Mapefibres For Concreting

Fibres are usually used in concrete to control cracking due to plastic shrinkage and to drying shrinkage. They also reduce the permeability of concrete and thus reduce bleeding of water. Some types of fibres produce greater impact, abrasion, and shatter–resistance in concrete.

The amount of fibres added to a concrete mix is expressed as a percentage of the total volume of the composite (concrete and fibres), termed “volume fraction” (Vf). Vf typically ranges from 0.1 to 3%. The aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d). Fibres with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio. If the fibre's modulus of elasticity is higher than the matrix (concrete or mortar binder), they help to carry the load by increasing the tensile strength of the material. Increasing the aspect ratio of the fibre usually segments the flexural strength and toughness of the matrix. However, fibres that are too long tend to "ball" in the mix and create workability problems

 

 

Some recent research indicated that using fibres in concrete has limited effect on the impact resistance of the materials. This finding is very important since traditionally, people think that ductility increases when concrete is reinforced with fibres. The results also indicated that the use of micro fibres offers better impact resistance to that of longer fibres.

Types of Fibres

Fibres include steel fibres, glass fibres, synthetic fibres and natural fibres – each of which lends varying properties to the concrete.

Benefits of Microfibres

Polypropylene Fibres

Improve mix cohesion, improving pumpability over long distances

Improve freeze-thaw resistance

Improve resistance to explosive spalling in case of a severe fire

Improve impact– and abrasion–resistance

Increase resistance to plastic shrinkage during curing

Improve structural strength

Reduce steel reinforcement requirements

Improve ductility

Reduce crack widths and control the crack widths tightly, thus improving durability

Steel Fibres

Improve structural strength

Reduce steel reinforcement requirements

Reduce crack widths and control the crack widths tightly, thus improving durability

Improve impact– and abrasion–resistance

Improve freeze-thaw resistance

 

 

Blends of both steel and polymeric fibre’s are often used in construction projects in order to combine the benefits of both products; structural improvements provided by steel fibres and the resistance to explosive spalling. and plastic shrinkage improvements provided by polymeric fibres..

In certain specific circumstances, steel fibre or macro synthetic fibres can entirely replace traditional steel reinforcement bar (“rebar”) in reinforced concrete. This is most common in industrial flooring but also in some other precasting applications. Typically, these are corroborated with laboratory testing to confirm that performance requirements are met. Care should be taken to ensure that local design code requirements are also met, which may impose minimum quantities of steel reinforcement within the concrete

Microfibres from Mapei

Mapei Mapefibre NS12/NS18 – Polypropylene fibres, for concrete are 12mm / 18mm long. Mapefibre NS12 /NS18 are 100% virgin mono-filament polypropylene fibres which are resistant to alkalis and which do not absorb water. They have been specially developed to reduce the formation of cracks induced by hygrometric shrinkage of the concrete at the fresh and hardened stages. The special “mono-filament” formation makes their distribution and position within the concrete mix easier, so that they are distributed uniformly, to create a particularly strong matrix, which is resistant to the stresses induced by the setting and hardening process.

 

 

Uses

Mapefibre NS12/NS18 are particularly suitable for the following:

Production of concrete used for industrial floors, airport forecourts and multi-storey car-parks.

Production of pre-cast reinforced concrete panels and pipes and concrete sections.

Production of fire-resistant concrete.

It is also necessary to ensure that the design of the concrete mix is correct to prevent cracking phenomenon, and that curing of the concrete is carried out accordingly to avoid sudden evaporation of the water from the surface of the cast concrete.

Mapefibre NS12/NS18 are compatible with other admixtures used in the production of high-quality concrete, and especially with the following:

PCE based super-plasticising agents from the Dynamon range, for an improved mix design, consistency and maintenance of workability.

Mapecure range curing surface films, for correct curing of the concrete.

Mapecrete System, innovative technology used in the production of concrete with volumetric stability.

Mapeform Eco and DMA stripping compounds, used for stripping concrete from moulds.

Mapefibre NS12/NS18 has been used in the following projects:

Palremo Airport, Italy

Auto Strada A3 – Macrolotto N 2 E3.3 Tunnel, Lauria Italy

T4 Frejus Tunnel, Italy

Loeriesfontien Windfarm, South Africa

Lamborghini, URUS SUV Production Plant, Italy

Grand paradiso Hotel, Italy

01/HY/2014 Tai UK Street, Hong Kong (Road maintenance)

Philip Moris International, Italy (Car Parking)

InstitutUniveristaire du cancer, France

Tienda Ikea Valladolid, Spain

Macrofibres

Macro synthetic fibres are typically used in structural concrete as replacement for nominal bar or fabric reinforcement. It can be used to provide the concrete with significant post-cracking capacity and hence can be used in some designs based on plastic analysis, such as for ground-supported slabs and for rock support using sprayed concrete.

Macrofibres from Mapei

Mapefibre BG 55 is specially extruded, embossed and precision cut monofilament polypropylene structural fibres for high-performance fibre-reinforced concrete and for sprayed concrete with high ductility.

Uses

Sprayed concrete as primary and/or final lining in tunnels construction.

Ready mix concrete and precast concrete segments for final lining of tunnels, curbs, wells, etc.

The fibres Mapefibre BG 55 are characterized by a high aspect ratio and a specifically embossed surface: this allows achieving a strong adhesion to the cementitious paste, increasing therefore the general performances of the fibres, including the concrete ductility.

The nature and the geometrical shape of the Mapefibre BG 55 do not compromise the concrete rheology. In addition to this significant advantage, the peculiar geometric shape of these fibres prevents the floating phenomenon, especially in presence of large cast surfaces.

The exclusive use of modified virgin polyolefin compounds for manufacturing the Mapefibre BG 55 makes them very inert to chemically aggressive environments. The polypropylene fibres Mapefibre BG 55, being resistant to aggressiveness of the alkaline environments, chemical admixtures are compatible with the basic matrix of concrete in which they are incorporated and are therefore more durable.