After decades of research, the use of UHPC (Ultra High Performance Concrete) in the last years is spreading to a larger number of real applications.
Now that it reached the market, it is clear the huge potential of this new material to boost the Precast concrete industry.
There are several types of special concretes depending on their properties, components and dosages. Some of them are:
Today I want to speak about Formex®, the brand name of an UHPC suitable in the market and one of its applications in civil engineering: The precast footbridges.
¿WHAT IS THE FORMEX®?
The Formex® is an advanced concrete which mix contains:
CEMENT+SELECTED AGGREGATES+WATER+ADDITIONS+ADMIXTURES+STEEL FIBERS
WITH THE ADEQUATE PROPORTIONS AND MIXING PROCEDURES, THE FINAL PRODUCT COMBINES SOME OF THE ADVANTAGES OF CONCRETE, STEEL AND WOOD.
The performance that this UHPC provides is much higher than the ordinary concretes. We can highlight, among others:
- Very high toughness and compressive strength (up to 200 MPa)
- Very low porosity, multiplying the durability even in the most aggressive environmental exposures.
- When the designer takes profit of all the Formex® properties, the structure can be as light as conceived with steel.
Obviously, a cubic meter of Formex® has a higher price than the same amount of ordinary concrete, but the question to evaluate what is more cost-effective is: What can we do with a cubic meter of each product? The question is answered with the increasing number of real applications performed with UHPC in the last years: A lighter and more durable structure is in many cases the most profitable investment.
If you want to know more about this product and the precast applications produced with it, I encourage you to visit the website of PREFFOR, the company that developed it.
WHY PRECAST FOOTBRIDGES?
Despite that in the future we will show here many other applications of UHPC, the precast UHPC footbridge has been the most common real application during the penetration of this type of material into the market.
The footbridges are conceived, in general, with light steel structures. They load carrying capacity is not high because it is limited to pedestrians and bicycles.
This solution is adequate in the less-demanding exposure classes (XC1, XC2…). However, when the element is not far from the sea, in risk of freeze thaw attack or in other corrosive environments, a frequent maintenance becomes mandatory to keep the structure with a good functionality. This recurrent and necessary expenditure is not incurred in many cases.
IT IS TOO FREQUENT, ESPECIALLY NEAR THE COASTLINE, TO OBSERVE THE FOOTBRIDGES DETERIORATED DUE TO THE PROGRESSIVE ACTION OF THE CORROSION. IF THE MAINTENANCE IS NOT RIGOROUS AND ADEQUATE, SOON THE NEED BECOMES A COMPLEX REPAIR.
In those cases, if we sum the manufacturing costs of the footbridges and the frequent maintenance costs, soon we understand that the most economical solution at medium and long term is a UHPC footbridge.
The high performance of the material allows a very slender design, so it can be easily confused with a steel structure.
ITS EXTREMELY LOW PERMEABILITY, MORE THAN 100 TIMES LOWER THAN ORDINARY CONCRETE, MAKES OF UHPC A PERFECT MATERIAL TO WORK NEAR MARINE OR AGGRESSIVE ENVIRONMENTS
Some of the most relevant advantages of these footbridges to highlight are:
· Much higher durability
· Minimum maintenance requirements
· Safety, as the deck is manufactured with an anti-slipping texture
· Up to 50 m of span with a slender truss design
· The design can be customized to the requirements of each client
ACHIEVEMENTS WITH PRECAST UHPC FOOTBRIDGES
I have been lucky enough to visit the 3 structures I am introducing afterwards, including the installation of one of them and the transport operations of other.
1-FOOTBRIDGE OVER THE OVEJAS RAVINE (ALICANTE)
This 44 m-span footbridge is an example of a customized precast solution made with Formex®.
The decision to produce this first full-scale UHPC structure in Spain was adopted after carrying out a detailed analysis of the costs, including the maintenance.
The footbridge was installed in Alicante to increase the mobility of pedestrians between two neighbourhoods separated by the Ovejas ravine.
During the manufacturing in the precast plant, all the fittings were inserted for the subsequent installation of the glasses, LEDs, etc.
The installation in the final location was made in one day.
The final appearance of the footbridge is shown at the head of this article.
2-PASARELA IN PUZOL (VALENCIA)
This structure was installed over the Highway V-21 near the Valencian village of Puzol.
Its proximity to the sea, and the influence of some disappointing experiences with steel footbridges placed near, were key-factors for the use of Formex®.
It was manufactured in the factory of the precast company LUFORT and installed in the final location by the company GRUAS RIGAR.
This project also included other precast elements as piles or lintels.
The assembling was divided in two steps.
The elements that did not affect the traffic of vehicles were installed during the day and without any limitation of in the schedule.
On the other side, the elements located on the highway were installed during the night, when the temporary lane closures are safer and have a lower influence on the citizens.
3-PASARELA IN GUADASSUAR (VALENCIA)
This project was carried out in 2016 in the industrial park of the company Ribera del Xuquer Recycling, located in the village of Guadassuar.
(Photo: Pedro Sancho. Image courtesy of Ribera del Xuquer)
It was also implemented in different stages, according to the customer demands.
The ordinary concrete piles, designed specifically for this project, were installed first; and afterwards and progressively, the different spans of the footbridge.
I want to thank Esteban Camacho, PhD for your help in the English translation of this post.
If your prefer to read this article in Spanish, please click here