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Ultra high performance fibre concrete

2019-09-03T07:10:30Z

Jean:

Ultra High Performance Fiber Concretes (UHPC) are cementitious matrix materials, reinforced with fibers and offering compressive strengths of between 150 and 250 MPa.

Advances in the field of admixtures, formulation methods and the use of ultrafine have led to a spectacular evolution of concretes.

The range has expanded: from standard concretes with compressive strengths of 30 mpa to high performance concretes (bhp: more than 50 mpa) and very high performance (bthp: more than 80 mpa). A technological breakthrough occurred in the early 1990s with the development of concrete whose resistance exceeds 150 mpa.

Their formulation uses superplasticizing adjuvants and specific granular compositions as well as fibers (metal or organic fibers). For structural bfup the presence of fibers and tensile performance lead to pseudo-ductile behavior to overcome all or part of passive frames.

These concretes revolutionize the techniques and methods of construction and allow the design of new structures.

These concretes offer exceptional performances:

A very great workability, 
A very important compactness 
Low permeability 
Characteristic compressive strengths at very high 28 days (for structural bfups) between 150 and 250 mpa, 
Mechanical resistance, at a young age, very high, 
Exceptional durability (which allows them to be used in very aggressive environments), 
Ductility (deformability under load without brittle fracture) important, 
High tenacity (resistance to micro-cracking), 
Very low desiccation shrinkage and creep, 
A very important surface hardness, 
High resistance to abrasion and shock, 
Aspects of particularly aesthetic facing and very fine facing textures, 
They make it possible to optimize the maintenance and maintenance costs of the structures and new constructive perspectives.

First companies that had used UHPFC are in France, and are [https://www.edf.fr/ EDF], [https://www.eiffage.com/ Eiffage], [https://structalis.fr Structalis], and [https://www.bouygues.com/en/ Bouygues].

The evolution of UHPCs compared to high performance concretes (BHP) is characterized by: 
Their great resistance in compression but also in traction, 
Their specific composition and their high dosage in cement (700 to 1000 kg / m3) and in adjuvants, 
Their specific granular skeleton (4 to 5 grain scales) and the optimization of their granular stacking, 
The use of aggregates of small dimensions and being the subject of a particular selection, 
A much lower water content, 
The presence of fibers (at a high rate). 
The UHPC may in particular be associated with prestressing by pre-tensioning or post-tensioning, more rarely with passive reinforcement.

The various formulations of the UHPFs make it possible to give them additional properties adapted to the specific requirements of the projects.

 
Principles of formulation of UHPCs 
Obtaining high resistances and low permeabilities to aggressive agents requires a very significant reduction in porosity and more specifically in the network of connected pores, by acting on two parameters.

Extremely low water content, thanks to the optimized use of superplasticizers which deflocculate the cement grains (e / c ratio of 0.15 to 0.25)

Maximum compactness, obtained using components corresponding to several granular classes (typically four to five which include cement, ultrafine, fillers and sand). The size and quantity of larger grains are considerably reduced (maximum diameter ranging from 1 to 7 mm, aggregates being specially selected). The optimization of the granular stack makes it possible to reduce the volume of the voids.

The bfup thus have a very low capillary porosity. Ultrafine used in UHPCs are generally silica fumes that fill the intergranular spaces, optimizing the compactness of the material, and react thanks to their pozzolanic power with the lime resulting from the hydration of the cement. They improve the rheology of fresh concrete, actively participate in the resistance of the whole and close the network of pores to the diffusion of ions and gases. Other ultrafine can also be used such as calcareous or siliceous microfillers and natural or artificial pozzolans.

The use of adjuvants, such as water-reducing plasticizers and superplasticizers, makes it possible to formulate bfups with a very low equivalent eeff / binder ratio.

Fibers, a key component of UHPCs, give the material its ductility. These fibers have a length adapted to the size of the larger grain and a weak section. They generally have a diameter of 0.1 to 0.3 mm and a length of 10 to 20 mm.

The metal fibers are used for structural applications requiring significant mechanical strength.

[[Category:Publications_/_reports]]

Ultra high performance fibre concrete

2019-09-03T07:06:58Z

Jean: Created page with "Ultra High Performance Fiber Concretes (UHPC) are cementitious matrix materials, reinforced with fibers and offering compressive strengths of between 150 and 250 MPa. Advances i..."

Ultra High Performance Fiber Concretes (UHPC) are cementitious matrix materials, reinforced with fibers and offering compressive strengths of between 150 and 250 MPa.

Advances in the field of admixtures, formulation methods and the use of ultrafine have led to a spectacular evolution of concretes.

The range has expanded: from standard concretes with compressive strengths of 30 mpa to high performance concretes (bhp: more than 50 mpa) and very high performance (bthp: more than 80 mpa). A technological breakthrough occurred in the early 1990s with the development of concrete whose resistance exceeds 150 mpa.

Their formulation uses superplasticizing adjuvants and specific granular compositions as well as fibers (metal or organic fibers). For structural bfup the presence of fibers and tensile performance lead to pseudo-ductile behavior to overcome all or part of passive frames.

These concretes revolutionize the techniques and methods of construction and allow the design of new structures.

These concretes offer exceptional performances:

A very great workability, 
A very important compactness 
Low permeability 
Characteristic compressive strengths at very high 28 days (for structural bfups) between 150 and 250 mpa, 
Mechanical resistance, at a young age, very high, 
Exceptional durability (which allows them to be used in very aggressive environments), 
Ductility (deformability under load without brittle fracture) important, 
High tenacity (resistance to micro-cracking), 
Very low desiccation shrinkage and creep, 
A very important surface hardness, 
High resistance to abrasion and shock, 
Aspects of particularly aesthetic facing and very fine facing textures, 
They make it possible to optimize the maintenance and maintenance costs of the structures and new constructive perspectives.

The evolution of UHPCs compared to high performance concretes (BHP) is characterized by: 
Their great resistance in compression but also in traction, 
Their specific composition and their high dosage in cement (700 to 1000 kg / m3) and in adjuvants, 
Their specific granular skeleton (4 to 5 grain scales) and the optimization of their granular stacking, 
The use of aggregates of small dimensions and being the subject of a particular selection, 
A much lower water content, 
The presence of fibers (at a high rate). 
The UHPC may in particular be associated with prestressing by pre-tensioning or post-tensioning, more rarely with passive reinforcement.

The various formulations of the UHPFs make it possible to give them additional properties adapted to the specific requirements of the projects.

 
Principles of formulation of UHPCs 
Obtaining high resistances and low permeabilities to aggressive agents requires a very significant reduction in porosity and more specifically in the network of connected pores, by acting on two parameters.

Extremely low water content, thanks to the optimized use of superplasticizers which deflocculate the cement grains (e / c ratio of 0.15 to 0.25)

Maximum compactness, obtained using components corresponding to several granular classes (typically four to five which include cement, ultrafine, fillers and sand). The size and quantity of larger grains are considerably reduced (maximum diameter ranging from 1 to 7 mm, aggregates being specially selected). The optimization of the granular stack makes it possible to reduce the volume of the voids.

The bfup thus have a very low capillary porosity. Ultrafine used in UHPCs are generally silica fumes that fill the intergranular spaces, optimizing the compactness of the material, and react thanks to their pozzolanic power with the lime resulting from the hydration of the cement. They improve the rheology of fresh concrete, actively participate in the resistance of the whole and close the network of pores to the diffusion of ions and gases. Other ultrafine can also be used such as calcareous or siliceous microfillers and natural or artificial pozzolans.

The use of adjuvants, such as water-reducing plasticizers and superplasticizers, makes it possible to formulate bfups with a very low equivalent eeff / binder ratio.

Fibers, a key component of UHPCs, give the material its ductility. These fibers have a length adapted to the size of the larger grain and a weak section. They generally have a diameter of 0.1 to 0.3 mm and a length of 10 to 20 mm.

The metal fibers are used for structural applications requiring significant mechanical strength.

[[Category:Publications_/_reports]]