Road Construction | Flexible Pavement | Rigid Pavement
Road Construction and Components of the Road Section.
Road construction is the process of building or upgrading roads and involves using concrete, asphalt, rebar, soil stabilization, paving, and other road construction and repair materials. The road construction materials create a long path with a paved or smooth surface for vehicles to travel along between two or more areas.
The road has several vital components, and they are essential as they influence the safety, comfort, and efficient movement of traffic. Here are the components
- Right of Way Road
- Road Margins
- Road Formation Width
- Road Side Slope
- Road Berm
- Service Road
- Road Shoulders
- Road Camber
- Road Kerbs
Right of Way Road
Right of way is with the land acquired for the road. The right of way should accommodate all the components of the road section.
Road margins are the various cross-sectional elements of the road, except the carriageway or pavement width. Service road shoulders footpaths are part of the road margin.
Road Formation Width
Road Formation width the road’s whole width, which includes median lanes, verges, and shoulders.
Road Side Slope
Side slope, the transverse slope with respect to the horizon connecting the shoulder to the stormwater drain to drain the water
Road berm is a barrier provided to help prevent the erosion of soil’s embankment into the storm drain.
The carriageway is the width of the road on which a vehicle movement is allowed. It can comprise one or more carriageways.
It’s an alternative road constructed between the road and buildings connected only at selected points, with the carriageway.
Road Shoulders are provided on both sides of the road edges. It helps accommodate, stopped, and the emergency vehicles and provide lateral support for base and surface courses.
Road Camber is the carriageway slope to raise the middle surface to ensure water will drain offs from the road surface into the side drainage systems.
Road Kerbs help indicate the boundary between the carriageway and the shoulder or islands or footpaths.
It also helps in confinement and stability to the base course.
Materials Used for Road Construction
Asphalt is a natural mixture of bitumen.
Bitumen is a solid or viscous material with binding and waterproofing properties derived from petroleum by the refinery process.
These are either crushed or broken stone crushed slag or laterite of suitable quality.
It shall conform to the physical requirements and size range before being used. It accounts for 75% to 98% of the material of base and surface courses.
Screening to fill voids in the coarse aggregate shall generally consists of the same material as the coarse aggregate. Murram and sand gravel can also be used. 95% of the materials should pass through 13.2 millimeters screen
These are 10 millimeters aggregates and the most common type of screening.
Type, of course, aggregates size 230 millimeters to 300 millimeters, nine inches to 12 inches.
The terms are used for quarry material. Coarse aggregates are available in standard sizes of 32 to 40, 40 to 63, 63 to 90 millimeters.
They are usually categorized as material less than 2.8 millimeters in size. It can be a natural sand quarry or a mixture of both.
The material is usually used for concrete work. This size of the material, if used to fill voids, is characterized as screenings.
It’s a type of soil which is mainly used for road work. It’s usually reddish to yellowish in color. When compacted, it forms a hard and impervious surface.
Flexible Pavement and Rigid Pavement.
Usually, the base and sub base courses are the same depending upon requirements, usage of roads where until conditions and choice between flexible or rigid pavement is picked,
The figure below is a typical components for each course layer of the pavement.
Each component has a specific function; the thickness and type of material to be used depending upon the road’s requirements for which it is designed.
After completion of the excavation, the layer of soil should be compacted adequately. Special arrangements shall be made to improve the properties of soil.
Sub Base Course
The sub-base course is the entire road rests on this. This layer must be able to resist loads whether, on subsurface water in right soil conditions, soil can be the sub base.
In recent years, sand or GSB is used. GSP stands for granule, a sub-base. It is made up using granular material; usually, natural sand, crushed gravel, crushed stone, or a combination of all the material should meet gradation properties.
It should be laid in layers not exceeding 150 millimeters.
The base course is the structural layer of the road. It is made up of crushed or broken aggregates filled with screening materials, which are mechanically interlocked. Voids are filled with screening and binding material with the assistance of water.
The stability of the road depends upon the thickness of this course.
WBM (water-bound macadam): The pavement based cause made of crushed or broken aggregates first spread, and then the voids are filled with screening material.
Finally, compaction is performed, followed by the addition of binding material with the assistance of water.
Each component (metal, screener, binder) and water are laid in a faced manner directly on site.
WMM (wet mix Macadam): is a newer mix in which aggregate and binding materials are premixed in a batching plant or concrete mixing machine and then brought to the site for overlaying and rolling.
Types of Pavements
Flexible pavements are made from bitumen, and rigid pavements are made from concrete.
The bitumen road is a pavement layer comprising a mixture of aggregates and bitumen, heated and appropriately mixed and then laid and compacted on a bed of granular layer.
The load is transferred to lower layers through contact with the granular material load in a broader area.
Bitumen road is constructed in multiple layers. The binder coats are intermediate coats that join the surface layer on the base layer.
The surface course, also called the top layer, has elastic properties, is impervious to takes, wear, and tear the traffic.
A prime coat is a coat applied directly to a prepared based course. It acts as an initial sealer in the asphalt laying process to block the other layers from moisture, dust, and debris. It bonds the base cost to the binder course.
Binder course is an intermediate course between the base course and the surfacing material, consists of intermediate-sized crusted stones bound by a bituminous material. It helps low distribution to the base course
A tack coat is a very light application of a binder to an existing surface to ensure born between the existing surface and new construction. The material is liquid and can be spread uniformly and sets quickly
Surfacing courses, the topmost layer of the road in contact with the traffic. Its purpose is to minimize roads’ operation and reduce the adverse effect of climate on the road. It should be made of superior quality
Seal coat is an application of the top layer with bitumen to seal the voids, followed by a cover of stone chips. It makes the surface watertight,
Road Construction -Surface Course (Bitumen).
What is Bitumen or Asphalt?
The tar mixture leftover from the distillation process of crude oil, which is known as asphalt. The leftover mixture is refined further to make road construction bitumen.
Different Layers in a Pavement
- Natural subgrade.
- Compacted subgrade.
- Sub-base cause
- Based course
- Binder Course
- Surface course
Bituminous Roads aims to determine the proportion of bitumen filler, fine aggregates, and coarse aggregate to produce a workable, strong, durable, and economic mix. Take care of the performance of work as per job mixed design.
Ingredients of a Mix.
It offered compressive and shear strength and showed good interlocking properties.
It fills the voids in the coarse aggregate and stiffness the binder, for example, sand, rock, dust, etcetera,
It fills the voids, stiffens the binder, and offers permeability, such as colon, rock, dust, cement, and lime.
It fills the voids, course particle adhesion and gluing, and offers permeability, such as colon bitumen ,asphal,t tar, etc.
Formula much provide details of;
- Gradation of aggregates
- Percentage of Betty meant to be used.
- Method of mixing
- Heating of material.
- The temperature at which it is emptied from the mixer
- The temperature at which it is to be emptied on the road
Bitumen Pavement Layers
Leveling course (binder course/ surface treatment) is an intermediate course between the base and surface course.
Nominal size aggregates is rolled with bitumen to fill gaps for better interlocking aggregate gradation and bitumen content established by site trials.
Ensure rolling till aggregates are embedded in bitumen.
Dense bituminous surfacing consists of a mixture of aggregates graded from maximum size, typically less than 25 millimeters, through filler (Less than 0.75 millimeters)
Material is laid hot and compacted to form a dense, impervious layer.
Seal coat could be applied if or as required,
Bitumen prime coat; It is a thin layer sprayed uniformly on the road base.
Bitumen Tack Coat ;It’s applied to make roads sticky before surfacing or carpeting is place.
Seal coat rolling of gravel size 2.4 millimeters to 10 millimeters.
Important points to be remembered before the application of bitumen
- The surface upon which bitumen mixed is placed should be thoroughly cleaned.
- Bitumen material should be placed only when the surface is dry.
- The entire surface should be primed evenly.
- No bitumen should be placed until the prime coat has dried.
- Tack coat to be applied to make layer sticky.
Important points to be remembered before the rolling.
- Dense bitumen surfacing to be done immediately when it can support roller
- Start longitudinally from sides to move towards the center.
- The roller should not be allowed to stand on newly laid material.
- Use of water over roller drums should be minimal to prevent cooling of bitumen
Causes of Pavement Failures.
Main causes are;
- Water intrusion
- Stress from heavy vehicles.
- Expansion and contraction from seasonal temperature changes and sun exposure.
The Requirement of a Bituminous Mix.
Stability: The resistance of the paving mixed to defamation under traffic load.
Durability, the resistance of the mix against weathering and abrasive actions, is known as durability. Weathering causes hardening due to loss of volatiles in the bitumen, and abrasion is due to wheel loads, which causes the strains.
Bitumen Durability Failures
A typical example of durability failures;
- Potholes deterioration of pavement locally.
- Stripping loss of binder from the aggregate and aggregates are exposed.
- Flexibility is the resistance to cracking of the surface due to shrinkage and brittleness of the binder.
- Skid resistance is the finished pavement resistance against skidding, which depends on the surface texture and vitamin content.
Rigid pavements are roads made from concrete. In this type of road, the load is distributed by slab action. It assumes that the road is a thick plate on will remain as it is after bending due to loading on temperature variation, the top players are made up of reinforcements cement concrete.
A plain cement concrete layer acts as a leveling course for the reinforced cement concrete layer. Each layer of pavement has a multitude of functions to perform, which has to be duly considered during the design process.
Different types of pavements can be adopted depending upon the traffic requirements. Improper design of pavements leads to early failure of pavements.
It understands the construction of rigid pavement known as reinforced cement concrete road. The diagram is showing the components of rigid pavement. RCC surface on top over a plain cement concrete surface with a separation membrane in between,
Advantages of Rigid Pavement
- The benefits of constructing reinforced cement concrete pavement are that there longer-lasting than compared to the flexible pavement on a bitumen road.
- The reinforced cement concrete road has better flexible strength due to which there is lesser deflection less waterlogging; therefore, means that less maintenance is required for pavement.
- Will not be affected in case of automobile fuel spillage.
- The structural design of the rigid pavement is based upon slab action. The top cause is reinforced concrete, and this helps to distribute the load in a larger area.
- Reinforced cement concrete roads have lower maintenance costs, though it has higher initial investment costs.
Materials of Rigid Pavement
The most commonly used materials in RCC Road construction are cement, coarse and fine aggregate, and water.
Cement is a substance that sets and hardens independently and can bind other materials together. It is manufactured by the careful proportion in a mixture of lime, silica, gypsum, and alumina, which is fed into ovens at 1500 degrees Celsius.
The mixture forms clinker which is then ground to fines.
Aggregates consist of sand, gravel, and stones either crushed or uncrushed or a suitable combination of them.
They should be strong, hard, dense, durable, and free from injurious amounts of alkali.
Water to be used should be free from acids, alkali, organic matter, and oils. What a waste it should be minimized. Ensure water is not wasted for cleaning machinery and equipment. Also, ensure proper leak-proof plumbing systems are used.
Construction of Rigid Pavement
A separation membrane is a plastic sheet spread over the top or bottom of the PCC layer.
It is HDP, or LDP sheet, with a thickness ranging from 200 microns to one millimeter, depending upon requirements. Ensure that it does not care while placing and pouring the concrete. The lane shall be done with overlapping from the ends. It prevents hydrostatic pressure and water loss from concrete.
It also helps for anti-termite in case of the great floor.
Sub based course, commonly called W B M/ W MM layer, is the layer directly below the PCC layer. Its primary function is load distribution and supports the cement concrete layers.
Sub Based Course
The sub-base course is the layer under the base layer, commonly made from compacted yellow soil used to improve soil conditions.
The leveling course in the rigid pavement is PCC. The PCC layer is provided to get uneven and hard strata for concrete placing.
The Surface Course
The top layer in a rigid pavement is reinforced cement; the concrete layer comprises a mixture of cement, sand, coarse aggregates, and water reinforcing by the TMT rods.
Rigid Pavement Formwork
The site forms are correctly fixed in a position to fulfill the desired profile of the finished pavement. The TMT rods of suitable diameter should be placed in a longitudinal and transverse direction according to loading.
It might be required on both sides, top and bottom, depending upon loading joints on the surface needed as it allows the surface to get expand in high temperature without harming it.
Then the concrete export informs manually or mechanically. The RCC pavement slab serves both as a strong base course and as a good surface course.
Tremix is a vacuum process in which surplus water from the concrete is removed immediately after placing and vibration. This reduces the water-cement ratio to the optimum level, thereby decreasing voids and increasing concrete strength.
Concrete has excellent strength, durability, and workability with ever-increasing demands of wear and tear to roads. Concrete roads are many superiors in terms of maintenance and life of the top surface.
Though the rigid pavement roads have higher investments, costs over the life of the road, reinforced cement concrete are cheaper. Ensure the RCC road design considers loadings and whether the effect
Road Construction Machines and Equipment
Commonly used equipment for road construction is listed.
- Hot Mix Plant
- Tandem Roller
- Vibratory Road Roller
- Sheep Foot Roller
- Paver Finisher
- Oil Tar Boiler
- Concrete Batch Mixing Plant
- Concrete Mixture
- Surface Vibrator
We will be discussing briefly each piece of equipment.
Hot Mix Plant
A hot mix plant is a piece of mechanical equipment designed to measure and mix various materials in adequate proportions required to form a bituminous and concrete charge.
Bulldozer is a tractor on the front of a curved strong adjustable blade, which is used for spreading and leveling various types of loose excavated material. It is also be used for cutting off topsoil.
Excavator is a bucket mounted wheeled equipment used to perform all type of digging and loading activity. It is fitted with two types: Wheeler and crawler
A grader is a machine provided with an adjustable blade or scraper within the wheel pace for shaping sub great or subsoil, and it moves loose outside ways.
A Tandem roller is a smooth two-wheel compaction machine. Both wheels are of equal width and made of steel plates that are good for initial rolling and surface pressing. It comes in various capacities, like 6 to 8 tons and 10 to 12 tons. It helps in compaction of up to 300 millimeters depth.
A vibratory roller is a machine with on smooth drum fitted at the front; the back wheel can be drum or pneumatic tires.
It comes with an inbuilt vibration mechanism, which gives better compaction up to 600 millimeters in depth.
Sheep Foot Roller
Sheep Foot Roller consists of rectangular-shaped boots fixed in a hexagonal pattern but has less coverage area. It compacts soil by static weight and needs of the respective layers. It is mostly suited for clay soils, where pressure varies from 1200 to 7000 kg.
Paver finishers are used to live with a bitumen concrete layer in the desired thickness. They have two main parts which selves two activity; A trailer and screed. Trailer receives asphalt mix, screed which lays the mixed, uniformly.
Oil Fired Tar Boiler
Our boiler is mobile equipment used to heat and liquefy raw tar at the desired temperature before its use.
Concrete Batch Mixing Plant
A concrete batch mixing plant is used to get concrete mix in mass quantity, which will then be transported by the transit mixture to the site. The capacity of the mixing plant is varied from 45 to 75 cubic meters per hour.
A transit mixer is used to transport concrete mix from the mixing plant to the respected site. They have to mix drums continuously rotating, and so they prevent the mixture from getting settled. It’s capacity 6 to 7 cubic meters in a single time.
Concrete Mixture Machine
A concrete mixture is used to make a concrete mix out the site for the small required quantity. Its capacity ranges from 4 to 6 cubic meters per hour. They are used in small works.
Surface vibrator used to make concrete compacted on to have even top surface.
Floaters are used to making the concrete surface smooth and to fill the voids on the surface. It will also remove the surface imperfection.
A dumper is a vehicle for transporting material and discharged material by tipping.
Dumber and Wheel Excavator in action.