|Portion of a road pavement showing cracks
Today on building contractor secrets, I’d like to look into the root causes of a roadway deterioration. I’m talking about this because its rainy season once again in my country, Nigeria, a season where we have so many hold ups as a result of bad roads.
What Is A Road?
A road is a properly constructed, convenient way, over which vehicles and all sort’s of traffic can law fully move. But whereby a road is not convenient i.e. it has deteriorated from its original value and shape. It becomes a source of worry and concern to the users.
What Is A Highway?
Highways are important paved roads in a road system.
What Is Highway Deterioration?
Highway deterioration commonly results from a combination of inadequate or lack of drainage system. Traffic and environmental effect. The rate of deterioration is basically determined by the design process or construction, maintenance and usage of the road, there are different causes of road deterioration and they are:
1. Traffic causes
2. Inadequate design consideration causes
3. Climatic causes
4. Human causes
5. Improper drainage causes
Traffic Causes: Vehicular traffic is the wheel loads that causes stress and strains in the pavement layers and sub-grade. The type of pressure determines the area of application. Imperfection in surface and at joints, causes additional loads due to impact. The repetition of loads causes plastic and shear deformation of the pavement. The concentration of wheel loads on a very small width of pavement can causes extra deterioration, because the small width of the road cannot with stand the weight of the wheel imposed on it. Also the movement of vehicles or equipment with track or steel wheels e.g. a smooth wheeled roller or bulldozer can cause severe or immense stresses and cracking on the pavements.
2. Inadequate Design Consideration: When the laid down design criteria are not strictly adhered to and applied, the dangerous result is the premature failure of the road. i.e. the material used in the wearing course, surface dressing or structural concrete etc. has failed before its predicted design life has expired.
So it is very necessary to determine, whether the design, specification, supplied materials or workmanship are adequate enough and up to the set standard.
The foundation of every structure determines the durability of the structure. For any designed road to be able to safely support the vehicle load on its surface and transfer the load to other layers successively i.e. from the base course to the sub-grade then to the undisturbed soil on which it rests. A lot of factors are being considered in the design criteria such as:
Number of vehicular traffic, expected to use the road.
The estimated yearly rate of commercial traffic growth.
The designed life period of the road
The type of soil on which road structure is to be built on.
The level of the natural water table in relation to the proposed formation level.
The type of road structure which will be used in building the pavement.
3. Climatic Causes: Climate activities could affect the soil and drainage condition of pavement. The intensity of rainfall affects the amount of surface and sub-surface structure, water present in the soil. The greater the water volume, the greater the intensity. The rate of sunshine has its effect on pavement element structures.
Excessive loss of moisture could lead to the elements of the pavement to shrink. The varying rate of sunshine could lead to alternate heating and cooling of the pavement structure.
This result in crack’s on the pavement, if the expansion joints are not provided in the design and construction of rigid pavements. And conditions could result in the wilting and eventual drying of vegetation cover. This then makes the soil prone to the actions of surface water.
4. Human Causes: some of the various activities of man can bead to failures in pavements. Cutting across the pavement to lay various utility pipes etc. without proper back filling can and will result to the gradual deterioration of the road. The deterioration of the road shoulders occurs when embankment and shoulder soils are excavated and carried out of its original site. Also stripping of vegetative cover could lay the shoulder bare. But over grown vegetative cover could lead to cracking of pavement elements.
5. Improper Drainage Causes: Highway drainage involves the removal of excess water within the limits of the highway and satisfactory disposal of it. Water gets to the road way mainly due to the precipitation of rain and surface runoff from adjacent areas. Drainage is one of the must important aspects for the design of highway. But in a situation where there is no drainage, the different forms of precipitation especially rain fall enters into the road pavement and destroys it. And once water has entered a road pavement water damage is initially caused by hydraulic pressure i.e. vehicles passing over the road pavement impart considerable sudden pressure on the water, this pressure forces the water further down into the road fabric and breaks it up, this process can be very rapid once it starts. Water if allowed to stay on the surface of a pavement will descend to the sub grade layer below the road pavement and weaken this layer thus lowering the CBR of the sub-grade, which the road pavement design was based up on and deep seated failure of the road will begin. Water that enters the road must have a drainage path out.
What are the effects of inadequate drainage?
Inadequate drainage will result in the following:
1. Hydrostatic head
2. Capillarity and water vapour
3. Water table increment
4. Flow of water within the pavement structure
5. Failure from surface water
Effects Of Improper Drainage
1. Results in embankment failure.
2. Stripping of bitumen from aggregate resulting in raveling and pot holes is as a result of continuous contact of water with the pavement.
3. Pavement made of surface dressed gravel becomes soft and looses strength.
4. The sub-grade may be softened and its bearing capacity reduced.
5. Excess moisture causes increase in weight and thus increase in stress and simultaneous reduction in the strength of the soil mass.
6. Erosion: Erosion is one of the main features of surface water activities erosion of pavement structure are promoted by lack of surface drainage systems, and where such systems are not present improper design and construction may lead to erosion. Other features in the pavement that promote erosion are improper flushing of carriage way. The faster the current, the larger the particles that will be picked up and carried along.
There are several factors contributing to the deterioration of roads or highways. These has been listed and explained too.
You can also use this material as an instructional material in colleges as it has been professionally researched to meet all needs.