Prefabrication of any structure component off-site during highway construction (or reconstruction) saves significant time and money over traditional cast-in-place methods of construction. The technology of precast prestressed road pavements provides a significant increase in durability while significantly reducing construction time and cost. Precasting bridge parts and elements offsite is also advantageous because bridges are among the most expensive objects to construct. It also provides significant safety benefits, reduces traffic disruption, and improves overall convenience for road users.
However, this technologically, economically, and environmentally advantageous approach has its detractors, most notably from the contractor side due to the inability to make each project unique and thus with a higher possible mark-up. The goal of this blog is to analyse and evaluate the advantages and disadvantages of the innovative prefabrication approach in comparison to the traditional cast-in-place construction method, and to come up with a set of general practise conclusions and recommendations. The current ageing highway infrastructure in India and South Asia in general is being strained by rising traffic volumes. Even though traffic volumes on the rest of Asia’s highways have not increased significantly, it is gradually becoming a reality in every country around the world.
However, this technologically, economically, and environmentally advantageous approach has its detractors, most notably from the contractor side due to the inability to make each project unique and thus with a higher possible mark-up. The goal of this blog is to analyse and evaluate the advantages and disadvantages of the innovative prefabrication approach in comparison to the traditional cast-in-place construction method, and to come up with a set of general practise conclusions and recommendations. The current ageing highway infrastructure in India and South Asia in general is being strained by rising traffic volumes. Even though traffic volumes on the rest of Asia’s highways have not increased significantly, it is gradually becoming a reality in every country around the world.
Alternative modes of transportation
Changing the way people use personal transportation is a very complex issue. As a result of large capital investments in fast train railroads, it has been partially successful for long distance travel so far. Reducing the number of passenger cars on highways for short and medium-distance travel has also not been accomplished. In terms of heavy transport, efforts to relieve the overburdened highway network by shifting volumes to the railroad have largely failed thus far. This is primarily due to the manufacturing and retail industries’ need for flexibility and speed of supply, as well as the various complications that transportation companies face when switching from road to track and back.
Road maintenance is becoming increasingly important.
The Indian highway system is deteriorating faster than anticipated. Because of the unexpectedly high usage and resulting wear on the road infrastructure, large amounts of repair and reconstruction are required. Logically, the need for maintenance grows in direct proportion to increased road usage. Simultaneously, maintenance must be carried out on a continuous basis while serving a growing traffic flow with minimal disruption. Road users expect refurbishment and new construction to be completed quickly and with as few road closures, traffic jams, delays, and detours as possible.
Precast prestressed concrete is the proposed solution
Analyzing the current capacities of India’s construction industry as of March 2017, it was discovered that they still lacked 80% of their pre-recession volumes to meet demand for investment and maintenance construction services. The challenge for public highway administrations is to find ways to build new, more durable routes while also restoring existing ones quickly and with minimal impact on users.
Precast concrete road pavement and bridge construction systems – cast off-site (at a nearby or on-site plant) and installed quickly outside of rush hours – not only reduce traffic disruptions and improve safety during construction, but they also provide unrivalled durability to new roads and bridges (for both substructure and superstructure; tunnels are not addressed in this paper due to their relatively rare occurrence and technical specificity).
Precast concrete road pavement and bridge construction systems – cast off-site (at a nearby or on-site plant) and installed quickly outside of rush hours – not only reduce traffic disruptions and improve safety during construction, but they also provide unrivalled durability to new roads and bridges (for both substructure and superstructure; tunnels are not addressed in this paper due to their relatively rare occurrence and technical specificity).
Precasting has several advantages over cast-in-place construction.
Precast concrete technology has advanced significantly since its use by the ancient Romans, from the composition of the concrete mix (by adding steel to increase tensile strength) to new casting and curing methods. The following are the primary advantages of precast concrete over cast-in-place (in-situ placement of pavement or object): Precast pavement panels or bridge elements can be cast and cured in a controlled environment at a precast plant, allowing for greater control over concrete mix consistency, vibration procedures, and proper curing. Curling and air entrainment issues that are common with traditional concrete paving are reduced or eliminated by precast objects. Precast objects are also prestressed during plant production and post-tensioned during installation, which cast-in-place objects cannot do.
By inducing compressive stresses in the panels, prestressing in the plant significantly improves performance (most notably tensile strength). This effectively prevents cracking and strengthens them for easier onsite manipulation, as well as bending and torqueing. This durability reduces maintenance costs over the life of the roadway as well as user costs due to shorter repair cycles.
According to the Indian Ministry of Road Transport and Highways’ testing project, post-tensioned panels have the same design life as thicker conventional concrete pavements using thinner slabs, which means that a 200mm post-tensioned pavement has the same life as a 355mm conventional pavement. Post-tensioning also improves durability by reducing or even eliminating cracking by connecting individual panels and promoting load transfer between them. Furthermore, post-tensioning not only reduces the required pavement thickness, but also significantly increases durability, reducing or even eliminating cracking in the pavement. This extends the life of the pavement while requiring less maintenance.
By inducing compressive stresses in the panels, prestressing in the plant significantly improves performance (most notably tensile strength). This effectively prevents cracking and strengthens them for easier onsite manipulation, as well as bending and torqueing. This durability reduces maintenance costs over the life of the roadway as well as user costs due to shorter repair cycles.
According to the Indian Ministry of Road Transport and Highways’ testing project, post-tensioned panels have the same design life as thicker conventional concrete pavements using thinner slabs, which means that a 200mm post-tensioned pavement has the same life as a 355mm conventional pavement. Post-tensioning also improves durability by reducing or even eliminating cracking by connecting individual panels and promoting load transfer between them. Furthermore, post-tensioning not only reduces the required pavement thickness, but also significantly increases durability, reducing or even eliminating cracking in the pavement. This extends the life of the pavement while requiring less maintenance.
How are Precast Concrete Pavement Systems used?
In the construction of precast concrete pavement, adjacent panels are assembled sequentially and connected onsite using post-tensioning or cast-in-load transfer systems. Precast concrete pavement systems can be used to replace single lanes, multiple lanes (an additional lane may be required to accommodate materials and equipment), or full-width roads. If properly organized, using precast concrete parts for road pavement reduces construction time by two to three times compared to traditional cast-in-place methods. Because no further curing of the newly laid road surface is required, such a pavement can be used by vehicles the very next day after installation.
Bridge Construction Has Been Accelerated
Precast technology can be used to replace/rehabilitate existing bridges as well as build new ones. Accelerated Bridge Construction (ABC) focuses on innovative planning, subordinates design to technology, and employs resources and techniques to expedite bridge construction and maintenance while maintaining safety.
As with precast pavements, the goal is to reduce construction time while increasing durability by using higher quality factory-made concrete. As a result, it makes sense to precast the majority of the bridge elements, including the pile, pier column, pier cap, beam, deck, and barrier/railing, with the exception of the column’s footing, which is usually cast-in-place. The cost of construction is determined by the quantity, which, when large, favours prefabrication, unification, and standardisation. In terms of user costs, which can easily exceed those of construction if high traffic areas are limited for an extended period of time, precast is a clear winner.
As with precast pavements, the goal is to reduce construction time while increasing durability by using higher quality factory-made concrete. As a result, it makes sense to precast the majority of the bridge elements, including the pile, pier column, pier cap, beam, deck, and barrier/railing, with the exception of the column’s footing, which is usually cast-in-place. The cost of construction is determined by the quantity, which, when large, favours prefabrication, unification, and standardisation. In terms of user costs, which can easily exceed those of construction if high traffic areas are limited for an extended period of time, precast is a clear winner.
In conclusion
As traffic volumes on Indian highways continue to rise, users are demanding greater comfort and quality. Given the construction industry’s limited capacity, prefabrication and precasting construction methods appear to offer the best solutions, with the following benefits:
- Increased construction speed to reduce traffic flow limitation time.
- Higher and more stable quality as a result of a more controlled production process in a dedicated facility, as well as the advantages of pre- and post-tensioning
- Long-term durability as a result of the higher quality materials used
- Less frequent maintenance of critical highway pavement and bridge components
- Cost savings from mass production of all standardised elements (mainly pavement panels and bridge elements)
It is hoped that public demand for high-quality, comfortable highway travel will prompt state highway administrations to take advantage of the precast prestressed construction method’s potential.