to prevent the disturbance of the material under traffic.
Joint maintenance consists of replenishing lost sealant, removal of deteriorated joint filler, and introduction of fresh filler material. The sealant is then poured to an excess height of about 3 mm and sand sprinkled for it to be compressed by the traffic to the level of the pavement surface.
Patch Repair of Slabs:
Sealing, spalling, depressions and irregularities can occur in a slab locally. Immediate patching up of such defective slabs can arrest further deterioration.
Premix bituminous materials are commonly used for this purpose, but they do not provide a satisfactory result. The best materials are epoxy resin mortars and concrete for such patch repair work. The sides of the area of the slab to be patched are trimmed, made vertical, and fresh concrete is laid and tamped; the areas are usually made of regular geometrical shapes like rectangles.
When water gets collected in the subgrade, heavy axle loads cause ejection of mud through joints, cracks and edges. This phenomenon is commonly known as mud-pumping and blowing. When this is observed, defective joints and wide cracks should be refilled and sealed.
To prevent further damage and recurrence, grouting of the slab is done through holes drilled in it; the grout can be of cement mortar (1:3.5 mix) or of bituminous material (the latter is preferred since it is effective in filling the void spaces between the slab and the subgrade), and raising the slab to the desired level. This process is called mud-jacking and is popularly used in advanced countries.
Restoration of Anti-Skid Surface:
When the surface becomes smooth and slippery, anti-skid surface can be restored by cutting grooves by grooving machines or by grinding machines.
A patching mix of epoxy mortar can be filled and compacted after chipping off the area and cleaning it thoroughly by using compressed air. This is adequate only when the crack depth is not more than one-third of the depth of the slab.
However, when the crack extends almost to the entire depth of the slab, cross-stitching with inclined tie-bars or stapling with U-bars may be adopted; the former is shown schematically in Fig. 10.9.
Mechanised Maintenance of Roads:
In India, road maintenance is mostly labour-oriented; however, mechanical maintenance of roads also can be practised with indigenous equipment for speedy implementation and better quality control.
Maintenance Management System (MMS):
In view of the several steps and factors involved in the maintenance operations of highways, systems approach is considered desirable to evolve an efficient maintenance programme for any highway network.
A computer package known as ‘Pavement Management System’ has been formulated to facilitate optimal resource allocation for maintenance.
The elements in this are:
1. Basic road data bank
2. Pavement performance model
3. Selection of maintenance levels
4. Evolving priorities for maintenance (renewal and overlay) for a given budget.
Several organisations have developed their own MMS packages and implemented them in their respective countries.