Nothing impacts roads as much as water ingress. As a part of a road design process, allowance is made for water to pass under the road by providing structures to convey the water safely under the road. The consequences of poor design or extreme flood events on a road and its surrounding area are multiple and can be severe. There will be a disruption to the road network, the risk to vehicles and passengers trying to pass through floodwaters on the road, flooding of surrounding areas, as well as damage to the road embankment and surface due to scour from flowing water. The stability of your pavement structure will depend on how well your base and sub-base are. Your “finish” over these, may it be asphalt or concrete, interlocking or not will still depend on your foundation stability.
Concrete Road is more preferable in a water-prone area than Asphalt road. The embankment if provided and the base of the asphalt road gets corroded due the waterlogging. Whereas in concrete roads, the CC layer acts as a continuous structure, hence even if the base gets corroded there will be little damage to the top layer.
Given below are few methodologies that could enable a stable road in a rain prone area.
Use of cement-treated base for road construction in rain-prone areas
Cement-treated base (CTB) is an intimate mixture of aggregate material and/or granular soils combined with measured amounts of portland cement and water that hardens after compaction and curing to form a durable paving material. A bituminous or portland cement concrete wearing course is placed on the CTB to complete the pavement structure. The thickness of Cement-treated Bases is less than that required for granular bases carrying the same traffic because CTB is a cemented, rigid material that distributes the load over a large area. Its slab-like characteristics and beam strength are unmatched by granular bases that can fail when the interlock is lost. This happens when wet subgrade soil is forced up into the base by traffic loads. Hard, rigid CTB is practically impervious. It resists cyclic freezing, rain, and spring-weather damage. The cement-treated base continues to gain strength with age even under traffic.
Rigid RCC Pavement overlay for road construction in rain-prone areas
Overlay thickness criteria are presented for three conditions of the bond between the rigid overlay and existing rigid pavement: fully bonded, partially bonded, and nonbonded. The fully bonded condition is obtained when the concrete is cast directly on concrete and special efforts are made to obtain bonds. The partially bonded condition is obtained when the concrete is cast directly on concrete with no special efforts to achieve or destroy the bond. The nonbonded condition is obtained when the bond is prevented by an intervening layer of material.
For rigid RCC pavement overlay, a sand-cement grout or an epoxy grout is applied to the cleaned surface just before placement of the concrete overlay. When a nonbonded rigid overlay is being used, the existing rigid pavement will be cleaned of all loose particles and covered with a leveling or bond-breaking course of bituminous concrete, sand asphalt, heavy building paper, polyethylene, or other similar stable material.
Compaction of road layers for road construction in rain-prone areas
Compaction means in simple words removal of voids filled with air or water and making it dense. To construct the road of high-quality, compaction is the key factor affecting the life of roads. Therefore, it is recommended in AASHTO & MORTH, compaction factor test, and Field density test are done at a given frequency. The quality & Design of roads also has an impact on on-road life. Water is considered as the most dangerous compound on earth for roads. All properties of the materials used in road construction (sub-base, base and wearing course layers) are determined using the specific gravity of the compacted materials because this is the state where they are stable and perform best. So, to extract the designed performance from the materials, you have to put them at the designed specific gravity. And this can only be done by compaction.
Use of road drainage system for road construction in rain-prone areas
The continued presence of water on the road surface weakens the pavement causing potholes and ruts; similarly, the presence of water in the subgrade reduces its bearing power and load dispersion capacity. Loss of subgrade support leads to the failure of the road pavement under traffic loads. Hence efficient drainage is an imperative need.
The three principal types of road drainage are:
Surface drainage:- Surface drainage consists of the arrangements made for the quick and effective draining of water that collects on the pavement surface, shoulders, slopes of embankments and cuttings and adjoining land up to the right of way. This water is let off into natural or artificial channels sufficiently farther away such that the functioning of the highway is not impeded in any manner.
Subsurface drainage- Moisture changes in the subgrade occur due to percolation of rainwater and seepage flow, as also due to the phenomenon of capillary rise. Subsurface drainage aims to keep the groundwater table (GWT) sufficiently below the level of the subgrade.
Cross drainage- Roads have to be aligned often as to cross natural drainage channels, streams and major rivers. Sometimes, the alignment will be across man-made channels like those for irrigation. In such cases, the need for constructing cross drainage structures arises to ensure that the water flows beneath the road without causing any inconvenience or instability to the highway structure.
Use of Plastic Coated Aggregates for road construction in rain-prone areas
Plastic waste (Carry bags, cups, thermocol, foams and flexible films) is shredded into small pieces The granite stone is heated to around 1700c. The shredded plastic waste is added to the stone. It is melted and coated over a stone in just 30 seconds. Then the bitumen is added 1 and mixed. The mix is used for road construction. From rural roads to National Highways all types of roads can be laid using this technique. The modified process can also be carried out using a central mixing plant. The shredded plastics are added along with the aggregate or a special mechanical device is developed which will spray the plastics inside the chamber to coat the plastics effectively. Central Mixing Plant helps to have better control of temperature and better mixing of this material thus helping to have a uniform coating.
These are a few of the methodologies through which we can try to stabilize roads in rain-prone areas. Road pavement design must comply with the sub-base specification of a particular terrain that adopts these measures. Take expert advice to understand the need for materials to be used for road construction.
Source – roadworks.inc, pavement interactive, intelligent construction technology, roadex network, tec.edu, cedeengineering, engineering notes.com, ijerst.com