What is a road pavement, and how is it designed?
A pavement is the top most surface of a road that bears the load of traffic, most often vehicular and should not be confused with a footpath. Now often this leads to confusion depending on the British or American style of English. Here, we’re referring to the surface in road construction. A paved road is also called the surface course, and can be made from a number of materials such as asphalt, Hot Mix Asphalt (HMA), concrete, and other mixed materials. The material choice for this layer in pavement design is an important design component for the pavement engineering designer because it carries and distributes the load of the traffic to the layers underneath it such as the subgrade, base grade, drainage layer and interconnected layers of reinforcement. The pavement design process includes consideration for the type of loads (repetitive, infrequent, etc) that it will be under, subgrade strength, sub-base layer, reinforcement techniques, soil mechanics, and other factors.
While potholes are a common occurrence on many roads, it comes at a very heavy economic cost to countries. A well-designed and well-constructed pavement reduces vehicle operating costs, decreases maintenance, and increases road safety. In this blog, we will focus on the construction of road pavement, its design principles, and updated methods used for pavement design.
What are the different types of pavements in road construction?
In road construction, the type of pavement selected plays a critical role in determining the overall performance, longevity, and maintenance needs of the road. Pavements are engineered to withstand the weight of traffic loads, the effects of environmental conditions, and the stresses placed on the road surface over time. While there are various methods and materials used for constructing paved roads, they generally fall into three main categories: flexible pavements, rigid pavements, and composite pavements. Each type has distinct characteristics that make it suitable for specific applications, depending on factors such as soil conditions, traffic volume, climate, and budget considerations. Understanding these types and their benefits is essential for choosing the most appropriate pavement system for any road construction project.
- Flexible Pavements: Flexible pavements comprise a number of layers, and typically the top surface layer, is often made of asphalt when it comes to paved roads or highways. Also known as the surface course, these types of pavements are flexible in nature and easily adopt the frequent movements occurring in the lower-lying soil beneath the structure along with loading of different types of traffic. Due to inherent flexibility, these pavements dissipate the occurring traffic load over a larger area that in turn reduces the developed stress on the subgrade.
- Rigid Pavements: These are pavements made of concrete slabs that possess high rigidity and structural strength. Unlike flexible pavements, the rigid pavements support loads over a relatively smaller area but provide strength and durability to a larger extent. The rigidity of the concrete allows the rigid pavement to bear heavy loads with very minimal deformation.
- Composite Pavements: Composite pavements combine the features of both flexible and rigid pavements. Both courses are made up of layers of asphalt and concrete. The main intention in the design of this type of pavement is to make use of the most favorable properties of both materials on one pavement structure, combining flexibility with durability.
What are the components of a road pavement?
Road pavement is a composite structure comprising several layers, and each layer has a different function. These layers are primarily responsible for the two aspects of the road pavement: stability and water resistance. Asphalt binds them together and prevents the road from bad weather and water infiltration. Explaining these factors is vital in understanding the whole layout and operation of a road.
- Subgrade: The bottommost layer of pavement which is called subgrade is the first load-supporting layer. A subgrade is usually supported by subbase soil i.e., natural soil or aggregates. Most of the time, the strength and load-bearing capacity of the subgrade decide the extent to which the more stable structure will stand. Weak subgrade conditions can result in the rutting of the overlying pavement and thus reduce its lifespan. Hence it is necessary to test the soil first and take proper measures to strengthen the soil quality before constructing a pavement. The best method to strengthen the subgrade soil is using the geosynthetic materials like geogrids and geocells as per the requirement of site. These geosynthetic materials are a type of confinement system which holds the soil in place hence increasing the durability of the foundation.
- Base course: In addition to the subgrade, the base course (the layer on top of the subbase) channels the pressures from the pavement into the subgrade. The essential construction elements for roads are granular materials such as gravel or crushed stone. These materials have high strength and a very long composition life, which can help them absorb the traffic loads and maintain a minimum resettlement under the road pavement. Factors such as traffic volume, climate, and soil condition determine the choice of material. It is very important to provide a stable surface for the base course because this layer distributes the load.
- Binder course: The binder course is a layer of bituminous material, such as asphalt or tar. This interlocks the base course and the top layer or the wearing course. It performs two tasks: smoothing the surface texture and strengthening the pavement’s resistance to moisture and weathering. The binder course is generally laid in hot or cold mix form depending on the conditions and requirements of the sites. This binder course provides additional structural strength and acts as a waterproofing layer.
- Wearing course: The top course, the wearing course of the pavement, comes in direct contact with the traffic and seals the surface. It is mainly constructed out of asphalt or concrete, which is selected depending on factors like expected traffic loads, environmental conditions, and maintenance considerations. The durability of the soil and the jump resistance are principal tasks for security and a comfortable passage of travelers in the street. The material selection is dependent on parameters such as traffic volume, climate, and aesthetics. For instance, asphalt is usually the choice for highways and residential roads, whereas concrete is the typical option for high-traffic areas like airport runways and central boulevards.
What factors influence road pavement design?
The road pavement design process is a multilateral approach that carefully considers different variables. These variables can significantly affect pavement performance, durability, and long-term maintenance costs.
- Volume: Vehicle volume, calculated by measuring the number of vehicles per day, directly affects the thickness and material selection of the pavement. High traffic requires thicker and more durable pavements bearing heavy loads.
- Weight: Vehicle weight, especially that of heavy trucks, is a crucial attribute. These trucks put more pressure on the pavement, and thus, the thickness of the materials should be increased.
- Speed: Rapid vehicle velocities can add more dynamic loads to the pavement, thus wearing it out quickly. Speed limits and design speeds are also crucial factors that engineers need to consider during the design process.
- Climate: The pavement response is sensitised by the variable thermal conditions exhibited by extreme temperatures, the presence of precipitation, and freeze-thaw conditions. Hot weather sometimes softens the asphalt, leading to its faster deterioration, whereas cold weather can lead to frost heave and cracking. Changes in pavement conditions can significantly impact pavement performance, and engineers must consider these climatic factors carefully.
- Soil type: The durability of the underlying soil depends on several properties, such as strength, moisture content, and frost heave susceptibility, which affect the pavement’s design. Soils in poor condition that have not stabilized may need additional layers or treatments to provide adequate support.
- Drainage: Good drainage is needed to avoid water breaking into the pavement structure and causing damage. Approaches like ditches, culverts, and subdomains should be used to withdraw water from the pavement properly.
- Long-term costs: The fundamental principles behind drawing a road surface should include the total costs of repairs and maintenance. Things like how often they are done, how much the various materials, and the labour needed for maintenance should all be factors the designer(s) includes.
- Life cycle cost analysis: This method involves not just looking at the construction costs but also the life cycle of a pavement (the whole time the pavement is in service), including construction, maintenance, and rehabilitation. It helps find the most suitable low-cost design factor.
- Geographical situations: Land topography, current infrastructure, and the utility near the pavement site can influence the planned pavement. For instance, possibly present steep slopes would allow for the protection of erosion. Still, at the same time, the underground utilities would also limit how deep you can get with the excavation.
- Sample budget: If the budget changes, the design costs will be reduced. The budget change can reduce the cost of building materials, labour costs, or the amount of equipment needed, or it may be eliminated if this is technically feasible.
- Materials allocated: A technical condition in using a certain material in the building process may help the architect realise the constraint of construction materials on the design itself. For instance, if a particular material is very expensive or hard to come by in a specific location, one might want to look for alternative materials.
What are the different ways of designing road pavements?
Pavement design involves identifying the appropriate amount of materials and level of thickness required to create a durable and functional roadway. Several methods are used to accomplish this, each with its own specific benefits and drawbacks.
- Empirical methods: This method involves using historical data and past experience to level the pavement. Straightforward formulas or charts typically compute these methods using a pair of factors, such as the traffic load and the environment in which the pavement is located. Though these methods only require a little data and are straightforward, they are sometimes less accurate in complicated pavement structures or unusual conditions.
- Mechanistic-empirical models: These methods employ the theories that pavement mechanics dictate together with empirical evidence. They investigate the injections and inconsistencies in the pavement structure due to the different loads. These approaches have a higher degree of reliability, especially in the case of complex designs, but will need more data and computer resources.
- FEA (Finite Element Analysis): It is a computational method that solves numerically steady-state problems using scattered data that causes convergence. This technique breaks the pavement structure into a network of elements and calculates the strains in each component. Although FEA may result in very accurate answers and be able to solve large and complex pavement geometry and loading conditions, it will be time-consuming and require various skills in programming and numerical analysis.
Using geosynthetic materials in road pavement construction
It is crucial to use durable and stable materials while constructing road pavements as the demands on road infrastructure is increasing. Geosynthetic materials, including geogrids, geotextiles and geocells, have emerged as key components in modern pavement design.
How geosynthetics enhance pavement performance?
- Soil reinforcement: Geosynthetics like geogrids and geocells are placed within the subgrade or at the surface of the subgrade for adding extra strength. They interlock the soil particles and form a composite that is resistant to deformation when under load. Soil reinforcement plays an important role in enhancing the load- bearing capacity of the pavement, especially on sections built on soft or unstable soils.
- Prevention of lateral movement: Geosynthetics also prevent the lateral movement of soil into locations that could cause the pavement to settle unevenly or prematurely fail. Confining the soil within an area, these geosynthetics maintain subgrade integrity and hence provide a stable foundation to the pavement layers above.
- Moisture control and separation: Geosynthetics, like geotextiles, act to prevent fine particles of soil from migrating into the aggregate layers. This function of separation is very instrumental in maintaining the properties of drainage in the pavement so as not to allow the accumulation of water, hence reducing the risk of erosion or washouts.
- Even load distribution: Geosynthetics have the ability to distribute loads more evenly across the pavement structure. By spreading the loads over a larger area, geosynthetics reduce stress concentrations on the subgrade and lower layers. This even distribution prevents localised failures-such as rutting or cracking-which occur when heavy traffic loads fall concentrated on certain points.
- Increased pavement lifespan: Geosynthetics prevent or minimize pavement deformation and deterioration by minimizing stress concentrations and therefore enhancing the distribution of load. Increased durability will equate to an increase in service life, hence reducing frequent repairs or reconstructions, improving the long-term maintenance costs.
- Reduced material and labor costs: The use of geosynthetics can result in appreciable cost savings. Geosynthetic reinforcement allows the pavement layers to be made as thinner sections because they reinforce the subgrade and distribute loads more effectively. This reduction in thickness can result in significant savings in construction materials and labor costs and, therefore, make geosynthetics cost-effective for modern pavement design.
- Sustainability: Geosynthetics enhance pavement durability and longevity to the effect that frequency reduces and, correspondingly, diminishes environmental impact due to repairs. Fewer repairs mean less interference to traffic flow, reduced fuel consumption by motor vehicles, and lower emissions of construction equipment.
- Resource efficiency: Geosynthetics enable the reduction of the thicknesses of pavement layers, conserving natural resources since less aggregate and asphalt or concrete would be required. This efficiency that comes along not only reduces costs but also decreases the environmental footprint associated with the construction process itself.
- Adaptability to various conditions: These materials can easily adapt to the different soil and pavement types. Whether applied on flexible pavements, rigid pavements, or composite pavements, geosynthetics provide a dependable solution in performance improvement and durability in the diverse applications.
Role of Strata Geosystems in modern flexible pavement construction are diverse
Geosynthetics have been proven beneficial in construction of not only road pavements but many such infrastructural applications. Strata Geosystems have taken a leading role in advancing our application of geosynthetics products to achieve low cost and sustainable foundations. We are known globally for our innovative approach of using geosynthetic materials, offering a range of products that meet the diverse needs of modern road infrastructure projects. Our solutions are specifically designed to enhance performance, sustainability, and cost-efficiency. We have a comprehensive range of geosynthetic products to address specific challenges in pavement construction. These products include:
Geogrids for reinforcing subgrade stability
StrataGrid Uniaxial (SGU) by Strata Geosystems is a high-strength geogrid used in soil reinforcement and erosion control in pavement construction. Made from high-tenacity polyester yarn woven into a stable grid, these uniaxial geogrids provide vertical and horizontal reinforcement, making it ideal for highway embankments, retaining walls, and areas with weak subgrades. Its UV-stabilized coating ensures durability in harsh weather, offering a lifespan of over 100 years.
StrataGrid Biaxial (SGB) is used to improve pavement durability by providing reinforcement in both longitudinal and transverse directions, ideal for high-traffic areas. With strengths ranging from 20 kN/m to 150 kN/m, it optimizes pavement base layers and reduces maintenance costs, promoting faster construction and sustainability.
StrataWeb®: Providing soil confinement and erosion control
StrataWeb is a geocell product that forms a three-dimensional honeycomb structure, providing additional confinement to soils and preventing erosion. Made from durable HDPE (High-Density Polyethylene), these geocells are highly effective in stabilising slopes, embankments, and soft ground conditions. This product is particularly beneficial in areas prone to erosion, offering a sustainable solution for soil stabilisation and improving the overall durability of the pavement structure.
StrataTex HSR™: Enhancing separation and drainage
StrataTex HSR is a geotextile product that serves as a separation layer in pavement construction. It prevents fine soil particles from migrating into the aggregate base, preserving the structural integrity of the pavement layers. This geotextile is made from high-quality polypropylene or polyester fibers, which provide excellent filtration and drainage properties. This product enhances the drainage of water from the pavement structure, reducing the risk of water damage and increasing the longevity of the pavement. StrataTex HSR is ideal for use in both new construction and rehabilitation projects, ensuring that pavements remain stable and perform well over time.
Success story of Strata: Construction of internal township road with StrataWeb® for Emami
Location: Jhansi, Uttar Pradesh, India
Client: Emami Developers, Kolkata
Product used: StrataWeb® 330-100
Application: Concrete road construction
Construction of internal township road with StrataWeb® geocells for Emami
Emami Developers initiated a large residential township project near Jhansi, featuring around 20 km of internal roads. The initial plan for conventional concrete roads was found to be too costly. Strata Geosystems proposed using StrataWeb 330-100 geocells filled with M20 concrete. This solution reduced costs and increased the roads’ lifespan. The geocells provided a durable, low-maintenance structure that minimized surface cracking and improved pavement quality. The use of StrataWeb® resulted in cost-effective, durable roads with a high-quality finish. They prevented cracking and provided a flexible yet sturdy pavement surface, demonstrating the effectiveness of StrataWeb® in road construction.
Strata Geosystems not only focuses on the technical performance of pavements but also emphasizes sustainability and cost-efficiency. These case studies illustrate how Strata Geosystems’ geosynthetic products, like StrataWeb and StrataGrid, provide innovative and cost-effective solutions for diverse pavement construction challenges. By choosing us for your next project, you can benefit from durable, sustainable, and high-performance pavement solutions that stand the test of time. To learn more about how Strata Geosystems can enhance your pavement projects, contact us or visit our website today.