What is UHPFRC?
UHPFRC (stands for “Ultra High Performance Fiber Reinforced Concrete”) is an advanced construction material. It is generally consists of high amount of cement and silica fume as binder, relatively short steel fibers, hard fine particles, very low Water/Binder (W/B) ratio and admixtures such as water reducer.
A high deformability with a pseudoplastic phase (multi cracking) and an increase in the tensile capacity before crack localization and strength depletion are caused by the incorporation of fibers, which considerably enhances the tensile capacity.
Particularly, UHPFRC offers very high strength characteristics that lead to a significant reduction in structural weight, with UHPFRC structures weighing only roughly 1/3 to 1/2 as much as conventional reinforced concrete structures under the same external stresses. In comparison to regular and high strength concretes, a UHPFRC has better performance, greater durability, and increased bearing capacity and toughness.
UHPFRC is ideal for concrete members subjected to long-term loads because it has a very low water to cementitious materials ratio (0.18 to 0.25) and a thick particle packing that completely eliminates shrinkage and creep.
In comparison to convection and high performance concrete (HPC), the main advantages of UHPFRC are its high tendency to avoid cracks due to high tensile strength, limited shrinkage due to the reduced w/c ratio made possible by effective R&D advancements in superplasticizers and mineral admixture, and significant viscous response, obtained by the very dense matrix which helps to relax the eigen stresses.
Nano-additives enhance the pore structure, promote cement hydration, and increase durability while also improving mechanical properties. Additionally, nano-constituents enhance the ability of concrete to self-heal in the cracked state. Because of the UHPFRC’s dense microstructure and damage-tolerance properties, concrete constructions are significantly more sustainable.
UHPFRC is used in structures as an efficient strengthening technique to increase the strength, moment capacity, stiffness, and shear of RC columns under eccentric loading because it has higher compressive, tensile, and flexural strength, as well as higher toughness and ductility than regular concrete. It increases the RC Beam’s shear strength. Additionally, It strengthens the seismically weak beam-column junction in constructions made of reinforced concrete.
It has a wide variety of uses in the building and restoration of structural components, specialties, and bridge superstructure. For instance, very thin layers can be used to create furniture and architectural components like staircases (around 30mm).
It may be used in structural applications to build wind towers, structural parts for large structures, and bridges with narrow sections (reduction of weight). Additionally, it may be used to restore and fix concrete structures including slabs, columns, and bridge decks.
Applications around the world
The Sherbrooke Pedestrian Footbridge across the River Magog in Quebec, Canada, was built in 1997 and was the first major construction to use UHPFRC technology. It was made of 3.3-meter-wide, 30mm-thin UHPFRC slabs.
Later, in 2005, four road bridges were built at around the same time, and all those elements were the first to be built utilising UHPFRC technology. One of these was the Shepherd’s Gully Bridge, an I-girder bridge with a 16-meter span and a 21-meter width that is 150 kilometres north of Sydney.
UHPFRC mixes generally comprise 650 to 900 kg/m3 of cement, as well as up to 1 mm-sized micro-silica and small particles (quartz, basalt, etc.). Between 0.13 and 0.17 is the water to binder ratio. A superplasticizer is used to combine the components and create an ultra-compact matrix.
In more recent times, limestone filler has been utilised to replace a sizable quantity of cement and to increase workability, resulting in UHPFRC that is more affordable and ecologically friendly.
In order to achieve high tensile strength and significant tensile strain hardening behavior, an important property for applications, in particular for composite R-UHPFRC – RC member, this matrix is strengthened with straight steel fibres of 13 to 15mm length and an aspect ratio of more than 65, with a dosage of at least 3% in volume (or 240kg / m3).
Excellent rheological characteristics of UHPFRC in the fresh state make it simple to cast the self-compacting fresh material on the construction site and in the prefabrication facility using standard concreting equipment. Additions may be added to the mix in order to obtain thixotropic behavior of the fresh UHPFRC in view of casting UHPFRC on slopes (up to 12%).
The composition, thermal treatment, and curing of UHPFRC all affect how its mechanical characteristics evolve over time.
- By utilizing a specialized batching equipment with separate silos for silica and steel fiber, high-quality concrete is ensured.
- Overall reduction in the structure’s dead load.
- Significant decrease in shrinkage cracks, especially in the slab of a deck, which are often common.
- Decrease in life cycle costs as a result of less routine maintenance.
- Attains early strength, allowing for quicker reuse of staging and shuttering than standard concrete.
- Significant Cost Savings as a result of concrete element thickness reduction.
- Only mega projects like extra dosage, cable stayed, cantilever bridges, long viaducts with continuous spans, or lengthy spans will be able to employ such concrete since its manufacture requires a modern, fully automated batching machine.
- Reduced concrete element thickness may result in flow of concrete and congestion of the reinforcing.
The Latur-Nilanga-Aurad Sahajani Section of NH-752K, located in the Maharashtra state district of Latur, saw the commissioning of a major bridge made of ultra high performance fibre reinforced concrete girder in November 2021 using this technology.
The bridge was built near the village of Masalaga and over a river. The bridge was constructed using UHPFRC, and instead of using steel, girders made of steel fibres were used to give it additional strength. It was also made to be lightweight and portable on the construction site to allow for quick construction and to provide new opportunities for the highway infrastructure’s future.
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